9mm HK MP5 Locking Piece Question

[medic21]

Many years ago when I purchased my 9mm Vollmer HK MP5, a #26 locking piece was included in the package price as an "extra". I seem to recall being told it would slow-down the rate of fire. I came across it last night in my parts bin and got to wondering about it. My reference materials tell me it was designed for .40cal so I'm not sure why the previous owner purchased it. I have not used it myself and it appears to be unused or slightly used. Several questions from the RKI on the Board: will it indeed slow down the rate of fire? Will using it damage or adversely effect the function in any way of my MP5? If I decide to sell it, what would be a fair selling price? TIA

[JTinIN]

Double check if it is not a #28 (suppressed MP5K-PDW and/or with 147gr ammo), which I have used to slow down a full size MP5 (have less energy reserve for when dirty or weak ammo, so don't use for anything critical). The cost of an HK #28 is fairly high now days, over a $100 new. #28 Locking Piece for MP5K - HKPARTS.NET


The #26 appears to have been the 40 Cal locking piece before / instead of the current listed (HKPARTs) Hi and Low impulse locking pieces.
HK Locking Piece Table What is interesting is both the #26 and #28 locking piece are 80 degrees.

[mt162]

Except the #26 won't fit a 9mm weapon due to dimensional differences. The 40/10 locking pieces won't interchange with the 9mm ones.

[medic21]

Yes, indeed it is a #26 LP. looks like I'll be offering it up for sale since I don't have a .40 cal. It has very light wear marks on it so someone in the past tried it out. Thanks

[JTinIN]

Except the #26 won't fit a 9mm weapon due to dimensional differences. The 40/10 locking pieces won't interchange with the 9mm ones.

Have only fired friend's MP5/40s so was not sure there were any parts swapping allowed, is interesting they both were 80 deg and possible someone just grabbed/ordered/got the wrong one years ago.