Ok so the fit between my BCM upper and Rainier Match barrel is TIGHT...I mean it wont go in and probably will  need a rubber mallet to help it out...assuage my fears and tell me this is OK and normal and will help accuracy and not damage my upper...

Shouldn't be that tight, no.  

Hammers should not be required for assembly!

not planning on using anything more than a few taps from a rubber mallet..maybe a little CLP...read this on BCMs website

 

NEW PRODUCT from Bravo Company MFG, Inc®!

 

 

Built to the correct Mil-Specs.

(Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle.)

 

 

 

 

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BCM M4 Upper Receiver Assembly (w/ Laser T-Markings)

 

 

BCM M4 Upper Receiver Assembly

Use the moly grease for the barrel nut. Lube is a good thing.

Use the moly grease for the barrel nut. Lube is a good thing.

I think the OP's issue is the ID of the receiver is undersized, not the OD with the threading.

 

Once the barrel nut is properly torqued, your barrel shouldn't move.  Outside of the ID out of spec and super loose, I don't see how having it super tight is any benefit over what's normal.

Sorry if I wasn't clear. It's the barrel extension fitting into the receiver. I am suggesting to use some of the same lube for the barrel nut on the outside of extension to help ease it in. A tight metal in metal fit gets exponentially easier with grease.

 

 

"Assuage" .... Excellent.

"Assuage" .... Excellent.

I was waiting to get flamed for that lol..

I didnt really spend a bunch of time fooling with the barrel and upper today .just wanted to do a preliminary fit..taking into account what BCM said, I'm hopeful with a little elbow (and real grease) it will fit...any other suggestions are welcomed

You could try freezing the barrel prior to installation

You could try freezing the barrel prior to installation

And heat the receiver.

 

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In my experience bcm uppers are very tight (and their barrels oversized. Personally I like that, I use a few taps with a rubber mallet. Good thing about rubber mallets is that there is no way to hurt the muzzle with one.

 

 

Now ... Getting them back out would be an adventure.

I was waiting to get flamed for that lol..

I didnt really spend a bunch of time fooling with the barrel and upper today .just wanted to do a preliminary fit..taking into account what BCM said, I'm hopeful with a little elbow (and real grease) it will fit...any other suggestions are welcomed

No flaming meant at all. It's just a cool word.

Bcm is tight, as are others like the Rainer billet upper. My solution is a block of scrap wood and drill a hole in it with a spade bit or equivalent. Put it over the barrel, put a piece of PVC pipe over that and use a hammer on the pipe.

 

Just be sure to put done grease on the extension if you want to get it back out. I used a delrin rod for that.

 

It really didn't take a lot of force in either direction.

I had the same problem with a vltor upper. I used a bit of emery cloth on the upper. I think the coating was a bit thick. I thought about a rubber mallet, but decided if, for some reason, I wanted to take it apart, I wouldn't be able to. The emery cloth  (real fine) worked. In fact, I did not take it all the way down to shiny aluminum. Just removed a bit and tried it until it slid right in. O and, yes, I did lube it on final install.