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Duplicating MK 262 Mod 1 Ammo

biggin69

biggin69

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Full Member
Minuteman
Jun 22, 2003
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New Mexico
Ive been trying my hand at reloading 5.56 rounds in an attempt to duplicate the Black Hills MK262 Mod 1 ammunition that supplied to the US Military for use in the 18" SBR. Im using LC brass, CCI 41 primers and SMK 77 gr with the cannelure. My understanding is the military load develops a velocity of around 2,750 fps. Just for note, I measured the volume of the case with a seated bullet set to 2.260 COAL so I would not overfill the case and have a compressed powder issue. In working up my powder charges, the cases reached the point where they were filled with powder. I first used RE15 powder but was not getting velocities above 2610 fps. CFE223 powder reached a max velocity of 2630 fps. IMR 8208XBR powder reached a velocity of 2720 fps. I now have some TAC powder that i will try next. Im not an expert in reloading but Im giving it the ole college try.

I was wondering if anyone else is trying their hand at duplicating the MK 262 ammo and if you would be willing to share your thoughts and receipts.

Thanks!
 
25.1gr H335, CCI41, and LC brass pushes a 75gr Hornady HPBT @2850 out of my 16" barrel. As always, work it up yourself and YMMV.
 
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8208XBR gives me excellent results when compared to real MK262 out of the same 16" rifle. Varget will work well too.
 
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2630 is pretty low for CFE-223. How much were you running, and what kind of pressure signs were you seeing? I run 24 grains of CFE in LC brass with CCI 41 primers and it pushes the 77 grain Nosler CC loaded at 2.25" (not crimped) to around 2820 FPS out of an 18" barrel.
 
My current duplicate load is 24.0 grains of TAC with 77 grain NOS CCs gives me 2750 from my 18" Mk12 Mod1.

Also, 24.0 grains of Varget give me 2640 out of the same rifle.
 
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OP,
We no longer need to use questionable "errornet" load data for many Ramshot/Western powders used on 5.56MM NATO application. Ramshot's 5.0 edition contains 5.56MM NATO pressure loading data that previously required handloaders to take our best guess on: http://www.ramshot.com/wp-content/uploads/2010/09/WP_LoadSpec_7-2-13.pdf HTH. Don't blindly attempt to load to MK 262 MOD 1 published MV of 2750FPS especially with shorter barrels. First question you have to answer is what is the actual velocity of the factory Black Hills MK 262 MOD 1 ammunition in your barrel. It makes a measure 2825FPS (5 shot average) in my 18" SS 1/7.7 Krieger barrel but won't make anywhere near that MV in a COLT 14.5" M4A1 barrel. Just food for thought, this 18" Krieger barrel shoots the 77gr. SMK a couple-three 0.1s tighter@100yds. at 2746FPS which is the MV of the BH 77gr. SMK AMU load in that barrel. Best powders I have used under the 77gr. SMK are TAC for highest MV & H4895 for stellar thermal stability. Keeping in mind the relative thermal stability of whichever propellant you choose, best to err on the side of caution when loading near full NATO pressure. High ambient temperatures &/or a hot chamber can easily put pressure of your handload over max. Because of the very-high-temperature stabilized non-canister grade spherical powder used, the factory Black Hills MK 262 MOD 1 cartridge makes high MV while generating no more than the 5.56MM mil-spec pressure of 58,700PSI. The safety margin engineered into mil-spec Black Hills 5.56MM MK 262 MOD 1 ammunition will not be there in a full NATO pressure 62,350PSI handload. I keep a good supply of factory BH MK 262 MOD 1 on hand for hot temperature use for that very reason. HTH.

Also look here for Mk 262 MOD 1 clone info: http://www.snipershide.com/shooting...ain-5-56-load-problems-updated-ocw-tests.html
 
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18-1/4" 7.5tw bolt
24.3gr H335
77SMK in RP brass @ 2.300" OAL (bolt gun mag)
2780fps

21-1/4" 7tw AR, Kreiger 4 groove
24.9gr A2520
77SMK in RP brass @ 2.250 (reliable feeding)
2690fps

Both loads are exceptionally sub MOA, the bolt gun is in the 0.1's

Hit me up via PM and I'll help you tailor a starting load that will likely blow your mind.
 
interesting your velocities were so low using RL 15.

I duplicated the load by running some AMU MK262 through my MOD-0 SPR with 1-7 white oak 18 inch barrel getting an average speed of 2,725

my load is- LC brass, rem 71/2 primers, 25.2 grains RL15, 77 gr SMK cannelured seconds from Sierra. This load has averaged 2,720 everytime ive chronoed a batch and maintains accuracy that matches if not beats factory MK262
 
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VJJPunisher said:
interesting your velocities were so low using RL 15.

I duplicated the load by running some AMU MK262 through my MOD-0 SPR with 1-7 white oak 18 inch barrel getting an average speed of 2,725

my load is- LC brass, rem 71/2 primers, 25.2 grains RL15, 77 gr SMK cannelured seconds from Sierra. This load has averaged 2,720 everytime ive chronoed a batch and maintains accuracy that matches if not beats factory MK262
Click to expand...

VJJ,
I am familiar with the BH AMU load & the BH MK 262 MOD loading but they are separate 77gr. SMK loadings with different velocities. The BH loads I have are either marked AMU or MK 262, not both (below). Describe the factory 5.56mm loading you used in more detail if you would so we know which loading you duplicated in your rifle.

 
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Ahhh I suppose I misspoke, what I have and duplicated is the amu contract stuff shown on the left in your pic, I reckon me calling it "amu mk262" is an error, sorry for the confusion
 
VJJ,
No problem & thanks for the RL15 workup on that loading. The BH AMU load shown makes 2746FPS in the 18" SS Krieger 1x7.7 barrel I use while the BH MK 262 MOD 1 SECONDS load shown makes 2825FPS. But as stated above, the AMU loading is 0.2-0.3" more accurate at 100yds.
 
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leid said:
VJJ,
No problem & thanks for the RL15 workup on that loading. The BH AMU load shown makes 2746FPS in the 18" SS Krieger 1x7.7 barrel I use while the BH MK 262 MOD 1 SECONDS load shown makes 2825FPS. But as stated above, the AMU loading is 0.2-0.3" more accurate at 100yds.
Click to expand...

then we are pert near close together, pretty cool we are only logging a 20 FPS difference. Like I said my "clone" load recipe above shoots the same but leans to better than the AMU contract ammo I was duplicating, out of my gun. I wouldnt necessarily recommend someone reading this to load this up and go shoot it, i'm only listing it as a reference for using RL15
 
blc-2. bit higher es, but works perty good and I think mil stuff is ball powder if that's what you're after. 23.6 is what I was loading I think. worked good for me
 
Here's some data from recent tests with my rifle and RL15

Barrel: BCM 18" SS410 Barrel 1-8 twist
Chamber: USMC SAM-R
Length: 18" SPR

Bullet: Nosler Custom Competition 223Rem 77gr HPBT
Brass: Speer 5.56mm once fired
Primer: CCI #450
OAL: 2.255"
Chrono distance: 10ft
5 shots per string

Powder: Alliant RL-15

Wt: 23.5gr
Avg Velocity: 2559 fps


Wt: 23.8gr [compressed charge]
Avg Velocity: 2611 fps


Wt: 24.1gr [compressed charge]
Avg Velocity: 2658 fps


Wt: 24.4gr [compressed charge] Most accurate load tested in this rifle
Avg Velocity: 2716 fps


Wt: 24.7gr [compressed charge]
Avg Velocity: 2771 fps


Wt: 25.0gr [compressed charge] MAX LOAD
Avg Velocity: 2834 fps
 
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Out of my Rock River NMA2 MK262 has a velocity of 2750 fps. 24 grains of Varget gave me 2700, 24.5 2750. We've been told TAC is the closest you can find to the issued ammo powder. I haven't played with the round much except working it up and deciding that the only difference I could find between 24 and 24.5 grains of Varget was 50 fps and the same measured group size. For 24 grains and MK262 I have a half minute elevation difference at 300 and one minute at 600 yards. The slower Varget load has a little more drop.

I have some Tac but once I hit the Varget load I went with it.
 
23.8gr 8208XBR under a 77gr Nosler was within a few fps of Black Hills 5.56 77gr OTM "white box" seconds.

23.5gr XBR is maybe 20fps slower, but has proven to be a hair more accurate in my 18" 1:8 BHW barrel.
 
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Mk 262

leid said:
VJJ,
I am familiar with the BH AMU load & the BH MK 262 MOD loading but they are separate 77gr. SMK loadings with different velocities. The BH loads I have are either marked AMU or MK 262, not both (below). Describe the factory 5.56mm loading you used in more detail if you would so we know which loading you duplicated in your rifle.

Click to expand...

Blackhill gets the MK 262 Mod 1 brass from Winchester using WCC brass and Win already pre primed it with Win WSR primers.

Not the usual CCI 41 that is normally used in LC ammo.

I have seen MK 262 Mod 1 ammo with LC brass and CCI 41 primers......but the last batch I seen was WCC brass.
 
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Alaska said:
Blackhill gets the MK 262 Mod 1 brass from Winchester WC brass and Win already pre primed it with Win primers.

Not the usual CCI 41 that is normally used
Click to expand...

I don't see it often but BHA has also loaded their MK 262 MOD 1 & AMU cartridge in LC brass. I would think that the LC brass used is also primed/crimped at LCAAP. Due to the current shortage of WCC & LC brass, Jeff Hoffman has stated that BHA was being forced into using more expensive but very high quality brass made by RUAG for some BHA loadings. At least one BHA .223 Sierra MATCH load utilizing RUAG/RWS brass has already been run.
 
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My try at mk262 clone through my 16" 1:8 twist Shilen barrel, Wylde chamber using Saker suppressor.
LC 11 once fired
23.8gr 8208 XBR
77SMK
2.245 COAL
CCI #41s
8208xbr loads.jpg
I will go back and run a ten round test to get better data. I will try the 23.5gr load again as well, don't know if I pulled that one or not.
 
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Cornholeo said:
My try at mk262 clone through my 16" 1:8 twist Shilen barrel, Wylde chamber using Saker suppressor.
LC 11 once fired
23.8gr 8208 XBR
77SMK
2.245 COAL
CCI #41s
View attachment 50418
I will go back and run a ten round test to get better data. I will try the 23.5gr load again as well, don't know if I pulled that one or not.
Click to expand...

I know it's an old post, but did you get a muzzle velocity on that 69 smk load as well? How did the 23.5gn load do with the 77's?
 
FWIW

Any clone is going to be specific to the gun and how 262 Mod 1 performs in that specific gun. That being said...my clone for my precision rifle is...

LC once fired brass
24.5 gr Ramshot Tac
77gr HPBT cannelure (actually pulled from Uncle Sam's 262 Mod 1 rounds -- whole 'nother story there)
2.245 COAL
CCI #41s
Lee Factory Crimp
Brass was trimmed to 1.75 and tweaked (primer pockets uniformed, flash holes deburred and chamfered internally, 20 degree VLD chamfer and deburring)
Test group / base line was 10 rounds of factory new 262 Mod 1 through ProChrono Digital (recently calibrated)

My build uses a 20 inch Criterion Hybrid Contour. My average is 2835 fps, but not that it matters...your results may vary.

Average, ES, SD were near identical between the clone and the factory new 262 Mod 1 and my drop tables are dead on between the two. There is that old saying, "Once a bullet leaves the barrel...it doesn't care where it came from." This rifle shoots .9 inch groups at 200 meters.

FYI, I did play around with CCI 450's vs the 41's for this project. The 450's gave me slightly higher pressure / burn / velocity (about 12 fps for exact same load), but...I like the hardness of the 41's. You can tell the difference when you hand prime.

 
this is my accuracy load with 24 grains of VVn140. atop a 77SMK i am using a 20" 5r barrel though
and a tikka 1/8 twist 20" in the other rifle

i had no idea i was loading that load until i read this thread...

nosler brass, federal 205 primers. 2.260 factory OAL
 
I'll be working on replicating 262 as well. I have the Magtec version and from a 20" National Match AR I was getting 2786fps average. I'd like to be able to duplicate that with SMK's or the Nosler 77g.
 
Maybe I missed it but what powder is Black Hills using? Magtech?
 
@bohem
Hey there,
New guy to this forum here.
I was reading through the MK262 clone thread and saw you posted to IM you for a starting load.
I'm going for accuracy and would like to get to 2400 fps out of an 10.3" barrel.
Here's what I got so far:
75 grain BTHP, A2520 powder (23.5 gr), OAL 2.242" and I'm getting a velocity of 2394 fps.
These are 5.56 pressure loads.
The velocity is there but it's not too accurate.
Would crimping and playing with OAL affect accuracy?
And I'll have to rework this load in the middle of summer when it's hot out.
Any help would be great!
Thanks!
 
BoilerUP said:
23.8gr 8208XBR under a 77gr Nosler was within a few fps of Black Hills 5.56 77gr OTM "white box" seconds.

23.5gr XBR is maybe 20fps slower, but has proven to be a hair more accurate in my 18" 1:8 BHW barrel.
Click to expand...

I run 23.0 XBR 8208—- 77 SMK BR41 — super accurate one holers out of all my 5.56
 
couple of points:

1. check out Johnnys reloading bench on youtube. He did a 15 part series on cloning the MK262 round. He broke down the rounds, bullets, primers. etc. he tested about 13 different powders, some got there, some didn't.

2. when cloning it is important to realize, a pure clone will be hard because we as the public do not get the exact powder the manfacture uses.

3. finally, and importantly. dont go by the numbers on the box........ go by the numbers out of YOUR gun. so if the black hills mk262 round shoots 2700 FPS out of your rifle, then that is the clone you are shooting for.
you will try to match those numbers with velocity, accuracy, SD, ES, even the pressure signs out of your rifle, so on and so forth. so if mk262 shoots 1 inch groups with ejector swipes at 100 then you only need your reloads to shoot 1 inch groups with ejector swipes at 100 for the clone. of course i would also shoot the mk 262 at 300 to get group size too.

so many guys get wrapped around the axle trying for 2750, but if the ammo doesnt shoot 2750 from YOUR rifle, then you dont need 2750.

that said these seem to be the powders that work:

2520: but will have velocity swings due to temp

Tac: same temp swings

8208xbr: running real close to pressure most times, but no temp swings

arcomp: again running very close to pressure, but no temp swings
 
milanuk said:
If you have *lots* of time to kill...

Johnny's Reloading Bench playlist: Cloning Mk 262 Mod 1

He has some other videos where he uses the B77OTM instead of the S77MK w/ cannelure that are interesting as well - though I generally recommend watching on 1.25x speed as long as you can stand it, then skip ahead to the shooting ;)
Click to expand...


I really enjoyed his series on the mk262, and his method. he really talks through the thought process of the entire deal and poses some good questions and even talks about things often overlooked or often not thought about.
great normal everyday guy talking about reloading.

his mk262 series is probably the best "baseline" anyone can have on the topic.
 
bohem said:
18-1/4" 7.5tw bolt
24.3gr H335
77SMK in RP brass @ 2.300" OAL (bolt gun mag)
2780fps

21-1/4" 7tw AR, Kreiger 4 groove
24.9gr A2520
77SMK in RP brass @ 2.250 (reliable feeding)
2690fps

Both loads are exceptionally sub MOA, the bolt gun is in the 0.1's

Hit me up via PM and I'll help you tailor a starting load that will likely blow your mind.
Click to expand...
Can you shoot me a PM? Thanks
 
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