Has anyone experienced assembly issues with their R51? I have had mine apart several times with no issues, however this time on installing the slide it went on to within 3/4" from the rear of the frame and froze. Now it will not move in either direction. Any ideas before I call Remington?

Sounds like something is different this time.

What has changed?

I recommend asking the question on the "Remington R51 Pistol Forum" website. There are a bunch of folks over there to offer good advice.
Good luck,
ShoT3

Can you tell at all what's hanging up on it? You might have caught the ejector on something. I would recommend smacking it with your hand or something soft while turning it over and rotating to knock it loose.

My guess would be the barrel is slightly off-kilter, and you can probably recover by jiggling the barrel while smacking the heel or slide.

One time, I managed to get the breach block inserted in just a little too far forward of where it was supposed to be. When I released the spring and the barrel, it got stuck and I had to use a flat tip gunsmith screwdriver to help me get the barrel off the block so I could re-position. First time was really hard as I don't have the strongest hands in the world. I have had the same experience as you had. I thought it was frozen up too, however, a slight jolt with a rubber mallet on the forward part of the slide should do the trick. I thought the ejector was hanging things up, after a visual inspection though, it didn't prove to be the case. Make sure the breach block is fully seated in the slide.. Then just try a good whack. Gently that is!

Happened to me one time. I gave it a good cussing, left it overnight and tried the next day and it came free without a problem. Who knows. There are so many glitches in these pistol there is just no telling.