Sass problem

[Travis sawyer]

Recently purchased a new armalite super sass and with much load testing I've been able to get consistent .50-.75 size groups from this rifle when single feed. The problem is that when feed from the mag the groups open up to 1.5". So tonight I loaded the mag and manually ran them through the rifle and checked bullet seating depth and this did not change, I use a crimp. Also rechecked run out, also no change. But when I measured the shoulder it had been set back .005". When loading for the rifle I measured a spent case and bump the shoulder back .002". Does anyone have any idea what would cause the additional .005" set back when the bolt rams it home? Can't help but to think this would causing my problem. Thanks in advance for your input.

 

[blksno]

Don't know the cause, but the result shouldn't make any difference when it's fired.
It's still getting "rammed home" whether you run it single shot or semi-auto.
It's at least getting ran hard enough to lock the bolt.
I highly doubt that's the reason.

Let someone else try...or drop it in a lead sled and do it over.
Driving a semi-auto single shot, where you get time to re-position between shots while you reach for the next round, is a big difference compared to just fine tuning your position between sudden bursts of recoil as you do with running semi from the mag.

 

[sinister]

You may only be pushing the shoulder back .002 (on your press), but in fact the carrier group is resizing back .005 when self-loading. This may be a brass-killer later down the road.

Does this happen with factory ammo?

The "Preferred" method is to use proper neck tension vice crimping which can contribute to bullet core/jacket separation and contribute to "Out-of-round wobble."

 

[ICANHITHIMMAN]

Are you trimming the brass, don't crimp if you don't have a crimping canalur. Why did you single round load when testing? Believe it or not the mags make a difference, buy the best!

 

[Travis sawyer]

Thanks for the input. I do trim to 2.08" every time I reload. I've tried to get the bullets to stay in place with neck tension, honed the expander ball to .004" under bullet size and still does not hold the bullet in place. The problem that I have is that the bullet actually pulls out of the case .002"-.003" when loaded. But have not had any issue with the bullet being set back in the case. I am shooting 175 SMK and the crimp is the only way I've found to keep things in place. Many things I've read say not to exceed .004" on the neck to avoid run out due to the bullet sizing the neck. Any other advice on this would be much appreciated. I do notice a different feel to the recoil when bullets are in the mag, guessing that this is due to the BCG returning back over the next round. But when shooting I always take my time and get back into position. I find myself always striving for the best possible groups. I've put run 600 rounds through the rifle in the last month maybe half of those through the mag and have not seen a MOA group with the mag yet. Im using new armalite mags and the reason for the single loading for load testing is that it is the only way i have found that i can get a good group. Thank you for your help.

 

[sinister]

Your die does not give you enough neck tension if bullets are advancing out of the case at all. If feeding from the magazine causes the inertia of the bullet to overcome your neck tension (the same effect as a body not wearing a seatbelt once the cartridge seats -- the bullet keeps moving forward until it jams into your lands).

You might try a Redding (or other brand) S-die or neck-bushing die. You can get either a neck-only die or a neck-sizing full-length die.

Crimping a non-cannelured bullet can contribute to a core-jacket separation, inducing wobble-about-the-axis and opening your groups.

 

[Travis sawyer]

Ok, so Ive been still wrestling over why the rifle is sizing my brass. fire formed brass measures form head to shoulder, (using hornady comparitor D-400) 1.626" I had previosly been setting the shoulder back to 1.624" and noticed that when cycled through the chamber it was setting it back to 1.619". So my thought was to just set them all to 1.619" and maybe cure the problem with the chamber sizing the brass. But then when I ran this brass through, again it had been sized to 1.616". Is this normal and somthing I should not be concerned with? Would it be stupid to think that the buffer spring in this rifle being to stiff is causing the bolt to slam shut so hard that it is causing both my problems, the brass to be resized and also the reason that the bullets will not stay in place with out a crimp? I have tried the neck tension only, sizing the necks to (ID) .334" and also .333" this still will not hold the bullets. Thanks for the help.

 

[ICANHITHIMMAN]

What dies are you using? I use the RCBS SMALL BASE X DIES for my M1A and my ar style rifles. Some say they are not needed, but I use them and have zero issues. Also make sure your full length sizing all the way down, function is everything in these systems.

Armalite is not new to this game so please give them a call.

Bolt bounce, it will effect things, the heavier your buffer the less you have. Single loading has only set you back in your quest.

This gentleman is well spoken and lays **** out very well
[ame=http://www.youtube.com/watch?v=dUXpESqNv28]Cutaway AR-15 - High Speed Video - Preview - YouTube[/ame]
Vltor A5 Stock System - Initial Impressions - YouTube