Magpul ten round mag modified to hold five???

[jurassic]

Has anyone successfully modified a ten round P-mag to accept five rounds and function properly? I was playing around with a twenty round mag and loaded six or seven Grendel rounds in it before any noticeable binding occurred.
I really want a four or five round (shorty) P-Mag to use for hunting, I like them much better for the lack of noise and they don't seem to get near as cold when temps drop.

Thanks.

I can get 3 in a 10 round Pmag before it swells, but its not ideal. I would get some metal mags and forget about plastic for the Grendel.