Hey all, just picked up another HK clone of sorts.  It's one of those old Special Weapons SP-10 rifles (for those that don't.. basically an MP5 clone with a polymer receiver).  I've had a couple in the past and had to let them go for financial reasons, randomly decided I wanted one again and just happened to find on semi-local.  So its mine now

The bolt gap is on the low side... 0.010".  I am looking to adjust it a bit since it's on the very edge of the lower limit.  I know this is done with oversized rollers, but how do I know what size rollers to go with?  Is there a way to calculate how much the bolt gap will change after adding +2 or +4 rollers?  The rifle currently has unmarked rollers, so I assume the standard 8.00mm but I still need to measure them to be sure.

Changing them is easy enough, I am just trying to avoid buying multiple sizes and testing them all out.  Any info would be appreciated.

According to this builder, +2 should get you into spec.

Thanks for the link.  I had searched around for posts like that but came up empty.  I guess I missed that one since the subject is for HK91s.

Each size roller effects bolt gap by .10mm or about .04 inches

If you’re at .10 and ideal is .18 then I would say you need +4 rollers. This is assuming you have standard size rollers. Measure your rollers and order two sizes up.

The ideal range is 0.010" to 0.018" and the max range 0.010" to 0.020". +2 rollers will get you right in the middle of the ideal range at 0.014"