How critical is case length for a .308?

Big Caliber · June 23, 2008, 05:56 PM

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.

azredhawk44 · June 23, 2008, 06:10 PM

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.

crowbeaner · June 23, 2008, 06:36 PM

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.

Bullet94 · June 23, 2008, 08:20 PM

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

Slamfire · June 23, 2008, 09:12 PM

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?

Whisper 300 · June 24, 2008, 04:45 AM

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

30Cal · June 24, 2008, 06:02 PM

Quote:

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

I'd agree with that.

Big Caliber · June 24, 2008, 11:21 PM

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

Threefeathers · June 25, 2008, 12:06 AM

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.

rn22723 · June 26, 2008, 02:59 PM

Too long of a case could act like a crimp the case mouth into the lands and spike the pressure! Nothing to fool with!

**44 AMP** · June 29, 2008, 10:22 PM

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.

June 23, 2008, 05:56 PM	#1
Big Caliber Senior Member Join Date: October 10, 2006 Location: S. CA Posts: 421	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.

June 23, 2008, 06:36 PM	#3
crowbeaner Senior Member Join Date: June 4, 2007 Location: Upstate SC Posts: 1,943	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. __________________ If you want your children to follow in your footsteps, be careful where you walk. Beware the man that only owns one gun; he probably knows how to use it. I just hope my ship comes in before my dock rots.

June 23, 2008, 08:20 PM	#4
Bullet94 Senior Member Join Date: September 8, 2004 Location: Kansas Posts: 723	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 __________________ PRO-SECOND AMENDMENT - Live Free or Die

June 24, 2008, 11:21 PM	#8
Big Caliber Senior Member Join Date: October 10, 2006 Location: S. CA Posts: 421	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

June 29, 2008, 10:22 PM	#11
44 AMP Staff Join Date: March 11, 2006 Location: Upper US Posts: 28,833	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. __________________ All else being equal (and it almost never is) bigger bullets tend to work better.

June 23, 2008, 06:10 PM	#2
azredhawk44 Junior member Join Date: September 28, 2005 Location: Mesa, AZ Posts: 6,465	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.

June 23, 2008, 09:12 PM	#5
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	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?

June 24, 2008, 04:45 AM	#6
Whisper 300 Senior Member Join Date: December 29, 2006 Posts: 155	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

June 25, 2008, 12:06 AM	#9
Threefeathers Junior member Join Date: June 7, 2004 Location: AZ Posts: 392	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.

June 26, 2008, 02:59 PM	#10
rn22723 Junior member Join Date: December 10, 2001 Location: Burbs of Minneapolis Posts: 676	Too long of a case could act like a crimp the case mouth into the lands and spike the pressure! Nothing to fool with!