30-30 on an SB1 - This time, with math!

[jkpq45]

Hello All,

Bear with me as I throw numbers in your general direction.

The SB1, with a 3", 12Ga barrel running at a SAAMI MAP of 11500 PSI and base diameter of ~0.809", produces 5911 lb (force) breech thrust.

A 30-30 WCF cartridge, running at SAAMI MAP of 42000 PSI and base diameter of ~0.4215", produces 5860 lb (force) breech thrust.

I think I've already answered my question; is it safe to put a 30-30 WCF barrel on an SB1 AND use factory SAAMI-spec ammunition at 42000 psi?

Thanks for your advice,
jkpq45

[jkpq45]

I just realized:

H&R will fit 3-1/2" 12 ga barrels on SB1s, which run at 14000 PSI SAAMI MAP.  That produces breech thrust numbers around 7037 lb force.

I think I'm in the clear, no?

[quickdtoo]

Yes, ALL vintage H&R Inc 30-30 rifles were on cast iron frames similar to the SB1, I had a my first 30-30 barrel on an SB1 TDC frame for a while, it worked fine. H&R won't fit em tho.

Tim

[gcrank1]

If you do it you may have issues with the large dia. shotgun firing pin. If you did and were back down the handload some it may be OK, though not a full load by modern standards. Keep in mind that the original 30-30 loading was something like a 165gr. bullet at about 1950fps and was considered quite a 'smallbore express sporting cartridge'.

[quickdtoo]

Primer problems shouldn't be an issue at 30-30 pressures with large rifle primers, not like with pistol and small rifle primers which have thinner cups, large rifle primers are .027".

Tim

[jpshaw]

Ditto on what Tim said.  I've never had a problem with my .30-30 on an SB1 frame even though it stays on an SB2 frame now.  My .357 pumped up a little bit with H110, now that was a bear to open.  That primer will flow back in there.

[jkpq45]

Agreed, all; I did the math for .223 and a number of other smaller cartridges.  All of those had NO PROBLEM with breech thrust numbers on the SB1 frame; the real bear was that you would DEFINITELY pierce the small rifle primer with the giant shotgun firing pin and/or experience flow into the big shotgun firing pin hole.  Bad news, certainly.

DO NOT TRY THESE AT HOME... or anywhere else for that matter.

[gcrank1]

After having some vintage rifles with their old firing pins and holes I know primer flow can be an issue even with 'low pressure' cartridges. I never minded trying different brand primers to mitigate the effect then backing off a tad if needed; they still performed fine for my needs (I have never needed full/max velo loads, I guess).
Hope you have no issues, I would try it and find out too.