You use the SBR or pistol that is 100% reliable, which you are comfortable using proficiently in a stressful situation. If you find your shot placement and proficiency superior when shooting 9 mm over other calibers, go with that.
I can shoot my AR 9 mm faster and more accurate than my .45 ACP UMP conversion on the clock. The AR 9 has better ergonomics and it’s easier to mount a light. I would hate to be shot with it if it were loaded with Federal HSTs (which it eats just fine). Food for thought.
.300 blackout is superior for a PDW in terms of terminal ballistics, but for most of us, 9 mm JHPs should do quite well unless your enemy has body armor.
I know a lot of people like to go to handgun calibers in PDWs, but for me, if you're going to the trouble of building it in an AR, put in a more potent caliber.
I built my SBR in .300 Blackout for my home defense gun. At 11.3" it's kinda big for what most people think of as a "PDW" but I call it that sometimes.
I do know the 5.56 gives a lot up in short barrels, (still better than handgun ammo) and I wanted the most power I could get, even though I was going to a small gun. The .300 with supersonic rounds are the ticket for me. I shoot whatever 147 or 150gr fmj for practice. I keep the very good (but unfortunately expensive) 110gr Barnes Vor-Tx as my duty round. I'm sure a 150gr fmj would be a decent round in a pinch. Soft points can be had as well.
You know what I like best about most people?
Their dogs.
300 blk
I have a 7.5" 300 BLK that I built to be as short and light as possible while still being reliable, and have enough barrel to make supersonics still get up to a decent velocity. If I was to go shorter than about 7" on a barrel, I have been mulling over a couple options.
With the CMMG guard coming out in 5.7, 9mm, and 45, I would imagine a 10mm would be on the way fairly soon. That is a project that seems interesting to me. With the 10mm, you still get the option of a heavy subsonic in the 200 grain ballpark, as well as the lighter 135 grain bullets you can get to over 1400 even in a 5-6" barrel. The CMMG delayed blowback system should help with recoil, and a suppressor along the lines of the SiCo Omega 9k (I know they make a 45 version, but it seems a little long for a PDW that you are trying to keep as short as possible), but for .40 would make a pretty neat package. Glock mags give you 15 rounds, and with TT extensions you can up that to 19 I think.
In my mind, if im going pistol caliber, I want the mag in the grip.
If im going less than 7” ish barrel, I want a pistol caliber.
I went through this excersize a few times.
>\=11.5 5.56
9-12” 6.8
7-10” 300blk
<7” pistol
And at this point I realize i dont want to afford to get good with non 5.56, then I look at uspsa rankings and realize that a pcc doesnt dominate a real pistol, so I just stick to my g19 and 5.56 rifle.
Ymmv
Last edited by MegademiC; 10-16-18 at 21:20.
If I were to start over again, I'm liking what I have seen so far with the 9" 7.62*39 CZ Bren 2.
Basically I would love to do a French GIGN clone build.
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7.62x39 is the best out of a short barrel in my opinion
assuming we are talking about an AK variant if we are talking about and AR id rather spend the extra to run .300
+1 for the bulgy 4 peice
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