223 5.56 , M855 62gr FMJ , W748 and 2460

[N555]

Next load development will be 62gr FMJ BT, but probably not true M855 ballistics, loaded for accuracy.
A Carbine and rifle load.
My 2 powders will be W748 and AA2460 and cci41 or cci450 primers.
My speer manual shows 25.5gr as the max load for 748 in a 223 chamber gun so if I don't get any over pressure hints at max I'll go up to 26 since mine are all 5.56 chambers and I used to load 26gr in my old mini14 that had the barrel pretty much shot out. I loaded up 24.5gr, 25gr and max. In my 2x fired lupua brass.
For AA2460 the max load is 24.5gr. I'll have to switch over to fed brass but I have plenty. I'll load up 23.5gr, 24gr, max and max plus 0.3gr, maybe a few at max plus 0.5gr.
I have a "3.8oz equivalent" silent buffer I'll be putting in the carbine for this test. Normally I run a 3oz which was needed to cycle the RE7 silencer load I poached off THR some time ago and my H322 loads. The rifle has a proper rifle tube, spring and 5.5oz buffer.

 

[N555]

Let me start out by saying ballpowder is so much dirtier than single base. Only tested W748.
So I thought it would be difficult to get a carbine and rifle to agree on a load.
At 25.5gr 1 of the 14 shots gave made ejector shear mark so that's a bit spicy.
Both guns agreed that 24.5gr was acceptable, 25gr was bad for both guns making 1 inch group at 25yd and then 25.5gr made 1 hole 7 shot groups with 1 flier for each group at 25yd with both guns.
The groups looked like a mirror image of each other. A lot more consistent than what I thought I would get. I thought I would have to compromise or pick one over the other.
No point in pushing it to 26gr.
The carbine and these loads has no problems cycling a 3.8oz equivalent silent buffer with a silencer.

 

[ParallelCode]

Were you using the SS109 bullet, or a non steel-core FMJ (like that from Hornady)?

 

[N555]

Just a regular old FMJ made of lead and copper.

 

[kmw1954]

Been loading a 62gr Hornady FMJ with Accurate 2460 and TAC with great results in a 22" bolt rifle. Been shooting these out to 300yds.

 

[N555]

The 2460 is perfect tiny spheres, should be a pleasure to meter.

 

[ParallelCode]

Been loading a 62gr Hornady FMJ with Accurate 2460 and TAC with great results in a 22" bolt rifle. Been shooting these out to 300yds.

I recently picked up a large quantity of that specific bullet from RMR. I haven't had a chance to try them yet, but I'm glad to hear they have potential.

 

[N555]

I always go to RMR first.
All however many thousands of Hornady 62gr FMJ-BT bullets I have came from RMR.

 

[N555]

I finally tested the AA 2460.
It is a great midlength carbine AR powder, possibly the best for 62gr.
Wasn't too terribly over gassed with a silencer and H3 buffer. Cycled great.
But it wouldn't reliability cycle my rifle, caused short stroking even with a silencer.
24gr mad a 1 hole 7 shot group at 25yd.
But the whole point of my 62gr loads was to have a good carbine and a good rifle round, I already have a great carbine only load.
So the remaining sealed 1lb container is for sale.

 

[kmw1954]

If you were close by I'd buy it.

 

[N555]

The 24gr of 2460 under a 62gr bullet is making the carbine over gassed again.
I think that's a perfect excuse to get the A5 EMOD buffer tube setup. Also the M4 stock max length of pull is about 2 inches too short for me.
The EMOD appears to use its own buffer, a hybrid. Something between a rifle buffer and a carbine buffer, the factory emod H2 version weights in at 5.6oz (equal to a standard carbine H3 buffer). So if I H3 the EMOD buffer it ought to weigh about 6.5oz or so.

Pic poached from here:
https://www.80percentarms.com/blog/ar15-buffer-weights-what-the-difference-is-and-how-to-choose/

 

[N555]

Chronographed the M855 bullets over 24gr of AA2460 out of my 1:7 midlenth 16 inch barrel.
2,872fps

 

[N555]

I picked up an AR stoner AR10 stainless buffer. Looks like it weighs 3.8oz with out any tungsten in it. So add tungsten and it should max out about 6.3ish +/-0.1oz.
That should help timing a bit.
So emod buffer or SS AR10 buffer I'll figure it out.

 

[N555]

I did the emod. The emod buffer is longer than a carbine buffer and uses 4 weights. It comes with 2 steel weights and 2 tungsten weights from vltor and weighs 5.3oz pretty close to a rifle buffer and H3 buffer.
Already tried an H3 carbine buffer and H3 is pretty close to the emod, so I popped in a 3rd tungsten weight, and the emod buffer weighed in at 6.2oz. Still over gassed.
Next step? Make the emod an H4 I guess.
If that doesn't do it, which I don't think it will, it's time to radically alter the gas timing, some how.
I know someone else that uses a silencer on a midlength carbine, H3 carbine buffer and has an adjustable gas block and they are still over gassed, "but its not that bad anymore".