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Discussion Starter · #1 ·
QUESTION- Is there any bolt carrier wear that would affect head spacing?

While the gap is measured from the front of the carrier, basicly the head spacing wear comes from the rollers which can be replaced and not from wear on the carrier.

Head spacing is determined by "using feeler guages, measure the gap between the back of the bolt and the front of the carrier (through the mag well. It should measure between .250mm (.010") and .450mm (.018") ideally, larger gap within the range is better, the gap gets smaller as the weapon wears."(source www.HomeGunsmith.com Static Archive)

So it shouldn't matter if you use a new or used carrier?

Thanks
 

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The Librarian
MP5-N and HK23E-K
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Technically, there isn't head spacing to worry about for roller lockers like there is for AR15. What effects bolt gap is how the barrel is pressed & roller wear over time. The carrier shouldn't play into bolt gap.


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The only way the carrier can effect bolt gap (assuming it's made to proper specs) is if it is hitting the end of the cocking tube support. This would create a false bolt gap. The gap can be visually checked in the cocking tube.

I swap carriers around through various guns and all with no ill effects.
 

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Discussion Starter · #4 ·
Technically, there isn't head spacing to worry about for roller lockers like there is for AR15. What effects bolt gap is how the barrel is pressed & roller wear over time. The carrier shouldn't play into bolt gap.


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That is what I meant to say. The carrier simply carries the bolt and locking pice into place- letting the rollers find their home and creating the bolt gap. The bolt gap is created by the delated blowback roller locking design where as the head spacing of an AR or AK is created by the relationship of the rotating bolt design. Different nomenclature but similar results.

Thanks for confirming my suspicions. I have been collecting parts for my build and was trying to understand the parts and their relationships. (Building a regular ol' MP5 N)I got to looking at the bolt cut aways and started to wonder about the bolt to carrier relationship.

I'm still going to get a new carrier. Mainly for piece of mind but also because I want all of my internals to be true Hk spec... so new Hk parts should be perfect, but pricy. Thanks again.
 

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The Librarian
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No problem & glad to help. I'm also going to be building a MP5F myself... At least that's my game plan for sometime next year. The one unknown that I have yet to find any information on is how far to press the barrel into the trunnion. I have seen jigs used but never seen/read anything regarding a measurement to set the depth of the barrel into the trunnion.


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As I understand it, .006 to .020 is the correct range. Higher is better since you can always use minus (-) rollers
 

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As I understand it, .006 to .020 is the correct range. Higher is better since you can always use minus (-) rollers
I think he is talking about depth of the barrel, in relation to the top edge of the trunnion. Basically, how deep to press the barrel in.

Like most over builders, a fixture is lathed down to the exact depth for this. Don't know who would have this on hand, but measuring with the end part of a set of calipers will give you depth.
 

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Except that's not what he said (Quote)

Head spacing is determined by "using feeler guages, measure the gap between the back of the bolt and the front of the carrier (through the mag well.
 

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The Librarian
MP5-N and HK23E-K
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I think he is talking about depth of the barrel, in relation to the top edge of the trunnion. Basically, how deep to press the barrel in.

Like most over builders, a fixture is lathed down to the exact depth for this. Don't know who would have this on hand, but measuring with the end part of a set of calipers will give you depth.
Yes, definitely referring about depth of the barrel in relation to the top edge of the trunnion.

Thanks for clarifying!


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