I'd first make sure the lock is clean. Take it out of the stock and use either automobile brake cleaner or carburetor cleaner that comes in a spray can to thoroughly flush it out. If you have an air compressor, blow it out with compressed air. If you don't have compressed air available, don't worry about it because the stuff that you use to flush your lock will evaporate very quickly. When it is dry, lightly oil it with any good gun oil or light machine oil such as 3 in 1. Replace it in the stock and see if it feels any better, Many lock problems can be solved with a good cleaning and oiling. If that doesn't do it, it will be time to consider taking it apart and polishing all of the contact surfaces. You may also look into finding a lighter main spring if the cocking action is too stiff.
Another thing to check is to see if it is fitting in the lock mortise properly and not rubbing somewhere. Often times, people don't know what they are doing and try to tighten a lock bolt like they were torqueing an automobile engine head bolt. Over tightening will cause the lock to rub on the inside of the lock mortise and can cause all sorts of problems. Never over tighten the lock bolt, All it needs is to be gently snug. If you find the lock to be rubbing on any part of the lock mortise, you will have to carefully shave off wood where the lock is rubbing. Do not remove any more wood than is absolutely necessary. You shave and scrape, you do not cut or, God forbid, use a Dremmel tool to remove wood.
It'll give you some fiddling to do while the weather is bad. Good luck and keep us posted on how it is going.