I only know this about MP5 bolt heads.
Early on when US Police depts started getting MP5's, they began to have bolt heads that cracked. This occured with low round counts, compared to the MP5's being used in Europe and England...
It was determined/discovered, that in the USA, the Police SWAT Teams were using their MP5's in "static training", ie non live fire, and were cocking the bolt back and "slamming" it closed, on an empty chamber so many hundreds of times, that it was causing the bolt head to crack, as slamming closed on an empty chamber was a lot harder on the bolt head than shooting several thousand rounds of live ammo...
SO, H&K re-designed the bolt head, to be "USA Cop Proof", putting more metal in the area that was cracking...
Sorry I do not know the H&K factory "numbers" of the two different types of bolts.
Early on when US Police depts started getting MP5's, they began to have bolt heads that cracked. This occured with low round counts, compared to the MP5's being used in Europe and England...
It was determined/discovered, that in the USA, the Police SWAT Teams were using their MP5's in "static training", ie non live fire, and were cocking the bolt back and "slamming" it closed, on an empty chamber so many hundreds of times, that it was causing the bolt head to crack, as slamming closed on an empty chamber was a lot harder on the bolt head than shooting several thousand rounds of live ammo...
SO, H&K re-designed the bolt head, to be "USA Cop Proof", putting more metal in the area that was cracking...
Sorry I do not know the H&K factory "numbers" of the two different types of bolts.
