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Can someone tell me the diferrence, as far as function, between the standard MP5/5K/SP 89 standard older flat face bolt head, the Action 3 Bolt Head, and the F Bolt Head? Does the difference have to do with what type of loads can be fired, or better extaction, or, just what is the difference between them? Thanks.
 

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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.
 

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The Action 3 bolt heads have a scalp cut on the front to help with feeding/ejection on certain rounds and are in general a little better option, being a later generation in product improvement.

A few links to reference threads:
http://www.hkpro.com/forum/hk-nfa-talk/109906-mp5-k-bolt-f-differences.html
http://www.hkpro.com/forum/hk-nfa-talk/140017-mp-5-bolt-carrier-group-what-difference-better.html
http://www.hkpro.com/forum/hk-nfa-talk/116914-what-do-i-have-action-3-f-modified-bolt-head.html
http://www.hkpro.com/forum/hk-long-gun-talk/146056-how-tell-if-i-have-action-3-bolt-head.html (Note the correction to my post and the wider slot is F type)
 
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