308 for AR-10 - do you need to crimp

[1911jerry]

I use a Redding type S match die set, the full length resizing set. I use FGMM brass only with Sierra 175 grain SMK projectiles.

 

The neck tension bushing is a 334 size, and the finished ammo comes out to 337. I seat 175 SMK's to 2.800. Case gauges 100%, goes into the chamber no issues.

 

Would you think I need to do any type of crimp if I am running these loads in an AR-10 platform?

 

This method holds the bullet really well.

 

Thanks

[Dan Sierpina]

I’ve never crimped .308 and have no problems with set back. I’ve been shooting a .308 AR for 8 years in heavy divisions.

 

[Guy Neill]

I expect you do not need to crimp.

 

However, every gun is different.  You might load two or three rounds, measure their overall length, then chamber them two or three times and remeasure. to see if the OAL has changed.  If it has, it may indicate a need to crimp. 

 

But repeated chambering should not be really common, with only the single chambering to shoot being the common situation.  In this regard, you might measure the OAL after each chambering of the cartridge(s) to see what happens.

 

 

[thermobollocks]

7 hours ago, Guy Neill said:

However, every gun is different.  You might load two or three rounds, measure their overall length, then chamber them two or three times and remeasure. to see if the OAL has changed.  If it has, it may indicate a need to crimp. 

 

Best to check it. I've had .223s that need it and .223s that don't. I also use just a smidge of crimp to deal with any irregularities from potentially ham-handed bullet seating issues. This is less of an issue with .308 but happens.

[TreblePlink]

In my experience, crimping will not help neck tension. But a slight taper crimp may improve feeding.

[Farmer]

You’ve got .003 grip which should be fine without a crimp. Brass that is getting work hardened from many reloading’s could lose some tension but other than that you should be fine. I have used the Lee collet crimp die on some. On some rounds/loads it helps accuracy and other’s it hurts it. Not by much but there’s a difference. 

[soflarick]

Test it yourself.  Seat your bullet into a sized case you use, no powder or primer.  Measure the cartridge overall length.  Place into magazine, seat mag into rifle with bolt to the rear.  Release bolt catch.  Slowly extract the uncharged cartridge, and measure the OAL again.  Did the measurement change?  That will help determine if you need more neck tension or a crimp.  I like to run the same cartridge a couple times to make sure the length remains the same.

Edited February 23, 2021 by soflarick

[1911jerry]

Follow up question(s) please:

 

I have had good success with no set back. I am reloading FGMM brass in 308, with 175 SMK projectiles. I have been using a neck bushing size .334. I am not sure if this is providing to much neck tension. I have bushings in 335, 336 and 337.

Will to much neck tension cause grouping problems?

 

What would be your recommendation. 

[Guy Neill]

Try test groups with each and see if there is a notable difference.

[Chills1994]

To answer your first question….

 

I keep my old shot targets in a 3 ring binder. I can’t remember if I have done any experiments with .308, but definitely in .223, using a Lee FCD, my accuracy got worse.

 

Or said another way:

 

Accuracy was better without the Lee FCD.

 

As to your second question about how much neck tension/which diameter bushing you should you use….

 

How thick is the brass at the case necks/mouths?

 

If you keep everything the same as you have it now, can you chrono your loads?

 

What kind of accuracy are they producing now?

 

 

[Farmer]

Yes it can. 
You need to measure your neck thickness, bullet diam and then figure your tension from the bushing used. Most brass is .010-.012 and usually thicker on one side and gets worse the more it’s reloaded. I have tested different tensions from .001-.005 and .002-.003 gave the best accuracy. Too little, setback and poor ignition becomes a problem, too much seems to distort the neck, cause more runout and can even push the shoulder back. 

Edited August 8, 2021 by Farmer
Added

[K-Tex]

Like anything.......preference!   I do on everything I reload and do so without any accuracy loss.