Bolt Head Types
(Small Hole/Large Hole)
Starting with rifles chambered in belted magnum calibers, Savage changed the design of the bolt heads and bolt head pin to strengthen the pin. The pin was less than 3/8ths and with a greater than 1/8 clearance for the firing pin there isn't much "meat" in the pin if a case gets stuck in the chamber.
The later Savages used a slimmer firing pin (main shaft is only 3/32) and reduced the passage in the bolt head and bolt head pin to match. As a result you have to either get a bolt head that matches the parts you have - or get new parts to match your new bolt head.
To determine if you have the later "small hole" or earlier "large hole" parts just pull your firing pin assemby. As shown below where the bottom firing pin is the newer type, if the shaft is 1/8 (actually around 9/64ths) you have the earlier "large hole" parts. The later small hole parts include the 3/32nd inch firing pin.
It was reported on Benchrest.com that it is possible to enlarge the firing pin hole in the bolt head to get a thin firing pin bolt head to work with a large firing pin. The hole has to be drilled out down to the vent hole. Also, on the small hole bolts there is an internal stamped "tit" that may have to be ground down on the end of the bolt body. After examining the .223 bolt head above that was installed on a magnum "thin pin" bolt it was found that it was in fact a large hole bolthead. This shows that a large hole bolthead can be used with the thin firing pin, at least for .223.
Some additional firing pin info courtesy of SavageShooters.com is as follows:
There are NOW 4 different F/P lenghts
2 for the long action
2 for the short action
long OLD F/P firing pin shaft .145 with tip 0.068 with 16 Threads on back
New Long shaft in .140 with tip .065 with 11 threads on back
Old parts number P110-77Y
New Part number 100152
OLD short action was OAL is 4.920 - 4 14/16 and a shaft on.145 with tip of
NEW short action is OAL 4.710 ( 4 11/16) shaft is .145 tip is .080
OLD number 113-77U
NEw number 174018