Let's talk PDW's

[MandoWookie]

So I was looking around for factory 4.5in 9mm uppers for my poor-man pdw build when I stumbled onto this...

https://www.rockriverarms.com/index....tegory_ID=2099

What kind of ballistics would that even have? How would that even function reliably? I almost want to buy it just to see.

[Norville]

So I was looking around for factory 4.5in 9mm uppers for my poor-man pdw build when I stumbled onto this...

https://www.rockriverarms.com/index....tegory_ID=2099

What kind of ballistics would that even have? How would that even function reliably? I almost want to buy it just to see.

I saw a picture of someone shooting a 5” 5.56, serious fireball.

There’s discussion about short barrel 5.56 ballistics buried in this thread or over in the ammo forum, but it’s more like “7.5” isn’t as bad as the internet makes it out to be”. Veritas Tactical posted in that discussion, and they make a 5” upper that I’d go with before RRA.

[wvincent]

I saw a picture of someone shooting a 5” 5.56, serious fireball.

There’s discussion about short barrel 5.56 ballistics buried in this thread or over in the ammo forum, but it’s more like “7.5” isn’t as bad as the internet makes it out to be”. Veritas Tactical posted in that discussion, and they make a 5” upper that I’d go with before RRA.

Veritas also makes a 4.5" 5.56 I've been looking at much too much.
I'm sure it does a hell of an "angry dragon" imitation".
But for what it is, and what would be used for, I think it has potential.

Does 5.56 even have any ballistics at 4.5"?

[OlongJohnson]

Pretty sure a PDF based on this same investigation was linked earlier:

http://www.sadefensejournal.com/wp/b...-nato-weapons/

BARREL LENGTH STUDIES IN 5.56MM NATO WEAPONS
8 February, 2012

[Norville]

Veritas also makes a 4.5" 5.56 I've been looking at much too much.
I'm sure it does a hell of an "angry dragon" imitation".
But for what it is, and what would be used for, I think it has potential.

Does 5.56 even have any ballistics at 4.5"?

Pretty sure a PDF based on this same investigation was linked earlier:

http://www.sadefensejournal.com/wp/b...-nato-weapons/

BARREL LENGTH STUDIES IN 5.56MM NATO WEAPONS
8 February, 2012

Another study here:

https://rifleshooter.com/2015/12/223...s-to-6-inches/

Interesting that neither goes below 6”. Looking at the data it appears velocity starts dropping faster under 7-8”.

Also curious is the change around 12”, noticeable in the data from the rifle shooter link and the bump in the graph. MV drops off more quickly under that, give or take.

[Rex G]

I just noticed that Primary Arms dot com has some BCM 300 BLK pistol-length complete uppers, in stock. For those with an inclination to assemble, rather than buy turn-key, i reckoned I should mention this.

For anyone not already aware, there is a Primary Arms link, in the “Support PF” orange-colored stripe, near the top of this page.

[OlongJohnson]

This is the only one in stock, or I suck at using their filters.

https://www.primaryarms.com/bravo-co...per-kmr-a8-9in

It's a KMR rail; I'd hold out for an MCMR rail. This would be the preferred version:

https://www.primaryarms.com/bravo-co...per-mcmr-8-9in

[Rex G]

Things do go out-of-stock really quickly. IIRC, before I posted that, earlier, two pistol-length, and one carbine-length, in 300 BLK, were in stock.

One can opt for automatic e-mail notification, when an item is again available. One has to jump on such notifications, right quickly.

[Duces Tecum]

Veritas also makes a 4.5" 5.56 I've been looking at much too much.
I'm sure it does a hell of an "angry dragon" imitation".
But for what it is, and what would be used for, I think it has potential.

Does 5.56 even have any ballistics at 4.5"?

Link (as posted previously) http://www.sadefensejournal.com/wp/b...-nato-weapons/, from the "Barrel Length v Velocity graph":

"The maximum velocity for the M855 projectile occurred in a 20-inch barrel. This is anticipated since the cartridge was designed specifically for this barrel length. Velocity drops rapidly as the barrel length decreases, especially below 10 inches where the velocity drops below 2,500 fps. M866 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel."

The reference to the lack of a lethal wound channel at is relevant here because the graph indicates a 4.5" barrel uncorks an M855 projectile at a velocity of less than 1,800 fps, far beneath the 2,500 fps minimum.

[wvincent]

Link (as posted previously) http://www.sadefensejournal.com/wp/b...-nato-weapons/, from the "Barrel Length v Velocity graph":

"The maximum velocity for the M855 projectile occurred in a 20-inch barrel. This is anticipated since the cartridge was designed specifically for this barrel length. Velocity drops rapidly as the barrel length decreases, especially below 10 inches where the velocity drops below 2,500 fps. M866 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel."

The reference to the lack of a lethal wound channel at is relevant here because the graph indicates a 4.5" barrel uncorks an M855 projectile at a velocity of less than 1,800 fps, far beneath the 2,500 fps minimum.

I so trying to make this work. I could avoid another caliber, I already have mags, etc.
So I'm back to 7" 300 Blackout or PCC choices.