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Discussion Starter · #1 · (Edited)
I recently acquired a cast receiver Special Weapons SW5 HK94A2 clone without chamber flutes. It seems to run OK on the new US made 10 round magazine I got from HK; and had some failures to feed on the included 10 round Special Weapons part which doesn't feel smooth when loading a round. OTOH, assuming it runs well on one magazine may be premature with only 70 rounds through each one.

Bolt gap measures between .15mm and .20mm (my feeler gauge increment goes up to .05mm after .10mm).

The MP5 armorer's manual calls for .25mm-.45mm as ideal with a .25mm-.50mm maximum.

When I popped the rollers out they measured .314" which is 7.98mm.

The manual says 1 Size = .10 of Bolt Gap which smells like nice, round German metric units.

So 8mm standard rollers should get me .25mm to .30mm; 8.02mm .35mm to .40mm.

I assume the higher end of spec is preferable because being closer to opening will help it overcome the unfluted chamber and it's going to close up over time?

Since I can achieve optimal bolt gap with larger rollers I assume there's no reason to replace the (unmarked) locking piece at this time, and leave it alone as long as the gun runs fine on known good magazines?

Or do I just leave it alone because it seems to work?

I'll verify I have a 9mm hammer spring installed in case that's slowing things down and contributing to my failure to feed, although the magazine is a culprit.

I'll definitely include a spare roller retainer (not much there), pin (is tiny and easy to lose), and extractor spring (mine is silver of unknown provenance and remaining life) in my parts order.

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