help with 77 TMK load, accuracy

[JDBAK]

So I have a White Oak Armory 3-gun upper (med profile 18" barrel, 1-8" twist), and have been trying a few loads out.
It's not a stellar shooter, get's about 1.4" 5 shot groups with Mk262 (77 SMK), a 1.6" ish with 77 SMK with 23 grains of TAC, about 2-2.5" with 62 mil ball, and 2"-3" with 77TMK over 23 grains of TAC.

For reference, my work M4A1 with M855A1 does at least as good (usually sub 2.0" 5 shot groups) as my WOA with 77 TMK.

Does my gun just not like 77 TMK for some reason, or would switching powders likely help? Is 1-8" twist not enough?

And yes, I know I should shoot more 10 shots groups with this gun, but when it's already over 2" at 5 shots, than what's the point of burning components?

Anyway, advice is welcome. I'd really like to be able to shoot 77 TMK for service rifle competition and hunting.

 

[Formidilosus]

So I have a White Oak Armory 3-gun upper (med profile 18" barrel, 1-8" twist), and have been trying a few loads out.
It's not a stellar shooter, get's about 1.4" 5 shot groups with Mk262 (77 SMK), a 1.6" ish with 77 SMK with 23 grains of TAC, about 2-2.5" with 62 mil ball, and 2"-3" with 77TMK over 23 grains of TAC.

For reference, my work M4A1 with M855A1 does at least as good (usually sub 2.0" 5 shot groups) as my WOA with 77 TMK.

Does my gun just not like 77 TMK for some reason, or would switching powders likely help? Is 1-8" twist not enough?

And yes, I know I should shoot more 10 shots groups with this gun, but when it's already over 2" at 5 shots, than what's the point of burning components?

Anyway, advice is welcome. I'd really like to be able to shoot 77 TMK for service rifle competition and hunting.

Swap powders.


And, shoot some larger groups sizes with M855A1- 30 round groups for most lot#’s are going to be between 5-7 MOA at 100 yards from Colt/FN/DD barrels.

 

[Dave Thomas]

I agree with above advice. Try a different powder.

 

[flyinsquirel]

Unless you already hit pressure at 23, and since you already have it on hand, I’d give 24-24.5 of TAC a try at a 2.26 coal with both the SMK and TMK. That would put you in the 556 load data range.

 

[JDBAK]

No luck trying BLC-2.
77 SMK averages about 2-2.5 MOA for 10 shot groups.
77 TMK 2.5-3.25 MOA for 10 shots.

Mk 262 is still in the low 1s. However I did pull off 10 shots under 0.6”. Incredible, best group I’ve ever fired from a rifle. That’s with a 4x Elcan over a pack.

My guess is mixed surplus LC brass with some random commercial thrown in is a big culprit.

 

[RDF1]

For the 73gr ELDM and 77gr TMK ive had very good luck using H4895. (20" ARP 8T)
Tac, Varget, And CFE223 didnt shoot to great with CCI 450s.
It would do 1.5" all day it seems tho, but was chasing them small groups.

Swapping to H4895 and Fed AR Match primers made all the difference,
Also used adjustable gas blocks and heavy buffers. (H3 buffer in Carbine Lowers, Rifle buffer in rifle lowers)
Turning the gas down once i found a decent load helped.
Velocity went up some (noticeable vertical shift on target) and group size shrank.

I did all the load workup with Lapua brass and Federal AR Match primers.
Noticeable group size difference between virgin brass and Once Fired brass Neck sized only.
Starline brass was very close to the same load and didnt hurt to loose like Lapua brass.

 

[JDBAK]

Interesting, thanks. I’ll try brass first and then primers.