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Old April 7, 2011, 03:02 PM   #1
deepcore
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Man-scaping .308

I'm talking .308 but my question I guess can be for any round...
My RCBS Trimmer 2 instructions says max length is 2.015 and trim length is 2.005.
Do you guys trim to the max or the min?
I there accuracy advantages to either?
I trimmed on to 2.005 and it seems like there's not a lot of neck left.

Thanks
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Old April 7, 2011, 03:12 PM   #2
HiBC
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Generally folks trim to the minimum,then the cases have a little room to grow.The difference,hi to lo,is only. .010,which is 1/100 in.I'm a little concerned that it seems the necks are visibly shorter.Could it be you cut them to 1.905? That might be a problem.
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Old April 7, 2011, 03:17 PM   #3
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When the length gets to 2.015 , you shorten .010 to 2.005 . That's why it's called " Trim to Length " .010 short won't hurt a thing . When I'm Neck sizing I always trim .010 under Trim to Length .
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Old April 7, 2011, 03:42 PM   #4
deepcore
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Will double check but my caliper was reading 2.005 on the one case I trimmed last night.
Just starting out on rifle rounds so going slow. I saw the neck (and it's not there's none there anymore) and thought to myself it just looked short holding the trimmed case next to a factory round.
I guess it will be something to get used to.

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Old April 7, 2011, 04:24 PM   #5
Clifford L. Hughes
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Clifford L. Hughes

Deepcore:

Case necks stretch mostly from pulling the expander plug throug them. To help prevent neck stretch clean the inside of the neck with a dry bore brush and then use a spray lub on the neck's inside. By trimming to minimun you will get several reloads before the brass needing trimming. Calipers measure the case from the mouth to the base. However, there's still and important measurement necessary: the shoulder to the base measurement. If, unknown to you, the full length sizing die pushes the shoulder back to far and then you measuer the over all length you could experience excessive head space.

Wilson makes a chamber type measuring gage. You just drop the sized case into the chamber. On one end if the nedk protruds above the maximun trim length, trim the neck back to minimun. On the opposite end of the gage you can read whether the head space is correct or not and adjust your sizing die accordingly.

I have found that neck sizing and inside neck lubrication reduces neck streth considerably.

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Last edited by Clifford L. Hughes; April 7, 2011 at 04:32 PM.
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Old April 7, 2011, 04:35 PM   #6
FrankenMauser
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Some sources will recommend trimming to 0.010" short of max length; some will recommend trimming to 0.020" short of max length. It doesn't really matter on bottleneck cartridges, unless you're dealing with a short-neck (like the Gibbs cartridges).

I consider 0.015" to 0.010" short of max to be my "butter zone". I tweak the trimmer until I'm in there somewhere, and run the brass through. Since it'll all be coming out at the same length, it doesn't matter if it's 0.013" short, 0.010" short, or 0.015"short.
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Old April 7, 2011, 05:18 PM   #7
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Just to correct some previous information: the trim-to length is not the minimum. If you look through the SAAMI drawings (links are here), you'll discover that most rifle rounds have plus 0.000", minus 0.020" case length tolerance. The trim-to length is simply in the middle of that, largely because the cutters used by the case manufacturers aren't as precise as a lot of hand loading trimmers are, and new cases can sometimes vary a number of thousandths, case to case.

Maximum length is a critical number. Too much length can jam the throat of a chamber and raise pressures rather substantially.

Minimum length is a non-critical number and is really only specified so bullets that will be crimped into their cannelures don't get seated too deeply into the case. If you ignore it, and trim more off, as some .308 match shooters used to do so they didn't have to trim again before they tossed the brass, there's no inherent safety issue. But in that instance they were loading match bullets to magazine length COL with no crimp, so as long as they kept their COL the same, there would be no substantial effect on pressure from crowding the powder charge. A benchrest or varmint shooter would want to keep neck tension more consistent than that, and I'm not recommending the method because of that; just pointing out could be done without creating a safety issue.
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Old April 7, 2011, 06:37 PM   #8
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Quote:
Case necks stretch MOSTLY from pulling the expander plug through them. To help prevent neck stretch clean the inside of the neck with a dry bore brush and then use a spray lube on the neck's inside.
I don't buy into the commonly repeated myth that inside case neck expanders PULL the necks forward. If an expander would be able to do that, you would need a LOT of force on the press handle.

What I put in bold font is the fix for expanders to make the trip through the neck effortless. I use a RCBS case neck brush set for all my rifle loading. It consists of white nylon brushes in 3 sizes that do most rifles calibers. I roll them on a lube pad to put the faintest amount of lube on the ends of the bristles. Then, they're run into the necks to put a very small trace of case sizing lube inside the neck.

http://www.midwayusa.com/viewProduct...tNumber=770172

What moves the brass forward is the pressure of firing causing the brass to flow into the neck. Also, an improperly set-up full length sizer die can force the brass to artificially flow forward.
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Old April 7, 2011, 07:43 PM   #9
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I trim to 2.00" plus or minus a couple of thousands.

Trimning is necessary to prevent the neck sticking in the throat. Other than that, unless you trim so much the bullet won't stay in the neck, trim length is unimportant.
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Old April 7, 2011, 07:56 PM   #10
deepcore
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This is what I was thinking while looking at the case I trimmed... That the variables are related somehow.
If case length is related to case headspace setting then are the published case length and trim recommendations based on what headspace value?
Is it possible to base the trim length just to the length of the neck alone?
Though I haven't seen a tool for that.
What if the Wilson gauge is not set for the headspace you'd like or need?
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Old April 7, 2011, 09:39 PM   #11
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I have kept cases trimmed at 2.01", a little extra case neck didn't seem to hurt when loading 125-130gr closer to the lands.
I have some Nosler pre-prepped brass that comes trimmed to 2.005".
The chamber of my rifle seems to have no trouble with 2.015" length brass.
It would be nice to keep my dedicated .308 Win. Wilson trimmer set to one length.
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Old April 7, 2011, 09:48 PM   #12
deepcore
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I trimmed some more and measured headspace and trim length with my trimmer set for 2.005.
I will work on my consistency.
Getting headspace readings from 1.626 to 1.628. Not true for all 50 cases but there is a trend where the case length is up or down (2.005 to 2.007) corresponding to the .002 difference in headspace.
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Old April 7, 2011, 11:47 PM   #13
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Quote:
Is it possible to base the trim length just to the length of the neck alone?
There is at least one powered trimmer that works off the shoulder datum (the Giraud) and trims consistently to a length you set from that reference. This is the length that you are trying to control so you don't jam the case mouth into the lands and raise pressures. However, this trim method will not ensure consistent case length unless you resize before trimming. (Which is the normal practice anyway...)

Quote:
What if the Wilson gauge is not set for the headspace you'd like or need?
The Wilson gauge is not adjustable (for typical bottleneck cartridges) and is made to SAAMI minimum / maximum headspace for the dimensions of the two steps on the bottom of the gauge. The instructions recommend the use of a straightedge in conjunction with the gauge -

http://www.lewilson.com/images/CASE_GAGE.pdf

This gauge will at least help you set up a resizing die to prevent dangerous excessive headspace if you follow the instructions and set up the die for "in the middle" of the two steps on the gauge.

There are other gauges available, such as the Hornady (formerly Stoney Point) pattern and the RCBS Precision Mike. However, you can use the "tail" of a standard dial caliper in conjunction with a Wilson gauge to measure the offset of the case head from the base of the gauge if you straddle the notch with the caliper to prevent rocking.

I have done this to set up a resizing die for 0.002" less than the measured length of a fired case.
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Old April 8, 2011, 12:29 AM   #14
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Hello, The best tool you can buy is a chamber length gage sold by Sinclair International. I laugh when I read of guys sweating over .001" on their cases..If they would only check the chamber on THEIR rifle..instead of taking some books measurement..I'll bet they would be surprised. I checked several of my own rifles, and some were as much as .030 to .040" over max length.
I think we are doing alot of brass triming that really isn't necessary.
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Old April 8, 2011, 10:45 AM   #15
Unclenick
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Deepcore,

No, trimming does not affect headspace except in pistol rounds that headspace on the case mouth. In a chambering that headspaces on the shoulder, it is the position of the shoulder that affects headspace, so the sizing die can change it, but not the trimmer.

As Dmazur said, you are really trimming to control how far the case neck sticks out forward of the headspace determinant (the shoulder). Cartridge length is an indirect measurement of this, where the difference between your headspace gauge and your bullet oigve seating depth gauge readings is what is an actual measure. The Giraud and Gracey motorized trimmers and the less expensive Possum Hollow hand/drill operated trimmers all provide that shoulder to ogive measure.

Hatcher showed that just closing the bolt rapidly on an Enfield rifle could shorten headspace up to around 0.006", IIRC. Some of that is the case fattening to fill the extra diameter in the chamber. A little may be neck lengthening. To allow for shoulder setback from this perhaps growing the neck a little, most modern commercial chambers have some extra neck length. 0.020" isn't uncommon. However, there are too many chamber differences out there to count on that, so you really have to do a chamber cast or measure it by other means to learn what your own chamber has available. You're safer sticking with the SAAMI maximum until you do.

When you fire a cartridge the case fills out into the chamber. When you run it into a sizing die, the die first starts to narrow the case, which actually lengthens its headspace (the brass has to go somewhere), then pushes it shorter again at the shoulder. Again, the brass has to go somewhere. In standard sizing dies for bottleneck cartridges it flows into the neck from the shoulder, growing the neck same as it did when the case shoulder was formed at the factory originally, and forms the "dreaded donut", a small internal bulge of brass at the base of the neck. When you withdraw the case over an expander it will try to iron that donut forward a little which contributes to neck growth a bit.

To see this for yourself, measure the length of a fired case, then use a headspace gauge and measure that, and record the difference in the numbers. Then resize the case with the decapper/expander removed, and find the difference between the two again. The increase in difference is in neck growth. Do this with a dozen cases to get an average. Put the decapper back in, and repeat the experiment with another dozen fired cases. The difference in the difference of the two methods is due to the expander. Note that expanders are famous for pulling necks off-axis, too, and that can affect your readings by making the shoulder slightly asymmetrical.

You can avoid a lot of the brass moving using an RCBS X-die, which maintains neck ID with a mandrel that doesn't pull anything anywhere. It does allow the neck to thicken slightly and I expect the donut brass will move down into the case, since the mandrel will block it. I haven't played with one long enough to be sure.

The other method, popular with accuracy shooters, is to resized the case body separately from the neck, using a Redding Body Die, then a Lee Collet Die, which also uses a mandrel and also does not upset the coaxiality of the neck, as demonstrated in this UK YouTube video.

If you want an inexpensive way to measure the headspace size on a case that's been fired in your chamber, you can use a caliper and a spacer or a journal bushing (as I show below). The big fat spacers or a journal with a flange (shown) are easier to keep flat against the caliper anvil. I like the bigger jaws on a 12" caliper for this, but anything can be made to work with some practice. A height gauge and surface plate are even better. Keep in mind that the hole in the spacer is not precisely the headspace datum diameter, so your result is relative. You can compare it to new brass measured the same way to get a vague idea of where you are, but comparison to a headspace gauge (shown in the first picture) is better for zeroing.

Brass will spring back a bit after firing, so measuring headspace on brass is not as precise as using a headspace gauge set in 0.001" increments or, done carefully, the Sinclair tool mentioned earlier. To improve the precision, neck size and refire the same case several times. When it is beginning to feel a little snug on chambering, measure it then. You can also make the same measurement after each of several firings and find a trendline regression toward its limit, but that's maybe a little more math than most shooters want to mess with (though Excel's trendline function will do most of the work for you).

Zeroing on the headspace GO gauge:



Comparing to a fired case (or to a resized one for sizing die setup):


So that case is 0.003" over SAAMI chamber minimum to go in a chamber that is 0.005" over minimum.
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Last edited by Unclenick; April 9, 2011 at 10:46 AM. Reason: Added a little info.
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Old April 8, 2011, 02:48 PM   #16
FrankenMauser
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Quote:
I laugh when I read of guys sweating over .001" on their cases..If they would only check the chamber on THEIR rifle..instead of taking some books measurement..I'll bet they would be surprised. I checked several of my own rifles, and some were as much as .030 to .040" over max length.
Long necks might be common in rifle chambers, but there's no guarantee any given rifle will fit that generalization. As UncleNick said, it's best to assume SAAMI maximum length is your own rifle's maximum length, unless you determine otherwise (which is a waste of time for most shooters; and an unsafe practice, if they don't know what they're doing).

For example:
I have a beat up Mossberg 800 in .243 Win. Since these were super-low-cost rifles, with fairly low quality control standards, they're not known to be held to tight tolerances. (The machining is so rough, you can get the bolt jammed in the action if you don't twist it to one side while operating the bolt!) It would be easy to assume it has a sloppy chamber, with all kinds of oddities and unusual measurements. ...But it doesn't. It has the tightest, most dimensionally "perfect" factory chamber of all my centerfire rifles.

With a properly formed case, running more than 0.005" over max length will cause issues.

When I got this rifle from my brother, it came with several hundred pieces of brass, ranging from 1960s production to 2000+ production; all unknown-times-fired. While trimming the brass, I ran across quite a few cases that had been no more than 0.010" to 0.020" over max length; but the necks had been extruded into the throat, when fired by the previous owner. On those cases, the neck now has a a throat-diameter 'extension' running from 0.003" to 0.008" thick, and 0.030" to 0.080" long. Those cases are all trash. The high pressure encountered when the over-length cases were fired caused the case heads to swell, and loosen the primer pockets.

Yet... my .270 Win will take cases 0.015" over length, all day long.

If you don't have the time, patience, and a reason to find out what the neck length limitations are in your rifle... just use the SAAMI max length.
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