Optimum Caliber for an AR based PDW.

[Rob72]

CMMG has both complete AR pistol and bcg+barrel for sale in 5.7x28.

Ammo & ballistics? I know the ammo is out there, but I'm not one of the latest & greatest chasers.

I have, know & like the 9mm in the PDW role. Low pressure, low concussion, tons of ammo options. .45ACP works too, but I like the faster baseline cartridges in 9 (115/124 gr).

The shorter the barrel, as you say you want, the more you want to lean to the standard pistol calibers, and I guess the 5.27 falls in that envelope.

.223 is brutal(to the shooter) out of a 10 inch, and shorter would have me wanting to grab safety glasses before hearing protection.

On any caliber, a good linear comp is your friend.

 

[nortac]

Thanks for all of the input guys. I will definitely use a linear comp on whatever caliber I choose. The 5.7 is an intriguing caliber choice that I hadn't even considered until @OkieStubble enabled me. He sure likes spending my money! Building a PDW is a ways off and I would have a hard time coughing up the money for the FN pistol. But who knows. I guess I don't know enough about the 5.7 cartridge's effectiveness to be totally comfortable with it, but it sounds good. If I built a 5.7 PDW, I could also build another upper in .223, whereas if I built a 9 mm, I could also potentially build a .40 S&W upper. But my understanding is that .40 S&W is a finnicky option in the AR platform.

 

[nortac]

So, upon the aspect of reloading the 5.7, it is no bed of roses. Very finnicky and short case life. Factory ammo seems to be running about a $1.00 to $1.50 a round. Upside is low recoil, flat shooting and accurate. Looks like a lot of fun to shoot. Less penetration in ballistic gelatin than a +P 9mm, Hickock 45 shot through and through an old truck door.

 

[Rob72]

So, upon the aspect of reloading the 5.7, it is no bed of roses. Very finnicky and short case life. Factory ammo seems to be running about a $1.00 to $1.50 a round. Upside is low recoil, flat shooting and accurate. Looks like a lot of fun to shoot. Less penetration in ballistic gelatin than a +P 9mm, Hickock 45 shot through and through an old truck door.

If you can find any of the old Hirtenberger Submachine gun ammo, or load out to 1600 fps with a 115 gr bullet, 9mm will go through both doors of a late '70s Olds. One door and a half, with a window down...

 

[Ad Astra]

Just thinking 300 BO can't be beat ... price per round has really come down, even now.


AA

 

[nortac]

Not sure how short a barrel you can run with .300 BO, I already have a 10.5 .300 BO barreled upper, it's way too long for what I'm wanting to do.

 

[Ad Astra]

Not sure how short a barrel you can run with .300 BO, I already have a 10.5 .300 BO barreled upper, it's way too long for what I'm wanting to do.

PSA has a number at 7.5" ...


AA

 

[KW Driver]

the Rattler gets small for a 300 BO

but that's not a home build kit yet.

 

[nortac]

I believe Faxon has a 6 in. 300 BO barrel.

 

[nortac]

the Rattler gets small for a 300 BO

but that's not a home build kit yet.

Besides, I don’t want an arm brace or need to register as an SBR down the line. A bit too spendy as well.

I have a lot to mull over before building a super compact AR pistol. I still have to ring out my larger AR pistols that I have just replaced the braces with bare buffer tubes.

 

[nortac]

Not sure how short a barrel you can run with .300 BO, I already have a 10.5 .300 BO barreled upper, it's way too long for what I'm wanting to do.

Seems to be plenty of short .300 BO barrels.

Just thinking 300 BO can't be beat ... price per round has really come down, even now.


AA

And the .300 BO is very easy to reload, which I've already done, and I have plenty of brass.

 

[OkieStubble]

@OkieStubble enabled me. He sure likes spending my money!

It’s what I do.

 

[dojpros]

"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?"

My considerations based on announced use -SD/HD/VD

1. Reliability
2. Ammo availability to build and maintain proficiency.
3. My knowledge re manual of arms/manipulation
4. Compatibility with existing platforms/mags/pouches/"holsters"/straps etc.
5. Ballistic capability/performance/predictability

My initial thought was 300 Blackout. After typing the list above, I am likely back to some flavor of a 5.56.

NO on the binary trigger. Unless that is the only trigger you have ever shot, EVER, I fear it is just a matter of time before an ND goes down range, particularly in a SD/HD/VD scenario.

 

[Mlee]

I have a Ballistic Advantage 8" barrel with a flash can. I've only shot 40 rounds through it because there wasn't a lot of ammo available when I put it together.

I also have a 4.5" Faxon 9mm barrel. I bought it as a BCG, barrel set. It would be very compact if I didn't have a 12" suppressor hanging off the end of it.

Have you thought about a 458 Socom? I worked with Tony Rumore (Tromix) about 20 years ago and he fixt me up with a 10.5" barrel when they first came out. Back then it was hard to find ammo and I didn't want to reload so I traded it off. That's a pretty hard hitting round.

 

[OkieStubble]

I have a Ballistic Advantage 8" barrel with a flash can. I've only shot 40 rounds through it because there wasn't a lot of ammo available when I put it together.

View attachment 1621251

I also have a 4.5" Faxon 9mm barrel. I bought it as a BCG, barrel set. It would be very compact if I didn't have a 12" suppressor hanging off the end of it.

Have you thought about a 458 Socom? I worked with Tony Rumore (Tromix) about 20 years ago and he fixt me up with a 10.5" barrel when they first came out. Back then it was hard to find ammo and I didn't want to reload so I traded it off. That's a pretty hard hitting round.

That’s a good looking AR right there. Faxon manufacturing is an up and coming company. Sooner or later, with their quality of their barrels and BCG’s, the name Faxon will be well known.

Socom out of anything less then a 10.5 and a can? That’s a lot of bullet….

 

[Mlee]

That’s a good looking AR right there. Faxon manufacturing is an up and coming company. Sooner or later, with their quality of their barrels and BCG’s, the name Faxon will be well known.

Socom out of anything less then a 10.5 and a can? That’s a lot of bullet….

I used to have a video of Tony at the Wynadotte machine gun shoot, shooting 458 Socom full auto. Fun times

 

[nortac]

"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?"

My considerations based on announced use -SD/HD/VD

1. Reliability
2. Ammo availability to build and maintain proficiency.
3. My knowledge re manual of arms/manipulation
4. Compatibility with existing platforms/mags/pouches/"holsters"/straps etc.
5. Ballistic capability/performance/predictability

My initial thought was 300 Blackout. After typing the list above, I am likely back to some flavor of a 5.56.

NO on the binary trigger. Unless that is the only trigger you have ever shot, EVER, I fear it is just a matter of time before an ND goes down range, particularly in a SD/HD/VD scenario.

Completely agree. Given my recent experience with my larger AR pistols, I'm of the opinion that 5.56/.223 is optimum. With .300 BO a very close second. Chances are I'll build uppers for both calibers with barrels no longer than 7.5 inches. Same BCG, same magazines, both very easy to reload for, what's not to love. I just kinda put the question of a binary trigger out there to see what others thought. Not at all practical IMHO plus the potential for an ND or worse. If something went awry in a self-defense situation, that would be a hard one to convince a jury that you weren't reckless or negligent.

 

[NewYorkBuck]

As others have said 7.5" is pretty short for a .223. Takes a lot of velocity away for a cartridge that depends upon velocity. Also leaves a lot of sound and muzzle blast for inside work.

If you said 11"+ I would probably say Grendel. At 7.5" I'd have to say 6.8 SPC or .300 BLK. IIRC being fired from an SBR was part of their design parameters.

 

[nortac]

As others have said 7.5" is pretty short for a .223. Takes a lot of velocity away for a cartridge that depends upon velocity. Also leaves a lot of sound and muzzle blast for inside work.

If you said 11"+ I would probably say Grendel. At 7.5" I'd have to say 6.8 SPC or .300 BLK. IIRC being fired from an SBR was part of their design parameters.

While the performance of the .223/5.56 may be somewhat degraded by a 7.5 in. barrel, it would still be far superior to a 5.7x28. I wouldn't want to be hit by either at close range. And again, this would be a close-range gun anyway. Projectile selection would be key to short range and reduced velocity performance. As for 6.8 SPC, that would probably be a good choice, but....availability, another caliber to reload for, another BCG? Things to think about.....

 

[OkieStubble]

While the performance of the .223/5.56 may be somewhat degraded by a 7.5 in. barrel, it would still be far superior to a 5.7x28. I wouldn't want to be hit by either at close range. And again, this would be a close-range gun anyway. Projectile selection would be key to short range and reduced velocity performance. As for 6.8 SPC, that would probably be a good choice, but....availability, another caliber to reload for, another BCG? Things to think about.....

I like these threads about short barrels and heavy calibers. .300 BO and .556 maybe better on paper then the itty bitty 5.7x28. But throw them all into a hot tactical mix of run & gun with speed at close ranges?

Instead of short barrels and real heavy? Or short ranges and really hot velocity’s?

Both of which creates a lot of recoil from a pistol that already doesn’t even have a stock? Give me a 5.7 any day.

I have an image in my mind of a huge crap scenario, where one is running around frantically, not only trying to engage fast moving targets, but getting easier, faster hits on fast moving targets. In those types of scenarios, from a small barreled miniature AR?

Do I want a small, faster caliber, where the velocity is the deciding factor of victory and the cheek welded gun is easier to control and get as many hits on target as possible?

Or do I want a hotter and much heavier caliber, bucking like a wild bronco, while I’m shooting and moving and trying to place as many consistent hits as smoothly as possible in the least amount of time which would seem to be needed in a close, fast moving engagement?

That was the paremeter’s you described? If not, then I’m confused. Do we only consider size and speed of various calibers from very short barrels that are only going to be shot from the cheek and not consider the importance of the tactics applied with those same caliber’s?

I’d think I would just go get a P90 with a stock and be done with it.