doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Gauge reducing inserts

Another thread got me to thinking about something. With all the worry about fiber wads sealing and keeping the gases behind the payload in the early days, the question arises in my mind again, as it has many times........... are plastic shot cup wads so much better at sealing that we can use ChamberMates, or any other chamber gauge reducing inserts, so that 20, 28, and yes, even .410 shot cups will seal the bore of a 12 ga. gun? Or, are those devices another gimmick foisted upon the shotgun oriented public? Not to be confused with full length tubes ...... ChamberMates, or Briley inserts, do not reduce the bore size, only the chamber and, maybe, the forcing cone.

My answer to your question: Chronograph.

All the data I have seen shows very little reduction in performance (50-75 fps).

Sherman Bell's testing reported to Gauge-Mate in 2006
20g AA Super Sport 7/8 oz. now is listed at 1300 fps. I don't know about 2006
28g AA Target 3/4 oz. is 1200 fps
The reported increased velocity is presumed to be from less friction with the larger bore, and it would appear that the plastic wad effectively sealed the bore 12 to 20 and 12 to 28

In the 12-gauge gun with 20-gauge adapters:

A Winchester 20-gauge A-A Sporting Clays factory load of 7/8 ounces of #7 1/2 lead shot, fired in a Silver adapter, gave a velocity of 1319 ft/second and developed a pressure of 7700 psi. The same 20-gauge load fired in a Gold adapter gave a velocity of 1324 ft/second and developed a pressure of 7800 psi. With all 0-rings removed from the Gold adapter, per your request, the velocity was 1302 ft/second and the pressure was 7900 psi.

In the 12-gauge gun with 28-gauge adapters:

A Winchester 28-gauge A-A factory target load of 3/4 ounces of #8 lead shot, fired in a Silver adapter gave a velocity of 1247 ft/second and developed a pressure of 8300 psi. The same 28-gauge load fired in a Gold adapter gave a velocity of 1285 ft/second and developed a pressure of 8400 psi. With no 0-rings in place on the Gold adapter the velocity was 1255 ft/second and the pressure was 8100 psi.

A different lot of the same Winchester 28-gauge A-A factory target load was fired with Gold adapters. The velocity was 1318 A/second and the pressure was 8200 psi. With 0-rings removed the velocity was 1297 ft/second and the pressure was 7700 psi.

Okay. No contention. But, how does it happen? Explain it.

Ad from 1971. The base cup of the polyethylene wad expands and seals the bore

Stan, you might think a 20 gauge wad could seal a 12 bore but there is zero chance a 28 or /410 wad does. So there must be enough powder burned d within the adapter to get the shot up to speed with slightly more as powder blows by down the barrel. Perhaps the lack of friction between the wad and bore helps.

But I do know that chamber adapters work well. For that matter I have a set of short, mid barrel length, Browning Super tubes which work well enough that I can break mid 90 score with them in my Superposed with full chokes. I also have a set of standard weight Briley tubes which have been cut down to 18” which will break birds just as well as full length tubes.

I do not think choke matters that much in either case as I have used them in both very tight choked guns and open choked guns with about the same results. When I was still a serious Skeet shooter I shot .012 and .014 chokes in my .410 so I know chokes do make a real difference. If I miss a couple birds a round, with chamber adapters or short tubes I do not think chokes or blown patterns are at fault. Sometimes I just miss.

Ads are cool, but how does a .410 wad expand to seal a .729" bore?

Our posts overlapped, Jon.

I don't think it does, Stan. Not enough wad diameter or wad elasticity to do so. I really believe this is one of those things that's unknowable.
JR

There has to be an answer, John. Either it works and we don't know how, or it doesn't and the reports are hype. Which is it? IDK.