Question on 223/556 running out of a Noveske Diplomate 7.5"

General Firearms NFA
1

Question on 223/556 running out of a Noveske Diplomate 7.5" pistol with flaming pig.

Before I get the flack for not running 300 or a 10.5" or longer barrel, let me just add a few details.

  1. This was purely a fun build.
  2. With the Aimpoint mounted forward on the receiver, cheek on the buffer tube and buffer tube on the shoulder, it puts a lot of rounds out fast on target. Yes, I have other ARs that I can shoot tighter groups, but the pistol is fun, (I can not make it a SBR in my State).
  3. So short, can be shot pistol style too.
  4. The noise isn’t that bad with the flaming Pig as it seems to toss the blast down range (Under cover is another issue).
  5. I know a 300blackout is a better option, but I wanted the to play with thousands of rounds rather than fewer more expensive rounds. That said, I may end up rebarreling someday.

If I wanted to use the Diplomate as a weapon in close quarters to replace a 9mm, I am wondering what round might help the über short barrel. For comparison a 115gr 9mm standard JHP delivers about 335lbs+ of energy at the muzzle. And it seems fairly universal that for the M885 FMJ to fragment, it needs 2500fps, with 2700fps being more realistic. I don’t know the velocity needed to create fragmentation, expansion or tumbling on various modern bullets, but I have heard as low as 1200fps on some rounds. A few LEO friends use the 55g Tap, but am leaning toward the 53g V max as long as the Noveske short barrel likes them. I of course realize I will have to make sure my choices group well and cycle perfectly. My questions relate to effective expansion and penetration from the short barrel.

  1. Does anyone have experience as to how these might perform in such a short barrel?
    2, Any other better performing suggestion?

Thanks in advance-

Here are a few choices. These numbers are not real word, but ran through a ballistics calculator just to give me a starting point.

9mm pistol 115g JHP Energy 335lbs+

M885 (I have tons so I put that in here)
20" barrel 3050fps
7.5" barrel 2414fps Energy 802lbs but below fragmentation velocity

Hornady Tap 55g Hollow Point
24" barrel 3240fps
7.5" barrel 2477fps Energy 749lbs

Hornady 53g Vmax Ballistic Point Expanding
24" barrel 3465fps
20" barrel. 3359fps
7.5" barrel 2649fps Energy 826lbs

Hornady 40g Vmax Ballistic Point Expanding
24" barrel 3800fps
7.5" barrel 2906fps Energy 750lbs penetration may be low

Hornady 35g Vmax Ballistic Point Expanding
24" barrel 4000fps
7.5" barrel 3058fps Energy 623lbs this put in just for comparison

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2

A fragmenting design will not make penetration. I’d pick one of the lighter bullet weight loads here:
https://www.m4carbine.net/showthread.php?t=19881
In 5.56 if possible, maybe 55gr 5.56 GD if you can still find it.

3

Per Jeff Hoffman, the Black Hills 50gr TSX will expand to at least 75m from this length of barrel.

Makes me wish we could get the other 50gr TSX, which has a lower velocity threshold for expansion.

4

I did a lot of research on this for my 8.5" 5.56 krink SBR. The military is having promising results using the 77 grain SMK2 from Black Hills and 75 grain Hornady TAP in SBR’s & precision rifles. I use the 75 grain Hornady TAP steel practice rounds shooting 3 gun in a 18" PREDATAR & all runs perfect. It runs 100% in my Arsenal 106 SBR 5.56 also.