Hey red, how do those new mags work?
Well you see, basically there's this thing called a ‘follower,’ and there's a spring which pushes on it, feeding the cartridges into the breech.
Ha, ha. They work very well for me, it was just the initial fitting that was a problem. They arrived far too tight for my rifles; matter of fact, when I tried to stick a magazine in to check the fit, it got stuck and required a bit of bracing and yanking to remove. You will need to grind or file some surfaces before they'll even lock in the well. The main thing is the pair of small square lugs on the back which engage in the mag. release: you might have to grind them down a bit, or remove some material off the bottom. Next is a bit of shaping of the beak on the front end. You may feel you need to grind down the sides because it's so tight, but probably not.
Grab your SVT and wiggle the mag.; you'll probably find it's a bit of a loose fit. I haven't adjusted the new ones to be so wiggly, I just remember to mount them with a firm smack. Just when you think you've got it, don't be surprised when you take it to the range if the mag. drops out on the first shot from the recoil. Test and adjust as necessary.
Haven't had issues with feeding (any more than the 1 out of 50 I get with the originals), but if you do, bending or filing the lips a touch should get it working.
Once you're done, a spray can of satin black paint and a few light coats will cover up the ugly evidence of your manipulations.