Calling DannyR, please.
Okay, this is still bugging the crap out of me. Took some caliper measurments. I measured the RSA hole on the muzzle end of the slide, after safely field stripping my Gen 3 and Gen 4 subcompacts. There are acutally two dimensions there. One is on the inside of the hole, and all 3 subcompacts were close from about .512 to .515.
Measuring from outside of the front of slide, the hole is .435 on the Gen 3 26 and 27. However, on the Gen 4 26, the dimension is .450. I wonder if this difference of .015 could be causing the occassional issue with the RSA and the slide not coming off.
It would be greatly appreciated if someone with a Gen 4 26 or 27 would make this measurement and post it. Of course, safely field strip the pistol before attempting to measure. I would like to see if mine is within spec.