You're thinking of 80gr+ match rounds. 77gr rounds will fit in a regular mag and fire just fine in semi or full auto, although you will need a 1/8 or 1/7 twist to use anything longer than a 75gr round.These rounds are usually used in .223 bolt guns or loaded one at a time into AR15s. They won't fit into mags because they are longer. Plus you have to have a different twist ratio (1:8 or 1:7 I believe) and at least 20" to 24" barrel to get full potential.
I've heard the ballistics and stopping power of this weight of round comparing favorably to 55-Grain round. Does anyone have any experience with this variety of round?
I can see that. In my experience the M855 had pretty good penetration on vehicles and small structures.There were a couple presentations floating around with info regarding penetration. One showed M855, M193, M995, and Mk 262 through cars and such. This presentation showed the M855 as being able to penetrate more/thicker barriers then Mk262.
Another one had gel shots after passing through a loaded AK mag, to simulate a bad guy wearing a chest rig. In that one the M855 penetrated 8 inches of gel vs. just 4 for the Mk262 (and 11-12 for a 6.8 round).
So the added accuracy and terminal effect on soft tissue of the Mk262 appears to come at the cost of barrier penetration vs M855.
There are actually two 77 grain GI designated marksman / sniper loads.
The MK262 Mod 1 uses the same weight bullet, but it has a cannelure to cause it to break in two and fragment as it tumbles for improved lethality.
Both fragment well due to the OTM bullet format. The cannelure was added to make the loaded round more rugged for field use. I don't think any Mod 0 is still around -- we got a bunch of it when my last unit first fielded SPRs, but everything after that was Mod 1. Don't recall the team guys noting any change in performance for better or worse training or downrange when we switched over.
I said this in my post earlier. Hornady sells two 75gr loads.Are there heavier than 62 grain .223 rounds on the civilian market then?
The increased penetration of hard barriers is at least partially due to higher velocity. Interestingly, at close range, M193 penetrates hard barriers even better than M855, even though the latter has a steel core and the former does not.There were a couple presentations floating around with info regarding penetration. One showed M855, M193, M995, and Mk 262 through cars and such. This presentation showed the M855 as being able to penetrate more/thicker barriers then Mk262.
There is nothing wrong with M193. IMO it is better than M855 for civilian use, although not as good as 75-77gr HPBT.Stocks of M193 ammunition remaining on hand are to be regulated to marksmanship training only and are not to be issued for use in combat operations.
Yes, the cannellure is there for that reason, but it is also a weak point in the bullet and does appear to encourage fragmentation. It was not put there for that reason, but it kills two birds with one stone, so to speak.MK262 uses a cannellure to prevent bullet setback into the case during full automatic fire, not to increase bullet break-up.