Had this EXACT same thing happen on a deer some 10 yrs back. Was a 700 LSS 7mm RM. Handloaded ammo, I thought at first I may have contaminated a primer or something. But on later inspection, only a very light pin strike was on the primer. Stripped the bolt completely, cleaned and de-greased the whole deal and went with a dry film lube...Sentry Tuff-Guard I believe. Never another issue. Cartridge fired fine later at the range, and yes I got the deer...228 yrds out so the snap wasn't an issue thank goodness.