Can't find the answer to this in any stickies so here goes.

Using a Polish 80% receiver on my first build and the rails are being welded up for me now.

Question is when I get it back is the bolt carrier supposed to easily slide back and forth on the rails like a M1 Garand while doing a tilt test?

For those not in the know the tilt test is when you put the bolt and op rod on a hammerless rifle and tilt it up and down. The bolt and op rod should move with a little tilt and not rub anywhere.

Prior to handing it off to be welded the bolt carrier did not slide that freely. It slide with hand pressure but not with just gravity.

Should the edges of the rails be filed a bit or is it the thickness of the rails that are keeping it from riding clear?

Build is going great so far thanks to all the info here. I have not been talking pictures due to lost camera but I have a new one now so maybe I'll snap a few this weekend.

Gun Porn will be provided in some form or another.

Are you going to heat treat the receiver or just the pin holes and ejector?

In my opinion, YES.  I test all my builds this way.  Just make sure the hammer is not installed and all is well lubed.  I "tweak" the receiver as needed to make the bolt carrier "free-fall" in both directions.  

I have never had to thin/file the rails as regards to thickness.  I have had to "adjust" receiver width a couple of times.  

If the receiver rails seem to be too "thick" for the carrier slots, then I would carefully massage those slots to provide just enough clearance to slide free.  Always modify the "cheap" part first.

Bear in mind that if the carrier isn't moving freely it could just be that your front and rear trunnions aren't installed. Once they are, it should definitely move freely by tilting it back and forth.

I got impatient and riveted the front trunnion in already so it's just gonna be the upper and lower rails and the FCG holes that get treated. In my defense the rivets look great!





As mentioned I have the front trunnion in already and I slid the rear trunnion in to test it. The center support is not installed so that may spread her cheeks a bit and makes it slide better.





Once I get it back (hopefully tomorrow) I will install the center support and see how she runs.



My feeble mind was telling me it should be loosey goosey but I wanted to check with those that have been there done that.

On a side note, Oxpho-Blue stuff is the cat's ass!

The Polish receiver will need to have the living shit sanded out of it to get the machine styrations off the sides. I don't want the thing to look TOO purty but have that previously loved look to it!


I have to drill the FCG holes and I am scared shitless I'm gonna screw it up. First build so I didn't want to have to bend one and NoDak was out so I went 80% and had to do the holes.

Trunnion holes were no sweat. Rear trunnion holes and underfolder holes were a bit harder but I bo-hunked em in there close enough for Gub'ment work.

Got the screw kit for the trigger housing so that won't be hard.

I need the right drill bits and reamers yet so I won't be doing them this weekend but I hope to have the center support and surface prep on the receiver done at least.

Thanks gentlemen!