6.8mmSPC special purpose cartridge

[Roger]

I just read an article in GunDigest magazine about the 6.8mmSPC ,a cartridge developed in 2003 by two special forces/marksmanship guys ,to obtain better combat effectiveness,with the military M4 carbine. They used the 1906 vintage 30 remington cartridge as the parent brass(not the 30 rem. AR). Some of you here may already know about this development, but it's all new to me.
My question is, does anyone think that this could become a wildcat round for the Rem. M-8/81 s. Obviously you would need a new chamber ,and have to sleeve down o barrel to .270". Could these old guns/barrels handle this round? Muzzle velocities are from2500 fps to over 3000 fps w/90 to 115 gr. Bullets. I don't know the working pressures yet, I haven't done any research yet,but I plan to.
I really don't know the feasibilites of this project,but I thought i'd throw it out there for discussion.I hope to generate some comments.
Thanks for your time,
Roger

[imfuncity]

Very interesting... new to me too - will be watching to see how this comes out.

[DWalt]

I did some of the very first evaluations of the 6.8mm SPC for the USAF back in the 2003-04 period, and still have a few boxes of the original lot of Remington white box developmental ammunition in my collection. I think I have posted my feelings about it here previously. It would make an excellent round for the M8/81, but it would require a complete custom barrel replacement, not a modification of an existing .25/.30/.32 barrel. I don't see anyone tooling up to do that in volume, although there might be a good gunsmith out there that might be persuaded to make up some of them for the right price. No doubt in my mind it would perform well in the M8/81 action, but it would be a little expensive to get a barrel fabricated and installed. It might also require at least a lighter buffer spring, such as used with the .25. In the extremely unlikely event that the M81 ever went back into production, I would definitely nominate the 6.8mm as a primary chambering for it.

[Roger]

Hey Dewalt,thanks for your input on this cartridge. It was all new news to me,but my youngest son, told me that it's one of the top wildcat rounds for the AR type rifles today. But it sounds like it might be too costly to convert a m-8/81 to fire this excellent round. I've got a few extra barrels and hoped it might be feasible.
Thanks for your time,
Roger

[81police]

if you go forward with the project keep us posted Roger, i'd love to hear (and see!) about it.

[imfuncity]

And if anyone gets a wild-hair (Pete you listening?) and it's not TOO costly I'd be interested in a barrel - converting one of mine.

[DWalt]

The 6.8 SPC is not a "Wildcat" and never has been, as it was a Remington development. There is a factory loading from several manufacturers, and it even has SAAMI specifications established for it. Guns factory-chambered for it abound, mainly of the AR variety, but other types too. A wildcat by definition is a non-factory round that some hobbyist has made up, usually by modifying a factory case to a different caliber and/or dimension. A few wildcats have later transitioned to become factory rounds (such as the .25-'06), but most never pick up any significant following or demand, as they don't fill any ballistic performance niche unfilled by factory loads.

One of the main attractions of the 6.8 SPC for the M8/81 is that factory ammunition, tooling, and components are readily available. A wildcat made up by necking down the .30 Rem case to .270 would be ballistically somewhat superior to the 6.8 SPC (which is shorter), but there would be no factory ammunition, reloading dies, nor chambering reamers on the market. Those would have to be custom-made.

[Roger]

Sorry,it was described as a wildcat round in the article I read. I don't care what it's called, I think it deserves some thought as a project for Rem.8/81 fans.
Roger

[Roger]

After doing some research,I would have to say that the saami working pressures for this round are somewhat higher than say,300 savage. So the safest option would be to have a new barrel/barrel extension/chamber made up.Most people agree that this round is a big improvement over.223@7.62 x39, both popular and well established calibers.True,it is being chambered now by just about every rifle Co.,but is it a feasible option for us m-8/81 owners? I feel like the gain in performance at least deserves a closer look. Are there any machinists out there who might be on board with this kind of experimental project? I know a couple guys that i might talk to, but I have no idea of what the initial cost might be.I have several shooter grade guns that might be able to be used for this purpose.FYI the bullet diameter is actually .277 same as 270 win.
Thanks for your time,
Roger

[DWalt]

Pressures don't run that much higher, at least the SAAMI chamber pressure specifications don't. SAAMI average maximum piezo chamber pressures for the 6.8 SPC and .300 Savage are 55,000 psi and 47,000 psi respectively. But with the newer SAAMI alternative 6.8 SPC chambering, which has slightly more freebore than the original design, peak pressures are reportedly somewhat less than the original SAAMI 55,000 psi peak limit to achieve identical velocities. Exactly how much the peak pressure reduction is for the new chamber, I do not know. At any rate, given the smaller base diameter of the 6.8 SPC vs. the .300 Savage, any additional peak chamber pressure of the 6.8 SPC over the .300 Savage would be of no consequence, and bolt thrust loading would be even less than from the .300 Savage due to the substantially lesser base area. From the 20" M8/81 barrel, I'd guess that 110-115 grain bullet loads could easily produce MVs in the 2700-2800 ft/sec range very safely.

I've also considered that 7.62X39mm Russian might also make a good chambering in the M8/81, but the rim diameter of the 7.62 case is a little too large for .25/.30/.32 bolt faces. It might well be possible (but not necessarily simple) to modify an existing .30 Remington chamber to accept the 7.62X39, without needing a whole new barrel. I am not sure how the bolt face recess could be altered. It might be easier to turn down the 7.62 case rim, turning it into a rebated rim case form. That sort of defeats the idea of cheap and available ammunition however. How well 7.62 rounds would work in the M8/81 magazine is also an unknown factor.

Does the world need a M8/81 in 6.8 SPC? I doubt it, but one goes into such a project for reasons other than need.