MK262 mod 1 load data help

[Clemonsds]

I'M looking for anyone that has loading experience cloning the MK262 round the military uses from black hills.
Here is what i have worked up so far and just trying to find more data, does anyone have any other load data to add?

I have had good results using IMR 8208 XBR powder, my results are an average 2,665 FPS with a standard deviation of 16.88 out of an 18" SPR wilson combat barrel 1:7 twist using 23.1 grains, LC brass, and CCI#41 primers. Seating is at 1.869" to ogive using 77 grain SMK w/cannelure. Chronograph placed @ 5'. shots taken in 68-91 degree temps.

This powder is a short extruded type, also the factory new Black Hills (red box)69 grain OTM is short extruded powder coming in at 24.2 grains, 2012 WCC headstamp.

CFE223, and varget don't even come close to the velocity i was looking for to match the MK262 without a compressed charge, Tac powder works well but changed with temprature, IMR 8208 xbr is not near as sensitive to temp changes like the other above mentioned that i have used.
My groups are consistently under 5/8"@ 100 yards.

P.S. If you attempt loading per my data, do so at your own risk. 23.2 is the max recommended charge for 8208 xbr@55,000 psi.

[markm]

You can likely shave your SDs in half with Wolf or Tula primers. And you might even improve your groups.. although, you're getting pretty good results there already.

A few of us here are running 23.4 or 23.5 gr of XBR with 77s. XBR is a little tricky. It'll turn on you with no warnings up around 23.8. I'd shot a bunch of that, then switched lots, and all of the sudden was getting a bunch of blown primers and heavy case head swipes.

[Clemonsds]

I do have #7-1/2 SR bench rest primers(Remington) but haven't tried them yet, i have mainly been checking consistency of this powder so far.
do you think those primers will be sensitive to primer strikes and or shrink my SD's? Do you show pressure signs at those charge weights, and i imagine those are compressed charges?

Thanks for the information

[markm]

We've burned through at least 10k of those primers with no issues. The WOLF SRMs are supposed to have a thicker cup, but I use any an all of them with no problems.

At 23.4, I get no pressure signs, and am getting 2730ish velocity from a 20 Colt. That charge is not compressed.

[Onyx Z]

Can I ask why you are trying to clone this ammo? I would much rather stack holes at a little slower velocity than have a .75moa group that achieves a certain velocity. Accuracy > velocity.

I'm running 23.4-23.5gr XBR under 77gr SMK/Nosler CC's and CCI450's or WolF SRM's. I haven't had a chance to run anything over a chrono in quite a while, but this load is a frickin laser.

FWIW, I was getting 2,700fps with 24gr Varget and CCI450. I imagine this XBR load will be fairly similar, if not a little faster.

[Clemonsds]

That round (MK262) was designed for the mark 12, why would I not want to clone that round after spending 2K plus building the mark 12 SPR. Besides, the whole fun of reloading for me is creating an identical round or close to black hills that is designed for my rifle.
I want 5.56 cartridges. If you're loading what you're saying you're doing the same thing too. 24 grains is a slightly compressed load in my experience and I'm wanting the velocity without a compressed load if I can help it. 8208 XBR meters better than varget because it's short extruded instead of long. Also Under 5/8" groups is laser accurate in my opinion. But that is my reason for wanting to get close to the MK262 round

[Clemonsds]

I just received two new boxes (red box) of black hills 5.56 77 OTM (MK262 mod 1) and can't wait to shoot them.

I was surprised that my chosen seating depth for my hand loads was the exact same as theirs (1.869" to ogive) but the powder is a ball powder which I didn't expect at a weight of 25.6 grains. I have not shot them yet to see how they perform in my rifle, but soon enough I will and will come back to tell my results.

[HambelA&A]

I'm curious to see what your results are with the MK262. I never could get that load to group better than an 1MOA with my 16in DDM4. I had to go with a lighter bullet (75gr) and drop velocity down to 2600fps, but now 0.25-0.30 MOA is easily obtained when I do my part. Was the consistency of the seating depth of the Black Hills on par with your hand loads?

[Clemonsds]

I'm shooting out of a Wilson combat 18" spr barrel with a 1:7

My hand loads are .628"@100 yards when I do my part. Velocity is 2,702 FPS

Their seating depth was within +/- .001 throughout the rounds I have, I randomly chose and didn't measure them
all. They are out of the same lot.

My hand loads are as consistent as theirs for seating depth.

As soon as I shoot me a group of 10-20 I will post the results, hope I do my part.

[Greentimber]

24.0 8208xbr behind a 77gr Nosler or SMK gives 2760fps and ~3/4 MOA from my 18" Compass Lake SPR. 23.0 (corrected from initial typo) was very slightly better accuracy but I'd rather have the 150+ fps. No pressure signs.