I have built a 40 S&W and a 357 Sig Uzi and I saw one in 10 mm. For 40 S&W you need a 45 ACP bolt with a 9 mm extractor installed in it. It works perfectly. I tried the 41 Action Express magazines first, thinking they would be best for the fatter cartridge. The 9 mm magazine works 100 percent and surprisingly the 41 AE magazine does not. No changes to the 9 mm magazine are required. The 10 mm conversion I saw used a 9 mm full auto bolt with the bolt face opened up. I used a semi auto 45 ACP bolt and added the 9 mm extractor which made for a perfect fit on the 40 S&W rim.