Winchester Model 37 single shot

[little bear]

Good Morning,
A friend gifted me one of these shotguns; it belonged to his brother who has recently passed. I have been doing some research, and these were made from 1937-63 with over 1 million made. It is in relatively good shape, a little surface rust on the barrel, but the bead is still intact and the wood is in good condition.
Anyway, he told me that his brother gave it to him because it opens when fired. He was going to try and fix the problem, but he is too busy at other projects. Before I take it apart, what would I look for that would cause this? I'm guessing that it does not lock together fully when closed, and the recoil causes it to pop open. I am planning on using this shotgun to keep in the truck and quad for grouse and rabbit.
Regards.

 

[Falconflyer]

I'd guess that the lock spring got weak over time and started letting the lock disengage the grove when being fired and allowing the action to open. Replacing the lock and spring is easy and chances are good that might fix the problem but if the grove that the lock engages into the breech block is worn then it will need to be welded up and filed down to fit. Numrich sells parts for these guns.

 

[kamlooky]

They are not an over complicated system.
Pull the butt stock off and have a gander inside.

 

[kc34]

Make sure the locking lug is clean and dry with no lube or oil on it. You want a good friction fit at that spot.

 

[little bear]

Thanks for the replies. I pulled the stock off last night and inspected the locking lug spring. Everything looked good as far as I could tell without taking it apart. I sprayed everything with oil and let it sit for a while, then wiped it dry and reassembled. Hopefully this will free up the lug and spring some more. I also looked at the notch on the breech block. There was some wear there, but nothing out of the ordinary. I will try a few rounds and get back to you guys. Thanks Falconflyer for the parts lead.

 

[kamlooky]

Is the thumb lever returning all the way when you snap it shut?

 

[little bear]

Yes it seems like it is. After I had it cleaned up and reassembled, I opened and closed the shotgun at least a dozen times and everything seated well.

 

[kjohn]

37's are nice shotguns. Simple and reliable. Classics now.

 

[little bear]

I tried the shotgun again yesterday. Not taking any chances, I tied it to a tree LOL. I stuck it in the branches of a birch, and tied the fore end, grip, and stock with rope. Looped a smaller line around the trigger, cocked the hammer, and stood back 10 feet and pulled the twine. BANG! As soon as the hammer went down the action flew open and the spent hull went flying back. I went home and pulled the stock off again, and took the spring off the locking lug. I stretched it out some, and today I will reassemble and try it again.