MK262 mod 1 load data help

[Greentimber]

That IS a typo. Should read 23.0 grains gave 2600 fps! Good catch. Thanks.

[Clemonsds]

I would edit that post just in case someone happens not to read the correction and attempt loading that overcharge.
Just my two cents if it matters.

[308sako]

My Elite Hbar 24" loves 24.0 XBR with 77 SMK's @ 2880 ft/secs... To avoid the case head swipes the use of a JP adjustable gasblock and Tubb CWS & CS Flatwire Spring has helped. Tula or Wolf SRM gives single digit SD's. 23.2 grains gives 2775 ft/secs in the Colt with the same level of precision. My 18" Rock Creek custom barrel which is melonited likes 1/10 of a grain less for 2775 ft/secs, but 23.2 is more accurate in the Rock at 2680 ft/secs. Loads are in LC '06 brass and cartridge overall length is 2.255" Further to control the apparent pressure signs I pay extreme attention to how much I am bumping the shoulder back on the brass. Simply put I use bolt-action tight .001 - .002" of headspace clearance. These rounds cycle just fine.

Lot to lot powder variation was an issue until I was able to acquire a substantial amount of a single lot.

Always work up, or be prepared to blow up your rifle!

[Costellow]

SD 's?

[308sako]

Colt with Wolf averaged SD's of 10 to 11

The rock creek barrel had one string where the first 6 were zero, but for the 10 rounds finished at 5. averages about 7 to 8. Oehler 35P data collector.

[Clemonsds]

Okay everyone, went to the range today and shot a few strings of black hills ammo. 29 rounds of 77 OTM (mk262 mod 1) and ten rounds 69 grain OTM.

I think everyone here knows my rifle. Here is an image of my results string one and three are the BH77gr OTM and string two are BH69gr OTM. I know I did only 9 on the first string, had a guy in my ear and didn't count right. As expected the heat increased my average velocity on the third string to 2,723.75 FPS as compared to the first nine shots of the first string only averaging 2,691.99 FPS. Either way it seems my reloading is just about matching the velocity of black hills mk262 mod 1 out of my rifle.

image.jpg

Here are 10 of my hand loads using Sierra 77gr OTM with 23.1 grain 8208xbr 1.869" to ogive and #41 CCI primers cases trimmed to 1.750" and crimped. I do plan on upping my powder charge and changing primers.

image.jpg

Don't ask for the grouping size, it's nothing special when you have someone on the range shooting a 50BMG just a few lanes away from you. I know you're not supposed to take out flyers but if I take those out the group falls at .822" first string and 1.870 with the flyers. Third string no flyers is .634" with flyers 1.635". The first string had five flyers and the third string had four flyers. These two are results of the mk262 mod 1 from black hills. Take out my flinching when a 50BMG shoots next to me and these rounds are fantastic Also this shoots 1.5" high at 100 yards and also rings the 10" gong at 300 yards without adjusting scope elevation.

[308sako]

As you have already learned speed alone is not the answer. Using the right powder will give you the greatest precision at a velocity near to what a factory round yields. It is your individual barrels harmonics which will determine where that accuracy node lies. The change in primes will be beneficial to your pursuits. Try not to oversize the brass as well.

Good luck

[Clemonsds]

I agree, at this point where my velocity stands I'm playing with the charge not so much for velocity but to see if my groups open up or shrink. Yesterday's results were more my error than that of the load itself.

While I would like to see 2700 FPS averages it really depends on how it performs down range at this point. My fourth string loads were my hand loads, not sure what happened with those two that shot over 2,700 fps, but had those been like the other eight shots my E.S. Would have been very little and SD would have been single digits most likely.

Load and shoot, repeat.

[Onyx Z]

Just an fyi, my old load of 24.0gr Varget, CCI450, 2.255 OAL averaged to exactly 2,700 fps...

I gave up on this load because Varget really sucks to work with and there are much better powder options out there.

[Clemonsds]

That's why I use 8208xbr. It's easier than varget to work with and meters well enough no to be a pain for an extruded powder. I will say that the black hills 77 OTM (mk262) with a 2013 head stamp have a ball powder in them weighing in at 25.5 grains!!!! considering they shoot around the 2700 FPS range out of my rifle and I'm shooting 23.1 currently and almost matching them something else must be adding to the weight that doesn't add to the velocity. Or I need to look up max loads for ball type powder.