I like to use a case gauge to check to see if ammo is within SAAMI spec. If you don't have one, at least pull the barrel out of the gun and do a "plunk" test with the loads in your barrel. You also could do a comparison by trying the same rounds in your HK barrel.
Also, have you chronographed the loads? If the loads are weak, your new gun may be too tight and/or highly sprung at present.
I hope you get it figured out and that it all works out for you.
Last edited by Cheyenne; 11/07/20.