I've got an older Mossberg 600AT that I bought back in the 70's brand new. Didn't really use it much as I never got into bird hunting. A few years back I got an 18-1/2" barrel for it for home defense. The few times I shot it it worked flawlessly. My son recently got me into turkey hunting, and I shot my first tom. Now I'm hooked. So, I decided to convert the old Mossberg  into a turkey gun, with new guns being hard to find. I bought a 24" vented barrel with Acu Choke, camo gun skin, and tactical camo pistol grip stock to trick it out. In the process I disassembled it completely using a couple YouTube videos. Pretty easy. Went back to the YouTube videos for reassembly which also were pretty straight forward. However, once I get it all back together, the slide will only run the bolt back about an inch or so, and then it binds. I've had all the pieced in and out more than a dozen times, and it still hangs up. I've double, triple, and quadruple checked the bolt, carrier, elevator, cartridge stop, and cartridge interupter for proper fit and placement. Everything works smoothly and flawlessley UNTIL i install the trigger group. Then the slide will only move the bolt back about an inch, then binds up. I am stumped. Everything worked fine until I disassembled it. I am completely stumped. Like I said, I've had it apart and back together over a dozen of times.
Any help guys? I'm hoping it's something really dumb and simple. But, man I am stumped. Thanks.

Update. I can pull the slide back now, but it seems to be sticking at the rear of the stroke. The only way I can get it to go forward, with the slide release depressed, is to bang it forward with a blunt object. Still stumped.

Thanks. I’ll try that. Weird thing is that it did the same thing with no barrel installed.

I’ll check that out too. The thing that is driving me crazy is that everything moves and acts normally until the trigger group is installed.

Think I had the same problem, although I might be confusing shotguns.  You need to make sure the shell stop on the side is being pushed aside before you put in the trigger group or it causes the stop to bend out and lock up the action bars.

This one is pretty good, fast forward to about 330-345.

Thanks man. That was the video I watched. Not sure what the problem was, but I was racking it back until it stuck, then putting the heel of my hand on the back of the slide until it broke loose and went forward. I did that maybe 20-30 times trying to see if whatever was binding would loosen up. Well.....guess what? All of a sudden, it kinda popped and now it works perfectly, just like it did before I switched out the furniture and disassembled/reassembled it. I still don't know what was binding, but whatever it was, it isn't now. Everything looks and feels like normal again. This one was a real head scratcher. I've always been a real tinkerer with my guns, and like to troubleshoot them when something seems off or broken. Thanks a million for all the suggestions, guys.
Here is the project from start to finish.

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I could have been one of the springs not seated all of the way. I had similar happen one time with my 410 Model 500. I rushed putting it back together and the slide would only go back if the release was pushed in. It ended up being a spring was not reinstalled correctly. It's been so long ago that I don't remember which spring it was though.

I swear, this thing is out to get me. Got everything working and took it to the range to pattern it today. First shot, the cap at the end of the mag tube that the barrel screw attaches (Mossberg 14-1/2" old style tube) started to back out. Same thing happened years ago, and I had my gunsmith silver solder it in. Not sure how it was originally held in place. Looks almost like it could have been some kind of C clip or ring. I found a replacement used old style tube on ebay and ordered it. Also emailed Mossberg about it. Trying to figure out if the new style mag tubes would work. Anyone have any ideas on this new attempt at my shotgun trying to drive me crazy?
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Those are exactly the options I was thinking about. I think the drill and tap idea would be the most stable solution.