As Larry said, a hard to press release button is caused by a poorly fitted barrel or too hot of load. If the load is too hot particularly on bottlenecked chamberings, you'll usually have a slight gap between barrel and standing breech after the shot before you open the action, hold it up to a light source and see if you can see the gap cross the barrel to breech joint at the top of the barrel. A poorly fitted barrel will probably have uneven latch engagement which is covered in barrel fitting.
Tim