..............For the shear joy, pain, suffering, elation, and hands on creating, I'd say the conversion of a 7.62x54R to 30 Rooski Shortski would be a soul filling experience! There are easier ways that are easier and just as satisfying.
This is a small ring Mauser I built, chambered to 7.62x39. The barrel came from GPC for $99, the stock was from Boyds for $69 and the action was one of a BUNCH of stripped recievers a friend and I bought from Century many moons ago for $4.95 each. To complete the actions we bought parts from Springfield Sporters so total action cost was $70.
For the $99 to GPC you get a magazine blocker (shaped piece of nylon) a follower (plastic) and follower spring (looked like it was stolen from a AK magazine). I chucked the plastic follower and cut down the steel one, soldering on a brass strip to bias the skinnier cartridge case to the right against the feed rail.
The nylon mag spacer would move forward under recoil so as to bind up the follower. I drilled a hole through the rear of the mag housing into the spacer block. No more problem.
I cut off the old boltknob and MiG welded on a replacement $5.95 from GPC and D&T'd for the Williams peep sight. The front sight ramp was a piece of keystock I filled to shape and serated the ramp with a thread chasing file. Then I cut a dovetail to take a Lyman #17 insert type front sight. It was soldered to the barrel.
So for what, less then $300 I made what I consider a very attractive little sporter. I must confess I was less then overjoyed with the appearance of the barrel. Both inside and out. The countour looked like it had been done by 2 different guys, both starting at either end and working toward the middle. That whoopsie had to be carefully turned smooth. Internally the bore appeared to have been reamed with a rotary file as the bore was 'naked eye' rough. The grooves though were smoothly cut rifled.
All that negative aside, the thing shoots way beyond it's initial appearance and will shoot like a house afire. The GPC barrel is available for small ring and large ring Mausers. It has a .300"x.308" bore-groove. A real neat deal is a load I stumbled across that fit's it to a T. That's 28.0grs of surplus 4895 (full caseload) and the Lee C312-165 gr cast slug. Velocity is 1950 fps and it'll eat the 10 ring out at 50 yards.
Since I doubt GPC has any of these small rings around, you could use a Turkish M38, M1903, or any of the fairly inexpensive M98 type Mausers out there and maybe offset a bit of the additional expense by utilizing the issue stock or selling off all the military hardware and just using the action.