Just purchased a used Remington 40X in 243 And am thinking of a rechamber to either 6-284, 0r the 243AI.I have had experiences with other AI 22-250 and 250 Savage and love both of them. Will the 6-284 give me that much more Velocity using the 55-85 grain bullets.?? The barrel is 27".
Thanx,

As luck would have it I have a Cooper 243 AI and a Hart Barreled 6/284 on a Sako action. Also a 6 Rem 40X 28" 1 in 8 twist Hart, added into the mix. Yes, the 6/284 is faster,BUT, is it worth the work... NO. The 243 AI is nice but not enough faster to warrant the fireforming and barrel wear that brings. I'll love the 6 Rem forever because it does it all the first time. Enjoy which ever spins your crank!

What's the twist of that barrel? In general overbore cartridges don't add much velocity to the lighter bullets.



I think the 6mm Rem Improved would clean up that chamber as well.



The Sierra #5 has loads for some of these wild ones.

Don't know what you are looking for in velocity, but using lighter bullets, I worked up a load with a 60 grain Sierra in a 243 with 50 grains of H380.

Velocity was over 4,000 fps, and in this particular Remington, was a one hole shooter. Everything else was a group of 3 to 4 inches at 100 yds. I was about ready to ditch the rifle, until I got this load.

Some people I know tried with a 6mm/06 and a 6/284 and they got no higher velocity than I did.

Everyone was telling me I was going to blow up the gun and myself with this load until Noslers last manual came out and they recommended 53 grains with their 55 grain bullet.

I personally think the max efficient cartridge in 6mm is the 6mm Rem. After that, the increase is minimal, for a dramatic increase in powder consumption, that will just lead to rapid throat erosion.

If you can get pass trying to impress a few unknowing guys, just stick with the smaller 6mm cases and good shooting.
Cheers,
Seafire

I have both a .243 and a 6mm/.284. I believe the difference is worth the trouble! But I agree that if you had a 6mm Rewm., it would not need improvement!!

I would go with the 6mm Rem, but it won't clean the chamber up unless you set the barrel back. Personally, I would go with a 6mm AI, as it will give you nearly 6-284 numbers but with fewer worries about feeding. That 27 barrel will do a good job ringing all the velocity out of it.

Good luck.

9.3