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

[Onyx Z]

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

Hey, there's nothing wrong wanting to clone it. I was just curious. Your brass will not last as long with such a hot load. Mk262 is a VERY hot load. It looks like you are getting great groups though.

Early on, I wanted to clone Mk262 too. I was chasing a certain velocity and not getting the results I wanted downrange. Nowadays, velocity is important to a certain extent, but it is not the end all. With Varget and XBR, I kept upping the charge until I got the accuracy I wanted, whether it's over or under recommended, I didn't really care.

I arrived at 24gr of Varget by seeing the results downrange. It is a compressed load with no pressure signs and excellent results, just a pain to work with. My XBR load is not compressed, but the tail of the 77gr SMK's do hit the powder just as it is fully seated.

As long as you work up to it and really understand what you are doing (not you specifically, generally speaking), I see no problem with going over a max recommended powder charge or using a compressed load as long as there are no pressure signs. I do doubt you will achieve Mk262 velocities with an extruded powder without a compressed load. Remember though, you will have diminished brass life with 5.56 pressure loads.

[Whiskey&beer]

Have you shot MK262 out of your barrel so you know exactly what velocity you need to get your goal on your loads?

Sounds like you've got a good load right there, but I'd bump the powder to 23.4-23.5 to see what you get, and definitely try Wolf and your 7.5 primers. I personally didn't like the #41 primers, they brought up my ES and SD's and they are more expensive.

If you really want play around buy some M193, pull the bullets and dump the powder, and put your powder and SMKs in and jump up another few grains to see what you can get consistently. That way you got brand new brass and crimped primers to help with pressure. Matching 262 is going to bring you into high pressure.

[Clemonsds]

my apologizes for not really knowing what you meant by your post. i'm getting the performance down range and very close to what velocity i'm wanting. I'm no just chasing speed, i am willing to sacrifice speed for accuracy. i haven't had to yet.

I have room to play on what i can charge the cases with, not sure i will need to.

so far i have been able to reload the brass 5 times with the lot i am using with no excess signs of case head bulge, or gas leaking past the primes pockets. i will say that beyond 5 loads the primer pocket isn't as tight but does seal off, i'm not working them past 6 reloads. That will change if i up my charge from where i am now.

Yup, i always work up loads. Having something blow up in my face doesn't sound like much fun. when it comes to my reloads i am OCD

talking to black hills they test this round(MK262) from a 20" barrel @ 2,750, so i figure if i am averaging 2,665 FPS now and work up a load to 2,700 FPS out of my 18" that's about where i plan on stopping as velocity is concerned as long as my down range isn't effected. I'm wanting both but ultimately accuracy is more important and always has been.

i am unable to get the factory new black hills of this load to test in my rifle, i know that's the best way to match the load but well calling them to confirm what 77gr OTM they use and barrel length is all they can give me, the powder has been by the book and tested, tested and yup tested.

[Clemonsds]

no i have not, i wish local shops had some on shelves. best i have seen in black hills red box is the 69 grain OTM, i have purchased two boxes ($50!!!)<per box. That round screams out of my rifle at 2,841 FPS with sub moa groups.

i think i will try my 7-1/2 matched up with my powder charge to see if i can lower my SD's, if it does then i will work up the powder charge checking both velocity and downrange. if my groups open up i will go back down. I did just recently change out my timney 4 pound trigger for a timney 3 pound, maybe that will help groups too? that's up to me.