I have a Zeinth Z5-RS and my Griffen Armament Resistance 9 can arrived the other day.  I am using the 3 lug mount.  I only put a few rounds through it, and it's chucking the brass pretty good, maybe more than normal.  The gun is using the stock locking piece.  I tried a few 115 gr and a few 147s.  Cycled fine.

Thoughts?

Jason

I would say it depends upon what locking piece you currently have in the gun and the ammo you plan to run.

On the full size gun most folks can run the standard 100 degree locking piece on a full size MP5 suppressed using 115 to 147gr standard spec ammunition without issue.

If for some reason your gun has a 110, 115, or 120 degree locking piece currently installed that you should move to the 100 locking piece as the 110 is for the K, the 115 and 120 are for the SD.

One thing some folks confuse is thinking they need to move to an SD locking piece (115 or 120) on a standard MP5 with a suppressor.   The greater the locking piece angle the "easier" the action opens.  The SD while suppressed has a ported barrel, so the available energy to unlock the action is actually less than on a standard MP5 or even the K with its short barrel.

If you were to move up to ammo with a higher grain weight (158, etc.), +P type ammo and or the cyclic rate or recoil significantly increases, etc. you may want to consider the 80 / #28 degree locking piece to further retard the action.

That said if you plan on running a dedicated diet of suppressed 147gr and have $50 to burning a hole in your pocket it certainly wont hurt anything to buy the #28 and see how your gun runs.  You will probably just have to swap the locking piece back to run 115gr unsuppressed.

Good explanation above.

I left the 100 in and never changed it. Tried a110 but would not work well unsupressed and steel ammo

Ymmv

I have a 100º in my fullsize, can't imagine it suppressing better. Runs suppressed and unsupressed excellently, won't touch it.

But... I had a K briefly that definitely was not as good suppressed and I should have tested the locking piece options more.

I have both the 100 degree and 80 degree locking pieces that I use with my MP5K-PDW.  The 80 degree piece was an impulse buy when I was ordering a new BCG.

It my tests, it shoots suppressed FA fine with both, even with heavier rounds.

Received 17 new HK MP5 PDWs,( K model with stock), last year.  Came from factory with 100 degree locking pieces.  HK stated that the hundred is standard with that model.  After using suppressed and unsuppressed, five now have 80 degree locking pieces in them.  Depends on the gun.  The five that were changed to 80 degree locking pieces were showing a lot of wear to the buffer prior to the change and they all use the 80 degree with or without the suppressor.

100%

Have 100 wouldn’t change it. Had K, they don’t suppress as well.

My MKE K and full size function 100% in both suppressed and non-suppressed with 124, 115 and 147 graim 9mm without changing a thing.

I use the regular locking piece for suppressed/unsuppressed in the full size

I use the 80 degree unsuppressed and suppressed for the K

This but add in 158 grain as well.