I have a lot of respect for them M-77's

[Delmonico]

My nephew has/had a Mark 2 M-77 in 308.  My brother called last evening and told me Dan had blew up his rifle and they were headed to the hospital.  We later met at mom's and Dan was ok, some metal in his thumb and some nasty zits on his face but not in his eyes thanks to glasses.  Anyway he'd bought some rounds a couple years ago at a gun show, 110 gr FMJRN.  That is what took it apart.  Anyway we got the bolt open, I have the mother of all flattened primers and the case head is in pieces. 

I took the other 7 rounds he had left, not counting the ones in the yard at the farm that blew out of the mag.

Found a full case of what appears to be 748 in 4 of them, 53 grs.  Right at max.  But the other 3 had about a 1/3 real fine ball powder mixed in. looks like AA2 or similar.  Gonna have the rifle checked out, I think it can be fixed witha few parts like extractor, collar, mag well, and floor plate,  A chambering reamer should remove the case, he wanted a synthetic stock any way.

I am nothing less than impressed as to how the gun vented the gas and everything considered, it could have been a lot worse.

[Mustang Gregg]

Glad he's okay. 
Good thing he had a M-77 & not a rifle of weaker design.  Then he may have not been so lucky. 
Rifles can be repaired & replaced!

MG

[Mustang Gregg]

Delmonico:

'Nother M-77 anecdote---
A Pard brought me an M-77 in .243 Win that was in similar sized pieces as the one you attached above.
This one was a known "wrong-powder-oops" SNAFU.  He loaded his favorite bullets with H-110 to the same weight as what shoulda been Win 760.  Wrong can on the 'loadin' bench can getcha. 
He came outta the rifle explosion pretty well, too. 

GLAD THEM RUGERS ARE SO TOUGH!!!!!

MG

[Delmonico]

Check, double check and check again.     Used to work part time A G&B  Center when he needed me, there are some dumb folks out there with loading equipment.  Mistakes can happen, but some folks are just plain dumb.

I would say this was a pour the powder back out of the measure into the wrong can BS.  One can of powder on the bench at a time and have all of it back in the can before it's put away.