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

The most informative test I can imagine is a series of high speed photography shots of the various gauges being shot with adapters. A 12 gauge barrel , 16, 20, 28 and 410 chamber adapters, and a supply of shells should be all that is needed to photograph the exit shot stringsand answer this question. If anyone knows on of the people who post these types of tests on the internet, they should contact them and propose a series of tests.

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.

Afaic, the only good reason for chamber inserts to reduce the gauge is for competition. It allows one to use the same gun for different gauge events. I've always felt like this made little sense because you're essentially shooting a 12 ga. gun, though with a reduced payload. The NSCA allows it to keep the numbers up.
JR

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.

The fact is that there has been quite a number of tests reported on this issue, and I don't remember any that showed a significant reduction in performance. The only assumption I can make is that they work well through some mechanism. I suspect that petal expansion is the answer, as I don't think the shotcups would expand to this amount. A telling test would to be test shotcup wads vs felt/fiber wads and check the pressure. I am guessing that fiber wad loads will perform much worse than the shotcups.

Also, look at some of the work being done recently with wadless shells (using only buffer products either below the shot or mixed into it). This is work by a reputable person in the industry and would seem to show that the whole wad issue is way over stated.

Also, I think inserts could have a lot of use in old doubes. When wads and hulls (say 10 gauge) are not available, they make shooting a gun possible. I think the biggest market being missed is the short shell vintage market. If the inserts stepped down from 2-1/2" chambers to 2-3/4" reduced gauge hulls, there would be a much large market.

AGS, thank you for disputing all of the naysayers by indicating where chamber inserts would be useful. They just "Don't get out much". I have a pile of chamber inserts that are useful in many situations. If you are interested, I will give you more than a dozen examples.

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.

Outstanding report and information, Steve. Thank you!
JR

My thanks to you too, Steve, for that excellent report.

SRH