I have a Ptr91 K3P that I picked up a tax stamp for and turned into a G3k clone. I’ve been using a suppressor on it with a #17 with no problem.
It’s fun to fire it unsuppressed sometimes, but it is sluggish with its cycling. Is it safe for the gun if I use it without a suppressor? If my understanding is correct the #17 is going to keep it looked longer than a standard piece, which would explain why it’s sluggish with out the suppressor.
I put a #17 LP in my HK-91. I works great with the YHM Phantom. It does not cycle properly without the suppressor. Some have suggested that if you are going to shoot suppressed and non suppressed set up a second bolt carrier group (costs about $350 at HK parts)
Running a #17 (36 degree) unsuppressed will not damage your rifle in any way. If it cycles (some rifles might not), and you will discover that it's quite pleasant to shoot that way. The smaller angle just keeps the chamber closed for an extra couple of milliseconds which allows more propellant gas to exit the barrel before the action cycles. I grind custom locking pieces for my Cetme rifles and typically run my guns with 37 degree LPs because 37 degrees is pleasant to shoot both suppressed and unsuppressed. If I decide that I am only shooting suppressed I drop down to a 35 degree LP.