MachIVshooter
Member
Well, I finally found my 10mm mag brass (buried in a box in the shed where it never should have been!), so I reamed the chamber deeper, loaded up a few rounds, and gave it a go. All I can say is holy fireball batman! 3 small batches, the first 180 gr. FMJ over 18.0 grs H-110. They cycled the action fine, lock on empty no problem! I did five more 180s at 19.0 grs. H110 and ten 200 gr. Hornady XTPs @ 19.0 grs. H-110. With some tweaking of the feed ramp in the extension and a little chamfering of the chamber mouth, the rounds feed from a standard 5.56 P-Mag in semi-auto. I did have to completely eliminate the bottom lug in the extension, but 10mm mag has lower bolt thrust than 5.56mm, so I don't think it'll be an issue.
So, we have determined that 10mm magnum uppers are a very feasible thing, and with the big bonus of not needing special mags like many other pistol calibers or larger bore wildcats.
I'll do a video soon, and then I need to get out with the chrony and do some load development! I've love to hit 1,800 FPS with those 200 gr. XTPs, and I would also like to swage some jackets to make and load 250 gr or heavier subsonic bullets.
The "rails" inside the P-mag are located perfectly for the ogive of 10mm bullets loaded into 10mm mag cases . 10mm case rims are only ~12% larger than 5.56, but the virtually straight case walls do cause the follower to bind with more than 15 rounds loaded, so I will have to make custom mags to have >15 round capacity.
So, we have determined that 10mm magnum uppers are a very feasible thing, and with the big bonus of not needing special mags like many other pistol calibers or larger bore wildcats.
I'll do a video soon, and then I need to get out with the chrony and do some load development! I've love to hit 1,800 FPS with those 200 gr. XTPs, and I would also like to swage some jackets to make and load 250 gr or heavier subsonic bullets.
The "rails" inside the P-mag are located perfectly for the ogive of 10mm bullets loaded into 10mm mag cases . 10mm case rims are only ~12% larger than 5.56, but the virtually straight case walls do cause the follower to bind with more than 15 rounds loaded, so I will have to make custom mags to have >15 round capacity.
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