I have a 760 pump master classic. But every time I go to reload the lever to open the chamber only opens half way. It gets super super hard to go anyfurther

There is help in the link

https://www.google.com/search?q=760+pumpmaster+won%27t+load+bb

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I have the exact same rifle, same bs, but you can tighten it up by adjusting the lever itself, it's adjustable butvto be honest I left mine alone bc it's hard to get it right once you start messing with it!

Is there a round in the chamber ( empty or live ) ?

Is the barrell bent ?

This is an H&R top break revolver, and it is chambered in the old .38 S&W caliber, which is not .38 Special! Do not attempt to load it with modern .38 Special - if you manage to put one in the cylinder, the pressure is too much for the weapon and it can burst upon firing turning your gun into a hand grenade. I cannot stress this enough. You can buy the proper ammunition for this but you will have to look for it online. No store will have this in stock. Most of what you will find will be brass or nickel cased with a soft lead round nosed bullet. It is a rather low powered cartridge and you can guess from the gun's size this was not a service round caliber. I would get a .380 ACP semiauto to carry and keep this one for fun shooting at the range. If you love the top break revolver, there are more potent calibers in larger framed guns like the S&W Scholfield in .44 black powder you can buy from outfits like Navy Arms. Lots of cowboy action shooters use them, but the 1873 is still the king with these folks. The rapid unload and reload with moon clips make the top break the fastest reloading system of the 19th century.

When Co2 is used to propel a projectile the escaping gas is very cold - below zero cold - and water vapor condenses on metal and that causes the pressure in the chamber to drop to zero or so little that it can't move the pellet. If you are firing this as rapid fire strings I am surprised you got through two cylinders of gas.

Contact Crosman Customer Service. You can send it back to them and get it refurbished with all new parts.

https://www.daisy.com/product/PowerLine-Model-880/?itemnumber=990880-001

To return a Daisy Product for repair or warranty related matters, ship to: Daisy Outdoor Products
1700 N 2nd Street
Rogers, AR 72756

Strip it and clean the slots the two stops ride in. If that doesn't fix it, replace the stops. Mossberg will replace them free of charge. If you're a Handy Andy, once you get the new stops from Mossberg, examine the old ones and file and stone them so they match the new, working ones. You'll see what was wrong.

If you're getting a good dent, it's the ammo, not the gun. The good dent is all you hired the firing pin and spring to do. They did their job....don't blame them for the screwed up part time workers.