I posted this in the Range Report section and didn't get any bites, and I hope someone here can help me out. I'm trying to figure out if match grade .223 Rem under-performs in a 5.56 chamber designed for MK262. I ask this because I know the NATO chambering should have a longer throat and I can't seem to get good information if there is a difference in COAL between 77gr (FGMM in particular) .223 Rem compared to MK262 spec/clone ammo. Anyone care to share?
.223 Rem in MK262 5.56 Chamber
- Thread starter rideHPD
- Start date
I dunno bout the FGMM, but I can get you some measurements off some black hills 77gr OTM after the weekend.
Define "underperforms"
The rounds are identical in dimensions although 223 Rem ammo is loaded to lower pressures.
The accuracy you will get will depend on how sloppy your 556 NATO chamber is.
The rounds are identical in dimensions although 223 Rem ammo is loaded to lower pressures.
The accuracy you will get will depend on how sloppy your 556 NATO chamber is.
Pretty sure the DMR chamber (aforementioned 5.56 chamber designed for Mk262) is pretty damn close to a Wylde.
FGMM 223 w/77 gr is anemic to begin with, Mk 262 is pretty darn warm. COAL for 262 isn't any different then FGMM because both are set up to fit in an AR magazine.
If you want Mk262 clone ammo.....there are ways to get that.
This is about what I expected; I've been shooting FGMM in a SPR-ish build with a MK12 barrel from Centurion arms, and I've been shooting very good groups then having some fliers here and there, and I'm trying to tell if it's me, the rifle or the ammo. I am about 95% sure it is due to my inexperience with gas guns, I just wanted to rule out the variables before I bought different .223 match ammo to test, only to find out that the bullet has several thou to jump before it reaches the lands.
The best way to get that is to reload. I use 24.8 gr. of RE-15 in a .223 chamber and 25.3 gr. in a 5.56 chamber. Otherwise, you might try the Hornady 'steel match'. It's made, and priced, so you can toss the cases away. They are steel, and therefore, not easily reloadable. The last I bought was just under fifty cents a round. But, it's 75 gr. Hornady match bullets not 77 gr. SMK's. They have about the same ballistic properties.
Black Hills 5.56 77gr OTM (or the White Box 'seconds')
Southwest Ammo 5.56 77gr 'run and gun'
23.8gr 8208XBR/24.0gr Ramshot TAC with any 75/77gr bullet loaded to AR mag length
No it doesn't under-perform.
MK262, Black Hills 77, it is actually pretty short COAL about 2.24-2.245, hornady TAP 75gr is 2.25", etc etc. I don't think I've seen any match ammunition that is 2.26" in the normal bullet weights. Stuff like 75amax will be way longer because of the bullet shape.
As far as 'match chamber designed for mk262' you need to know what reamer was used honestly that sounds like a sales pitch so it is most likely a variation of a wylde chamber. 556 wylde they all have fairly long throats I believe for 1) bullet jump (it is a good thing) and 2) running heavies single fed.
I spoke with Monty at Centurian Arms about this, the chamber is cut for the mk262. I have this same barrel, mounted in his DMR upper with Vltor VIS 3. I'm getting great results using 69gr Nosler CC projectiles too.
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I'm curious as to what the actual reamer dimensions are for above mentioned chamber optimized for the mk262? It seems like the Wylde has a much longer than necessary freebore, and so too the 5.56 NATO.
Some reference material.
B
Some reference material.
B
