It's made from the exact same receiver casting, same parts, same machines and same people. Same gun, just diff levels of work. Hung up in what way?
Sounds like a common "pulling on the pump" problem, It. Pump and dry fire it a few times fast and keep backward pressure on the forearm the entire time while firing. Pull it back while you're triggering it. Is that lock up what you mean? The gun won't release the bolt carrier/bolt until you release that backward pressure....push the forearm *forward* after you pull the trigger and see if that works for you. That wiggling the forearm sounds like you're pulling the pump and you're fixing it without realizing it.
If you pull your trigger group, that long thin thing right there on the top is the bolt lock. Hold the hammer and let it down slowly and watch that part drop. With the group in the gun and cocked, you can look up into it just at the back edge of the bolt carrier and you'll see it locks it in place. With pressure backward on that lock as you fire, the lock is held in place by the bolt carrier and prevented from dropping to unlock the slide. It just takes a split sec of forward pressure to release it.
Work on your form a bit by dry firing it any time you get the urge. It won't hurt it. Right hand pulls the grip/stock tight to your shoulder, left hand stays relaxed, forward to back I mean, and just aims the firearm and works the pump.
There's nothing a half to a third of the way back that it can snag on. Not that I know of anyway. You got me.
If you're wanting to work it out, rack it. If you want to work on your form and timing, dry fire it. Nothing really complicated there.
so the action is the same in the 88 and 500 models? i'm just wondering because my 88 has hung up on me two or three times, but i've not put more than 100 shells through it either.
For the most part yes, actions/receivers are the same with the differences noted above. If you bought your gun new, then at 100rds it is probably not quite "broken in" yet. Lube the slide and bolt and with unloaded gun work the slide back and forth about 100 times--see if that helps.
I prefer to "ease in" my guns by careful disassembly and cleaning/dressing of sharp edges on stampings and smoothing roughness here and there. I am mindful to not remove TOO much metal as it is very hard to put back... I would only do this if you are confident you can put it back together properly. And I am careful not to remove edges that are meant to be sharp like the sear/disconnector and extractors.
BTW, Welcome Aboard!