Like most new folks on here i have been reading and reading and scouring the internet and have finally come to a question i cannot find the answer to. i want to explain thoroughly so this post may be kind of long so thanks ahead for everyone's time. Im building an mp5 clone from a German A3 parts kit and am using a clipped and pinned navy style trigger group. I had completely finished the build in all areas accept for the finish but i had a small gap in the cocking tube butt weld where i stopped and re-positioned to complete the weld (i did not spot weld/plug weld the side of the cocking tube sleeve like i understand is done on factory hk builds). I did several functions checks, made sure it cycled properly and ensured that magazine fit was acceptable and then prepared to apply the finish. Then i noticed the gap and couldn't leave well enough alone so i decided to trace over the butt weld without filler with low heat (about 20 amps) to fill the 1/32in gap for cosmetic appearance. BIG MISTAKE! After i finished this i decided to do one more check of the fit for the cocking tube support inside of the cocking tube and DING! it stopped about an inch short of fully seating. I instantly felt nauseous. I began to check for the problem and noticed that the fully round aft half inch of the cocking support appeared to be getting stuck either at the beginning of the cocking tube sleeve or slightly inside of it. It felt like a problem that would come from a bent cocking tube causing the aft end of the cocking support to be dragged either against the top of bottom of the sleeve cause it to bind up but everything appeared straight. no obvious bulges caused from welding heat and no flattening of the beveled end of the cocking tube. I cannot figure out why this was happening but it was apparent that it wasn't right so i removed the cocking tube and barrel/trunnion. I was using an aftermarket cocking tube and not a demill and was using a piece of copper round bar turned down to fit through the cocking sleeve to about 1/8in past the butt weld to prevent burn through. I need to figure out why this happened so i can prevent it with my next attempt. Im asking a lot of people to help solve a problem they cant see when i couldn't figure it out with it right in front of my face but i figure that some of you have probably seen it all including this problem. Is it imperative that i do the plug welds on the side of the cocking tube sleeve (i have no ability to spot weld it) and if so whats the best way to prevent distortion from weld heat? Thank you to everyone for your time. I know this is a long one but any advice on how to proceed without this problem occurring again is very much appreciated.