What are the best?? I am thinking the .243 AI is probably the best from looking at different ballistics.

It very well may be, particularly from an efficiency standpoint. The 240 Weatherby is a little faster, but brass is expensive and barrel life is shorter. The 6MM-284 is a little faster yet and is capable of phenomenal long range accuracy, but has only about a 1200 round barrel life.

I personally shoot the 6MM-284 and try to avoid high volume varmint hunting pursuits. I got ten years out of my last barrel. Best long range coyote, antelope, and deer combo caliber out there, IMO.

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ive been shooting a 6mm rem now for a little over a year now using 85 grain gamekings. between targets, P-dogs and coyotes its been shot alot I would estimate 2,000 rounds over the last year. Im gonna give it a break and put it away it shoots phenominally thats probably why I shot it so much I dont want to wear it out, originally it was gonna be a pronghorn and coue's deer gun which now thats likely what I will only use it for now except maybe a yote or two a year. Im now looking at buying 243 which i will probably use the 85 grain gamekings in aswell the 243 isnt much of a loss of performance compared to the 6mm but this one will be primarily a varmint rig with better barrel life.

IMO if you want a fast 6mm where brass is relatively inexpensive and barrel life shouldnt be to bad I would AI improve the 6mm rem.

I have been considering a 6.5 X 284 Encore barrel for what I consider long range varminting(550 yards max). However the 6 X 284 sounds interesting? Tom.

I certainly concur that the 6mm/.284 is an excellent round. It will easily equal the ballistics of the .240 Weatherby Magnum, and is more accurate to boot. I can get 3350 with 100-grain bullets and 3500 from 85-grain bullets from my26" barrel in that caliber, and looky how it shoots! That's a 5-shot group, and there are others just as small.....

The 6mm/.284 sounds like a great round but it is too long. I'm looking at the Howa/Christensen Varminter, Tikka varminter, and the Winchester Coyote lite. And they don't come in that caliber and it would probably be too hard to rechamber one. So I'm thinking the .243 Win and then blow it out to the Ackley Improved. What do ya guys think??

I think what jeepkid is asking is that he wants a standard factory rifle in 243 and then have its chamber reamed to the AI version.This would be a little more economical that have a new rifle re-barreled. That would'nt be a bad idea if funds were limited.

Back to the 6mm-284, I had onebuilt 14 years ago and have had very good results with it as a varminter and a deer rifle. It shot like "a house of fire" with the now discontinued Barnes 75gr X bullet..here's it's best group. With the Nosler 95 gr Ballistic Tip it's like a death ray on deer.

I'll have to contact my gunsmith about the re-chamber. It just looks too long to fit in a regular short action. If it is possible to doa simple ream job then that would be sweet. What about the brass, I looked in Midway and they didn't have any. Would I just by the 6.5-284 brass and size it down to 6mm?? What are the smallest bullets that can be reloaded for it?

Yes it will fit into a short action as that is what I have. On regards as to if the 243 win chamber is concerned I beleive that RR has a valid point. Your smith will enlighten you on this.

You are going to have to form 6mmx284 brass. With the 6.5x284 brassbeing available now it's simply a matter of running it through a 6mmx284 FL/neck sizing die. I have always used 284 Win brass with a form die that necks it to 25 cal and then run through the 6mm sizer. Either way, it's no big deal. For sure the 6.5 brass is the way togo these days. Norma and Hornady make it.

As far as I know the 55 gr Nosler Ballistic Tip is the lightest, they are great for impressive speed but dont have the B.C. for the longer ranges.