Standard HK GmbH factory-produced HK33K's were shipped with # 3 locking pieces (58 degree, ID# 203384). This same piece is used with the HK53 with 1/7" twist and M855 ammo (or the # 15 piece with M193 ammo).
Generally speaking as the barrel length DEcreases the angles of the locking piece INcrease.
Examples:
G3 = 45 degree, G3K = 50 degree
HK33 = 55 degree, HK33K = 58 degree, HK53 = 65-70 degree
G41 = 43 degree, G41K = 45 degree
The MP5/HK94 family is the notable exception - they are all over the scale for various reasons (desired rate of fire and/or stock and suppressor use on the K, barrel porting and suppressor in the SD, calibers in 10mm and .40 S&W, etc.). The subguns tend to be somewhat less sensitive to locking piece variances.
I most conventional small arms want the chamber to remain closed/seated until the projectile and high pressure gases leave the muzzle. It is the angles on the locking piece that greatly determine "unlocking" time or more accurately for the unlocked HK-style roller-"delayed" bolt system "opening delay". This determines proper and reliable function and rate of fire to some degree.
Of course all this varies based on the ammo type used and other factors (suppressed, box versus belt fed, special coatings, condition of the gun, etc.). At one time there were over 80 different angle locking pieces for the G3 family alone based on the variances in ammo around the globe.
That should help.
I will ask Straightgrain to post the "Appendix B" locking piece list here which provides a more detailed list than that posted here in this thread.
G3Kurz
