Jello:
From and earlier post some time back on the subject. Can't speak to the extractor fit issues on clone guns. Check with Adam or the gun maker on what hey used/recommended.
G3Kurz
A buffer in any 10mm Auto MP5-style weapon would certainly help REDUCE damage to the stock and/or receiver it will not prevent it depending on the ammo used. 5.56mm HK roller-locked rifles like the HK33 and 53 have spring piston buffers and still we have seen torn butt stock locking pin holes due to "overfunction" with certain ammo types not matched to the appropriate locking piece and why HK’s last 5.56mm roller-locked rifle (G41) had dual locking pins. That is also the case with 10mm Auto and to a lesser degree .40 S&W caliber MP5's and clones.
As we learned during the development of the MP5/10 for the FBI, the functional range in 10mm Auto ammunition is very wide ranging. There were/are loads with 135 to 220 grain projectiles and MV ranging from >900 to over 1500 fps from the smg-length barrel (the original 170 grain Norma JHP)! Contrary to popular belief even roller-locked HK's can't "run" on each and every type of ammo without "help". That is why there were/are over 80 different locking pieces for the venerable G3 series.
We tested and classified the available 10mm Auto ammo as "HI Impulse" and “LO Impulse" based on the degree of recoil energy imparted to the bolt and thus the velocity the bolt is driven to the rear which also determines the amount of rearward travel and ultimately how hard it bottoms out on the stock backplate and receiver. In best case operation the bolt carrier should not touch the buffer or only slightly “kiss” it. We learned that one locking piece could not cover the entire range of 10mm Auto ammo function and thus two were offered in the MP5/10 and then a third “MID Impulse” variant for the MP5/40.
The initial FBI 10mm Auto load fired a 180 grain JHP @ 940 fps as I recall. That but it in the upper ranges of the LO impulse category and LO impulse locking pieces were installed at delivery. Life was good. However the FBI later increased the MV of the round by @ just 30 FPS which pushed the weapon into the HI impulse range, especially after extended used when the weapon was well broken in. A later change to a bonded 190 grain JHP bullet sealed its fate as HI impulse and we sold LOTS of HI impulse locking pieces to the FBI for retrofit.
So what does this all mean in response to your question? Yes. Have the buffer installed. It will be a good indicator if you have the correct locking piece installed for the ammo you are shooting with the weapon condition (break-in) and/or if you are shooting it suppressed which also adds to bolt velocity. If you witness impact marks on the buffer you MAY be operating in the HI impulse range and should change out your locking piece with a piece marked "HI". That will reduce the bolt velocities somewhat and thus the potential for damage to the system. Roller bulges will appear if you operate in the HI range with a LO impulse locking piece for as few at 5-10 rounds. After roller bulges come torn locking pin holes and a trip to the welding and refinishing shop.
So G3, can't you just tell us which ammo types are HI and LO impulse? I once had a list and could but it is not 100% as changes are made in ammo loads and each weapon can be different, especially in clones with their many variables such as barrel length and break-in. The solution is to test the ammo you want to use for bolt impact by looking at the buffer or metal backplate for indents of the bolt carrier, or in lieu of a retractable stock buffer some modeling clay (1/4”) spread into the back plate. Fire 1 round semi and check for indent. Do that 3-5 times. No impact you’re good to go.
In addition I would own and keep the alternate locking piece stored in the cavity of the trigger group for use on the range when you need it. If you are running LO impulse ammo and locking piece have the HI impulse piece stored in the PG. If you EVER shoot suppressed, use the HI impulse piece.
Remember that as your 10mm wears it may need the HI impulse piece. If your gun is running in the LO impulse range and you have the HI piece installed you will see a weak ejection pattern and maybe an occasional failure to eject.
While this may sound like a pain in the butt plate, it is necessary to prevent permanent damage and provide proper function. But it also allows you to fire 175 grain Winchester Silvertip ammo that leaves a sub gun at over 1575 fps and hits targets at 200 meters with more than twice the ME of even the best 9mm round and most all .40 S&W's and outclass any .45 ACP smg at all ranges. It is well worth having two locking pieces onboard to have the world’s most powerful pistol caliber smg at your control!
If you have one of these beasts you MUST have a copy of the light blue "HK MP5 Family Operators Manual" which explains all this, provides the locking piece angles, markings and ID#'s and some 10mm ammo classifications.
To a slightly lesser extent this same guidance applies to .40 S&W caliber HK roller-locked platforms as well.
G3Kurz
