[6500rpm2]

Several threads concerning shrinking bolt gap issues, but I don't recall seeing anything regarding why it occures under normal conditions with a factory HK (the whole reason HK has different sized rollers). "My" assumption, and it is just that, is that bolt gap in a proper gun (good barrel to trunion fit and properly pinned) should never change due to movement between the barrel and trunion. I am of the impression that bolt gap should normally change due to wear and seating in the bolt head parts and rollers/and mating area in trunion. True or false?

 

[Holescreek]

Constant impingement of hardened object requires the softest of the parts to start to deform. Rollers, trunnion, locking piece and bolt head all have about the same hardness but the window in the bolt head and the LP shoulder seems to get the brunt of it due to the pressure of the recoil spring. That's normal wear.

 

[hkshooterusp]

What is the normal reason for bolt gap to change?

In a factory built gun, wear of the parts.
In a clone that uses non HK made parts, just about anything including trunnion to barrel fit problems, undersized barrel pin, soft bolt group parts, or failure of key parts such as the recent debacle with the PTR cracked trunnions.

 

[REARSPROCKET]

I think HKShootr sumd it up nicely

 

[Chopstix Kid]

The breech face will also deform to the shape of the face of the bolthead. Constant impact over time causes this as the barrel is softer than the bolthead. This is also normal and will cause gap to shrink.

 

[6500rpm2]

This could turn into a add for Ghilliebear real quick, but once again my assumption is that hard parts wear occures over a prolonged span of time. If you have a sudden
unusual change in bolt gap on a low round count, barrel movement in the trunion is suspect. My feeling is that if this is the case, even at some point it seats and shrinkage stops, unusual amounts of pressure are being applied to the barrel pin and even if movement has stopped that the root cause should still be corrected.
I don't stop by this forum often, but when I do there's always a lot of bolt gap questions related to clones. Lots of posts that say send to Ghilliebear, but often little explanation as to why this is so important.