Look up a parts diagram or exploded view at Numrich Arms Gunparts. If you can't find any parts in the diagram called bolt hold open something or other, then no. Or somebody may chime in soon who does know. Thing is though if it is supposed to hold open and yours doesn't you will still need those parts from Numrich.

 

I have a model 50 and I just checked. It does have a hold open feature. There is a bolt release button on the receiver. The model 50 is a great shotgun, maybe a little heavy though. It has the least recoil of any of my semi shotguns.
The only complaint is I can't keep the rear stock tight. The castle type nut that holds it on just will not stay tight.
HTH

 

The Model 50 (and 59) are supposed to Hold Open after the last shot,,or when you just pull the bolt open on an empty gun of course.
When they don't it's usually a Timing problem with the mechanism.
It's not unusual for these to be found in the condition where the bolt will not lock open as it should.
BUT..
That can be adjusted.
It can also be found in the orig Owners Manual for the Gun(s) if you can find one on line. Sometimes they are in pdf form so you don't have to actually buy the hard copy manual.

Anyway here's an explanation of how to Time the action so the bolt will lock open.

...Remove the butt plate or recoil pad, Remove wire retainer,,, close the bolt.
Screw IN the slotted plug till bolt won't lock in the rearward position. (Yours is already screwed in far enough that the bolt won't lock back.)
Then back OFF the slotted plug till the bolt will lock by pulling back hard on the bolt handle.
Once you find that position,, continue backing off the slotted plug about 1 3/4 to 2 1/2 turns.
That extra couple turns backing off will give you about 1/16to 1/8 of an inch of extra rearward bolt travel past the point where it will lock and hold when the last shot is fired or you are pulling the bolt open on an empty gun...

 

The Model 50 (and 59) are supposed to Hold Open after the last shot,,or when you just pull the bolt open on an empty gun of course.
When they don't it's usually a Timing problem with the mechanism.
It's not unusual for these to be found in the condition where the bolt will not lock open as it should.
BUT..
That can be adjusted.
It can also be found in the orig Owners Manual for the Gun(s) if you can find one on line. Sometimes they are in pdf form so you don't have to actually buy the hard copy manual.

Anyway here's an explanation of how to Time the action so the bolt will lock open.

...Remove the butt plate or recoil pad, Remove wire retainer,,, close the bolt.
Screw IN the slotted plug till bolt won't lock in the rearward position. (Yours is already screwed in far enough that the bolt won't lock back.)
Then back OFF the slotted plug till the bolt will lock by pulling back hard on the bolt handle.
Once you find that position,, continue backing off the slotted plug about 1 3/4 to 2 1/2 turns.
That extra couple turns backing off will give you about 1/16to 1/8 of an inch of extra rearward bolt travel past the point where it will lock and hold when the last shot is fired or you are pulling the bolt open on an empty gun...

 

Got around to the model 50 this weekend. Removed the butplate and the recoil spring lock spring. Backed off the recoil spring plug untill the bolt would lock back. Found there is a fine line between the bolt locking back and be able to get the plug locking ohm shaped locking spring back into place. Turned plug in untill I was just get able to get the plug lock spring in. Now it works. Am still able to move the bolt back after locked back with a little rear movemont afterward.

 

Now that I finally got around to shooting I have a problem loading. Push button on side of receiver, push shell into magazine, elevator pops up then the catch that holds the shell in magazine lets the shell pop out about 1/3 in. Then when I pull the bolt back to load shell into chamber it comes out of magazine and just lays there. Elevator doesnt come up to load the shell. Button on side that is connected to lever would not let elevator come up. If I slightly push button in the elevator will come up. The up movement of the elevator is by a long wire spring. The gun is in nice shape doesnt seem to have been used much. I know it is not a common shotgun being Winchesters last recoil operated shotgun but maybe someone had run into a similar problem.