well..... after consulting the kuhnhaussen manual........ i'm gonna bet dimes for dollars this is one of two things
A) reloader error , nothin to do with powder charge, though personally from my readings 45 grns of 4895 is definately on the upper scale of a hot load for the m14. I would be looking at incorrect primer or incorrect primer seating depth.
B) Operator error, that rifle shows evident signs of cosmoline and i'm going to guess the bolt has crud in it, causing a stuck firing pin.
We can rule out a "slam fire" caused by hammer follow by asking this simple question... is the rear tang iof the firing pin intact? If it's broken off, it was a slam fire...... if not ..... we are now leaning 99% towards an out of battery fire..... see A and B above.
My comments aren't meant to stir the pot or belittle the guy posting this.
No one should feel hesitant or embarrassed to share thier catastrophies

we can all learn from this.
Reloaders...... there's all kinds of opinions, books and internet articles on how to reload for these rifles..... some are good, some are not.... some are out to lunch entirely.
IMR or H 4895 is standard fare for the m1 and m14 rifle, as practiced early on in the developement stages of this rifle.
Search the net, call brownells, or get a stateside buddy to order from fulton armory and send you..... the 30 cal service rifle shop manual by Jerry Kuhnhaussen, the difinitive work on what's safe and not safe when it comes to reloading for the m14. It has incredibly in depth info on this exact situation experience here in the start of this thread. I'm confident to say that you experienced a reloaded ammunition related or stuck firing pin related out of battery detonation. Will be interesting to read Savage's report on this rifle once he get's a chance to inspect her.
There's a lesson to be learned for everyone here..... READ THE STICKIES >>>> the threads at the toip of this battle rifle forum...... all that FREE info is there to ensure your #### does'nt fall off........