When Jim Carmichael designed the 6.5mm cartridge which Remington adopted as the .260 Rem he based it on three conceptual premises. To load it differently than that certainly is possible within SAAMI specs but violates the targeted levels of velocity/ recoil, and his other two bases (it's been waaay too long since reading the article in Outdoor Life).
The 6.5 CM was designed for accuracy at a much higher CUP spec than the .260. To say that they are (external) ballistic twins may be close to correct. Their internal ballistics are quite not the same. Too, the chamber specifications, particularly in the throat, speak volumes as to the intended bullet weights the CM will handle in contrast to the Remington round.
Now, the point that absolutely tips the scale to the middle in favor of them both!! A man told me almost 20 years ago, regarding my two 6.5 Swedes, that relaoding the 120 pill was neither fish nor fowl in terms of a varmint or a game weight. For weeks I wrestled with that comment until it dawned on me he meant that bullet is a 'do it all' weight.
So, if you can get good accuracy from the CM chamber with fly-weights despite its longer throat, well, bully for you! Just don't expect it. The .260 may be better suited to the lighter bullets depending on how the mfr cut the chamber. And both casings have what it takes to drive 140s clean through big, tough animals.
The scales of ballistic justice will usually tip toward the middle since every single cartridge has more good than another cartridge but also carries into the comparison equally bad characteristics, be that recoil, price per box, availability in your area, harshness on barrel life, lack of punch down range, etc. (ie: a .300 magnum is better than a .243, or vice versa, the .243 is better than the .300)
So there you have it, tongue planted firmly in cheek, the definitive comment on why to avoid a difficult choice and just buy one of each!!
I have the lrp, I get 2880 with 43 gr. Of h4350 behind a 140 amax, Fed match primers and fully preped lapua brass.
I shoot both 260 Rem and two 6.5x47's and I have no idea what "lrp" is?
Depending on the powder and bullet, I get up to 2950 with 140 VLD's with 24.5" of Broughton barrel, in 6.5x47.
The 6.5CM was built to run higher pressure than the 260 Rem. I agree with that statement. Well, the 6.5x47 was built to run higher pressures than either. With a good chamber, minimal brass sizing, the brass, with it's small rifle primer pocket, the -47 will handle stuff in the 70k psi range and laugh at it.
Now, if Lapua ever decides to make 6.5CM brass, oooooohh. Watch out!
Love the fact that Lapua is making 260 brass. It's just that that dang shoulder likes to grow necks and I HATE trimming necks. After 10 or so firings in one rifle and 14 in the other, I've got a few pieces of brass that are "finally" within .001" of my max trim length.
Last edited by Alan Griffith; 05-13-2012 at 03:57 PM.
An article in American Rifleman stated the CM round has a SAAMI max of 62,000 psi. Elsewhere, I've read that the -47 is spec'ed at 63,000 max psi. That is so close as to not even enter my radar screen for performance considerations. As it is fact, 63k is more than 62k, I submit to the argument of a potential performance difference. Realistically, since higher pressure = higher velocity, if someone is looking for 1.6% more speed then I would suggest adding 1" barrel length as an alternative on the premise that each inch adds about 35fps; +35fps/2900 = 1.2%. Ahh, there we have it!! A profound argument as to whether +/- 4-10ths of a percent merits high blood pressure and fist fights in defense of one cartridge over another.
Hey folks, laugh at ourselves, you have to. At the other end of the trajectory the paper target or game will have a hole in it and bullet placement will decide winners, losers and suffering cripples.
Shoot straight, shoot strong, dine well at the end of the day with the satisfaction of a good shoot!!