870 malfunctions, please help

I am usually pretty handy with my guns, but this one has me stumped. I just picked up an older 870 wingmaster magnum. After bringing it home, i noticed a problem while dry firing. Once i rack the slide shut, if i pull back on the action and continue to hold that pressure (as if trying to rack the slide open), the action will stay stuck shut after the trigger is pulled. No matter how much i jiggle the pump action, it will not open until i release the trigger. I have another newer 870 and it does not do this. Any advice is much appreciated.

So you are putting rearward pressure on the action while pulling the trigger? The action bar lock should move out of the way of the action bar after pressing the trigger. It is the same INTERNAL action as pressing on the external action bar lock to open the action without pulling the trigger. Perhaps the rearward pressure of the action bar is preventing the action bar lock from falling out of the way. Does it function normally if you aren't exerting rearward pressure?

Here is a photo of the action bar lock. The projection on the bottom right is what you can see and manually press. The far left piece is what hits the back of the action bar and prevents the action from being pulled rearward.

https://www.gunpartscorp.com/pub/products/94570.jpg

Your shotgun is doing what it is supposed to. You don't want the action to partially open up from the recoil after a shot. Could lead to a jam if you short cycle.

I would be more concerned about your other shotgun that does not do it.

The trigger is not what is locking the action. Its the pressure on the slide. Try shooting it without any pressure on the slide and keep the trigger pulled. The slide will cycle.

Thanks for the suggestions. To answer some questions, yes i am referring to rearward pressure, as if pulling the gun into your shoulder. And yes, the gun functions normally when i dont apply rearward pressure on the action.

The problem is that with rearward pressure, after i pull the trigger, the action will lock up, even if i wiggle the action back and forth, and will not rack open until i release the trigger. Having to remember to release the trigger before you can pump the gun makes it impossible to shoot multiple rounds quickly. Also, just to mention, ive shot thousands of rounds through many different pump guns, mostly at the skeet range, and i can tell you something is clearly wrong with this shotgun, and not my other gun.

Pop out the trigger pack and clean it.

So i just finished pulling out the trigger group and doing a deep clean with a toothbrush, then oiled everything down real good with some slip2000. Did not solve the problem. I was looking at the mechanism to try to figure out whats wrong. Seems like maybe there Isnt enough spring tension on the action bar. I noticed that it doesnt travel as far as it should, but im not entirely sure how far it should travel.