Mk12 Setup for High Pressure Loads?

[FredHammer]

The biggest question you have to answer for yourself is whether or not primer-piercing velocities do anything of merit for you down range.

For example, does 2750fps vs 2670fps mean much shooting 77gr?

2750fps 77gr SMK Doppler Radar data, 2.7” optic height over bore, sea level 59˚F
400yds 2 mils drop 1.2 mils drift 1829fps 572 ft-lbs
500yds 3.2 mils 1.5 drift 1635fps 457ft-lbs
600yds 4.6 mils 1.9 drift 1456fps 362ft-lbs
700yds 6.2 mils 2.4 drift 1289fps 284ft-lbs
800yds 8.2 mils 2.9 drift 1138fps 221ft-lbs
goes subsonic between 800yds and 825yds

2670fps 77gr SMK Doppler same conditions
400yds 2.2 mils drop 1.2 drift 1768fps 534ft-lbs
500yds 3.4 mils 1.6 drift 1579fps 426ft-lbs
600yds 4.9 mils 2 mils drift 1403fps 336ft-lbs
700yds 6.7 mils 2.5 drift 1240fps 263ft-lbs
775yds 8.2 mils 2.8 drift 1130fps 218ft-lbs
goes subsonic before hitting 800yds

Both are really anemic already at 500yds, you won’t see or hear any different on impact at 400yds, so it really doesn’t matter. I would find a happy load that doesn’t trash your brass, that behaves well, groups around an inch at 100yds, and go blast with it unless you’re just chasing paper groups at 100yds, which doesn’t matter what you do velocity-wise at that point. Just chase groups.

These carbines were meant to extend the reach of the AR-15 within dismounted small units without having to lug around an SR-25 or Mk.11 Mod O, while maintaining magazine/ammo compatibility between Assaulters and Sniper Support elements, who could also maneuver as a contingency if things went south. SOCOM drifted away from that with the SPR, making it more of a belly-rider blaster and less of something that worked well for CQB like the original 723 JSOC Mod Sniper Carbines.

Once SOPMOD Block II caught up to that more or less, the SPRs got put out to pasture.

BC @ .372?

 

[FredHammer]

That's one of the reasons I've moved away from TAC and completely over to AA2520 (I also have a bunch of 8208 but there hasn't been a need to trial any 5.56 loads w/it). Plus I got about 40 fps more MV out of my 77smks with less overall pressure, gas volume and a bit lighter recoil (though it'd be a stretch to call any sort of recoil from a 5.56 gun hard to manage. Ejection pattern moved from 1-2 oclock w/TAC to between 2-3 w/AA2520 across all my AR pattern platforms. Even brass seems marginally cleaner but could be my imagination.

I got a couple lbs of AA2520 too! IMI Razor Core has been the most precise factory ammo I’ve shot. Two 60 shot strings between two barrels clocked 206ES and 50SD 117/35. I certainly imagine I can load with much more consistency. Weird tho, it was consistently inconsistent.

Edited for accuracy

 

[MontanaMan]

I don't have my load data available as I am at work, but I used the online hodgdon load data and a Hornady 75 gr and at mag length in a 18" white oak battel I got 2820.

Well, here are your loads from an earlier thread on Staball Match, & since Hogdon's max load is 24 gr @ 2754 FPS & 54,700 PSI, it looks like you may have gotten a typo in your post in you load data. It's seems that for you to have gotten 2820, you would have been over the book load of 24.0 by 1.3 gr & at 25.3, & no one else is reporting anywhere near that velocity at that charge weight.

So maybe you can please clarify what the right numbers should be.

I'm asking/concerned because I just got a lot of the Staball Match for initial testing & from most of the data in this & other threads, I've pretty much settled on starting at 24 & working up........................but your data (for velocity, not load weight) is an outlier in all the info that I can see.

Maybe I'm reading your data wrong??????????? Maybe you really did get 2820, but not at the book max of 24.0

MM


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MK20​

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Minuteman

• Feb 10, 2023
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• #43

I just got my jug of Staball Match in today and ran some loads through my gun to just test velocity.

I will be ordering more of this stuff.

Here are the specs.

18" WOA SPR running a H3 buffer.

LC cases.

Win primers

75 gr Hornady BTHP


Hornady's starting load gave me 2600 fps

25.0 gr 2730 fps

25.3gr 2818 fps

25.5 gr 2824 fps

25.9 gr 2832 fps

I saw an ejector swipe on the 25.3 but not on any higher charges, so idk. Primers looked fine on all. The higher charges were flat, but not overly so.

Hodgdon's data tops out at 25.3 at 55K psi. As you can see from my shot data, the velocity seems to top out there so there is no reason to drive the pressure higher.

I did get noticeably more gas in the face as I went above the book max.


As seen above, this powder lets me beat MK 262 velocity with an easy metering powder that is supposedly temp stable.

It beat my hot 8208 load by 50 fps in the same gun.

I will be doing some temp sensitivity testing in the next few days.

Already, I will be picking up more of this stuff just based on the velocity numbers.

 

[MK20]

Ok. I am traveling for work but that data is what I remember. I am pretty sure you are looking at data for the 77 gr and not the 75 I was using. I just pulled this from Hodgdon's website right now.

So the online data for Hodgdon was indeed what I posted in that other thread. I double checked it repeatedly at the time because I was shocked at the velocity.

I also tested over online listed max as the Hodgdon data listed was only to .223 pressures so that leaves a bit of a margin until 5.56 pressures.

Seeing as how my brass/primers looked just fine, I will keep running at the book max.

If I remember correctly, I am also running an H3 buffer in that gun to slow unlocking as WOA runs their ports kinda big on the 18" rifle gas.

 

[MontanaMan]

Ok.
Yes, I was looking at th 77's data.
I have both 77 SMK's & 75 Hornady's.

I'll load both & compare.

MM

 

[LRRPF52]

BC @ .372?

Hornady’s doppler program now has actual doppler track data for many common competitor’s bullets. I plugged in Sierra 77gr Match King from their drop-down list.

The Doppler data does not match up with theoretical BC data as you move farther out, and shows how many bullets have inflated BC values. For any distance where I’m looking at over 600yds, I use G7 BCs if there is no doppler data available.

Either way, there isn’t much practical advantage to pushing the loads between the high 2600s vs mid 2700s.

 

[Scarface26]

Following

 

[Alaska]

In my MK 12 and 16” Reece rifle my hunting load
70gr TSX with TAC @ 26.0 with LC brass and CCI 41 primers excellent accuracy !

 

[nn8734]

I got a couple lbs of AA2520 too! IMI Razor Core has been the most precise factory ammo I’ve shot. Two 60 shot strings between two barrels clocked 206ES and 50SD. I certainly imagine I can load with much more consistency. Weird tho, it was consistently inconsistent.

How far were the farthest targets you were shooting at when you took those MV readings? Am curious to see app what your 'hit rate' was at whichever distances you were shooting to..

 

[FredHammer]

How far were the farthest targets you were shooting at when you took those MV readings? Am curious to see app what your 'hit rate' was at whichever distances you were shooting to..

I fucked up. The 77SMK handloads I had contracted out ran 206/50. The IMI ran 117/35. 100yds is where I tested them just recently.

Over the years I've shot IMI 77SMK on IPSC plates to 500yds 98%. Past that got dicey. I wasn't as good with my wind calls 5-6yrs ago, and didn't use wind flags. With no backstop other than the plates I stopped at 500yds with the 5.56.

Now that I have my shit together better, I too am curious how the ES/SD comes into play at 500-600. Gotta get my handloads rolled up and test them and their precision at distance. Can't wait.