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Old June 23, 2008, 05:56 PM   #1
Big Caliber
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How critical is case length for a .308?

How far over or under can you go from the "trim to" length before accuracy is affected? Is plus or minus 0.001" a big deal? The rifle is a "tack-tickler" used for bowling pins at 400-600yds. I don't sort by weight, but do neck-size after each session. At my age & with my eyes I have no illusions about being on a par with a trained military sniper, I'm just having fun. (They need to design an affordable, programable, case trimmer.) So, can I get away with (+-)0.001" -0.0015" tolerance using Lapua brass? I value all your opine's.
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Old June 23, 2008, 06:10 PM   #2
azredhawk44
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I found out the hard way (well, not the KABOOM hard way, but I digress) that .308 doesn't like case lengths in excess of 2.015".

I had a batch of ammo that I trimmed to 2.015 with a Lee trim system and then re-sized.

Stupid me. Re-sizing brings the neck out longer a little bit. I didn't retrim after the fact.

None of that batch of ammo would feed properly in my M1A as a result. I had to tear it all down, salvage the powder and bullets, then trim the cases. They were running between 2.016-2.019 prior to trimming.

Now I use a Hornady case trimmer since it is more adjustable than the Lee, and I trim all the way down to 2.000". This gets me 3-4 firings before I have to re-trim, and my rifle is brutal enough on brass that that's about all I get anyways.

I hate case trimming too.
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Old June 23, 2008, 06:36 PM   #3
crowbeaner
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I just FL size my brass the first time and then trim to the minimum length. After 3 firings I do the same thing again. Most factory chambers are cut a bit longer than a benchrest rifle, so you can get away with brass that is 2.015 to 2.020. If you size before you trim you don't have the stretch when you trim and then size. I just made 550 .223s into .222s, and that trim job was left to the Lyman with the drill chuck shaft. The Black and Decker made short work of the 2 mm I had to cut off each one. The RCBS trim die just didn't appeal to me, and the hand crank on the RCBS trimmer makes a lot of work when you are trimming that many cases.
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Old June 23, 2008, 08:20 PM   #4
Bullet94
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You might try these if you want to really know -

http://www.sinclairintl.com/cgi-bin/...308&type=store

If you want to make trimming easy you might try one of these -

http://www.giraudtool.com/prod02.htm
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Old June 23, 2008, 09:12 PM   #5
Slamfire
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Trim length is a safety consideration. You do not want a long case neck pinching the bullet in the throat.

I trim my brass to 2.00".

Plus or minus .005" makes absolutely no difference on target.

The cartridge headspaces on the shoulder, but case length is measured from the base. How accuracy critical can it be?
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Old June 24, 2008, 04:45 AM   #6
Whisper 300
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Years and years ago before I knew what case trimming was-back in the late 60's or very early 70's I learned the hard and expensive way that if you let the case grow and just cam down HARD on the round to get it to chamber, a new .243 action is costly.
Did not lose any body parts but did have to get new underwear

When that bullet is jammed tightly around the neck of the case and then jammed again into the barrel, the pressure go sky high.

Ah, the joys of youth and inexperience. If you live through it you learn(hopefully).

So, to answer you question does it matter in a .308-Yeah, it matters.

Gary
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Old June 24, 2008, 06:02 PM   #7
30Cal
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Quote:
Plus or minus .005" makes absolutely no difference on target.
I'd agree with that.
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Old June 24, 2008, 11:21 PM   #8
Big Caliber
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Thanks guys. I always measure my brass after each re-size. The hand crank RCBS trimmer is not the most precise instrument on the bench, depending on how much lateral pressure I apply while turning the crank. That's why I wondered how big a factor 1 or 2 thousandths inch would be was down range. I have a chamber gauge that tells me my chamber is/ 0.002" uder minimum printed specs. And yeah, I probably should break down and buythat Giraud trimmer...Hmmmmmmmm

Last edited by Big Caliber; June 24, 2008 at 11:28 PM. Reason: add on
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Old June 25, 2008, 12:06 AM   #9
Threefeathers
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I am very careful about triming rifle brass. I have the lyman trimmer with the drill atatchment. It is accurate and fast. I do 100 pieces at a time so I can put 100 perfect bullets together.
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Old June 26, 2008, 02:59 PM   #10
rn22723
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Too long of a case could act like a crimp the case mouth into the lands and spike the pressure! Nothing to fool with!
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Old June 29, 2008, 10:22 PM   #11
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Note the trim to length....

is about .01 less than max length for most cases. This is just a convienent number to stop at, short enough so that a minor (.001-002) variation will not get you in trouble for max length. It is simply a good number for uniformity, which is needed for crimping, where uniformity matters.

Don't worry about it if you are .001 +/- trim to length, as long as you are safely below max case length you are fine.
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