Not totally up to speed on AR's at this point in life. Have a Bushmaster Varmint--it shoots --I clean it--shoot it some more. Thats about the extent of my involvement with AR's. Was wondering about what would be needed to convert that rifle over to a .243. NO-I do not want a 6mm or a 6.8 something. .243win is the only coversion I'm interested in, thanks
G

Can't do it. not a 223 Remington AKA 5.56mm basically to a 243 Winchester.

First is an AR15 platform round
Second is an AR10 platform round.

BTW a 6mm is a 243....

I agree! My only thought is the "commonality" of the .243, verses a 6mm. Mom and Pop in Backwoods,USA almost guarenteed not to have 6mm.
G

Not going to happen on your gun. The best thing you could hope for is a 6.5 grendal or some wildcat using a necked down 30AR case. A wildcat 243 built on the 30AR case should be pretty close to the 243 in preformance. The 243win case is nearly 2x as long as the .223/5.56NATO.

Gotcha. I too easily forget many don't reload. And then it can become an issue.

Its one of the things I look at in the general store when we fly places in AK. Whats common if I were so inclined. Unfortunately I like weird calibers but carry plenty of ammo

That must be the new math. 51mm is 2x the length of 45mm...interesting.

The magazine well on your 5.56mm AR-15 is too small to accept magazines for a .243. The ejection port on your upper is too short for .243. The bolt for a .243 is too big in diameter to fit in a 5.56mm upper and a 5.56mm bolt is too small in diameter to convert to .243. You cannot fit a .243 upper on a 5.56mm lower. You would need a complete new AR-10 style rifle.

Go 243 wssm. That will fit.

Never caught that one....

Rost ain't telling you that the .243 WCF is the 6mm Rem. He's saying that the .243 WCF is a 6mm cartridge, just like the 6mm Rem., 6mm PPC, etc. They're both 6mm (.244") in bore diameter. The 6mm Rem., which is what we're assuming you're speaking of when you say you don't want one, is a different cartridge and also won't fit in an "AR-15" platform. In fact, it's a little longer than the .243 WCF. The AR-10 platform has a longer receiver and will accept such cartridges as the .243 WCF, as was said. The 6.8 SPC is a .277 dia. cartridge, like the .270 Win. I can't think of any cartridge other than the 5.56mm/223 Rem. that would be commonly available and still chamber in the AR-15. The AR-10 will take the .308 WCF, 243, 260 Rem., 7mm-08, etc. It might chamber the 6mm Rem. too. I dunno. At least a couple of those cartridges are real common.

If you want a rifle that shoots 6 MM, do the 6x45. Converting to the 51 mm case requires a whole new rifle. kwg

so my math was wrong. I was trying to make a point about the length. Add a long 105 gr bullet to the 243 and it is quite long.