We suggest to do this step before you even start assembling anything with your 80% build

check your rails please.

to test, use just stripped slide / barrel and front rail.

lay your slide with barrel installed as shown in the pix above insert your front rails, same orientation as if the frame is being installed to your slide

Move the Front Rail forward. Check if the Front Rail "bridge" makes contact with your barrel lug. If no, then Front rail should be able to "unlock" your barrel. Its good to go. If yes, it does make contact. then you will need to do some modification on your front rail.

Picture of unlock barrel. Also make note that the front rail should be 100% smooth moving/sliding into your slide. Any bidding can cause malfunction. We recommend to sand and polish pretty much all front rails to fix this issue before it even comes up. Sanding and Polishing Rails also helps with the break-in period of ALL 80% If you need to modify your front locking block, here's a quick picture

Rough sand the areas that makes contact. Use marker to see which areas needs work. If you can create a ramp on the bridge of the front rail, this will help with feeding issues as well. Once you test fit the front rail and its all good to go, we suggest to sand it with fine sander paper then polish it.