So I bought a .40 usp and .40 barrel, and ream kit to make the 10mm barrel

Bought the 18lb spring and sti mags as has been previously done (YouTube video by hotpotato)
But I don't like the idea of the slide not staying open on last round
So I swapped the .40 slide onto the .45 usp frame and it actually fit
There is a few mm's of frame extending forward. But that is not a deal breaker
It shot that way, except a few rounds nosed up over the barrel and made a 3/4 stovepipe

Do you wizards think it possible to bend the feed lips On the .45 mag to lower the angle of entry into The barrel?
The usp .45 mags are solid metal and boxed in on the rear corners
Not sure if I would need to put relief cuts to change geometry?
My crazy idea is to take the metal insert out of a usp .40 mag
And sleeve it into the .45 mag. Then use the .40 follower
It does lock the slide back with the .40 follower now while fitting it into the .45 mag.

If you want to try the feed lips adjustment You will want to get a piece of round stock set in a vice and lightly shape by tapping it to roll over the round stock as a form.

thanks
Had not even thought about that....

I saw feed lip tools at Brownells, but was moving slowly on it

I just got my ream in, so I will tackle feeding the 10mm next

update:

So, I gently bent the feed lips in a small amount to mimic the .40 lips.

I polished the feed ramp area and gave it more "free bore" not sure if that's the correct term; but the longer rounds needed a bit of room to feed reliably....

My only test was 3-4 extremely fast shots with Hornady self defense ammo (shooting at a running deer from a stand)

It cycled great.

So, at this point;
It uses stock mag, last round hold open works; loaded ammo ejects by hand cycling;
It pretty much is as good as a stock USP .45 or .40 should operate...
I will get a video up asap

Sounds good.

FYI, free bore refers to the part of the barrel between the end of the chamber and the start of the rifling.  I think you mean you chamfered the chamber opening.  This is removing any hard edge from the chamber.  However, it should be done with great care.  To much and you risk compromising head support.

Glad the gun is working well for you.

thanks for the info
It didn't sound correct when I was speed typing, but couldn't think of the correct terms...
I compared it to the USP .45 when did the work.
I did as little as possible  and bit by bit...
I need to gather up some shot brass and inspect things.....