Some say putting half a tube of grease in is the main part. Chop a bit of the barrel on some rifles . Bit of a de burr and put it back together then put a sticker on the compression tube and charge you about £100.
To be honest .
De burr the coking slots . Smith off rough parts . Polish trigger parts . Modify triggers if needed . Change the spring guides for better fitting ones . Chop the barrel on some rebuild and put a sticker on it.
Same as many tuners on here or other forums can do or supply bits so you can do it yourself .