PDWs...and other small arms.

[Tony Williams]

One would think that a major challenge for pistol cartridge PDW's with diameters less than about 10 mm is getting sufficient lethality.

Is there any testing that illuminates this issue?

The gel tests I have seen show little difference between 9mm and .45 ball. Make of that what you will...

The real difference is between an FMJ ball and a well-designed hollowpoint: a good 9mm HP blasts a huge wound track compared with a .45 ball.

I agree about the 7.62x25, it would make a good PDW cartridge (although the hot SMG loadings are rather hot for a pistol - too much flash and blast). I suspect that some interesting things could be done with it given modern bullet designs, but it's been ignored for a long time.

[JASmith]

Thanks!

I wonder if it's possible to establish a minimum performance standard?

The M-1 Carbine used a pistol-class cartridge but seemed to be essentially ineffectual compared to the 30-06.

[GregP42]

Here is a gel test on the 7.62x25 vs vest over the gel block.

http://www.brassfetcher.com/index_files/Page1242.htm

[Tony Williams]

The M1 Carbine, like the 7.62x25, uses a pistol-type round-nosed FMJ bullet which tends not to yaw too well and punches a rather small wound track. There have been experiments with pointed bullets which ought to perform better (in range as well as terminal effects) but I've not seen any test results.

Even so, the M1 Carbine performed well enough for many US soldiers to prefer carrying it in WW2.

Of course, with a modern JHP loading the Carbine round is dramatically more effective, and makes an excellent home defence weapon (or so I am told!).

[JASmith]

Here is a gel test on the 7.62x25 vs vest over the gel block.

http://www.brassfetcher.com/index_files/Page1242.htm

Very good picture!

I will admit to surprise, but that wound channel looks pretty narrow -- similar to Tony's description of the M-1 Carbine ball round.

I know that the blunt shape of .38 Special wadcutters and semi-wadcutters make a difference on rabbits. I wonder if a truncated cone might still get through the vest but have more effectiveness in the gel.

Alternatively, go with a longer, pointed bullet.

[stanc]

Somebody mention my all time favorite gun?

[JASmith]

Ref #26 --

That carbine bullet seems to have tumbled!

Next question: "How much room do we have for lengthening either the 7.62X25, 7X25, or 6.5X25 to at least the same as the 110 gr M-1 Carbine FMJ bullet?"

[Tony Williams]

That carbine bullet seems to have tumbled!

Yes, but not very quickly....I think that the contrast with the JSP makes my point very well.

Next question: "How much room do we have for lengthening either the 7.62X25, 7X25, or 6.5X25 to at least the same as the 110 gr M-1 Carbine FMJ bullet?"

That means that either the overall cartridge length will increase significantly, or the bullet will extend a lot further into the case, further reducing performance.

[JASmith]

...overall cartridge length will increase significantly, or the bullet will extend a lot further into the case, further reducing performance.

The principal driver for cartridge length is to more readily back-fit into existing 9mm firearms. Remove that constraint and things change.

Could this mean we have an opportunity to do for the PDW what you're working to do with the rifle?

Base a new design on plastic cartridges to favor ease of carry but don't get too greedy with ballistic performance? This could mean a stretched version of the 6.5X25, one based on the .401 Win, the 7.62X39, or one based on the .45ACP/7.62?

A big part of the weight penalty of the .45 was that 230 grain bullet. Bottlenecking to say, 6.5, and using 50-100 grain all brass, steel&brass, etc. bullets in plastic cases could allow reasonable velocities with an interesting combination of barrier defeat and lethality while remaining compliant with the Hague/Geneva interpretations.

[Tony Williams]

The 7.62x25 is significantly longer overall than the 9x19 (unlike the 6.5x25 CBJ) so wouldn't fit into 9x19 actions anyway. I suspect that is one reason why it hasn't seen any recent development work: you need a long action to use it and a long barrel to exploit the velocity potential.

I think that the plastic-cased telescoped LSAT principle brings fewer advantages to the PDW table than it does to rifles and (especially) MGs. The reason is partly that very little PDW ammo tends to be carried or fired (and it's relatively small and light anyway - .45 excepted!), so weight is less of an issue. The other is that the LSAT rounds are fatter than equivalent conventional ones, which would make stacking lots of them in a pistol-grip magazine rather problematic. And of course, the cylindrical shape doesn't aid feeding in conventional actions.

[Variable]

Since Variable has been shooting a similar short-barrel carbine in 6.5 Grendel for some time, it would seem like a suitable option for a military PDW.

Yep, and it still is my personal PDW. I have a Colt Commando, M11, a suppressed SBR PS90, we have MP5's at work, have shot P90's, etc., etc., etc., but my 10.5" is my go to rig period. Sound pressure, and blast: You betcha. Mine keeps the can on always.

If someone redesigned the P90 envelope to incorporate the 6.5 Grendel cartridge, I'd sit up and get pretty excited about that one....

Overpenetration in a crowd? GI- use a frangible projectile. LE- use the Sierra 85gr. HP. Problem likely solved, if not use a different projectile. I wonder how well a P90 style magazine would adapt to the Grendel cartridge? A relatively compact bullpup in 6.5 Grendel with a 10.5" or so barrel, a horizontal top mounted mag, etc. would be pretty sweet. The mag (and hence the weapon would be wider), but I'd be willing to make that sacrifice! The controllability would be considerably less in auto, but with a Grendel cartridge you wouldn't need bursts. One well placed hit would be far more decisive. I have SS190 ammo (and some SS191) that is supposed to penetrate k-pots at 200 meters from the P90/PS90, but you wouldn't even need AP to do that with the Grendel cartridge. If 6.5 Grendel AP ever does become available, I bet it'll still do peachy out of a 10.5" tube at PDW distances.... I'd be glad to test that one!

What the heck happened to Colt's "SCW"? I still would like to have one of those too. I wonder how hard it'd be to Grendelize it? I just wish they'd have folded the stock to the right instead of the left if possible...

[stanc]

I wonder how well a P90 style magazine would adapt to the Grendel cartridge?

My first thought was that it probably wouldn't work. IIRC, the 5.7 FN cartridge case has no taper, making it emminently suitable for a long, straight magazine. In contrast, the 6.5 Grendel case has noticeable taper, which would seem to require a curved magazine for capacities greater than 17 rounds.

However, there was the Hill 9mm SMG, which -- decades before the P90 -- had a long, straight, top-mounted (and transparent) magazine. Since the 9x19 case has significantly more taper than 6.5 Grendel, now I'm not so sure it wouldn't work.

[LRRPF52]

I graphed out an assault rifle design following the P90 magazine orientation back in 2005, but ran into trouble with the exact problem stanc pointed out: case taper for longer cartridges. The 5.7x28 does in fact have zero case taper on the wall. The P90 uses a recoiling barrel to deal with pressure, which would not be conducive to accuracy for a modern assault rifle, so I looked into a rotary locking system in a larger bullpup profile with a longitudinal top-fed magazine, with bottom eject.

Another big constraint with that concept is the magazine width, as mentioned already. It would make a pretty bulky gun, especially if the COAL was increased to escape the limitations of the AR15 magwell. It is an interesting idea though. I toyed with several designs based off that system to include PDW's, DMR's, and grenade-launcher combos that pack a lot of firepower into a very small profile. One of the things I addressed was firing hand functioning of common controls: selector manipulation, bolt catch, mag release, and others I won't mention. The P90 requires two hands to operate when changing mags if you keep your firing hand on the grip.

If any of you have felt the FN2000, it is horribly bulky...to the point where you can't even get a good sight picture without canting the gun with iron sights. It also has no bolt hold-open device, and sucky mag change characteristics. There is another way of dealing with bullpups that has not been explored yet.

LRRPF52

[Tony Williams]

There is another way of dealing with bullpups that has not been explored yet.

I explored a few alternatives here: http://www.quarry.nildram.co.uk/bullpups.htm

[warped]

Hey why not borrow an idea and size up many of the aspects of the FN P90 if we want the mag to not be a problem and the shells ejected below?

Of course we could probably only get 30 rounds in an enlarged mag but the rifle would need top be wider anyways due to the bolt and bbl size.

[LRRPF52]

Tony,

You touched on one of the avenues I've been looking at in your discussion, but it still needs to be thoroughly-tested before it can be deemed viable. It's the most practical one, and several designs in buttstock/cheek geometry currently would support it. One of the challenges with the top-mount magazine design I ran into is magazine capacity for assault rifle cartridges, which the 5.7 easily overcomes being so small. It's very difficult to get a 30rd magazine into that P90 style configuration when dealing with a .444" cartridge base.

LRRPF52

[stanc]

Despite the objections to an SBR -- and an M16 SBR, in particular -- raised earlier in this thread, note that Israeli AFV crews are actually using such a weapon as a PDW:

https://www.flickr.com/photos/shimshon/1...otostream/

[Trooper]

Despite the objections to an SBR -- and an M16 SBR, in particular -- raised earlier in this thread, note that Israeli AFV crews are actually using such a weapon as a PDW:

https://www.flickr.com/photos/shimshon/1...otostream/

We had a number of Human Intel teams using 11.5 M4s. Same with Psy Ops and CA.

[stanc]

15 years ago ARMOR Magazine published my idea for a "true" PDW:
http://ciar.org/ttk/mbt/armor/armor-maga...6pdw01.pdf

Now, B&T is marketing a PDW that is virtually identical in concept:

[video=youtube;26fIRAAtaPE]https://www.youtube.com/watch?v=26fIRAAtaPE[/video]
https://www.youtube.com/watch?v=26fIRAAtaPE

[video=youtube;yw58PTbkjoo&t=68s]https://www.youtube.com/watch?v=yw58PTbkjoo&t=68s[/video]
https://www.youtube.com/watch?v=yw58PTbkjoo&t=68s

[BjornF16]

Nice article...well done! IMO, long overdue in coming to market