Col. effect on pressure and improving runout ?

[ragwd]

Greetings, I am loading some 5.56 today to get my year started. Loaded pistol rounds during bad weather and now that good weather is here i want to tweak my best load from last year and see if i can get it a bit better. Starting with the same load last year , working with over all length and run out (concentricity of bullet to neck). I have about .010 runout now and would like to get that better. Im guessing I should have did a better job of case prep. Is there anything that can be done once bullet is loaded? Also in over all length does pressure go up as col. is shortened? Im trying to max the length and I was hoping pressure would decrease as col. is lenghtened. As always , thanks for taking the time to red my post.

[steve4102]

Also in over all length does pressure go up as col. is shortened? Im trying to max the length and I was hoping pressure would decrease as col. is lenghtened.

223 or 5.56 AR-15?

Increasing OAL will also reduce the distance to the lands. This will Increase pressure, not decrease it.

[wncchester]

"Increasing OAL will also reduce the distance to the lands. This will Increase pressure, not decrease it."

True. That applies to all rifle and revolver cartridges but the reverse is true for the few hot loaded 9 & 10 MM and .40 pistol cartridges.

[ragwd]

Steve and Winc, thanks for the info. so what i take from this is , if i want to stay at the same pressure with a longer col, i need to lighten the powder? I am close to the max powder as per several resourses. I am concerned about the added pressure with the close to max load.

[wncchester]

".. if i want to stay at the same pressure with a longer col, i need to lighten the powder?"

Well, yes, but... no one can tell you how much less powder you may need to remove to maintain your present unknown pressure. How did you establish your present seating depth and why would you wish a longer OAL?

[Unclenick]

ragwd,

At the COL's you are probably using, getting nearer the lands is likely to increase pressure. If you go deep enough into the case, you find a pressure minimum, after which going still deeper raises pressure again.

The best way to check is with a chronograph. If your pressure is going up, your velocity will. Reduce the charge to match the average pressure you had before you changed the seating depth. The most difference I've seen between a normal seating depth load and one actually touching the lands has been equal to the effect of about 10% of the powder charge, so reducing the charge 10%, checking velocity, then working back up to your original velocity should get you where you want to go safely.

There is a lot you can do to reduce runout if you need to. First, though, let's find out if you need to.

Measure runout on 26 randomly chosen rounds. Use a Sharpie to mark the back of the casehead with a line from the primer to the rim, so the line points at the high measurement side. (High side or low side actually doesn't matter, as long as you mark them all the same).

Take the marked rounds to the range. Set up a sighter bull and two additional bulls that we'll call 2 and 3. Fire two rounds as fouling shots at the sighter bull to make sure you're on target.

Now place one round in the chamber (or at the top of the magazine in the AR), with the line up at 12:00. Load and fire it at target 2.

Now place one round in the chamber (or at the top of the magazine in the AR), with the line also up at 12:00. Fire it at target 3.

Now place another round in the chamber (or at the top of the magazine in the AR), again with the line up at 12:00. Fire it at target 2.

Now place another round in the chamber (or at the top of the magazine in the AR), with the line this time at 3:00. Fire it at target 3.

Now place another round in the chamber (or at the top of the magazine in the AR), with the line up at 12:00. Fire it at target 2.

Now place another round in the chamber (or at the top of the magazine in the AR), with the line at 6:00. Fire it at target 3.

Continue, always firing with the line up at 12:00 on target 2, but indexing 90° each time for target 3. Thus you should end up with 12 rounds on target 2 that were all fired at 12:00 and 12 rounds on target 3 with three rounds each fired at 12:00, 3:00, 6:00, and 9:00.

Now look at targets 2 and 3. If they are the same size, or 3 is not significantly larger than 2, either your gun's chamber is immune to bullet tilt with your bullet seated the way it is (the chamber is straightening it out during firing), or the groups are so large due to other error sources that you can't tell the difference, so there's no point spending money on fixing it. At the other extreme, if the group on target 2 is half the size of the group on target 3, then your chamber is sensitive to bullet tilt in your load and it is the dominant error term.

Correcting tilted bullets in loaded rounds can be done. Put a hole in your bench that is the size of the bullet (note to self: use a drill next time ). For .224 a 7/32" drill is good. Mark your cartridge high spots with a dot on the bullet. Push the bullet end of the cartridge into the hole with the dot toward you, then hook a finger around the case head and gently pull it toward you. Re-measure the runout. Keep repeating and practicing to get the feel until you have them straightened out to about 0.001" runout. See if these shoot still better than the 12:00 rounds did or not.

To avoid getting much runout in the first place, you want to use a sizing die that has no expander. You can get either a Redding or a Forster full length bushing die and replace the the expander with a next size smaller expander, or you can cut the expander diameter down. One way I've done this is to chuck the expander in a drill and pull a loop of 600 grit wet/dry paper against it until I had reduced the diameter to about .0015" smaller than the bullets. I then selected the smallest neck bushing that didn't let the expander drag on the case neck as I pulled it out of the die. The idea here is to stop the expander from pulling the neck off axis.

Another method is to use a Lee Collet Die to size the neck separately, then use a Redding Body Die to set the case shoulder back the desired amount without touching the neck.

Finally, you want to seat the bullets straight. I like the Redding Competition Seater die for this for the reasons in this review. Some prefer the less expensive non-micrometer version of the Forster Benchrest Seater die. Both use a full-length sliding case alignment sleeve. Redding's design is newer and adds a floating seating stem for what they claim is better self-alignment with the bullet. I started using the Redding when it first came out and they have worked so well I've never tried the Forster product for comparison, so I can't give you a review of that.

[ragwd]

Winc, thanks for the reply, i am searching for the most accurate reload that i can produce. I used the data from my reload books to establish my original seating depth or COL. I did a ladder of powder loads starting at minimum and going to maximum with doing 5 shot groups. My most consistent 5 shot pattern , is now my starting point for this year. Using a variations of COL and powder loads ,using the ladder technique again.
Uncle Nick, You always surprise me with the most thorough and informative answers. I will try the loading at different clock postion shooting at different targets and look for a pattern. Also I will use the hole in bench 7/32, for fixing the runout, i do have a micrometer style seater with a sleeve, I have to take a look at my expander.
thanks to everyone who took the time to read and help.

[rebs]

If you don't use an expander in the sizing die won't that make the bullets harder to start when seating them ?

[Unclenick]

Rebs,

A standard sizing die has to have an expander because it is designed to work with all makes of brass. It sizes the outside of the neck down as much as it would have to do to the thinnest brass made. As a result, it over-resizes necks whose walls are thicker than minimum (most of it). It then needs the expander to undo the excess resizing. This makes it universal but also means it works most brass more than is strictly necessary and tends to pull necks off-axis.

The excess resizing and elimination of the expander can be done two ways. One is to use the Lee Collet Die. It sizes the inside of the neck to the size of a mandrel, rather than controlling the outside of the neck as the standard sizing die does. But it only sizes the neck, so if you want to set the shoulder back and narrow the case walls, you then have to use a body die as a second step.

The other method is to use a bushing dies. These resize the neck from the outside, like a standard die does, but they use a neck bushing for the neck portion of the sizing job, and those bushings are interchangeable and are available 0.001" diameter increments. You select one with a diameter that sizes the necks of your particular lot of brass to the same neck inside diameter the expander would have given them, but without resorting to an expander. This avoids the expander pulling necks off-axis, but adds the complication that you usually have to own several bushings and keep your brass sorted by lot because because neck thickness isn't the same for all makes and not even for all lot numbers of the same make of brass. On the other hand, you can get one that sizes the case body at the same time as the neck, so it's one less step when you want to do that, as compared to using the collet die plus a body die.

[rebs]

Thank you, now I understand better

[Bart B.]

Unclenick, should not the hole used to bend rounds to reduce bullet runout be the size of the case neck?

Otherwise, holding just the bullet and pushing on the case body's back end will change its seating in the case neck and therefore change release force. Isn't the neck's axis relative to the body axis the biggest cause of bullet runout? And preventing neck bending when sizing is important?

At least this is what I learned decades ago. So for 30 caliber ammo, I put a .338" collet in a bullet puller, run a round up into it, gently tightened it then bent the case neck pushing on the case rim. That kept the bullet the same fit to the neck. Accuracy was much better this way than just holding the bullet when bending the round.

One other thing for most bullets, seating them so they touch the lands (or have a crush fit) when chambered improves their centering to the bore as well as accuracy. Yes, this may increase pressure, but not much. A grain or so below max listed is typically enough to do well. Berger VLD usually seem to shoot most accurate with a bit of jump to the lands.

[Unclenick]

Bart,

That's a good point. I've seen three tools that are sold for correction. One pushed the bullet (Bersin), one the middle of the neck over the bullet bearing surface (Hornady), and one the base of the neck (NECO). I've seen plenty of bullets off-axis in a case neck (bulge in neck at bullet base more pronounced on one side than the other), so not all the tilt is in the neck. Perhaps the ideal system is to adjust the neck to zero runout first, and then the bullet only if there's any runout still left?


Ragwd,

If you're seeing this and want to try the neck, on .223 use a 1/4" drill and wobble it a little until the necks fit (0.253" is .223 case neck max diameter).


Bart,

I've seen two conflicting measurements of the effect of seating into the lands on pressure. One was Dr. Lloyd Brownell's study which had the pressure rising only about 1% over the last 0.030" of seating to touch the lands, and the other is at RSI's site where before and after firing of a 6 mm BR showed a 20% pressure difference between 0.030" off the lands and seating out to touch them. Not enough difference to get you from a good load to a proof pressure, but still not good for case life. So I'm expecting which effect it has on pressure is another one of those things that varies with individual chamber and cartridge and bullet dimensions. Certainly, if you develop the loads touching the lands and don't get any pressure signs, you are in good shape.

Interestingly, Berger found that seating to touch the lands with their secant ogive VLD bullets did not always shoot best. Another shape factor thing. There's a letter about their experience with it, here.

[Bart B.]

Unclenick asks perhaps the ideal system is to adjust the neck to zero runout first, and then the bullet only if there's any runout still left?

Yes, yes, a thousand times yes.

And for bottleneck cases, full length sizing dies with necks about 2 thousandths smaller than a loaded round's neck diameter (no expander balls whatsoever) produces the straightest necks best centered on the case shoulder that's set back a couple thousandths from its fired position. This first guarantees the round will chamber nicely with the bolt in the same place for every shot; no binding at all. This also guarantees perfect bullet alignment with the bore when the case shoulder centers in the chamber shoulder when fired (and in most rifles, when chambered) and its neck is well centered in the chamber center floating there in space with a bit of clearance all around it.

This is the main reason Sierra Bullets chose to properly full length size all the bottleneck cases used to test their bullets for accuracy back in the 50's. And also the reason why high power match rifle competitors have done it just as long. Benchresters finally figured this out a few years ago.

No bullet seating die fully corrects for bent case necks. So get the case neck straight and well centered on the case shoulder before you prime, charge and bullet the case.

And runout up to 1% of the bullet diameter doesn't effect accuracy any significant amount anyway. .0022" for 22 caliber rounds, .003" for 30 caliber ones.

There's other things more important for best accuracy to get right that trying to get under .001" bullet runout for any cartridge.

[ragwd]

Bart, excellent information. I always felt that I was going wrong not in the seating but in the prep. The full length sizing dies that you describe , do they have a particular name or brand ? I have a RCBS competition die set, it was pricy so I thought it was the correct one. It says "elevated expander ball". It does not seem to expand and the calipers show that it doesn't. I rechecked some cases I have ready for powder, for run-out and they have average of .005, so that is at least half the problem. In looking at my dies it looks like the primer removal rod sizes the neck from ID and the body is sized by OD. Is that right? I am fairly new to reloading bottle necks so I might be wrong, but if Im right wouldn't that promote run-out? If I get my run-out down to .003, i will put this to rest. Also this spring Im working on COL to try and get the olgive closer to lands to decrease pattern. What other issues should I be looking for ?
Again thanks to all that's taken the time to read and especially to the people who have taken their time to post.

[Scottish Highlander]

Forgive me for asking as I have been following the thread and trying to understand everything you guys are talking about. Some of which I don't fully understand yet as I am just learning reloading and the science to it all but Bart you said this below.

......"One other thing for most bullets, seating them so they touch the lands (or have a crush fit) when chambered improves their centering to the bore as well as accuracy. Yes, this may increase pressure, but not much. A grain or so below max listed is typically enough to do well. Berger VLD usually seem to shoot most accurate with a bit of jump to the lands".......

I 100% understand what you are saying here and I have been told by no uncertain terms load a bullet so as it is touching the lands when firing. This increases pressure and could be catastrophic to you or your rifle or have I missed something or misunderstood your post ????

Correct me if I am wrong but the discussion is to do with the bullet being seated perfectly straight in the brass and so that when it is pushed out of the neck of the brass and jumps to the lands it is already on a perfectly straight line of direction rather that bouncing of the lands and finding its way down the barrel. Sorry this is the best way I could explain the way I am interpreting your posts.

[wncchester]

"If you don't use an expander in the sizing die won't that make the bullets harder to start when seating them ?"

High seating resistance usually causes more run-out so using a proper diameter expander is better. I prefer a ball that's full bullet diameter, that's what has to go back in the neck anyway so I'm not losing any bullet grip.

A tight throat will limit the maximun bullet tilt but few throats are tight enough to eliminate it. Any bullet that hits the rifleing tilted will tend to straighen up but not completely, leaving the meplat to cut a helix down the bore and degrades accuracy.

As a personal thing, I have no interest in bending a cartridge straight. I prefer to prep my cases and load them straight to start with.

[ragwd]

Wynn, I could not agree more with your statement......."As a personal thing, I have no interest in bending a cartridge straight. I prefer to prep my cases and load them straight to start with." But I do have about 50 loaded with about .01 run-out, the suggestion to bend back was trying to help me with this batch. next batch I will hopefully do better, thanks for your help.

[ragwd]

Scotty, your question "Correct me if I am wrong but the discussion is to do with the bullet being seated perfectly straight in the brass and so that when it is pushed out of the neck of the brass and jumps to the lands it is already on a perfectly straight line of direction rather that bouncing of the lands and finding its way down the barrel. Sorry this is the best way I could explain the way I am interpreting your posts."

I am really not sure of what happens once the bolt is closed but I do know it has a effect on accuracy. How much I dont know. the exercise is to determine how much if any improvement. Same with the COL, how close to the lands is best for accuracy. I have reloaded pistol straight wall shells for a few years and now moving on to rifle bottle nose for accuracy. Last year I tried different powder loads and I think I found a good result with 23.5 grains of Hodgdon H335, pushing a Nosler69 grain hpbt. My ar has a 1 to 9 rifling. This year I want to work with Col to get closer to lands without touching and improve upon bullet concentricity. SO im asking the the guys with more experience how to proceed.

[Unclenick]

The proximity of the lands is a variable, and some guns like it more one way than another, as this old page (item 3.) describes. Loading to touch the lands will raise pressure in some instances more than others, but if you work the load up with it that way, there's not a pressure problem with it. You'll just possibly end up with a lower load. This is Berger's approach to the problem.

[Bart B.]

If one uses a standard full length bottleneck sizing die without an expander ball, the result will be a case mouth so small that seating a bullet into it will cause two things.

First, the neck will bend a lot into the shoulder when the bullet's seated.

Second, the neck tension, or release force needed to push the bullet out, will be so great that high pressure will happen and may well be over the accepted limit for the cartridge.

As a result, poor accuracy happens, along with an extra loud bang and more recoil.

Such dies need their necks lapped out to a couple thousandths smaller than a loaded round's neck diameter. Some folks started doing this back in the 1950's long before full length bushing dies were available. They would have a set of dies so modified, each with .001" increment in die neck diameter. I've as set of four .308 Win. RCBS dies so modified.

[Unclenick]

Brush Research makes their BC Flex Hones small enough for this job. I recommend you watch their basic video on how to size and use these tools, then watch their Firearms-specific video which mostly spends time showing how to turn a 12 ga. into a 12½ ga., but you'll get the idea. You will want graded hones to smooth a die down for a polish, then to finish with Flitz on a bore mop. It looks to me like their chamber hones might be able to customize a die.

I read at, I think, Redding's site, that they nitride dies about 0.030" deep, so you should have some cutting room to work with to tweak a neck.

[ragwd]

I guess im a typical rookie. everytime I come here for answer I get a ton of information helping me with my question, but it always ends up opening new questions in my mind. i have taken apart my sizing die and have measured the ball at .220. Also I measured case length before and after sizing and I seem to be stretching the case by .007, hmmm, is this why people " bump back the shoulders"? I know there are pros and cons to bumping the shoulders, Can we open this discussion? how is it done? with the sizing die ? Thanks again for helping me muddle thru this.

[Unclenick]

When I was still shooting my M1A with Remington brass I would get, in the same bunch of cases, some that grew 0.010", some that grew 0.000", but 0.005" was about average. A case that grew one time might not grow the next. It varies with the brass and with how warm the load is. So there's nothing unusual about your number and it may change the next time.

To set a shoulder back, you need a way to measure it. The Hornady LNL caliper adapter has case headspace datum inserts available for this. The RCBS Precision Mic for your chambering has a separate thimble for this. You can even just improvise with a caliper and a spacer or a bushing or a bearing, as shown below. For .223 you ideally want a .330" diameter hole, but a 5/16" bearing or bushing is close enough (0.3125").



What you are looking for is to screw your sizing die into the press just far enough that after resizing that shoulder measurement will be 0.001" to 0.002" shorter than it was before resizing. Those numbers are for a bolt gun or single-shot. For a gas gun you want 0.002" to be the dead minimum, so 0.002"-0.003" is the target and anything less than 0.002" setback should get sized again, as shorter is a safety issue in a self-loader. Depending on how rigid your press is and on how consistent the brass is (sorted to have a matching lot and load history is best) this number can move around some. RCBS makes special shell holders that are thicker on top than normal in 0.002" increments so you can set the die up with the normal shell holder contact compression and still have the case come out longer than with a standard shell holder. That compression can help compensate for some case variation. Shim washers are also available that you can slip over each case before sizing to do the same thing.

[ragwd]

Uncle Nick, As always very informative answer , complete with pictures. They always help, sometimes it hard to visualize. But yet again I seem to be taking a step backward instead of forwards with your information. I set up my full length sizing die the way RCBS explains in the pamplet that came with the competition set. It says to raise the shell holder and then screw in the die until it touches the shell holder. then back off the shell holder and turn die in a additional 1/4 to 1/2 turn. I do that and it stretches the shell .005 longer than before sizing. My question is how do you set the depth of the die to achieve set back of .002. Sorry if I missed something obvious. I guess i should try the bushing and measure first,
Thanks again