5.56 AR Only Loads

[WeR0206]

I finished load development with.223/5.56 77 SMK and AR-Comp a week ago on my 14.5" AR-15 with an Aimpoint red dot sight. I strongly advise using a chronograph to compare to a known load, such as MK 262 Mod 1, as you progress up the ladder. I backed down around 0.6 grain and got the following results from 20 shots at 100 yards. If I can attain this accuracy at 100 yards with a 14.5" barrel and red dot, I believe I'm ready for anything I plan to use the SBR for in the future. The next stage will be to shoot these through another of my ARs, a 14.5 SBR with a 1-6x variable scope, to do a more critical accuracy assessment.

I love AR-Comp but ive been avoiding doing load development recently with Alliant powders since they will practically be unobtainable in the US pretty soon. Im switching to mainly VV (N140) for its excellent price & performance…also doing some with AA 2520 and TAC for mk262 clone loads. TAC kicks ass as a cheap all around easy metering powder to have on hand.

 

[bf2junky]

Love TAC. Performs even better when you load it on the hotter end of the range.

 

[WeR0206]

Love TAC. Performs even better when you load it on the hotter end of the range.

I just shot some 77 smk’s in LC 556 brass @2.246” with 25.0gr TAC with zero burrs etc on the brass and primers were fine. Avg speed out of a 16” Wylde barrel was 2806. Black Hills 77 otm in same barrel is 2692. 2806 is pretty smoking fast for those 77gr pills. Love it!!

Side note there is a free reloading software called Gordons. I somehow just found out about it this last weekend and it helps a lot with load development. You give it inputs for your chamber, COAL, spent case volume, bullet length, pressure limit, etc and it spits out the estimated pressures and velocity for each step in your ladder.

 

[jLorenzo]

I finished load development with.223/5.56 77 SMK and AR-Comp a week ago on my 14.5" AR-15 with an Aimpoint red dot sight. I strongly advise using a chronograph to compare to a known load, such as MK 262 Mod 1, as you progress up the ladder. I backed down around 0.6 grain and got the following results from 20 shots at 100 yards. If I can attain this accuracy at 100 yards with a 14.5" barrel and red dot, I believe I'm ready for anything I plan to use the SBR for in the future. The next stage will be to shoot these through another of my ARs, a 14.5 SBR with a 1-6x variable scope, to do a more critical accuracy assessment.

Pics?

 

[MustangGreg66]

I just shot some 77 smk’s in LC 556 brass @2.246” with 25.0gr TAC with zero burrs etc on the brass and primers were fine. Avg speed out of a 16” Wylde barrel was 2806. Black Hills 77 otm in same barrel is 2692. 2806 is pretty smoking fast for those 77gr pills. Love it!!

Side note there is a free reloading software called Gordons. I somehow just found out about it this last weekend and it helps a lot with load development. You give it inputs for your chamber, COAL, spent case volume, bullet length, pressure limit, etc and it spits out the estimated pressures and velocity for each step in your ladder.

Interesting. TLDR: Case volume matters a lot at the upper end of pressure.

I found it interesting you're not getting any pressure signs with that load. I've been loading some 77gr SMK 2nds @2.255" and 25.0gr of TAC for spinner targets in 3gun. I got some ejector smears on the brass and can tell it's pretty hot. I'm not getting the brass back so it's one and done for this purpose and I'm fine with it.

I tried to duplicate it in Gordon's reloading tool and it took me a while to match your pressure results. The difference I found was the brass I'm reloading measured case volume (h20 on scale) at 30.00gr for LC '95 brass where yours is 30.88gr. That difference in case volume gives me 67k psi to your 61k. I've been using random year LC and still getting some pressure signs with that load, but I'm ok with it for the small number of these rounds I use.

 

[WeR0206]

Interesting. TLDR: Case volume matters a lot at the upper end of pressure.

I found it interesting you're not getting any pressure signs with that load. I've been loading some 77gr SMK 2nds @2.255" and 25.0gr of TAC for spinner targets in 3gun. I got some ejector smears on the brass and can tell it's pretty hot. I'm not getting the brass back so it's one and done for this purpose and I'm fine with it.

I tried to duplicate it in Gordon's reloading tool and it took me a while to match your pressure results. The difference I found was the brass I'm reloading measured case volume (h20 on scale) at 30.00gr for LC '95 brass where yours is 30.88gr. That difference in case volume gives me 67k psi to your 61k. I've been using random year LC and still getting some pressure signs with that load, but I'm ok with it for the small number of these rounds I use.

View attachment 8664999

Yeah case volume seems to be a very sensitive input, even changing it by hundredths of a grain will swing chamber pressure by a few hundred psi. My measurements were actually closer to 31 grains on avg but I errored on the side of caution and used the smaller of my numbers when I saw how much slight differences could swing chamber pressure.

Most of my LC brass was newer 21-24ish.

Bullet length was also a big driver. I measured about 10 of my 77 smk’s and they were well under the default value of 1.0”….more like 0.977”. That also allows for slightly higher loads before hitting pressure limits compared to the 1” input.

Here’s a pic of the brass. The row furthest from camera was the 25.0gr load, there were definitely some swipes but no burrs (I also just installed a fresh sprinco ejector spring in my bcm bolt):

 

[Snuby642]

So you can shoot the difference in one hundredth of a grain? 0.003 thousands worth of case capacity?

Nice.

Last I heard LC brass was made at multiple locations. It seems to vary instead of brass made at one location it seems. I use it for blasters to use up odd lots of powder and bullets.