I have shot the 6mm Rem. for several years and found it to be very flat and potent on deer sized game with a 100 grain bullet. Why would it not also be the ideal round for the AR-15?

A rifle in your "perfect" caliber exists. ArmaLite makes the AR-10 in .243 Win.(basically the same as the 6mm Rem.)

You can also get a AR-10 and have a smith rebarrel it in 6mm Remington.

Anything compatible with a .308 bolt-face will generally work.

I think the .243, in general, is one of the most superior cartridges today.  The .243 should be a viable choice for the "next" U.S. military rifle configuration, after they take a good, long look at the .223 and see its slight disadvantage (for combat, low fragmentation range, for competition, too much wind).

But yeah, who wouldn't want a caliber that has 50% more weight than the M193 bullet, at the SAME velocity??  Sure the recoil would be a bit stiffer, but as has already been unofficially confirmed, that of the .223 AR15 is not exactly a shoulder-bruiser.  When I have some money to throw around in the next few years, I'll probably cough up the money for an AR-10 A2.

What exactly is the 6mm?  It's a very popular Highpower Match round, is it as flat/fast as the .243?  What original cartridge specification is it "derived" from, like a necked-down 7mm or something?

The 6mm was Remington's answer to the .243 Winchester. They both came out in 1955. It is a necked down .257 Roberts, which is a necked down 7mm Mauser. It has a little more capacity and a longer neck, but the ballistics are similar. The nice thing about the .243 Winchester is that it is basically a necked down .308 Winchester, so the same magazine can be used.
I also think it should be re-introduced as a military cartridge. It was first introduced by Winchester, in 1895, as the 6mm Lee Navy. The propellents available then were not well suited for small calibers and the cartridge held little interest for the sporting public. Now, it kicks ass, like a .223 with an attitude.

coyote3

5.56X45!!!




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howabout an AR10 upper in 8mm to take advantage of all the cheap ammo. i know mag caps would be low because its a rimmed cartridge. might be fun

Only problems I have with a .243 as a "battle round" are:

You have the same mag capacity as a .308 without the power of a .308.

You will go through barrels quickly.

It'd be good for armor penetration, though.

The .243/6mmRem are barrel burners. A ballistically superior round would be the 6.5-308/260Remington. If you understand Ballistic Coefficients (BC) and what they really mean, check out the BC of 6.5mm bullets compared to anything else.

David Tubb, 9 time National HiPower Champion has won with several different rounds, including .243 (essentially a 6mm/08), 7mm08, .308, and most recently 6.5/08(i.e. the .260 Rem now).  It is interesting to see the evolution that the best long range HP shooter in recent times go through in selecting his caliber of choice.  BTW, ballistically, the .260 or 6.5/08 is not much different from the (very) old Swedish 6.5x55 Mauser round, which are known to be excellent shooters.  The Swedes shoot up to moose with that (with appropriate heavy bullets) as it does have excellent BC, even better than the 7mm's.

Quoted: howabout an AR10 upper in 8mm to take advantage of all the cheap ammo. i know mag caps would be low because its a rimmed cartridge. might be fun

If you are talking about 8mm mauser then it is not a rimmed cartridge it has the same head as the 30.06 or .308. However the cartridge is too long to fit in an ar10 mag. But maybe it would fit with short light bullets. So it would still be a handloading proposition.

thanks J, never shot an 8mm so i was just taking a guess. howabout rebarreling a garand (blasphemy i know) so you can swap in the 8mm barrel, blast cheap ammo at the range then conver it back to 30-06. naturally i dont advocate this on matching# or collector rifles but it would be neat for parts bin guns and basket case re-imports