This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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The 6x35 would definitely utilize its propellant load more effectively than the 5.56x45 in a very short barrel with its combination of higher swept volume and lower propellant volume. Of course, a sabotted round with a straight-walled case would maximize the swept-volume, with the added complexity of dealing with the sabot, its mass, accuracy issues, etc. Has anyone seen a formal analysis of the current state-of-the-art sabot round that does a decent job of quantifying the tradeoffs between it and a bottlenecked cartridge?
Theres the 223 timbs... a tokarev firing .224 bullets.
The 300blackout CBJ would be good for this gun but i doubt sabots have good accuracy in 6 inch barrels.
The .221 fireball is my first choice. No muzzle flash in short barrels and roughly 650 ft lbs from 6 inchers....thats better than 5.7x28
My ultimate fantasy GPC has always been a .224 valkyrie shooting 40grain FABRLs.
At high energies i wonder if they would stabilise well....the FABRL document mentions a twist rate of 1-in-5
6x35 is an equally valid answer, especially with a good projectile behind it.
However my preference is for something with a generously sub 1.0 FF and the .89 of FABRL sounds really nice.
IDEALLY you wrap that .89 ff bullet in a sabot similar but not identical to the cbj to push as much velocity as possible.
My reason for that preference is pretty simple, it'll give said projectile serious legs simply by it shedding velocity slower.
But yeah, I'd be down with 6x35
I have a friend whose messed around with a pdw cartridge based on a slightly altered fireball case, and that can very much get you to a "pocket carbine" performance level.
I wish cbj would just upsize their original sabots so we could throw a really nice existing 5.56 projectile on the lighter side out of it. Something like I can't remember the company's name but they do a 50 grain projectile that's already very well known for good performance.
Personally I've got a couple projects I'm finishing up and then I'm going to start gathering parts to build myself a "cheek pistol" either loosely based off the old Argentine "almara MPA" concept OR an americanski diy pp-2000 inspired... "Thing" that takes some cues from the existing fgc9 build (which is shockingly similar in the bolt and carrier area to pp2000)
Whichever one I decide to do first I'll be doing it based around printable 9x19 Glock magazines initially running single feed to get the concepts functional.
Once I get them functional, the plan is to slowly work alterations to get it to function in double stack double feed.
After I get that working, I'll be transitioning the caliber to .22 tcm, which is a much more fun and appropos caliber for something like a "cheek pistol"/pdw.
In either concept's case I'll be going with a non reciprocating charging setup.
Personally, I think that the "pp2000ski" will work best since the grip to muzzle alignment actually has a slight reverse cant to it. The issue with it though is going to be getting the fucker to feed reliably at all even in 9 single feed, getting it to double stack double feed... Well let's just say that if anyone can get me a gsh 18 magazine (or just the body and follower) that'd be very helpful LOL.
Getting one or both to running double stack double feed is the first step towards exploring more interesting pdw concepts though, so I figured I'd talk a little about it here.
Here's the pictures of the conceptual basis of version A and B.
My buddy who has worked through more bullet designs than anyone else I've ever met has illustrated before the danger of going that route.
If your projectile doesn't have enough mass to integrate both a sufficiently large penetrator AND enough fragmentation mass to reasonably assure fatal wounds in a human it winds up either Being a glass hammer that will zip straight through things and people leaving minimal damage. Or, it will fragment messily and be utterly turned by even light intermediate barriers. In many cases it will be the worst of both of these.
Near as he and others can tell, 37 grains is just too small. In 5.56 projectiles the optimum seems to be between 50 and 65 grains.
I was thinking a 43grainer with a 30mm long 'rod' running all the way through
Surely a sabot wouldnt work with fabrl bullets because the bearing surface is too short
Could a fabrl bullet work in a CT case if the long bullet was seated right to the bottom...i cant see how it would stay concentric as it rises up through the case.
6.8 is easier because the bearing surface is much higher up
On the sabot situation, short bearing surfaces may preclude some kinds of sabots but the original 6.5x25 cbj sabot design could match well with something like that.
When it comes to CT and very high L:D bullets I'm not really sure how it would work but I think if you poured enough money in it you could make it work. The question is, would it be worth it.
I also have no idea what you're talking about in reference to 6.8 because that's just a bullet diameter and could refer to any one of a hundred projectiles a good 5 or six chamberings.
I'm definitely not necessarily against using a 6.8 spc case as a starting point though. It's a tad girthy but who knows man?
Maybe you could make it work?
I'm basing all my comments and commentary in this particular thread on the purpose we're going for being let's make something like an mp7 except it doesn't suck.
To me that means what we're going for here is a small machine pistol with an optic and possibly a can that a trained user can use to dominate the 0-150 meters range bracket with. Bonus points if it's dangerous enough to poke 3a at 200 meters with a lethal behind armor wound and dangerous enough to generate reliable potentially lethal wounds on unarmored AK wielding adversaries at the full "AK 300 meters"
Bonus points if there's also a subsonic loading you can run with a can for specialist use.
If you just want to be pretty dominant in the 0-150 block, we already know that you can do that with essentially a Colt SCAMP 2.0 with a red dot or prism sight on top, modern projectile design and construction, and lightweight high pressure cases.
The whole thing that makes the Caleb Crye patent interesting is the potential for what's essentially a true pocket assault rifle.
That's the part that interests me and makes this something that really gets my gears turning.
Frankly the 300blk would have only average penetration at 150m...not even remotely close to something like 6.5cbj
If the goal is a improved MP7, i was thinking a variation on 4.6x30 which doesnt suck.
In other words use reverse feeding to cram in a 10 inch barrel and send a 5mm bullet with 850ft lbs.
My concern with a FABRL in CT was that if its a 32mm bullet the bearing surface will literally be at the bottom of the case.
Normal CT has little walls which hold the bearing surface but you cant do that here. I noticed that lockless are also CT and they have a different style of walls....look at the cutaway pics.
EDIT: i just noticed that the original P90 ammo (ss90) used a fabrl bullet.
It was 2.7mm longer than current P90 ammo