is there long term damage done by having the mag extend out of a pistol?  i have a USP45 compact and want to try the full size mags.  thanks!

Never heard of such a thing.  In fact, many manufactures cite this as a positive feature ie. being able to use larger mags for "back up"

That's a new one to me as well...

that's all i needed to hear.  your quick response let's me get 'em tomorrow.  thanks.

Quoted: is there long term damage done by having the mag extend out of a pistol?  i have a USP45 compact and want to try the full size mags.  thanks!

They don't fit , 8 is all you can get for a USPC 45 , and the 10's that were listed on a few
H&K sites have gone from Pending , to No ETA

Could there be the posibility of hurting certain parts like the ejector if you were really slamming the mag home?  Like if the bottom plate wasnt able to contact the bottom of the grip to stop it?
I dont know, just a thought.

Full size mags from a USPf will not fit your Compact.

As for stressing the mag catch, the answer is both "no" and "maybe". If you only use them at the range, or for a backup mag then no harm. If, on the other hand, you carry all the time with the extended, heavier, mag in place, there can, indeed, be stress placed on the mag catch and spring that the pistol was not designed for. I have never seen anyone do this with an H&K but I have seen guys try it with 10rd. 1911 mags and 20rd. Sig 9mm mags. IN both cases, the mag catch springs fatigued somewhat within several months, and caused some problems...especially with the 1911s...when using the larger mags. (no issues when the standard mags were used, but I am sure that would have been just a matter of time) I am pretty sure that the fact that the mags were taking a beating while being used in pistols carried in duty holsters was also an issue. Use these things for spare mags or, as done by some teams, such as the SAS, for high risk entry use, etc, but IMO they should not be carried in the gun all the time.