Optimum Caliber for an AR based PDW.

[nortac]

I pretty much have it built in my head. Aero Precision Kodiak Brown anodized receiver set and handguard, AP NiBr BCG, AP CMV 7.5 in. barrel, KAW linear comp, some V Seven Ti parts, as mentioned probably a TT trigger, Strike Industries 5.5 in pistol buffer tube, possibly a FAB vertical grip and the already acquired SIG Romeo RDS. I knew there was a good reason to buy a 2nd SIG RDS! I might try a Kynshot recoil buffer, depending on how the Strike Industries unit works out. Probably an adjustable gas block.

 

[OkieStubble]

You buy one and give us a write up, then I might consider it, maybe... Reading a review on the Ruger 57 showed poor accuracy and a mushy trigger with a slow reset...kinda defeats the whole purpose of shooting the 5.7

https://www.cabelas.com/shop/en/smith-wesson-mp-57-semi-auto-pistol-with-thumb-safety

 

[nortac]

https://www.cabelas.com/shop/en/smith-wesson-mp-57-semi-auto-pistol-with-thumb-safety

Same reply, but it looks better than the Ruger, could be a game changer, but I don't want to be a beta tester again.

 

[Mlee]

Have you thought about what ammo/load your going to use for good penetration and maximum expansion? That can be a problem for .556 and low velocity (I'm sure you're already aware of that).

Twenty something years ago, I put together a 7.5" AR just for the fun of it. All I shot through it was 55 grain Wolf at bottles and cans.

It took a bit and a few trips to the range but I finally got it to run pretty good. A friend of mine had an M16, we put it on his lower, burnt up a lot of Wolf that day . Good thing you could buy 1000 rounds for $69 back then.

I don't remember what components I used, but I'm sure they were as cheap as I could find. Back then there weren't as many options as there are now, I didn't even have the internet, just gun shows and Shotgun News.

 

[nortac]

Probably some varmint load. If the 5.7 will work with a V-Max bullet for defensive purposes, surely a .223 load with a similar projectile would suffice for close range self defense.

 

[HDSledge]

Probably some varmint load. If the 5.7 will work with a V-Max bullet for defensive purposes, surely a .223 load with a similar projectile would suffice for close range self defense.

Are you mainly going for a home defense/pdw setup? I keep a 9mm upper on my lower in case shtf in the house. You might consider a pistol caliber upper on an AR lower. If 9mm is suitable you can buy the upper from CMMG ie. Banshee (5") and use Endomag 9mm inserts that they sell direct now. The inserts allow Magpul magazines to accept 9mm. They work. I have put thousands of rounds down range and the only failures were from me playing around with buffers and springs.

 

[nortac]

Thanks @HDSledge, I already have a dedicated 9mm AR pistol set up.

 

[czgunner]

If you were going to build the most compact PDW based on the AR platform, what do you think the most practical caliber would be for SD/HD use, vehicle defense, etc. Not just a range toy, but for serious purposes. Would you consider a binary trigger?

6.8 SPC is in it's element at 12.5". It's extremely efficient and effective. That's what I have and highly recommend.
I also shot deer with it this last fall. Worked great.

 

[HDSledge]

If you were going to build the most compact PDW based on the AR platform, what do you think the most practical caliber would be for SD/HD use, vehicle defense, etc. Not just a range toy, but for serious purposes. Would you consider a binary trigger?

After reading about the 6.8 I looked it up out of curiosity. It has advantages over my favorite, .300 BLK. There are also some drawbacks. Interesting read here:
6.8 SPC vs. .300 BLK

 

[czgunner]

After reading about the 6.8 I looked it up out of curiosity. It has advantages over my favorite, .300 BLK. There are also some drawbacks. Interesting read here:
6.8 SPC vs. .300 BLK

I own both. Personally, I find zero drawbacks for practical use. My 8" 300 BO suppresses nicely, but that's it. It's 100% a range toy. If I'm shooting supers it's 6.8 SPC.

 

[HDSledge]

I own both. Personally, I find zero drawbacks for practical use. My 8" 300 BO suppresses nicely, but that's it. It's 100% a range toy. If I'm shooting supers it's 6.8 SPC.

I have an 8" suppressed .300 BLK set up as my primary PDW at home. I don't consider it a range toy though. I have read that you can't load as many 6.8 SPC into a standard 5.56 magazine since they are bigger and can bulge the sides. Is that correct? 6.8 is primarily for hunting? Not familiar with it ftmp, just getting my facts straight.

 

[czgunner]

I have an 8" suppressed .300 BLK set up as my primary PDW at home. I don't consider it a range toy though. I have read that you can't load as many 6.8 SPC into a standard 5.56 magazine since they are bigger and can bulge the sides. Is that correct? 6.8 is primarily for hunting? Not familiar with it ftmp, just getting my facts straight.

I didn't mean to imply it was a range toy for anybody except for me. I was just saying I only use it for shooting quiet subs. I apologize that came across poorly.
It was developed after the Somalia disaster to kill bad guys better. Sadly the SAAMI drawings were screwed up by Remington and it took other people to push the correct drawings through as the "SPC II" and as a result, there was a lot of confusion about what barrel and what ammo to get and use. That was resolved years ago and I haven't seen any rifles or barrels available in anything but "SPC II" for many years. It is one of the intermediate cartridges that I always find on the shelf, so it is in common use. It has become very popular for hunting and has killed just about everything in North America. You should check out 68forums if you have time. I use 6.8 SPC magazines made by PRI (25 round) and Barrett (30 round), so I don't haven any mag issues. Like many cartridges, the best performance will be realized by handloading (also way cheaper).

 

[HDSledge]

I didn't mean to imply it was a range toy for anybody except for me. I was just saying I only use it for shooting quiet subs. I apologize that came across poorly.
It was developed after the Somalia disaster to kill bad guys better. Sadly the SAAMI drawings were screwed up by Remington and it took other people to push the correct drawings through as the "SPC II" and as a result, there was a lot of confusion about what barrel and what ammo to get and use. That was resolved years ago and I haven't seen any rifles or barrels available in anything but "SPC II" for many years. It is one of the intermediate cartridges that I always find on the shelf, so it is in common use. It has become very popular for hunting and has killed just about everything in North America. You should check out 68forums if you have time. I use 6.8 SPC magazines made by PRI (25 round) and Barrett (30 round), so I don't haven any mag issues. Like many cartridges, the best performance will be realized by handloading (also way cheaper).

I will check out the 68forum looks like the same format as HKPro. The history of the cartridge sounds interesting.

 

[nortac]

How does the 6.8 fare with the really short barrels of 8 in. or less compared to .300 BO or 5.56? I have yet to see a 6.8 barrel offered in less than 16 inches. I suspect that the 6.8 SPC is not compatible with my ultra short PDW concept.

 

[czgunner]

How does the 6.8 fare with the really short barrels of 8 in. or less compared to .300 BO or 5.56? I have yet to see a 6.8 barrel offered in less than 16 inches. I suspect that the 6.8 SPC is not compatible with my ultra short PDW concept.

12.5" are very popular, ARP barrels are the top of the pile. I've also seen some 10", but can't say much about 8". Most guys using these now are using them to kill 4 legged things, so the 12.5 and 16 are most common. The cartridge is extremely efficient and is designed around the 12.5" barrel length without compromising.