doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Shell Pressure through Inserts

I would think that a 2 3/4" 20 gauge shell would protrude about 3/4" from a Gagemate or Lil Skeeter shortened for a 12 ga 2" chamber. I do not even know if I can shorten Lil Skeeters to fit a Brit 12 ga 2 1/2" chamber and use regular 28 ga shells. Maybe chamfering the end of the adapter might do, not shortening it in a lathe. I'll try it out and let you know.
Mike

Mike,

http://www.gauge-mate.com/index.htm

It discusses a chamfer on the front of their tubes to fit short chambers.

Gauge-Mates are made of SS. I didn't intend to simply cut them off at 2" but turn them down to fit inside the bore. They would still measure the full original length. I would make casts of the chambers first so as to get an exact profile and make the Gauge-Mate to fit.
Nial

I'll bet the guy at guage-mates will make you a set.

I think I'll get a pair of the Gold 12 to 28, I like the idea of leaving them in the gun. And these and Lil Skeeters and the others work!.
I put my pair of 12 to 28 in my Perazzi Mirage skeet gun and handed it to an International Skeet shooter buddy of mine, who was very skeptical, and a far better shot than I, he broke 5 pairs of doubles at station 4. No one could believe how these stubby little things worked, as well as a full lenght tube, but with no added weight.
Mike

Per the original question, the pressure in the insert would be just like in a typical chamber for the gage shell. Peak pressure occurs typically while the payload is in the forcing cone or just clearing the cone (depends on cone length and powder burn rate). As the payload clears the adaptor, it will see the barrel as an expansion. Assuming the wad obtrudes sufficiently to seal all gas, the pressure as the wad clears the adaptor will be "typical" for the shell in a normal chamber. As the wad travels further into the barrel, the volume behind the wad will increase faster than typical and the pressure will drop faster than normal. The pressure drop will be off-set by the increased area of the obtruded wad's base. The force accelerating the payload will be about the same as normal. Therefore, velocity will be about normal.

The kicker here will be the first inch or so of barrel travel. A high pressure shell will still have fairly high pressure at this point. It would be necessary to calculate barrel stress at this point to say for sure as to safety. Note also that firing high pressure shells in an older gun can give too much back thrust on the breech face (compare peak pressure times shell area for the gun's chambering and for the proposed sub-gage shell. Post back if this is not clear or anyone wantws to discuss further.

So if I'm understanding comments which seem to be pretty consistant, shooting a low pressure shell through a subgauge insert does not significantly change the pressure? My intent was to be sure that when shooting a low pressure subgauge with an insert that the insert was not increasing the pressure.

Thanks.

garywms,
shooting any shell in a gauge reducing adapter will not increase pressure. If anything, it likely reduces the peak pressure or doesn't change peak pressure. But the relavent thing is the stresses that the gun barrel sees. A 410 shell, producing 11000 psi, fired in a 12/410 chamber adapter, will not exert anywhere near the stresses that a 12g/11000 psi shell will. As the diameter/gauge increases of the shell being fired in a chamber adapter, the difference in stress from a shell fired in the adapter will be closer to a full sized shell of the same pressure.

Rocketman: Check your PMs.