Been there done that... Once!
Those are good guns. I had one in .270 and sold it to a friend. I remember he had some issues with cheap imported ammo where the extractor ripped through the brass case rim leaving a stuck chamber. Put in some of my reloads using good quality brass and it ran like a champ. Which pawn shop was it? The stores on Blanding seem picked over every time I go in.
In the event you encounter this, check the neck dimensions on an extracted case. I bought a used 742 Carbine in 30-06 many moons ago, ran into this with name brand factory ammo. Don't remember what I was shooting at the time. Returned it to the sporting goods store, and they sent it off for repair, came back supposedly fixed; did the same thing.
Was NOT even a little impressed since I lived an hour from the store where I bought it. Especially when they wouldn't take the Winchester 100 I traded in because it had been sitting for years and needed a shot of lube on the bolt. It hung up on 1 round out of 5, when he test fired it; little pfft of WD-40 and I went through an entire box of shells with no problem. Salesman refused to give it that much effort, couldn't believe that was all I did to it when I brought it back. The 742 on the other hand, hung up every round.
Stopped by local gunsmith on the way to take it back, the second time, told him what it was doing. He took it to the basement, fired 1 round, encountered the problem, and came back upstairs scratching his head. Grabbed his micrometer and started checking case dimensions, found a bulge in the neck of the case of about .002" after cooling and extracting it. He surmised it was likely a little more than that when hot, immediately after fired, or possibly that was enough to hang the case in the chamber tight enough for the extractor to rip through the base of the shell when cycling. After cooling, the case extracted with ease every time.
Gunsmith blamed it on someone hogging the chamber out with a cleaning brush, said he'd never seen anything like it. I have since encountered 3 other people on-line, with Remington guns that had encountered the same problem. Only thing we could attribute it to in discussion, was erosion as a result of hot gases blowing back around the tip of the case neck, over time.
As for mine, I assume they reamed the chamber slightly behind erosion, when they sent it back the last time (
with notes on what was causing the problem), I've never reloaded for it, and thus never had need to check a case. Do know it's never given me problem since. Been through many rounds, never hiccuped even once, been an extremely reliable gun, just as I anticipated in buying it.
Bear hunted when I was a kid, killed my first bear with a borrowed 742 as cause for wanting one. Family that owned that one, had 2 at the time, and they were flippin indestructible. Drug through the swamps in North Florida relentlessly during hunting season, bounced around under the seat of the pickup all year round, they cleaned them with a water hose, air hose, and can of WD 40, literally. When they started to hang up, they'd wash them out, blow them dry, then spray them down with WD. Toughest guns I've ever seen in my life, and thus I have a hard time putting much store in the "Jam-O-Matic" reputation they've been given over time. I know folks have had trouble with them, but the things I've seen them put through, I don't know what you'd have to do to one to make it jam, aside from eroding the chamber.