There have been, over the years, a variety of inventions and refinements that have come down the pike to make our shotguns more versatile. Depending on the maker, these include niceties such as screw-in chokes to change the pattern, adjustable stock fit, chambers that will handle anything from 2 3/4" to 3 1/2" loads, and pads and stock gadgets to lessen recoil. And now a variety of chamber inserts that can change the actual gauge of your break-action shotgun by reducing the size of the chamber so that, depending on the type you buy, you can get a 12-gauge to handle .410 shells if you want.
Several companies are making them, and without exception, there have been good reports on the size and shape of the patterns they throw as well as reports that penetration on the target has not been compromised, at least not so anyone would notice, least of all the bird or the clay target.
Why would anyone want to reduce the gauge of a gun? There are a few reasons. First, if you are recoil-conscious or just want to save yourself some pummeling if you are going to be shooting a lot, like at clays or maybe in a hot dove field, a smaller shell In a bigger gun is going to kick less; it makes it great for kids and small shooters who are just learning and don't need the enthusiasm walloped out of them. Maybe you are hunting fragile birds in close cover, such as woodcock in the alders, and you don't want to risk ruining a centered bird with a 12-gauge load and want to use a 28-gauge shell. Maybe you've got an old classic Parker or Fox or some between-the-wars British gun you just feel doesn't need to take a pounding with modem shells of the guns gauge and you want something a little milder, say, a one-gauge reduction. Finally, maybe you shoot an odd gauge gun like a 16, the definition of odd being "the shells can be hard to get" and you'd like to do your practicing and maybe some of your hunting if you need to with cheaper and easier-to-get loads, like 20-gauge. That's the major reason I latched on to these reducers. When I travel to hunt with one of my 16s, I can't always take the number of shells I'd like to and have to depend on local supplies, which are sometimes non-existent. So I can pack a pair of 20-gauge reducers, and if and when I run out of the shells I did bring, I just start using those.
But there's been a couple problems with them, namely cost and ease of use, in that the easy-to-use ones are expensive, and the cheap ones are hard to use. I'll explain. There are several companies that make reducers that are simple chamber-length sleeves that slide in like a shell, then you load the shell into them, fire it, remove the sleeve, remove the shell from the sleeve, and start all over again. These are the cheap ones, anywhere from $40 to $50 a pair, and you can reduce practically any gauge to any smaller one. Then there are those that stay in the gun and the shell is removed and the gun reloaded in the usual manner; the ejectors and extractors work just like they normally would. Some of these are chamber-length, some are longer, and some, like Briley has made for years for competitive skeet shooters, are full-barrel length. All of this sort that stay in the gun are more expensive but, of course, easier to use. And some of the sets are not "complete" - by that, I mean you can't downsize to all lower gauges. For example, Briley's Sidekick Chamber Inserts (these stay in the gun and are not the full-length tubes mentioned earlier) start with 12-gauge and reduce 12-20, 12-28, and 12-.410, but not 16-something smaller or 20-something smaller. These sets cost $249, with the 12-.410 running $279. Of course, these are pretty much intended for the fellow who shoots skeet's four gauge classes. Browning's Little Skeeter Gauge Reducers will take any gauge to everything smaller, even 28-.410, but they don't stay in the gun. They are $50 a set. And Chamber Mates™ sets, at $239.99 are nifty stay-in-the-gun sets with a great reputation, but for me, they don't offer a 16-20, only 16-28 and 16-.410. These are $239.99, $289.99 in any .410 model. Now, all of these work, all of them have great reputations and followings, and all of them do exactly what they say they do. There's no question that they are all of the highest quality.
The ones I've found to be the best for my use, traveling with an odd-gauge gun, ease of use, and price all being factors, is the new GaugeMate Gold series. These stay in the gun (the company makes an inexpensive take out and reload GaugeMate Silver series as well, the first product they offered), they are priced lower than some of the others, and they fit all gauges from 28-gauge up to 10-gauge, which we'll ignore for our purposes here to reduce the confusion factor. The sets that reduce by one gauge, from 12-16 or 20-28, for example, are split down the side. This split acts like a spring to keep the insert tight enough in the chamber that it won't come charging out when the ejector functions, For a two-gauge reduction, like from 12-20 or 16-28, the inserts stay in the gun using O rings that make for a tight, slip-free fit - a small container of lubricant is provided in case the fits a little too tight with either the one or two gauge reducers, Since not all chambers for a given gauge are the same exact size in every gun, it takes a couple minutes of fine-tuning to get the inserts to fit, function, and stay in the gun. But that's a one-time deal, I found, when I tried the GaugeMate Golds out. Besides the reducers, the set contains a tool that extracts the inserts, the lubricant, a chamber brush, and a set of pretty nice snap caps you use to get the inserts regulated and working right without using live ammunition - smart. All this stuff comes in a small zip pouch that can be easily tossed into a gun case or duffel when you pack for a trip.
Cost? For 10-12, 12-16, 16-20, 20-28, it's $129,99, For 10-12XL (for 3 1/2" 12-gauge loads), 10-16, 10-20, 12-20, 12- 28, and 16-28, it's $136.99. For 12, 16, 20, or 28 down to .410, it's $149.99. All of these, if you order off the website (www.gaugemate.com), also have $6 s&h tacked on.