Short version:

The grip circumference is not symmetrical on my USPC 45 from one side to the other in the area where the backstrap meets the tang area.
Why?
Is it made for Righty-Only?
Are the HK45 and HK45C symmetrical on the grip? (I am considering upgrading to a HK45C).
Can I file the left side of the grip to match the right side without weakening the frame?

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Long version:

I am considering updating my carry pistol to a 45C from a USP COMPACT 45.

In reading about the HK45 Endurance Test, and an HK45 article, both by Todd Louis Green @pisto l-Training.com, where he interviewed Larry Vickers and Ken Hackathorn about their pivotal involvement in the development of the HK45 and HK45C, Larry describes taking a file to a scrap USP frame;

LV: "We had a scrap USP45 frame cut from the trigger guard back that I took home one evening and took a file to. In the grip beavertail tang area I rounded it to show the Germans this is what we want, we want to be able to get a higher grip. And that followed through right into the HK45, HK45 Compact, and the P30 as we know them today. It retained the dimensions needed for the trigger module but rounded it dramatically to make it more tolerable."

This reminded me of something that I have noticed on my USPC 45 in that area; something odd from one side to the other.

There is what I would call a "corner" on the left side of the frame where the backstrap rolls up to the underside of the beavertail tang. It is a small radius that can somewhat uncomfortably push into the web of a Lefty shooting grip.

However, the right side of the grip where the backstrap meets the tang (the place where the web of the right shooting hand presses against) is a noticeably more rounded, larger radius, larger curve than on the left side.

🤔 Well, sum beach.

Is this unique to all the USPC's, only the USPC 45, or present on all of the USP's?

Why is this odd difference on the grip from one side to the other present? Is it simply designed and molded for a RH grip? Looking at the outside of the frame of the pistol in the grip area and inside the mag well, I really cannot see why this would be dimensionally necessary. I see no obvious reason for it.

I am nearly ambidextrous, however I write right-handed and wave the occasional "You're No. 1" sign with my RH, but being left eye dominant, my shooting grip and stance is much better Lefty, so I shoot pistol LH. I used to shoot pistol RH, crossing over to use the left eye on the sights before I switched to Lefty.

The "corner" in the backstrap pushing into the web of my left hand is slightly annoying, but not when shooting Righty, and not when gloved Lefty.

Is the grip of the HK45 and HK45C identical in curvature on EACH side of grip in this area?

Can I file this area of the USPC 45 to match the other side without weakening the frame significantly? I am sure others have noticed this irregularity.

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I searched for "USP grip tang", and didn't see anything relevant.

-Quote of Larry Vickers is from the aforementioned article by Todd Green on Pistol-Training.com
http://pistol-training.com/articles/...-larry-vickers