AR - violent ejection with handloads

[sir_n0thing]

I suppose this thread could potentially go under the Reloading section, but I am thinking it may actually be related to the rifle, so checking here first…

I recently started hand loading for the AR I built myself two years ago (one of these days I’ll post a write up on it, I think it came out really nice). First trip to the range with my test loads… I found that it really flings the brass out quite violently during ejection. Factory loads also do fly pretty good, but the ejection on the hand loads was just over the top. After the first shot I actually thought I must have measured my powder charge incorrectly and loaded it too hot. I finished out that day shooting factory 55gr ammo and went home, pulled the remaining 4 hand loaded cartridges and checked the charges. Everything was well within spec and on the lower end of the data (I always start low and work up on the other cartridges that I load for). I loaded a few more and went back to the range a few days later. Same thing, violent cycling of the action with the hand loads, brass flying up into the ceiling (the shooting benches are in a sheltered structure) and ricocheting all over. Didn’t see any signs of excessive pressure, just a lot of dented brass from bouncing off of everything after ejection.
Then a thought occurred to me… I was loading “heavier” 68gr BTHP bullets. I wonder if I need to go to a heavier buffer/spring system? Is the heavier bullet just too much for the standard buffer assembly?
If it matters, the rifle has a 16” government profile barrel with “carbine” length gas system, and standard weight buffer and spring.
Load data includes minimum/low end charge of Varget, CCI Small Rifle primers and 68gr Hornaday boat tail hallow point “match” type bullets.

Any insight would be appreciated.

[hagar]

Do you have an M16 bolt carrier or an AR15? Going to the heavier M16 carrier might help some, as might a heavier spring.

What do you consider low end charges? I normally load 24.5 - 25 grains of Varget with the 68 Hornadys for my NM uppers. You may also try a lower charge with a faster powder, like Accurate 2460 or 2230, BLC2 etc.

One of the reasons I prefer the mid length carbines, my CAR/M4 style uppers do throw the brass pretty good, but not as bad as you describe.

[Theohazard]

If it matters, the rifle has a 16” government profile barrel with “carbine” length gas system, and standard weight buffer and spring.

A 16" barrel with a carbine length gas system will almost always be over-gassed. The rifle will be extracting the fired brass even while the round is still in the barrel and pressure is still very high, leading to violent ejection, sharp recoil, and chewed-up brass. This is why mid-length gas systems are becoming more popular in 16" barrels.

That said, an easy way to fix your problem is to install a heavy buffer. I'd recommend at least an H3 buffer, but anything heavier than your standard-weight buffer will be an improvement.

[sir_n0thing]

Thanks for the replies.
The rifle does have an M16 BCG in it (from BCM).
I'll use this as an excuse to tinker with some alternate powders! And I am definitely considering a heavier buffer.

I wonder if it's worth looking into an adjustable gas block...

[Mobuck]

The buffer and spring don't care what weight bullet you're using. How far was the brass flung and where did it land in relation to the muzzle of the rifle? Using a "faster burn rate" powder will help lower the residual pressure in the bore.

[mehavey]

How far was it flung?

I think "...brass flying up into the ceiling" qualifies as a bit much.

I recommend both faster burn (which will drop what calculates out to be VARGET port pressures of 16,500psi by several thousand), and heavier buffer (which may allow you to use med burn powders again)

[Mobuck]

The only semiauto I've seen that would send brass"flying up to the ceiling" was a Mini 14. I didn't know it was possible for an AR to throw brass UP.

[Theohazard]

You don't really need an adjustable glass block to fix your problem, a heavy enough buffer will take care of it. That said, an adjustable gas block will let you fine-tune your gas flow to make it perfect.

[RC20]

What powder was used?

Data taken for a bolt action 223 or a semi auto?

COAL of the round?

[sir_n0thing]

To be fair, it's not actually straight UP... it's more of an upward angle. But yes, it really flies out fast and hard, quite noticeably more forcefully than with factory ammo. In my opinion, even factory brass comes out of the port with a bit more UMPH than I would feel is normal. I'm not an AR expert though.
A brass catcher was the first thing I went out and bought after my first trip to the range!

I don't have my load data Excel doc handy, but if memory serves it was in the range of 24.2gr of Varget and a COL of around 2.36". That's memory though, so don't quote me on it. Definitely was well within spec of all the load data I could find.

[TMD]

24.2 gr of Varget is fine for a 68gr bullet but I would double check your scale.

[stubbicatt]

Hm. It has been awhile since I tinkered with the AR 15, but IIRC, the ejector is a button in the bolt face. When I used to shoot match rifle with mine, I trimmed 2 1/4 coils off of the ejector spring, and the brass used to land pretty much at my feet.

Based on this recollection, I am having difficulties conceptually figuring out how bolt speed would increase the ejection forces, as it is bolt speed one would be seeking to regulate with an adjustable gas block or maybe a faster powder, etc., and bolt speed would *seem* to be a variable independent of ejector spring forces?

[mehavey]

...difficulties conceptually figuring out how bolt speed would increase the ejection forces...

The brass is effectively "flung out" with the same speed of the thing that's carrying them when the case mouth
clears the front of the receiver cutout. So ejection speed becomes effectively the same as bolt speed at that point.

And if the bolt is being over-driven relative to restraining forces (i.e, the buffer spring), well.....

[stubbicatt]

The brass is effectively "flung out" with the same speed of the thing that's carrying them when the case mouth
clears the front of the receiver cutout. So ejection speed becomes effectively the same as bolt speed at that point.

And if the bolt is being over-driven relative to restraining forces (i.e, the buffer spring), well.....

I guess you learn something new whenever you are open to learning. I can see that bolt speed would affect ejection velocities if we were talking about a fixed ejector such as a Kalashnikov or a HK 91, but I'll take your word for it with respect to bolt speed and the AR type rifle, even though it doesn't really make sense to me.

I can see where as bolt velocity increases, the spring tension under the AR ejector might become important as there is less "dwell time" where the ejection port is open to allow the empty to be kicked out. But the transition from linear bolt velocity to tangential case velocity with the bolt face ejector button being spring loaded like that...

In essence, if one were to remove the ejector spring altogether, there would be no ejection from the AR. If one were to put a mild spring in there, ejection would be slow, but it would happen, if one were to put a stout spring in there ejection would be more vigorous, regardless of bolt speed.

[mehavey]

The ejector spring/button serves only to "tip" the case toward the mouth of the open receiver cutout. The case then is moving at bolt speed, and at a significant angle to the bolt face when everything comes to an abrupt halt.

Sorta like a body falling flat, but then it's legs hitting one of Titanic's propeller blades after building up velocity from falling 100 ft. Things get nasty after that.

Watch the first five seconds of this SloMo video.

http://www.youtube.com/watch?v=fuQayLVbiSU

You will see that the case is moving backwards from bolt speed until the bolt stops; then it starts to spin from being at an angle to that bolt face (still moving backwards toward the shooter); then it's finally deflected to the side by the deflector "bump" on the receiver.


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