doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com A question about barrel pressure

I know a guy who's got a 12 ga SxS gun with Damascus barrels. He's concerned about barrel pressure, so he wants to get sub-gauge inserts & shoot 28 ga. in the gun.

The question is: If he used something like Briley Side Kicks, what would the barrel pressure be, compared to a standard 12 ga. shell? For this discussion, we'll use a 12 ga. 2 3/4" shell, 1 1/8 oz. of shot, velocity 1150-1200 fps, and for the 28 ga a 2 3/4", 3/4 oz. of shot at a similar velocity.

I believe the chamber & Side Kick would be strong enough to fire the rounds, but what happens with the rest of the barrel?

Full length tubes apear to solve all problems, but they also add close to a pound of weight, which is not beneficial.

The peak pressure is always in the chambers, 1 to 1-1/2" from the standing breech. Therefore, the shorty chamber inserts would cover it. It would seem likely that pressure, from the chamber forward, would be less than a 12 ga. shell, fired in the same gun. Smaller gauge shells usually produce more pressure than 12 ga. but I don't think it would be a problem. The best performance would surely be from the full length tubes, IMNTBHO,
in spite of what the shorty makers claim.

If he reloads there are plenty of low pressure low velocity loads in both the Hodgdon site and Alliant site. I use many of these loads in my Damascus barreled guns. You can get loads with 7/8 oz of shot, 1 oz and if you like, even 1 1/8 oz.

I shoot 28 ga. in a modern gun made for today's shells. I used to reload the 28 ga and now still shoot it with factory and some left over reloads. I do believe that the 28 ga. has higher pressures and I don't know what the Side Kicks will do as far as pressure.

If he does not reload, there is a few companies making shells for old guns, and keeping the pressures down, RST is one.

Why go to 28ga in the twelve? He can either reload as JDW suggests (best option in my opinion) or use the chamber inserts for 20ga which will perform better in the 12ga barrel than the 28. The skirt of the 20 wads seem to stretch enough to provide a better seal than does the 28ga. Neither 20 nor 28 gauge in the chamber inserts will be useful beyond skeet ranges in my experience.

He could simply order a flat of shells from RST. Reloading is cheaper.

Pete

I'd buy a MEC 600 and load a low pressure shell. I shoot a 7/8 ounce 1100 fps load, no worries. If you don't want to reload, I'd go with 20 gauge adapters.

You can buy RSTs for what 28s cost. I just can't get excited about 28 gauge when the guns weigh the same and the shells cost twice as much.

I guess I'm cheap.

I have a pet 12g 1 oz load at 1150 fps/6500 psi. I just switch shot size to go from a clay/small bird load to a pheasant load. I've used this in my damascus guns of a couple makes. It's also a full 2 3/4" star crimped load that has no pressure problems in a 2 9/16" chamber.

I have a 1904 Baker Batavia Leader 12ga twist barrels with considerable pitting and multiple small dents.

I've used 'Four Tenners' for years. They add about 10 oz. and about 9" long. When a smaller guage load enters a 12 bore, pressure drops rapidly.
I see the 'Four Tenner's for sale now and then on the gun sites.
They were made by Savage.

Has anyone ever tested the pressure in front of those chamber inserts or shorty tubes? Although smaller bore guns do generate higher pressure, it seems to me that running a 28ga or 20ga load down a 12ga bore would reduce the pressure somewhat because of the increased bore diameter. Comments?

Larry I tend to agree with you. Here is my take on it from a "Layman's" stand point. I have no pressure taking equipment however. "Max" pressure will be reached within the chamber proper itself. In fact the 1" location for the pressure recorder was chosen many years ago to insure it was close enough to the breech to always catch the max.
Assuming then this small gauge insert has internal dimensions proper to the gauge I can see no reason the "Max" pressure would be reduced, however at this point extra metal has been added to the chamber wall.
As the charge moves down the bbl pressure falls due to the expansion of the combustion area. In the case of the inserts as soon as it leaves the insert expansion will be greater than would be the case in a bore normal to the gauge, thus I can see no reason at all that pressure would not fall from that point forward.