I have a 1936 Mexican action, with a short chambered 260 Rem barrel 24" long. I already have brass, ammo, and dies in 6.5x55, but my buddy Doug already has a 6.5x284 reamer. Was really thinking about cutting the barrel to 22", would the 6.5x284 perform well? I know the 260 would be sweet, in a 22". Maybe I should go 6.5x57?

Since you plan on going to a 22" barrel and you`re set with the short chamber already cut in your barrel, I`d stay with the 260. I doubt the 6.5x284 would show any improvement over the 260 or Swede with the short barrel, and I don`t feel the 6.5x57 offers any more than the x55.

Since I have 7 6.5x55's Id say make it a 6.5x55. A 6.5x284 would be cool. 260 would be my last choice for shooting 120 gr or less.
What size bullets do you want to shoot? I like shooting 140s out of my swedes

it's a 1 in 9 twist should do o'k from 100gr to 140gr, 129's will be the normal weight.

The 6.5x55 has a more reasonable neck length than the others and generaly a deeper throat; both features allowing it to handle heavier, longer bullets more readily. The 6.5 x284 in a reasonable barrel length will reach out a little farther but erosion is a lot greater.The 6" reduction in drop at 400 yards ( 6.5x284 vs 6.5x55) would be hard for most good riflemen to take advantage of.
And the winner is the 6.5x55. roger

I would have liked the barrel to be 24 inches

My advice is to make a 6,5X55.

CHEERS
/ JOHAN

Since the barrel is already chambered for a 260R and it may require significant setback to get a 6.5-55 reamer to clean it out along with a non standard twist for the "55" it seems it's not the best choice.

If it's a true lightweight hunting rifle then having the large 6.5-284 will not matter much. There will be more blast but how much will you shoot it?

Neither the 260R nor 6.5-284 are all that popular but the 260R is more so.

Just get what you want. It seems that wildcats accumulate here and I have too many. Thus I come down on the side of whatever is the path of least resistance.

I have owned and shot all three and I like all of them. Since all of mine were Sakos with the medium length AII or L579 actions, the problem I had with the 260 and 6.5x284 was that I could not seat 140+ gr bullets out far enough because the magazine was too short - I am not familiar with the M36 action or what cartiridges it can handle.

My 6.5x55 is built on the longer AV action and therefore I can seat the longest of bullets as far out as needed. The Swede also realizes great performance increases when improved when compared to the 260. I don't have any experience with the 6.5-06(AI), but I would go that direction if I were going to build another 6.5 on a long action. However, the Swede will do anything the others will do and do it with class. FWIW, I would go with the 6.5x55 first and the 260 second. I would not go any shorter than a 22" bbl. Lou

I think we "gun-people" have a tendency to get caught up in "paper-numbers" and forget what the gun is for. I would ask you if You will try to kill bigger animals with the 6.5-284 than you would with the 6.5X55. (probably not) The 6.5X55 will often handle the 160 grain bullet better than the 6.5-284. So I guess I am saying that I'd rather have the old Swede. It lacks nothing. I don't see any real improvement in the game field with the widlcat, and many times you'll find that the feeding from the magazine is not as smooth with the widlcat.
In the real world, I think the old shell beats the new one.