Small firing pin SB1 frame questions

[Doc Fillem]

I picked up a nice case colored SB1 frame for $35 on Gunbroker. When I got it home I see that it has the small firing pin. I confirmed this by comparing with another H&R shotgun that I have with the large firing pin.
I have an extra 12 gauge barrel that won't fit this frame with out fitting. My question is will the small firing pin work with the shotgun barrel or should I try to find a .357 or .44 barrel for it? What application did the small firing pin SB1 frames have originally?
The frame is an NJ so I guess it's too old to send in and have a .357 or .44 barrel factory fitted, right?

[quickdtoo]

NJ qualifies for 357 and 44 mag barrels(FAQs   ), H&R has made all sorts of size firing pins from ~.060"-~.098", the hole in the breech face is what makes the difference in primer flow, not an issue at shotgun pressures, can be on 357mag and above tho, small pins work fine with shotgun barrels. 

Tim

[jpshaw]

What Tim said.  I've had no problems using my 28 inch 12 gauge barrel on my SB2 frame with the small firing pin.  Works fine.

[murphdog]

+2 reinforcing what Tim said.  I've shot 28 ga and 20 ga barrels on my SB2 with small firing pin, and never had a problem. 

[yipper]

"the hole in the breech face is what makes the difference in primer flow, not an issue at shotgun pressures"
 
Did H&R make multiple hole sizes along with multiple firing pin sizes?
 
At what diameter does this become an issue?
 
Thanks,
 
geoff

[quickdtoo]

That's very possible since they've made pins is such varying sizes, those with a larger hole and pin that doesn't fit the hole close would be more prone to primer flow issues with the pistol cartridges.

Tim

[yipper]

I ask because I recently bought a used 12 ga shotgun (NT receiver) as the basis for a .357 mag rifle.  I got the barrel back from Remington, and it is now at the gunsmith having a front sight fitted.  Reaming to .357 max was an option I considered, but if I could determine beforehand that primer flow would or would not be an issue would make that a simple choice.  So rather than eyeballing it as a large or small firing pin and hole, I was wondering if there was an actual diameter at which such flow began that I could put some calipers to…
 
thanks,
geoff

[quickdtoo]

Using small rifle primers with thicker cups in the Maxi should make it non-issue. 

Tim

http://www.jamescalhoon.com/primers_and_pressure.php