Bushing firing pin hole with aftermarket firing pin?

[calvados.boulard]

Hi everyone,

This may be a dumb question, but I have an aftermarket firing pin for my Rem 700 build coming. Looking at the services that my gunsmith offers, one of them listed is "bushing firing pin holes". Since I won't be using the factory firing pin, does bushing the firing pin hole provide any advantage?

Thanks everyone,
Cal.

 

[Leeper]

If your after market pin is the same diameter as the factory pin, bushing will accomplish nothing unless the hole is oversized. If the hole is oversized, bushing will correct this. The whole purpose of bushing the bolt, in most cases, is to enable one to reduce the firing pin tip diameter and eliminate primer cratering. So, if you want to have the bolt bushed, your aftermarket on will have to be altered at the same time to see any benefit.

 

[calvados.boulard]

Thanks Leeper. How much clearance should I have between the pin and the wall of the hole? i.e. How can I determine if my hole is oversized?

Thanks again Leeper,
Cal.

 

[Leeper]

Typically, there will be a difference in diameter of between .002 and .004" between the pin and hole. The clearance is not of great concern but the hole size is. If the hole is too large, there is just too much of the primer which is unsupported. The post-64 Winchester Model 70's were an example of an action which had a firing pin tip and hole which were just too large. This was especially problematic when the rifle was chambered for a cartridge using small rifle primers. Blanking of the primer cup is common with this combination. Again, the problem was not clearance around the hole but just the sheer size of the hole and pin.
The Remington 700 pin is smaller in diameter but it is still a bit large and the 700 often has holes which are oversized or bevelled.
There are other influencing factors as well. The firing pin tip shape, the weight of the striker, the firing pin protrusion, the strength of the spring, and, of course, the strength of the primer cup, are all factors which affect how the action handles pressure. I have bushed a lot of bolts and turned the pin diameter to 1/16" to eliminate cratering or blanking but this is only necessary if one is loading hot (as we sometimes do). There is a downside to a smaller pin. The small pin must strike more precisely to ensure positive ignition. Not usually a real issue, this is still a factor for a rough-use field rifle where reliability is even more important.