I just finished fixing the problem on mine. It's a brand-new Butler Creek sporter stock that I bought on fleabay. Yesterday was its first outing.
First I removed the stock, and then loaded and dropped the mag from the bare action. No problems at all.
Then I put the mag into the correct position where it would go in were the stock installed. Sure enough, the mag hung up on the inside of the stock.
After five minutes with a Dremel sanding drum and then some 320 and 600 grit paper by hand to smooth out what the Dremel left, it works perfectly. I probably took off about 1/32 of material in total from the inside of the mag well (that's 1/64 each side).