Any Cool 7mm Rounds I should Know About?

[barnbwt]

I'm considering diving into an barf AK build, though I hate the thought of it (just can't stand the guns, if you can't tell). There's a twist which would make it more appealing to me, though; it will be built upside down and dressed up to look like a ZB30-series LMG --only little, maybe

Details of the build concept so far:

For those who don't know, the ZB30 is the direct progenitor of the BREN LMG used by the Tommies during WWII, designed by Czech weapons genius. It locked with a tilting bolt rather than a rotating one, but was operated by a long piston fixed into massive bolt carrier that rode on rails; just like the AK

I sourced a 7mm barrel that will work (an old Madsen LMG barrel with the chamber cut off, and cooling rings down its length), but obviously that bore diameter isn't something normally associated with an AK. So I'm wondering if there are any good 7mm wildcats I should check out.

The ZB30 shot 8mm Mauser originally, and had straight 20rnd magazines unlike the BREN's ginormous swoopy ones. So any straight mag would work here; FAL/M1A for 308-sized rounds, or even 20rnd AR15 mags for smaller ones. I suppose AK mags could be used, but I think a long, curved mag wouldn't look right (maybe for a Madsen or BREN MK II lookalike)

The dial sight knob on the left side will be the safety, since that's where it will be when flipped (this is a lookalike, not a copy/clone). Sights would probably be fixed or even adjusted with a drum on the same axle as the safety (that'd be slicker)

Gas tube would be stretched, as would the piston by necessity. The barrel is like 20" long IIRC, so probably 6 or so inches further out would get the look right. With an aluminum piston keeping the weight down, it seems like it should be doable (though it might not be as overgassed as a stock AK)

Trigger group might be relocated, but it might be just as easy to trim off the trigger spur and use an internal linkage

Tapered dust cover (now on the bottom) will be made into a box, and will have the grip/trigger attached to it

Carve up a stock, grip, and carry handle from some walnut and steel laying around, slap on an RPK bipod, and Bob's your uncle!

Back to the subject of the thread:

-I presume 7mm Mauser would work for a more 'full size' build, provided I find a PSL/M76/SVD kit that doesn't break the bank (seems like a poor proposition, though). Suitable magazines might be tough to locate, though (might BAR's be close enough?)
-7mm-06 would work for sure with BAR mags (does it use Mauser bullet diameter?) but might have issues with the action, being so long
-7mm-08 would keep the power up there with the real-deal, while keeping a slightly smaller magazine profile that would fit nicer with the scaled-down proportions of the receiver. As before, this requires a PSL-size kit (or does it?) which may limit my options
-7TCU (223-blown out to 7mm) is comparable to Blackout, so should be closer to a match for typical AKM parts (or 74 parts, rather). AR15 20rounders would match the actual ZB30 capacity and look.

I don't expect this to be my go-to gun, but a pure range toy, so ammo obscurity doesn't bother me hugely. The main thing is bullet diameters that match the 7mm Mauser bore, and the ability to fit into available magazines (the mag-catch might be modifiable, but the body is the part I can't make myself too easily). I'm mostly torn between 7-08 and 7TCU, but am open to others in the 308/223 size ranges if there are any good ones I've missed (I don't know much about 7mm caliber offerings, if you can't tell )

TCB

 

[barnbwt]

Bump because; really, no opinions on a cartridge selection?

TCB

 

[Jim Watson]

The problem I see is that there is no cheap 7mm ammo,
If you don't mind handloading for an automatic rifle wannabe, then you should be guided by what will run through your choice of magazine and action length.

If you want to get into custom dies and case forming, a British design, the .280/30 is a 7x43 and would fit a shorter magazine than a 7mm 08.
http://www.quarry.nildram.co.uk/Assault.htm

There are others there. The Germans worked with a 7x39 before staying with their standard 8mm barrels and the 7.9x33.

 

[barnbwt]

280 Brit would be cool; the round NATO should have shoved down our throats post WWII . Also the whole British/BREN connection. Sadly, it's like 1/4" or so longer than 223, so I doubt there's a mag out particularly suited for it (could always use a 308-length mag, though). I'll have do some more digging to see if there's a case head it could be based upon (ooh, it apparently shares one with 308 Win! )


Who knows, with a lighter and more sane bullet ogive, I could see it fitting in an AR mag (a bit lower capacity, of course). Funny, it's basically a 7-08 but fun-sized, and I assume it would be very close in performance to 6.8SPC. Interesting. I actually like that much more than 7TCU, which is practically a straight-wall case (i.e. pretty inefficient for a rifle cartridge). Bonus benefit of being able to use cheaper AKM-pattern action parts, probably.

So, 308 brass cut back & necked down to a 7mm-ish projectile (I gather there's a zillion bullet diameters right around here for some reason, all within a thousandth of two of eachother ). Probably use the neck and shoulder dimensions of 7-08, but with 308's taper, and set the case length to match the cannelure of whatever bullet I choose to go with. For a wildcat/custom cartridge, that actually doesn't sound totally unfeasible.

Thanks for the tip, I'll cogitate on this some more...

TCB

 

[Jim Watson]

Now I think of it, check out the 7mm Remington Benchrest.
It is a 39mm case with dies and data already available.
I hate wildcats or obsolescent rounds requiring as much trouble.

A zillion diameters?
Not really.
US and Euro standard 7mm is .284".
The British have done some funny things in the vicinity, I think .280 Ross is .289", but no need to get caught up in that.

 

[barnbwt]

7mm BR on the right


According to Wikipedia, it's a necked up 6mm BR, which in turn is a chopped and necked-down 308. Looks like a progenitor of the short magnum concept, almost. I really don't like that sharp shoulder angle; looks annoying/hard to feed, but it's probably just me being used to a 308-type taper. Apparently all these 308 wildcats were spawned from the Barnes 308x1.5" (just a shortened 308), but the Barnes ones tended to keep the 308 neck taper. So I guess the round I'd be looking at would be more like a 7mmx1.5" units-conversion abomination. The 1.5" case length would give me a full 3/4" for bullet ogive, too.

I need to chop down some 308 brass and see if it can stack in an AR magazine. AKs are great and all, but I think I'd rather avoid its curved mags at this point, which pushes me more toward 308/223 cases.

I agree that wildcats are annoying, but if I make up 100 cases, and only load them to 40,000psi or so, they should last forever, and be no harder to load than anything else out there, and should be plenty for any given range trip. And most importantly, brass will be available for forming until the end, if need be.

TCB

 

[jakk280rem]

How about the wssm case for a wildcat.

 

[barnbwt]

I found one of those at the range, once (243WSSM) and there's no way you'd get those things to feed reliably in an autoloader.* There's just too much bullet, and too fat a base. The things are over .5" across at the bottom! And that's not even getting into the bolt thrust issues inherent in such a fat case head. Soul brother too boucoup. That, and the brass is always expensive, and I doubt it will be made much longer (I don't normally preach on the death of cartridges, but WSSM seems to have been a flop of rather epic proportions).

Like I said, if it must be a wildcat, I'd rather base it on something incredibly common and/or invaluable to the shooting sports.

Just look at the size of that crazy thing next to a 7.5 Swiss GP11 case, which is about the same at the rim as 7mm Mauser!

*I have seen a 50cal wildcat of WSM/WSSM cut back to fit an AR15 magwell --the 510 Reedwhacker-- that puts low-end 50 Alaskan payloads into a AR15 platform. An AK version was done as well, so it's bolt/trunny can handle the girth --but it's a nonsensical route unless you are rolling with a large bore bullet, which I am not

TCB

 

[WestKentucky]

7mm bore kinda kills the fun for me. As others said there's no cheap surplus ammo so all you would be doing is either reloading an odd chambering for grits and shins or paying a colossal amount for ammo. If it were a 30 cal or 22 cal or even 5.45mm you could run it pretty Inexpensively with surplus rounds or even reloading from pull-down stocks. The weapon design makes it very hard to see aiming precisely at anything so your left having fun with the build itself and rapid fire point-shoot strings. Seems a great way to spend a lot of money quickly without much to show for it. If you enjoy the build and can afford to feed the beast in rapid fire then have fun and post pics. If not I would start by sourcing another barrel where I could use surplus supplies.

 

[barnbwt]

The weapon design makes it very hard to see aiming precisely at anything

Uh, what? The BRENs were as accurate as any other LMG made as well. The sights were just set off the side, but parallel to the bore.

I do see the point about barrels, which is why I am simultaneously looking for other offerings (for example, there's a rusty Thompson barrel in 7.62x25 out there, as well as GM's ringed AR15 barrels, which may or may not be a good fit). Actually making a ringed barrel is fairly tedious and risky on a manual machine (risk of screw-up, not injury), so I'd like to avoid that if at all possible, but that would be the fall-back fall-back.

It is kind of funny that, despite the numerous famous/effective cartridges in 7mm, and despite the comical diversity of chamberings offered nowadays, that the bore size remains so unloved. Just too close to 7.62mm, I suppose

TCB

 

[jmorris]

From my first box to this day, I have always loved the 7mm BR. Not a real popular round though. They had completely stopped making brass for a while.

 

[CB900F]

Barnbwt;

There's a cool 7mm round you should know about, but it's not gonna be any help for your project. It's the 7mm Practical, and is nothing more than the .300 Winchester magnum necked down to 7mm. Basically it gives the performance of either the 7mm Shooting Times Westerner or the 7mm RUM without the immense powder charges and barrel throat erosion. Can be accurate as all get out too. I've personally seen a 2 liter pop bottle really get popped at 1240 yards.

900F

 

[oneounceload]

As mentioned above, the 7mmBR would be cool. I had an XP-100 in that and it was a tack driver out of the 15" barrel