First of all, welcome to the board. You'll find a lot of good information here. Feel free to ask all the questions you like, and someone will certainly try to help you.

See if you can find a brass or phosphor bronze (NOT stainless steel!!) chamber brush for (I'd assume) the .303 British or similar (.30-06 should work). Put if on a short cleaning rod and chuck it up on a variable speed drill. Put some Break-Free CLP on the brush (get it good and wet), insert into chamber, and scour the chamber on low speed working the chamber brush back and forth. Swab with a patch to get the rusty/dirty CLP out and repeat until the patches come out rust free. Clean the chamber/bore until it is as dry as you can get it, and then inspect it to see if you can see any obvious deep pitting. If you can, I'd take it to a gunsmith to see what he thinks after looking at it with a borescope. If the chamber appears smooth, it should be fine to shoot.

However, for safety's sake with an old battle rifle like that, I'd consider taking it to a 'smith before I'd shoot it anyway. Some of those old rifles are still as rugged as the day they were made, but many have been beaten and abused in general military service for years and may not be in servicable condition as is now. Only a gunsmith can really make that call after a thorough inspection.

Good luck,

Mike