My test of bullet set-back in AR

[spegt]

I had seen some posts here and there about crimping or not crimping to prevent bullet set back with AR's. I loaded up some rounds and did a test. I loaded the test handload and then a factory federal 55gr fmj. I fired the factory load and let it auto load the handload. I then ejected the round and measured it. It actually sets the bullet forward in the chamber(the OAL increased) I have attached my note card of before and after measurements of OAL.

Notable variables:

60gr v max flat base bullet (no cannelure)
Lake City brass (once fired)
Rifle length gas system
Rock River 223 wylde chamber
Redding type s dies no crimp

 

[rcmodel]

You simply don't have enough case neck tension.

With proper case neck tension, it should take close to 60-70 pounds force to slip a bullet in the case, without crimping.
Or several very hard hits with a hammer type bullet puller to knock one out of a case by foreword bullet momentum when the puller hits the concrete.
Several magnitudes more then you get during feeding.

And crimping will not fix poor neck tension.

Using bushing neck sizing dies for auto-loading rifles is going to be an exercise in frustration.

And even more so if you load mixed brass of different neck thickness.

Buy a FL sizing die and use the neck sizing dies for one brand of cases, in a bolt-action rifle!

rc

 

[spegt]

I would say if the bullet set out an average of .0005" then the neck tension is on the good side. I'm new to the game, but I have fired about 80 or so hand loads with out a crimp. This test was simply for my own curiosity. I figured I would share my findings.

 

[rcmodel]

But, my point is, they should not move at all due to the minor G-forces involved in the bolt shaming shut during clambering.
Crimped or not.

But you do what you gotta do.

rc

 

[Drail]

RC is correct. A round that does what you have described is defective.

 

[243winxb]

http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm. See the part on neck tension by Sierra.

 

[steve4102]

243 is correct. Read the link from Sierra, forward creep is common in the service rifle, even with Factory ammo with it's Higher bullet grip than handloads.

What you are experiencing is normal and very common. Nothing "Defective" about it.

Neck tension will not stop it, crimping will not stop it, but the Lee Factory Crimp die will reduce it to almost non-existent.

 

[243winxb]

.0005 is nothing. A non-issue.

 

[spegt]

Very good read. Thanks

 

[243winxb]

Spegt, doing your own testing is the only way to know. Good test. What size bushing are you using? The military 5.56 ammo has a bullet pull of about 40 lbs as there standard. On seating a bullet, the neck should expand about .002" or more to get this 40 lb pull. My test may not be very accurate using a bath room scale while slowly pushing the bullet into a dummy round. I also found that the neck wall thickness may thin after repeated loadings with standard dies, but not always. Your bushing die is the way to go. I use a Redding type-S FL bushing die for 243 win.

 

[243winxb]

Xm193

BULLET PULL: Minimum individual 35 lbs. http://www.woodburyoutfitters.com/product_p/300423.htm Federal American Eagle Tactical Ammunition, 5.56mm NATO, Full Metal Jacket Boat Tail, 55 GR. XM193

 

[spegt]

i used a redding type s FL sizing die(223)
and the accompanied redding seating and crimping die(backed off for no crimp)

 

[steve4102]

Bushing info?
What is the outside diameter of your sized neck before seating a bullet?

What is the same dimension after you seat the bullet?

Are you sizing with our without the expander button?