Originally Posted by BlackRifleFan
pictures of groups
I picked up some 77gr SMK and read this whole thread, very nice data!! However, most of the loads are too hot for my taste. I don't believe in beating up a gun for that extra 1/16th inch. Also to get that 1/16th you have to shoot on a bench in ideal conditions
NATO Mk 262 (77gr) ammo is super hot, like 2850 fps out of a 20" barrel. That's about 2720fps out of a 14.5". It appears you guys are trying to match that? Way too hot for my taste.
Most reloading spec sheets I have read for the 77gr tops out at 2700 fps. I was reading about lots of defective powder and primers where they were a lot hotter than normal, that added with 100+ degree days, and maybe your barrel chamber is a little tighter, in addition to a well worked hot barrel. I imagine a KB would quite be possible. I am beginning to understand why Mk262 is very rare, even for DSM's in the Military.
My favorite accuracy round is 24.5 gr Varget with 69gr SMK's and LC brass. It's good for just under sub MOA out my LWRC at 100 yards, and just over MOA out of my Noveske. My 14.5" Noveske pushes this load 2620 fps, and my 16" LWRC is about 20fps faster than that. At 600 yards, I am only half a human lower than what my ACOG BDC shows (M855 ammo out of 14.5" barrel). Best of all it does not beat up my brass. I can't see 77gr being more accurate than 69gr at distances under 600 yards. Only reason I see to go to 77gr is to be supersonic past 700 yards. However to me the .223 is a 500 yard gun, and 600 at most.
Dam I just talked myself out of 77grainers, but too late. Got 300 on the way in bound.
Yes, this is exactly what I've been trying to tell people. A few years ago I tried to duplicate MK262 just to see what it would take. I was able to get it as I had posted prior, using 25.3gr Varget, 77gr SMK, LC brass, with a Winchester SR primer. Accuracy was decent (1" at 100 yards), but not the greatest. But that load is hotter than it needs to be. In my opinion, MK262 as it was originally spec'ed, is bordering at the top end of the accuracy pulse and should be dialed back in speed for better accuracy.
I think the key thing with MK262 velocities is that it's supersonic to 600 yards with the M4 (14.7" barrel). If you're running a 20" barrel, there's really no need to hot rod a 77gr that much. My 200/300 yard load for High Power matches is 77gr Lapua, 24.0gr RL15, LC brass, and a Wolf SRM (or CCI BR4) primer. I haven't clocked it, but I'd be surprised if that is moving more than 2750fps out of a Wylde chamber 20" 1:7 twist SS White Oak barrel.
For 600 yards I'm still using Berger 80gr VLDs with 24.0gr RL15, Lapua brass, and a Wolf SRM (or CCI BR4). I think those are moving 2750fps out of the 20" 1:7.
You might want to reconsider the 77gr if you want improved wind drift performance at short range (200-400 yards). You should look at the Hornady 75gr BTHP. It's a good bullet and is less expensive than the 77gr BTHP offerings by Sierra, Nosler, Berger, Lapua, etc.