Since the rifle is 6 months old, has it worked properly up until now? Are we talking about one misfire, an occasional misfire, or a refusal to fire anything? Will the misfire fire on a second attempt to shoot it?
If the rifle has worked normally up until now, something has changed, either rifle related or ammo related. Excessive headspace could produce a misfire, but brass failure would quickly point to such a problem from the first time you fired the rifle. Sometimes misfires are a result of light firing pin strikes, and can be resolved with a new firing pin spring. If the bolt is degreased, clean, and free of damage, you probably have an ammo problem.
Have you changed the brand of ammo you've been shooting up until now, or changed to another brand of primer in you handload? Some primers, particularly the primers in military surplus ammo, tend to have hard/thick cups. If your ammo is handloaded, and the primer was not bottomed out in the primer pocket, combined with a slightly expanded primer pocket, the primer could move enough to cushion the impact from the firing pin, causing it not to fire, although one it should only occur occasionally, and the round should fire on a subsequent try. If your primers somehow became contaminated with oil, the priming compound will desensitize, and round will misfire.