CZ75 Compact barrel fitting

[dagle]

How do you guys figure out interfering spots when fitting barrel lock-up? I bought a CZ75 Compact in 40S&W (all steel P-01 in 40) and I am currently in process of fitting an SP-01 barrel to it (0.550" barrel OD to match my slide).

Thus far I filed off the extra locking lug on the barrel and some of the extra corners so that it fits in the compact slide. Currently, the barrel engages partial lock-up with the slide but leaves a small gap (0.5-1.0mm) from locking up fully. I used dykem on the lug area and engaged the lugs 100x hoping to see a mark showing interference, but there was none. I did the same with mallet whacks and still do not see any marks of interference. Does anyone have a better way to figure out which part of the barrel is interfering?

I took external measurements with a micrometer to see if there was a difference between the original 40S&W barrel and 9mm barrel and the only difference is where the lock-up lugs are. The location of everything is approximately the same with the biggest deviance being 0.004" at the lug.

Currently my steps moving forward is to use a grinder + wire wheel to strip down the barrel to bare steel and try again with the dykem. If anyone has a better technique, that would be really helpful.

[ar15barrels]

Prussian blue is helpful as it will transfer from the barrel to the slide or the slide to the barrel depending on where you place it.
It's also MUCH thinner than dykem so it won't effect up your fitting checks.

[dagle]

Thanks. I used some engine clay I had left over and it turns out to be the lug and partially the hood (they're the same height).

After inspecting the barrels, I think a custom bushing in the slide would have made the 40-9 conversion much easier. The only thing different is the 0.550" OD of the barrel, so a custom bushing for the slide to fit a 0.500" barrel would let the 9mm barrel for compact slides fit. Everything else appears to be drop-in.

[jr-abs]

Did you check for interference with the extractor? It can often get in the way.

[dagle]

Yeah I did and it cleared the extractor, the barrel is just overall bigger so it’ll need some reducing. I found a couple of tight spots on the sides of the barrel near the locking lugs but have been busy so haven’t picked up the file.

To find the spots I used wax (frog lube) and a heatgun to melt an even layer of wax on top then carefully fitted the barrel And engaged the lugs to see where the interference was. Melted wax is smooth/clear so any marking is very apparent.