trying to duplicate mk262

smogmage · Mar 19, 2014

So I'm trying to match a mk262 loading for my rifle. I'm using lake city brass fed 205 primer 77gr nosler 25.0grn of mr pro 2000 which is giving me about 2515 fps from my 16" barrel.

The factory lists max charge velocity from a 24" barrel at 2,856 and I'm getting 2515 from a 16" barrel, yet I know a mk262 load will give 2700fps from a 16" barrel. My question is this, is it possible mr pro 2000 burns so slow that it will only yield faster velocities in longer barrels and a faster burning powder would give me more speed from a 16" barrel?

Any suggestions? I still have a slight margin to increase the charge but I'm not seeing how I'm gonna make up 175fps with .2 -.3 grns

I have H335 but maxxed out it gave 2460, clearly not optimized for the heavy bullet.

joustin · Mar 19, 2014

I know some of the clones were good for one shot, as in the brass was toast after firing. RL15 is what was used in one version of the ammo, but it was well above max and as mentioned the brass was dead. Ramshot TAC seems to be used by several people to duplicate this load. Have you ran any of the factory mk262 over a chrony from this rifle to verify the speeds you are expecting?

ETA - I'd like to see how it works for you, I have about 300 Nosler 77gr Custom Comp waiting to be loaded

wanderinwalker · Mar 19, 2014

Two things I can think of.
1) Pressure. That Mk262 load is going to be running at full 5.56 pressure; Alliant's data is going to adhere to .223 limits.
2) Powder. You don't have access to whatever powder is used in Mk262. It can make a difference, but I'm leaning more toward point 1 being the biggest hurdle.

FWIW, I've used Varget and RL-15 extensively in a 20" AR with 69, 77 and 80gr bullets. I never got close to what a lot of people claimed to be able to do with those powders and bullets. My best 69gr load only averaged 2850-fps with Varget. My best shooting 80gr loads for 600-yard stages were in the ballpark of 2600-2650 fps, while everybody told me they shoot best at 2700+. It's possible you just won't make the number target you're looking for.

smogmage · Mar 19, 2014

I have a feeling thats going to be the case. With the powder supply being what it is currently I don't have any other choice. Hopefully I can get to 2600fps and great accuracy. That I could live with.

BoilerUP · Mar 19, 2014

23.8-24.0 8208XBR will get you very close to 5.56 Mk262 velocity...for 5.56 (ie. over 223 book!) pressure.

23.8gr XBR is within a few FPS of black Hills 5.56 77gr OTM "white box" seconds in my 18" 1:8 BHW 5.56 barrel.

joustin · Mar 19, 2014

There are multiple threads on other sites where people where chasing the load specs for the mk262, 90% of them wound up falling short and trashing their brass. If you had virgin primed LC brass it might be easier, without that primers tend to start popping before you hit the same speed. Remember, the military doesn't care if the brass is good for reloading as long as it fires and extracts in one piece.

trying to duplicate mk262

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