Could you call a .257 Roberts a 6.35mm X 57mm Mauser? Might make a better compairison to the 6.5mm X 55mm Swede.
Roger that.
Thanks to everyone for the suggestions so far. Here's where I'm coming from, in case it helps.
The 7x57, even when downloaded with 120gr bullets stepping out at 2700fps, seems to be a bit much for the smaller deer (fallow/sika does). Most deer that I shoot at are within 150 yards of me, and truth be told most of 'em are less than 100 yards away. (I'm not a great shot off-hand or kneeling, and I hunt around this limitation as best I can.) I'm happy with the range-n-trajectory *on paper* that I get with my Barnes 120gr and 140gr .284 handloads in the 7x57. I don't feel the need for longer-range punch than the 7x57 as much I'd like to have something a little less, well, destructive. That's the background.
Now the fun part. I can get a butchered (drilled/tapped, no stock, mismatched numbers, but otherwise sound) small-ring Mauser action in 7x57 for $100 and rebarrel it to 257 Roberts. That was my intended approach to all of this - until this past weekend. This weekend, I was offered the purchase of a 6.5x55 Swede action. The receiver on it has been D&T but it, too, is in good shape and has a great bore on the barrel. I can get into it for $200.
And therein lies the dilemma. The 257 Roberts *appears* to have better support for the 80gr - 100gr medium-game bullets that would nicely complement my 120gr 7x57 loads (both hot and mild). These 257cal bullets will have a slight loss in BC and SD when compared to the 6.5x55 (.264) stuff, but for my purposes that appears largely irrelevant. On the other hand, the .264 caliber doesn't SEEM to have the same support in the lighter hunting ranges (80gr-90gr) as does the .257. So you're thinking - he's talked himself right into the 257 Roberts, right? Well, no. After all, the 6.5x55 I'm looking at is already barreled and headspaced, so it's certainly the path of least resistance. Having to just reblue and restock the rifle is a lot more appealing to me than rebarreling it, too. Hey - I'm lazy.
So - do I get the 7x57 and rebarrel it (mo' money, but maybe a little mo' appropriate for the game) or do I get lazy and run the 6.5x55 and hope that I can find some decent 90gr offerings? Am I correct in reading the bullet ranges and such for each of these calibers, or have I overlooked some killer options?