30-06 to .308 Headspace Confusion

[BulletFactory]

The rifle is an M1A.


I ran into a problem today I dont understand. When I sized the 30-06 brass down to .308, I checked the headspace on each newly sized round one at a time with the Hornady headspace gauge. (the one that goes on the calipers).

My Rifle headspaces at 1.631.

I set the headspace of my rounds at 1.626

When I drop the cases into the Lyman headspace gauge, (the barrel shaped one that mimics the chamber), The case head sticks out too far. Actually quite a bit.

I took the round, and checked the headspace on the Hornady tool again, and it checked fine at 1.626.

I took the round and slowly chambered it into the rifle. I still had the extractor in the bolt, so I bumped the charging handle to catch the round, then pulled it out a bit, and slowly let the bolt ride forward, and it closed with only a little "bump" from my hand.

I dont get it.

Are these rounds safe?

[BulletFactory]

I only loaded one round with powder and a bullet to check, so I dont have to pull a bunch of them. What I have, is a pile of brass that has been sized, neck turned, deburred, the primer pockets have been reamed, the length is 2.005, and they all headspace at around 1.626. They are ready for primers.

[oneokie]

Quite possible that your chamber is on the large size of SAMMI dimensions and your Lyman headspace gauge is at minimum SAMMI dimensions.

[HangFireW8]

The taper of these two cartridges differ, not just the shoulder height. When you resize in a standard 308 die, they get fatter. When you put it in a minimum cartridge gauge, the sides engage before the shoulder.

If you use a small base size die, you'll have better luck getting it into the gauge. But, you are not done yet. When you shoot it the first time, the sides will fill out fully. To do this it will have to draw from somewhere. Either the case length will get shorter or the case head walls will get thinner. In extreme cases this can lead to incipient or actual case head seperation.

To make sure it always draws from the neck, oil the neck and shoulder lightly and make sure the chamber is clean, dry and oil free as well as the case base, for each and every shot. Load to full pressure and after fireforming you'll have good brass (if a bit short).

[Mooseman]

Sounds to me like you are confusing case length with headspace or something...
Headspace is the clearance from the bolt face to the shoulder Datum line...in the rifle.

[Larry Gibson]

Forget the Lyman guage, let the rifle's chamber be the guage. You are not going to fire them in the Lyman guage. You have them sized/formed correctly for your rifle as evidenced by them chambering. Yes they are safe. Once fire formed and then resized you will probably find a different measurement. I do not recommend SB dies for use with the M1A as it has milsurp chamber dimensions which are generally generous. I do suggest the RCBS regular .308W X-die. With it you will get much longer case life in the M1A.

Larry Gibson

[BulletFactory]

Its not a case length issue., I've ruled that out.

I'm using RCBS small base X-dies. I cut the 30-06 brass with a tubing cutter, then I trimmed them to 2.010, then I ran them through the X-dies. with the mandrell removed

oneokie may be on to something here.

[HangFireW8]

Its not a case length issue., I've ruled that out.

I'm using RCBS small base X-dies. I cut the 30-06 brass with a tubing cutter, then I trimmed them to 2.010, then I ran them through the X-dies. with the mandrell removed

oneokie may be on to something here.

Sure he is... But where is the brass stopping?

I missed that this is for a self loader, I always assume bolt when I think of 308. Nonetheless, after the first firing, I would still check for incipient case head seperation. This holds for any cartridge conversions, and also for reloading for semi's as well.

HF

[popper]

Check to make sure the neck isn't too long, from your post it isn't. Use the paper-clip test for an internal groove. If that's ok, shoot em. That's a lot of work for 308 cases.

[Larry Gibson]

Have you annealed the necks and reamed/turned them?

Larry Gibson

[ShooterAZ]

Forget the Lyman guage, let the rifle's chamber be the guage. You are not going to fire them in the Lyman guage. You have them sized/formed correctly for your rifle as evidenced by them chambering. Yes they are safe. Once fire formed and then resized you will probably find a different measurement. I do not recommend SB dies for use with the M1A as it has milsurp chamber dimensions which are generally generous. I do suggest the RCBS regular .308W X-die. With it you will get much longer case life in the M1A.

Larry Gibson

+1...

Larry is correct. Fireform them and check case length again. You do not need small base dies for M1A, contrary to popular opinion.

[BulletFactory]

Have you annealed the necks and reamed/turned them?

Larry Gibson

I have turned the outside of the necks, but I have not annealed them.

[Larry Gibson]

I have turned the outside of the necks, but I have not annealed them.

If the cases "chatter" when pulled out over the expander button after FL sizing you may be pulling the shoulder back slightly forward.

Larry Gibson

[sbowers]

I think mooseman is the one with the correct answer.
Steve

[BulletFactory]

They worked perfectly, thanks all.

[fredj338]

I guess I want to know whay bother cutting down 06 when there are so many 08 cases available. Even necking up 7-08 would be preferable. I am thinking maybe the case shoulder isn't forming nicely until fired, so maybe size down just a bit more to get the bilt to chamber. Neck thickness would be the other thought. Your internal volume should be quite a bit diff than 08 brass BTW, make sure you work those loads up separate from other brass.

[BulletFactory]

I did have to adjust the sizing die to compensate for the shoulder. I then had to expand the necks a bit, neck turn , and fire form them. A friend of mine has an -06 and I can get the brass for free. Im on a limited budget, so I am happy to use whatever I can get my hands on.

[Cadillo]

If you are sizing a 3006 case to .308 Win, you must have some awfully thick case necks. If I were to be so ambitious as to try that, I would either ream or turn the case necks. Good luck, and maybe warn shooters at nearby benches. That first firing will really expand the webbing, but maybe this conversion is done with sucess, and I just never heard or thought about it.

Good luck!

[BulletFactory]

How much should I reduce the charges by?

[popper]

Fill the cases with H2O and compare(mod 308 vs .308), post diff here and maybe some one can answer.