Back in '86 I built a custom mauser single shot. I used a '98 action and a sheilen #8 barrel that was made to finish at 28". I used a single shot follower that I tack welded in place. I then fully glass bedded the action. The gun is a 25-06 short throated for a 85 grain sierra bullet. It has no saftey and a 4oz trigger. Needless to say, the gun is never loaded until I'm ready to fire ( when its bagged in for woodchucks I leave the bolt handle up). That gun is screaming death on chucks. I did all the work myself at a sheet metal shop I used to work in, we had a machining center. I found that the mahining was simple and that the real key to doing a good job is in meticulous set up.  
    Now I got the bug to do it again. A gunsmith I know has a 6.5 stainless barrel that he says was made by pac-nor.  I just happen to have a mauser '98 that shoots shotgun patterns. I was thinking 6.5-06 or 6.5x284. I want to use sierra 107gr match bullets. Can anyone tell me which of the cartrages tend to be more accurate? Suggestions on other cartrages would be welcome.

Dear Armedfree...I'll pick up on this one. Although there is a trend today for short fat cartridges, in the long run I think the 6.5mm-06 is a better choice. Cases can be made using 270 Win brass with one pass and in most cases will not need to be neck reamed. The case is "supposed" to be 2.540", it's best to trim to 2.530" to squared up shoulders. We have found Winchester brass to hold 62.1 grs of water vs R-P's 61.5 grs. Technically, if you have your reamer cut to have an case length of 2.540", it's a 6.5mm-270. Some of the older versions had a case length of 2.494"( 30-06 length).
We have worked most with 100 gr Nosler Ballistictip and Sierra Spitzer, plus the 140 gr Sierra Spitzer Boat-tail.
Our best loads:
120 gr - 55 grs IMR 4530 - mag primer-@3225 fps/ 24" barrel
140 gr - 54 grs IMR 4831 - mag primer-@2920 fps/ 24" barrel
We have one load given by another 6.5mm-06 shooter for 100 gr bullets: 62 grs H-4831 @ 3450fps, but I don't think you can get that much H-4831 in the case? A more resonable load would be 56 grs of IMR 4350. All rifles, etc are different and these loads should be dropped 10 and worked up to.
The overall lengths work in our Mausers, but check you mag box to be sure. No work at all needs to be done to the feed rails or bolt face. As you know, polishing the feed ramp helps. Hope this helps!
Best Regards from The Hammock....James

Thanks JG. I'm probably going to go with the regular 6.5-6 for the reason that I can get a reamer eaisily. The throat will be ground off. Magazine length doesn't matter because it will be a single shot with a 4-6oz trigger. Thanks again