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Old March 6, 2012, 08:04 PM   #1
thedaddycat
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Measuring actual chamber length?

A while back I was reading a post about case length and trimming. Someone mentioned measuring chamber length by using an insert in a case to determine the actual chamber length of his particular rifle.

As I recall, part of the insert was turned to bullet diameter and then a small section was turned to case neck diameter. When chambered, the insert would hit the forward end of the chamber and then be pushed into the case as the bolt was closed. When extracted the insert would be sticking out from the case to the length of the chamber and a measurement could then be taken.

I decided to try making a tool like this and here is what I came up with. I made the inserted part slightly undersized and boat tailed to give a good slip fit and the neck diameter lip to drawing spec. I left a handle forward of the lip (for now) to facilitate working with the insert and if left in place to act as a pilot in the bore. The case has been fire formed and neck sized with the Lee Collet neck sizing die. It was also sonic cleaned but I did not clean or polish the case mouth. The tool was turned from a 5/16 SS bolt. Tool dimensions are as follows: inserted part .263, lip diameter .296, lip width .085, pilot max. diameter .254. Case dimensions are as follows: case mouth OD .291, case length 2.160. Another case that has had identical case prep but has not been neck sized has a case mouth OD of .299 and a length of 2.153. Both are R-P brass while the bulk of my 6.5X55 brass is PMC, which I have not measured of sized yet.



Here the dimensioned diagram of the 6.5X55 case is linked. I do not believe it is accurate as length dimensions are shown from the extractor groove. The numbers may be right but the drawing seems to be wrong. As you can see, the case mouth OD on my fire formed and neck sized case is .005 under spec which leaves the tool lip slightly larger than the case (though still at spec).

http://en.wikipedia.org/wiki/File:6.5x55-SE-scheme.svg

My goal here is to have brass that fits my chamber as exactly as I can get it to fit while not working or trimming the brass any more than is necessary. I will probably anneal it at some point as part of achieving this goal.

So now I have a few questions that I hope you can help me with. I would really like for the guy whose post I read to see this but anyone else please feel free to give your input.

Does this tool look like it is correctly made? Is it OK to leave the pilot on or should I cut it short or cut it off?

Is the lower than spec OD of the neck mouth an issue (neck wall thinning)? Does this indicate that I have the collet die set too tight?

How far back should I trim my "Test" case to allow proper movement of the insert? When fully pushed into the case, the boat tail end of the .263 section is well below the shoulder. Would .200 be too much or about right?

When I do need to trim the brass, should I use my Lee trim gauge to trim it back to minimum trim length or would it be better to get something like a Wilson trimmer with Sinclair upgrades (micrometer adjustment) and trim it back "just enough" (.020?) to work safely without taking too much brass off?

Maybe some of this seems a bit over the top, perhaps like using benchrest techniques for a 100+ year old milsurp rifle? Maybe it's a waste of time and effort? All I can say is that once I learn how to do it the best way possible, I can cut out the steps that don't make any difference, but at least I'll know how to do them if I ever want or need to...

As always any input is greatly appreciated, and thanks in advance for sharing your thoughts.
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Old March 6, 2012, 08:19 PM   #2
5R milspec
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I would have turned the BT part to .308 just as a bullet.the outter lip should be just enough bigger to just be able to get the measurement.not really what to say.do you really need the handle part no.

when you get your measurement of your chamber just trim the brass back .010 and you will be fine.

no do not use the Lee trimmer when you come up with chamber Over all length.it will cut to much off.but it might be able to be set not sure.( by unscrewing it out )most likely you will need a new trimmer one you can set to the length you are looking to get.
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Old March 6, 2012, 08:45 PM   #3
wncchester
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"When I do need to trim the brass, should I ... trim it back to minimum trim length or would it be better ..."

There is no "should I" or "would it be better" to it, just do it the way you want to do it and be consistant about it.
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Old March 6, 2012, 09:20 PM   #4
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You can't use the Lee trimmer to adjust trim length. It is made to trim to Sammy specifications.
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Old March 6, 2012, 09:39 PM   #5
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Right on on trim length.......as long as it's uniform it shouldn't matter. We just had a discussion a couple threads down about seating depth. The way I do it, I seat a bullet in a dummy round and chamber it, let the rifle seat the bullet, then seat the bullet 1/16 deeper.
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Old March 6, 2012, 10:04 PM   #6
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http://www.brownells.com/.aspx/pid=3...-CASTING-ALLOY
You want actual chamber dimensions, try this. I've used it and it's good to go.

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Old March 6, 2012, 11:34 PM   #7
F. Guffey
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I make gages to determine the length of the chamber from the bolt face to the shoulder of the chamber and another for determining the length of the chamber from the bolt face to the throat of the chamber, then, I make transfers for setting up my seater die for seating ‘off the lands’.

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Old March 6, 2012, 11:59 PM   #8
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Hello, thedaddycat (would love to here the story on that one!) I made a gage like yours for a .22 Hornet & .222 Rem. I shortened case neck up by about 3/16" No handle on mine..just sharp edged, flat face brass rod..fairly snug fit in case neck..outside of end same dia. as case neck. I have found some of these chambers..even on custom guns are .030" to .050" or more longer that max. trim length in loading books. I think the reamer mfg. do this as a built-in liability safety measure.
Wayne Schwartz did a write up in the Cast Bullet Association's Fouling Shot magazine on this. In his case it was a .30-30..one of the worst offenders. Shooting soft-cast in schuetzen matches, the soft lead was obturating out into this excess space, before being swaged back down in leade..not good for accuracy.
I see alot of posts from new guys sweating over a few thou. difference in their case lengths..when they are probably using cases far too short already!
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Old March 7, 2012, 09:33 AM   #9
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“I have found some of these chambers..even on custom guns are .030" to .050" or more longer that max. trim length in loading books. I think the reamer mfg. do this as a built-in liability safety measure.”

Again, I make gages, more than a reloader needs to know, the neck of the 300 Win Mag is short at .274, need to know? because there is nothing they can do with the information, others can order a neck reamer, increase the length of the neck, then extend the throat for more powder without raising pressure, some swear they can keep up with the 300 Weatherby, and all the time keeping the maximum overall length of the loaded round short enough to feed from the magazine.

I have checked chambers for length including the throat, I checked one that was built for a bullet that did not exist, I used a 170 grain 7mm bullet to determine where the bullet contacted the rifling, the bullet came out of the case and traveled an additional .200+ before it contacted the rifling. I did not have to wonder what he/they were thinking, I was talking to one of them. He loaded close to 100 rounds we went to the range,
strange, there was a half way point, more powder, less powder, accuracy disappeared, heavier bullets, lighter bullets, accuracy disappeared. We know that was not the answer, while the bullet was between the case and rifling gas, hot, metal cutting gas was passing the bullet, so we knew the throat would not last long. I am the fan of the running start, I am the fan of knowing the length of the run.

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Old March 7, 2012, 08:05 PM   #10
thedaddycat
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F. Guffey, I have to ask, was it your posts that I read about the chamber measuring tool that I tried to copy? It seems like you know quite a lot about the tool and how to use it properly. Does my tool look like it was correctly made? I think that I will end up cutting the pilot off completely to eliminate any effect on the chamber measurement. Having it on while I polished the tool with crocus cloth was a big help but it is no longer needed.

Please correct me if I'm mistaken, but is the purpose of measuring the chamber to allow you to let the case neck "grow" to just short of chamber length and then trim it back to .010 less than chamber length? Will thinning of the neck wall be an issue? Would annealing help mitigate it?

As far as trimming goes, it would probably be easiest to get the Wilson unit with upgrades. I suppose I could make a spacer to fit between the Lee length gauge and the cutter but it would need to be machined to exact thickness to give me the desired trimmed case length. Alternately Lee will custom make a gauge to your length spec, or perhaps I could try making one myself.
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Old March 7, 2012, 08:54 PM   #11
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Sounds like you are trying to make this
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Old March 8, 2012, 09:33 AM   #12
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for the most part it does not matter to what length you trim the brass as long as it does not come in contact with the chamber.but for him it must matter for he has made a tool.

the longer you can hold your brass to a chambers length the better it will be for the rifel.it helps out in the long run of things by saving the throat of the rifel.premature throat erosion will cause less accuracy in a shorter time for the life of the barrel.it really shows when we load our rounds to max and keep them their.or when we load really big bullets.so by cutting the brass to fit the chamber helps prolong the life of the chamber.how much better does it help I cannot say for I have never tested for it.better yet I have never shot out a barrel.most shooter or say me like to keep our load in the middle to save our throats.

again for the most part it really doesn't matter.most just cut their brass to the spec given to the chosen case of choice.one thing does come to mind though.I shoot a 308 and with my loads it should be able to get 5000 or so rounds with no trouble.I even cut the brass short and not to the chamber.( spec )for me I'm not worried about it.when or if accuracy falls I'll just have a smith cut it back and rechamber it.
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Old March 8, 2012, 05:50 PM   #13
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Thedaddycat,

Proving that clever minds think alike, what you have done is create your own version of the Sinclair chamber length gage. Their picture shows three sizes together, either to confuse folks or hint that you should buy one for every chambering you own, I suppose, but you can buy one for just under $7 plus S&H for 6.5 mm or any of a number of other calibers. I bet you could call Sinclair (now owned and operated out of Brownells) and learn what diameters they use and learn how yours compares.

I think another aid you might want for reference is a chamber drawing for 6.5×55 rather than a cartridge drawing. One is attached. This should give you the worst case for how much neck to trim on your test case.

The way SAAMI does dimensions is a little confusing, as they don’t use the familiar plus and minus expression of tolerance. Instead they list the critical limiting dimension then a tolerance away from it. For the cartridge, this means linear dimensions are stated as maximums with a minus tolerance only, while chamber linear dimensions are stated as minimums with a plus tolerance only.

Radii are handled differently. Since an outside corner on the cartridge case corresponds to an inside corner in the chamber, and vice versa, they always pair one outside corner with one inside corner. The outside corners must have a minimum and maximum radius, but the inside corners may be left sharp, so they have only a maximum and no minimum

The diameter tolerance on the 6.5×55 case neck used by SAAMI is the same one they use for most rifle cartridges and that is a maximum over a seated bullet with a tolerance of -0.008”. For this cartridge that maximum is 0.2972”. The bullet has a maximum of 0.2638”, with a -0.003 tolerance. So, for a case neck to lay over top of a bullet within specs, it must not exceed 0.2972” over a maximum diameter bullet, nor be less than 0.2892” over a minimum diameter bullet. The first criterion requires neck wall thickness no greater than 0.0167”, while the second requires it be no thinner than 0.0142”. Since manufacturers mostly hold bullets to maximum these days, I’ve noticed a lot of brass favors the small end of that range. Note that since bullets are seldom undersize, you normally have about 0.015” you can turn off the outside before you undershoot the OD tolerance. That’s enough to remove neck wall runout from the majority of brass if you are inclined to take the trouble.

As to trim length, this is a little complicated. The 6.5×55 cartridge headspaces on its shoulder, meaning the shoulder is what stops the case mouth and bullet from going too far forward into the chamber. The idea behind trimming is to prevent neck contact with the mouth of the freebore and to control bullet ogive distance from the lands. Yet, if you pushed the shoulder too far back (see exaggerated drawing below), you’ll see you can have two cases trimmed to the same length and one performs this function properly while the other does not. All it takes is for the shoulder to be pushed too far back to mess it up.



In the real world, the throat jam depicted above isn’t so severe because the case rim is captured by the extractor hook, and that stops it from going that far foward (headspaces the cartridge on the extractor hook).

The standard sizing and trimming strategy is to use sizing dies that correctly limit shoulder setback, then trimming to achieve the same end. This means you are maintaining two interdependent tolerances, and 0.005” variance in the length of the neck coming off the shoulder isn’t too uncommon to encounter using the standard approach. It is better if all cases have the same load history and are always trimmed together. Most chamber designs give the neck ten thousandths or more extra room beyond case maximum for the above reasons. In 6.5×55, the base to case mouth dimension is 2.165” -.020”, while the chamber breech length to the freebore is 2.1772 +0.015”. So the minimum extra chamber neck length is 0.0122”, and the maximum is 0.0472”. Since suggested trim-to length is in the middle of the case length specification range, an average case is 2.155” long, and since the middle of the range for the chamber neck is +0.0075, it averages 2.1847”. From those numbers the average extra neck length in a chamber is 0.0297”, or about 30 thousandths in this cartridge. You only need to maintain the minimum, though, and can adjust your trim length to your chamber, accordingly.

A variation on the standard method that increases precision is to use the Wilson trimmer with Sinclair's optional micrometer adjustment. Measure each sized case to the shoulder datum line with a case gauge, and when one is a thousandth long, you turn the micrometer back a thousandths, and vice versa and so on with whatever shoulder lengths you have. Slow going if you don't sort the cases by shoulder length first so you can run each length as a batch without stopping to adjust, but possible to do.

Another control strategy is to neck size only, where it's practical. Neck growth occurs mainly when the expanded diameter and stretched shoulder position of a fired case are narrowed and pushed back, respectively. During resizing the extra metal needs somewhere to go, and the neck is the open end it flows toward. If you neck size only and you aren’t pushing the stretched parts back anyplace, the case doesn’t grow much. For example, Lee claims using their collet die for neck sizing, trimming is mainly eliminated. The only problem with this is that even neck sized cases eventually get tight and need to be sized and trimmed and started over. But this will cut down a good bit on trimming duty.

Still another strategy is to use a trimmer that registers on the case shoulder and fixes the neck length from there, regardless of where sizing has located the shoulder. The least expensive of this type I am aware of is the Possum Hollow trimmer. Next is the WFT. At the other end of the cost spectrum are the motorized Giraud and Gracey trimmers. These have the advantage their cutters chamfer and de-burr at the same time as they trim, so you're done in one operation. The only failing Ive notice with that kind of cutter is that if a neck wall is not uniformly thick, because the outside surface locates the case, the length and outside de-burring will be right, but the chamfer will be off center. I don’t have any evidence this measurably affect shooting precision; I just know you’ll notice it happens. I use the Giraud and ignore it, though I admit I sort out cases with uniform necks for long range precision loads anyway, so I'm not giving it a chance to be seen if it could be.

So, when do you need to trim? Well, if you know your rifle's chamber length, you can walk up to the minimum distance from the end of the chamber neck for sure. Since necks don’t change much in length during firing, you could go further. Some old timers ignored the whole issue and didn’t trim at all, instead letting the force of closing the bolt on a long neck push the shoulder back a little. Apparently you can get away with that in at least some guns. I wouldn’t want to try it in one with a steep angle into the freebore, like the .30-30, though. Indeed, I think it’s wiser not to introduce that variable at all because it might affect bullet alignment, so I keep trimming to a constant and usually conventional average length. If I had a very long chamber and was having trouble getting a short bullet located as close to the lands as I wanted, then I'd go for all the length I could. It might take several rounds for the case to get out there, I suppose, and I'd have to eat a little inconsistency until it did.

That reminds me to mention a lot of service rifle match shooters used to trim necks back about 15-20 thousandths below SAAMI minimum. The idea was, since case life in the M14/M1A was often only about five loadings, they would never have to trim again before retiring the cases. They didn't seem to have accuracy issues doing this, and you know the cases didn't grow uniformly. So major precision is likely a lot of unnecessary fuss for anything but benchrest shooting. But of course, the only way to be sure it doesn't affect precision in your particular gun is to try it and see.

Nick
Attached Images
File Type: jpg chamber fit.jpg (62.5 KB, 100 views)
Attached Files
File Type: pdf 6_5×55 Swedish Chamber.pdf (46.1 KB, 6 views)
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Old March 8, 2012, 07:34 PM   #14
1Hobie
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Thanks1

Unclenick blah blah.

That was one of the best disertations that I have read on the subject. I'm going to create a folder to store it in because I could understand it.

Thanks for taking the time to post it. Great stuff!

BTW, the Sinclair tool looks like something to have for the bench.

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Old March 8, 2012, 09:54 PM   #15
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Unclenick, WOW... Thanks so much for that, I really do appreciate you taking what must have been a decent chunk of your time to write that up. I will have to go over it a few times to make sure I'm getting it all straight in my head. Yes, what I have done is very similar to the Sinclair gauges but I used stainless steel so I may have to scrap it and use something a little bit softer.
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Old March 9, 2012, 10:36 AM   #16
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Thedad, wait on scrapping the stainless, there is injected molding as a means of manufacturing, in the old days fishing lures were made the same way with the aid of a huge press and the model (lure) sandwiched in-between aluminum blocks.

I understand your design, it is not that I disagree because I understand the logic behind the additional work. I am the fan of bullet hold, a case can not have enough bullet hold, others are fans of neck tension, a different standard.

To accomplish the same goal (objective) in determining the length of the chamber (and knowing you are sacrificing a case, I do not hesitate to dedicate 50+ ) you could have stopped at the plug and not added the means of removing. That leaves you with pulling the plug/tool out of the case mouth and a reduced purchase (nothing to get ahold of), back to the sacrifice case with the short neck: Pull, some insist on pulling, I don’t, there is pulling and there is pushing, to speed up your effort you could drill the primer pocket/flash hole to a diameter that would accommodate a means of pushing, cleaning rod, dowel, you could drill a hole in the bench,work stand etc., mount a short rod in the bench/work stand, this would allow you to use both hands for better control when pushing the plug/tool out of the case. Understanding when using the modified case with the tool it is designed to be used while extended and compresses (shortens) when chambered.

Gets complicated: For those that can keep up with two thought as one time, forget the bolt, leave it out, use a push rod to push the tool/plug out of the case until it hits the lands, stop, ALMOST! the same thing, the length of the case plus the extended plug will indicate the length of the chamber LESS! head space. Again, that does not lock me up, I never thought precision gages were made on Mars, I have always believed precision tools were/are made by humans, I guess that is the reason when someone runs out of ideals he says, “THIS STUFF IS NOT ROCKET SCIENCE” or “KEEP IT SIMPLE”.

This is not for everyone, Thedad, you have a lathe, I have 2 plus, and I said I make tools, not for machines but for reloaders that understand the incline plane/threads, case sizing and forming. I have forming dies, lots of forming dies, again, If I had one forming die it would be the 308 W, because it is short. When forming cases (with a forming die) the shoulder is erased and formed further back, tools used to check the length of a chamber does not need a shoulder, all that is necessary is a case that is all neck, but the purpose of forming the shoulder back (moving the shoulder back, and for those that are listening? sounds like a conflict) is to get it out of the way. Forming a case by moving the shoulder lengthens the neck and at the same time shortens the case body from the head of the case and and shoulder (and that is the reason the shoulder is considered ‘out of the way’),

After forming the case with a long neck carefully attempt chambering, the neck should hit the throat and require effort to advance the bolt, it is possible to seat a bullet backwards in the modified case to support the neck and make it more difficult to chamber if the modified case is too long, for those that are stingy with cases and refuse to make sacrifices, they can seat the ‘turned around’ bullet with a means of control, trim the case and attempt chambering and then continue the process until the case chambers without collapsing the mouth of the case, and do not forget, the chamber supports the case, but, it is possible to squat/crush the case slightly when the mouth of the case hits the end of the chamber, for those that are willing to make sacrifices can do the work in advance, move the shoulder back to get it out of the way then trim cases to a predetermined length, start with .015 thousands too long and them trim other cases that are shorter by .003 thousands. doing so would give the reloader the equivalent of gages for case length from go-gage length to just beyond field reject length.

Nothing changes when determining the length of the chamber from the bolt face to the bullet (ojive) contact at the rifling, except, do not move the shoulder back, use a standard full length sized case, again, I am the fan of bullet hold, others choose to ‘squidify’ as in shred the neck to reduce neck tension? And I ask “WHY?” go to all the effort to reduce bullet hold when bullet hold will/would allow the reloader to use the modified case as a transfer when adjusting the seater die to seat the bullet off the lands in thousands. I know and understand how impressive it sounds when someone says “I seat my bullets with the Redding seater die with the dial indicator on top......etc..”

I am the fan of transfers, standards and the verifyer, nothing like making an adjustment and verifying the adjustment afterwards.

F. Guffey
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Old March 9, 2012, 03:29 PM   #17
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F. Guffey, Again I have to say thanks for the time and effort you have put into your response. I don't have a problem using cases for this project. I have four or five hundred PMC cases that will be used for my hand loads. I also have lesser amounts of other once fired brass: 25 R-P and about 40 or 50 military surplus brass which can be used for the project. On top of that I have a couple hundred more assorted factory (PMC, Winchester, Remington) and a few boxes of milsurp (all new never fired) on the shelf. All of this is for just one Swedish Mauser rifle.

I understand about moving the shoulder back but how far is enough, .010? Would two extra turns on the FL sizing die do it? When I start playing with this I'll probably use the milsurp brass as some of it is Berdan primed and will never be reloaded.

I think maybe I'll order some of the Cerrosafe and make a casting of my chamber. Then I can check the measurement with the tool against the casting to see how they compare. I've never made a chamber casting before, so this will be a learning experience for me.

Thanks again to one and all for your input on this thread, I do appreciate it.
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Old March 9, 2012, 05:17 PM   #18
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thedad,there are gigs and gigs of threads about sizing a case, the objective is to get the shoulder out of the way, best way is get the shoulder out of the way is over size it, full length sizing should size the case to minimum length/full length size, that should be accomplished by adjusting the die down to the shell holder with an additional 1/4 to 1/2 turn, when a case is sized according to the instruction (example 30/06) the case length from the head of the case to it's shoulder is .005 thousands shorter than the length of the chamber from the bolt face to shoulder of the chamber.

When I build a rifle and ream the chamber I do not finish the chamber until I have test fire it, I leave the chamber .010 short then size/form cases to fit. I form cases for short chambers by placing a .012 thousands thick feeler (leaf) gage between the deck of the shell holder and bottom of the case being sized (I do not use 5 time fired cases), Lee shell holders allow for more room, the .012 feeler gage represents .017 thousand head space with the perfect go-gag length chamber, all that is necessary is to get the shoulder out of the way, and when using your new tool, the neck must be trimmed back, without the tool, seat a bullet with the flat end out and even with the end of the case mouth, then start making attempts to chamber and if necessary trim. check etc., until it chambers. When the shoulder is moved back the neck gets longer, measure before and again after.

Again I use forming dies, the most versatile forming dies are are for the chambers that use the 308 W as it's parent case, again, because they are short.

Again, full length sizing should get the shoulder out of the way, I use the feeler gage to add an additional .010+. When using a forming die I can move the shoulder back an additional .200+, advantage? added neck length.

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Old March 9, 2012, 06:06 PM   #19
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Thedaddycat,

There seem to be two lengths now involved in the discussion here. The length of the neck off the shoulder and the length from bottom of the case head to the shoulder datum intersect, which the sizing operation controls prior to trimming.

For the first consideration, sticking to the SAAMI minimum difference between the case neck and chamber neck for any particular cartridge will be adequate by by definition. For 6.5×55, specifically, that will mean making the case neck 0.0122" shorter than the chamber neck. But frankly, 0.010" is a number used in other chamberings and will be fine in any scenario I can dream up, if you prefer to use it. If you chamber gently so the chamber never sets the shoulder back any further, you could go even shorter, but I don't think any measurable benefit will result.

As to shoulder setback, neck-sized-only cases will fit and fire several times before they need to be resizing at all, except periodically when they get tight. Glen Zediker and others commonly recommend 0.002" shoulder setback by a sizing die for reliable rapid feeding, especially in semi-autos. A lot of benchrest shooters use 0.001" setback, feeling it self-centers slightly better than neck-sizing-only, but keep in mind they load singly rather than from a magazine, as a rule. You can experiment with these loading approaches for yourself. They all assume you start with a case that fits in your chamber easily for the first fireforming, as Mr. Guffey described.
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Old March 9, 2012, 06:08 PM   #20
F. Guffey
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"...... how far is enough, .010? Would two extra turns on the FL sizing die do it?



Two extra turns of the die could render your press scrap, When the die contacts the top of the shell holder, THAT IS IT! The ability of the die to size is limited to the distance from the deck of the shell holder and sizer die body, the case can offer more resistance than the press has ability to size, in that situation the reloader could look under the die and determine if there is contact with the shell holder, no room means the case was stuffed into the die with nothing hanging out, and can be called full length sized, if the press flexes and the die is not contacting the shell holder, the case won and for some reason has more resistance to sizing than the press has ability to size, (Uncle nick has suggested lowering the ram and then raise again, it works, seems there is a Chinese finger cuff effect, just a guess) the press, die and shell holder may not have the ability to overcome the resistance. Resistance could be caused by the lube, the case could be a 5 time fired case that someone is tying to full length to restore to minimum length after fire forming once and neck sizing 4 times.



F. Guffey



Then there is determining if the die full length sized the case by measuring case head protrusion.
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Old March 9, 2012, 07:23 PM   #21
1Hobie
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is my math correct?

If I understand it and please correct me if I'm mistaken, 2 turns of a standard 7/8-14 thread = .1428s of an inch. That is huge.

I truly have learned a great deal with these excellent posts!

Thanks for you time folks.

Hobie
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Old March 9, 2012, 11:40 PM   #22
Ideal Tool
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Hello, everyone. Good posts! When I made my chamber-length checking plug for the .22 Hornet & .222 Rem. I copied Sinclair's..I knew their's was of leaded steel..just didn't want anything harder than brass in my chamber.
What I have not heard in these posts is the detrimental effect this too-long (or too short for that matter) brass has on the accuracy of a cast bullet.
A C.B., even when cast of lyno, is fairly soft compared to a gilding metal jacketed one. That bullet must bridge that gap for a brief millisecond..during this time, pressure can obturate bullet metal into this gap..which will then be swaged down again as bullet traverses into rifling leade..not a good thing for accuracy. The .30-30 is one of the worst offenders.
I shoot cast in both these .22 center fires & even though my Hornet was a full custom job, barreled & chambered by Shillen, there was a gap of .030" in there. I don't know if the reamer/firearm mnfg. build that extra space into the chamber reamers for a safety issue, or when re-sharpening, the reamer is naturally made smaller in dia., and in chambering, goes in further?
As I said before..some of these guns have .030" to nearly .060" longer chamber lengths than the longest factory brass to begin with..and the reloading manuals tell us the first thing to do is to trim our brass before loading...when in most cases it's already way too short!
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Old March 10, 2012, 07:43 PM   #23
Unclenick
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When the .308 Win was invented everyone said it would never shoot well because its neck was too much shorter than the one on the .30-06. When the .223 Rem was invented, everyone said it would never shoot well because its neck was too much shorter than a .222 Rem neck.

The dire predictions were not born out. As long as your neck length is great enough to keep an adequate grip on the bullet, you should be able to devise chambers and loads that will work well together. That does not mean, however, that you can't design bad combinations. Leaving a bullet with so little grip on it that the neck can't keep it straight through feeding and chambering will be at a distinct disadvantage. I've seen up to 2 moa of group error documented from that in some chambers.

An observation made in a number of guns is that a second seating depth sweet spot is often found when bullets are somewhere around one caliber into the case mouth. If you could have a one caliber seating depth achieved at the same time your bullet nose was at its happiest distance off the lands, you would likely be pleased with the effect.

More neck grip means more starting force for the bullet, or at least higher pressure build before it gets moving, and that tends to help with muzzle velocity consistency and barrel time consistency. These are most often issues for long range trajectories, though, note that long range is relative to the extreme range of the bullet. A handgun is affected by velocity variation at a shorter range than a rifle is.

So those are potential factors. Like everything else they will matter much more in some guns with some load components than others.
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Last edited by Unclenick; March 11, 2012 at 04:43 PM. Reason: typo fix
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Old March 11, 2012, 01:28 PM   #24
F. Guffey
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“More neck grip means more starting force for the bullet, or at least higher pressure build before it gets moving......”

And I am the fan of bullet hold, I want all the bullet hold I can get.

Neck length and bullet hold? I have a 30 Gibbs, the neck length is .217, when determining the chamber length all the guess work is taken out of the equation, the Gibbs chamber was reamed from a 30/06 chamber in a Belgium barrel, meaning the length of the chamber did not shorten, cases after forming shortened .035 thousands +. I did not have to look far for a longer case, the 280 Remington case is .041 thousands longer than the 30/06 case, problem solved, necking the 280 up to .30 shortened the case length ‘almost’ perfectly and required little trimming.

Point, case with short necks, the short case neck of the 30 Gibbs can be improved from .217 to .257, and back then when I was told about the 300 Win Mag and it’s short neck being too short at .264, and my Gibbs neck .007 shorter I stopped taking their advise.

Not for everyone, but some reamed the neck of the 300 Win Mag further out, then seated the bullet further out and added more powder, and I wondered? Why didn't they lengthen the neck to gain bullet hold by forming 300 Weatherby/300 H&H cases to 300 Win Mag.

F. Guffey
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Old March 11, 2012, 06:22 PM   #25
thedaddycat
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OK guys, this is all good stuff. I have this one marked for future reference, that's for sure. Here's what I did this weekend:



Sorry the pic is a bit fuzzy. Note that there are small variations in all these chamberings. I will have to use the calipers on each of these brass inserts and put each in the correct case. The chamber measuring tool (shortened case with insert) will then go with the dies for that chambering or perhaps they will all go into a small box set aside. I don't forsee a need to use them again once I have measured my rifle chambers unless I get another rifle in one of these chamberings. I will have to make another insert for 6.5X55 out of brass as I messed up and cut the lip about .002 too small. In fact I may end up making a whole new set just to practice some more with the lathe.

I used some old scrapped valve stems for the brass, hence the holes in some of them. I had to turn them down to get a smooth brass rod to start with, then dimension them from there. I should have cut them all to the same length but wasn't thinking about that at the time. I'm a power plant operator by trade, not a machinist, so you'll have to excuse the oversight on my part... I promise I'll do better next time.
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