doublegunshop.com - home Forums Thread Like Summary - 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 first project at GaugeMate was velocity testing, for which I used an Oehler 35P chronograph.
The results were vexing as I expected a velocity decrease but recorded a modest velocity increase.
My advice to the boss was to have independent testing done as it might be difficult for some to
accept our data. At that time the Sherman Bell/Tom Armbrust series was running in the Double
Gun Journal. That combo seemed a logical choice, so adapters and AA/STS ammo was dispatched. His
results, which we posted on the web, mirrored our results. Chamber pressure couldn't be measured
because the adapters constituted a chamber within a chamber. As the adapters were used by more clients,
some of them reported their testing results.

Two of those reports were very memorable -
The first was a fellow in the Upper Mid-West who was a 10-g 'buff.' He cast his own shot and alloyed the lead
he used. If that wasn't enough, he also counted pellets. We gave him as set of 10 to 20-g inserts for testing.
He reported velocity of the 20-g through a 10-g barrel to match 20-g through a 20-g barrel. He also opined
that patterning was improved - nice, but purely subjective. That is the segue to the second example.
A client with a 16-g Drilling wanted to have a lesser recoiling option. We sent him a set of 16 to 28-g adaptors.
Initially, he had a problem - they were too long for his chambers - that were allegedly 65mm. I told him that
some chambers were short and that he should have a gunsmith check it. Sure enough, his chambers were 63.5mm.
Chambers lengthened, he began his testing. He reported, among other things, that patterning was better than
16-g through his 16-g barrel. Nice, but how did he know. The answer was that he had a computer program that
allowed him to shoot at a large piece of white paper, photograph it and then have the image analyzed by the
program. He provided us with some excellent images and plenty of data. Obviously, he was not your average
shotgun shooter. What he was - was the retired president of a major American firearm manufacturer.

In either 2004 or 2005, I had some business that took me to the Federal plant in Minnesota. I was able to spend
time with the gentleman in-charge of shot shell production. He had never seen a chamber adapter before
and I explained the seeming velocity anomaly. He wasn't surprised. This is the 'Reader's Digest' version of his
explanation. Maximum pressure occurs 1" from the breech face. Adapters are 2 3/4" long, so the ejecta is
getting a full push for that length. Once the ejecta enters the bore, there is gas leakage but the trade-off is
less contact with the bore by the plastic wad. Anyone who has cleaned a shotgun barrel can see the plastic
residue. The wad acts like driving with your parking brake on.

Some thoughts on less traditional uses -
* If you have a 14-g gun, where do you purchase ammo? Fourteen to 28-g adapters were the answer.
* A well known shotgun writer had a 24-g Ferlib. We made him .410 adapters
* A group of 8-g Parker shooters had us make 12-g adapters so they could shoot skeet.

PS - Our adapters were designed to allow use of 2 3/4" cartridges in 2 1/2" chambers.

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.

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

I have had no issues at all shooting 10 gauge to 12 gauge Gauge Mate Silvers at Skeet and sporting using my 12 Gauge low pressure 7/8 oz vintager hand loads. They smoke even handicap trap targets if I do my job. The Gauge Mate Silver is just a chamber sleeve so 3 inches long maybe....
It makes life much easier and cheaper than loading 10 gauge target loads

[quote=Lawrence Kotchek]I have had no issues at all shooting 10 gauge to 12 gauge Gauge Mate Silvers at Skeet and sporting using my 12 Gauge low pressure 7/8 oz vintager hand loads. They smoke even handicap trap targets if I do my job. The Gauge Mate Silver is just a chamber sleeve so 3 inches long maybe....
I/quote]


Well yeah. A "2" gauge difference is nothing. With a .410 in a 12 ga., you're talking a "55" ga. difference (67 vs 12).
JR

Stan, I understand your thoughts, I think. I think the shot is mostly contained in the wad. It must expand to mostly fit the bore and that has to have some pellets in direct contact with the bore. Most likely the shot becomes a shorter shot string in the bore, trading length for larger diameter. Perhaps the choke does have some influence on patterns even in this case. I just have not seen any major difference in how tight the carrier barrel chokes are and pattern performance. As a rule I never pattern a .410 with what I expect to have weak patterns. Plays too many games with my confidence when you see all those holes on paper with gaps here and there.

But there is no doubt that short tubes like Browning Super Tubes and even sidekicks like Briley makes can have serviceable patterns at reasonable ranges. I have not had as good luck with a straight chamber length adapters but they did work at shorter ranges. Breaks on station 4 were weak. Use a set on a good Sporting Clays range and you will quickly find that they are range limited. I have found anything past Skeet ranges just run out of dense enough patterns to be worthwhile and I would never use them on live game. A half ounce or even near 3/4 ounce shot is a very small payload for longer distance use.

Stan, my friend, it isn't NSCA, but in the first year of the Southern Side by Side, I won the .410 overall event with a little 20 gauge Parker equipped with Briley tubes. I think this is my biggest sporting clays win since I placed third overall in the Maryland State sporting clays shoot. I think in those days it was USSCA. I was younger then. Tubed guns were outlawed shortly after my .410 win at the Southern.

It was a beautiful morning out at Ben Avery shooting with Borderbill; who is claiming some sort of disability from a fall, but it was certainly not apparent by his shooting!

So I collected a bunch of spent wads, all from different makers, and measured the diameter of the base/cup. The depth of the cup varied from 2/16s to 3/16s and the wall of the cup would need to expand to seal a larger than gauge bore. Despite lying in the Arizona sun for an unknown period, the cups were impressively flexible.

12g - .702", .710", .719", .729" & .735"
20g - .600", .603" & .623"
28g - .550" & .588"
.410 - .405" & .408" with a much shallower cup

IMHO the cup of the 28g and 20g could expand adequately to seal a 12g .729" bore; not much chance that a .410 wad could.

I don't suppose there is any way to actually know what's happening in the bore with these under gauge wads unless someone was to build a clear barrel that would withstand the pressures, and use the high speed photography. That would be a "labor of love", though. I can see no financial incentives for going to that expense and trouble, especially given the limited usage/need of these inserts in the first place. They're no more than a curiosity to me. I just have a wondering mind.

Outstanding report and information, Steve. Thank you!
JR

I have never owned or used sub-gauge inserts, and feel they are mostly an unnecessary gimmick. If you look at the plastic shotgun wads available, you will see there is a bewildering number of styles. I just don't see how anyone could declare that all of them would effectively obturate and seal the bore without extensively testing all of them.

Some are little more than cups that contain the shot, while others have the more common flared section that we hope would flare out under pressure to contain the powder gasses and seal the bore. But among those wads with the flared section, there is also quite a bit of variation, and it can be seen that some would do a better job than others. And I don't think any at all would do well when going to extremes like shooting a .410 payload down a 12 gauge bore. I just have too much experience with pneumatics and hydraulics to think that a piston seal that is much too small for a bore is going to be perfectly and consistently effective at containing pressure without leakage or blow-by. Then, even if the front section containing the shot spreads out to fill the bore, there will be spots between the petals where the shot can lead the bore, and also become out of round due to friction against the bore. I'm sure the choke would pattern differently with this much shorter shot column too. Another consideration is the age of the wads. It is said that the plastic used in wads becomes much less flexible as it ages, and that this affects ballistics even in the proper size bore.

From what I've seen of those high speed images of shotgun muzzles at the moment of firing, I really don't think that would give us a lot of answers either. Here's a link to a site with a bunch of these images. It can be seen that some wads do show much more flaring out from the powder gasses than others. But you would also need to measure the effect upon velocity by firing several rounds of each shell and wad type using both a sub-gauge insert, and the correct size gun. Then you'd have to do extensive pattern board analysis with all available wads as well:

http://kuulapaa.com/home/highspeed/Misc.html



Anecdotal statements such as "hits seemed weak" or "they seemed to work well" don't tell us much at all. I just don't have any need for sub gauge inserts. If I want to shoot a 12 gauge, I grab a choice of several 12 gauge guns and the correct shells. Same for shooting 10, 16, 20 ga. and .410. It would be kind of dumb for me to shoot 20 ga. or .410 shells in a heavier 12 gauge gun when I have perfectly good smaller gauge guns sitting in the safe.

I suppose that substantially built sub-gauge inserts might permit safe shooting of smaller shells in guns that have pitted bores or chambers. They might come in handy for some almost unimaginable SHTF or survival situation where one had a 12 gauge gun, and only had smaller gauge ammo. Other than that, I suppose they could be a tool for those poor guys who are in such fear of their wives that they are afraid to just buy more than one shotgun. In that event, you might as well just castrate yourself.