October 2004

Small-Gauge Inserts: Briley, Seminole Products Save Money

We try out Briley Manufacturing’s Side Kick Chamber Inserts and Seminole Gun Works Chamber Mates to see if sub-gauge inserts can make 12 gauges more versatile.

The option of being able to shoot two, three or even four gauges of shotgun shells in the same firearm is being considered by a growing number of budget-minded bird and clay target shooters. We tested two insert packages in a 12-gauge over/under. At left are the Briley inserts, which included tools for inserting and removing the devices. At the top of the Briley box is a three-piece screw-together rod used to knock out installed inserts. The mallet is used to install the inserts. In the Seminole box, there are three sets of inserts, a container of lubricant, and an insert puller. Separately, the manufacturer provided extra 0-rings, which kept the inserts in place.

Mixing two gauges of shells in the same shooting pouch is a recipe for disaster in most bird hunting or target busting situations. As any safety conscious shooter is aware, a 20-gauge shell dropped into the chamber of a 12-gauge shotgun will lodge just far enough down the barrel to allow the loading of a 12-gauge shell. Serious damage and possible injury can result if the 12-gauge shell is fired with the 20-gauge shell stuck in the barrel.

However, there is a safe way to fire small-gauge ammunition in 12-gauge shotguns, courtesy of smaller-gauge inserts that fit in the chambers of most break-open firearms.

The inserts reduce the size of the chamber to fit the smaller-gauge shells, allowing the shooter to safely fire 20, 28 and .410 ammunition through 12-gauge barrels without any appreciable change in the weight or balance of the firearm.

Full-length tube sets, which perform the same function and extend the length of the shotgun barrel, do add to the weight of the firearm and have been put into play by skeet shooters for many years. Since they are often required to shoot all four gauges at targets, skeet competitors have relied on tube sets and inserts to avoid the option of purchasing four shotguns to pursue their pastime.

Shooting smaller gauge shotguns is also becoming more popular with bird hunters, who are seeking the fine handling ability of a 12-gauge firearm without the recoil of the 12-gauge ammunition. Taming the old thunder-buster with 20, 28 or even .410 loads is quite a promising prospect for both veterans and beginners alike.

The price tag for full-length tubes can be about double the cost of the inserts, and if a shooter is looking at the option of a new set of barrels for his favorite smoke pole, he can expect an even heavier dent in his shooting budget.

Two manufacturers stepping up to the plate to offer economical sub-gauge options for 12-gauge shooters are Briley Manufacturing, with its Side Kick Chamber Inserts, and Seminole Gunworks, which carries a line called Chamber Mates.

Neither of the inserts add any ap­preciable weight to the firearm being reduced to a sub-gauge shotgun, and both allow normal function in shooting situations. Unlike full-length tubes that extend throughout the barrel, the inserts keep all their added weight on the gun, between the shooter’s hands, with very little impact on balance.

Because of manufacturer recommendations, which involve potential ejection problems with some ammunition, our main test loads were limited to Winchester AA shells in the sub-gauge testing.

The shells used were Winchester AA Super Sport Sporting Clays 20 gauge 2.75-inch shells with 7/8 ounce of No. 7 1/2 shot with a muzzle velocity of 1,275 fps; Winchester AA Super Sport Sporting Clays 28 gauge 2.75-inch shells with 3/4 ounce of No. 7.5 shot with a muzzle velocity of 1,300 fps; and Winchester AA Super Sport Sporting Clays .410 gauge 2.5-inch shells with 1/2 ounce of No. 8 shot with a muzzle velocity of 1,300 fps.

We also shot several 20 gauge B&P Trap-Skeet 2.75-inch, 28-gram shells with 1 ounce of No. 7 1/2 shot and Federal Field and Target 2.75-inch, 2.5 dram shells with 7/8 ounce of shot, but as stated in the manufacturers’ recommendations, these rounds had a tendency to swell and jammed in the inserts. A cleaning rod inserted down the muzzle was the only way to eject the fired shells — not the best way to maintain a good shooting rhythm on the clay target field.

Our test firearms were a Beretta 686 Onyx Pro Series X-Tra Wood Over and Under 12 gauge with 28-inch barrels and a Perazzi MS80 SCO3 Over and Under 12 gauge with 27 5/8-inch barrels. Screw-in chokes for both shotguns were Improved Cylinder in the top barrel and Light Modified in the bottom.

Here’s our test report:


Briley Side Kick Chamber Inserts, $239 and up

Made by Briley Manufacturing, 1230 Lumpkin, Houston, TX 77043, (713) 932-6995, these items begin at $239 per two-barrel, one-gauge set and run up to $289 per two-barrel one-gauge set. If you want all three gauges (six total inserts), that will set you back $600.

Included with the inserts was a plastic mallet necessary to pound the tubes into the chambers and a three-piece metal rod needed to eject them from the firearm.

The Briley inserts, unlike the Seminole versions, required a good bit of hammering with the mallet, but also provided a very tight fit and seal. Unlike the Seminole inserts, there was not a single situation when the Briley inserts backed out of a chamber during firing situations. In fact, a good bit of elbow grease was necessary to push the inserts out of the chamber.

Color-coded (green for 20, blue for 28 and red for .410), the inserts were also a little longer and heavier than their Seminole counterparts. The weight of the pair of 20-gauge tubes, which were 5.25 inches long, was 6 ounces; the pair of 28-gauge tubes, which were 4.25 inches long, weighed 7 ounces; and the 11.5-inch-long .410 tubes weighed 9 ounces.

We found no difference in the balance or handling ability of the firearms after the inserts were put in place. Target breaks at various ranges were acceptable, including most shots attempted with the .410.

Patterning tests provided expected results. Both the 20 and 28 gauge inserts produced solid patterns with both Improved Cylinder and Light Modified chokes, mirroring the 50-50 performance of the 12-gauge loads used as a standard. The number of 3-inch holes in the patterns (capable of allowing a clay target to escape unscathed) was an average of seven, also very close to the 1-ounce loads used in the 12-gauge.

However, there were thirteen 3-inch holes in the 30-inch patterns of both the improved cylinder and modified chokes with the .410 inserts. This could explain the difficulty in our testers attempting to break targets beyond 35 yards with the .410.

The only function problems occurred when one of the testers attempted to fire different ammunition, other than the recommended brands, in the test firearms. On several occasions, both B&P and Federal ammunition would jam in the inserts, and the fired shells had to be removed with a rod inserted in the muzzle of the shotgun. The problem appears to be with the composition of the shells. As both the insert manufacturers point out, shells with two-piece wads, paper base wads or thin brass, aluminum or steel heads have a tendency to swell and stick in the inserts. This is a minor drawback, but should be one to take into consideration when putting the inserts into service.

Shooters should also be prepared for some extra duty at the gun cleaning table after putting the inserts through their paces. Both types of inserts became very dirty and caused quite a bit of fouling in the receivers of the shotguns.

Seminole Gunworks Chamber Mates, $240 and up

Seminole Gunworks of 3049 U.S. Highway 1, Mims, FL 32754, (866) 410-2820, offers its Chamber Mates for $240 to $290 per gauge set, or $650 for three gauges. Since 2001, the Seminole inserts have been used to win an impressive number of high-overall sub-gauge events at major competitions across the country. The list is available on the company’s web site and includes the names of many topnotch shotgun swingers.


Our group was impressed by the ease in which the inserts could be put into the chambers and removed — a big plus on the clay target field. The weight of the inserts was also a pleasant surprise, with the pair of 20-gauge tubes, which are 3 inches long, tipping the scales at only 3 ounces. The 28-gauge inserts, which are 2.75 inches long, weighed 5 ounces; and the .410 inserts, which were 9 inches long, were 10 ounces. None of the inserts altered the balance or handling ability of the test firearms.

While our test group found the Seminole inserts were easy to install — no hammering was required as with the Briley inserts — there were a number of situations where the inserts backed out of the chambers or failed to eject shells. An extra supply of rubber O-rings was included in the package, and they were needed. After only about 10 shots with the 20 gauge insert, one ring broke and the insert became loose in the chamber of the shotgun. Reinstalling a new ring was easy, although this step would have been a little more difficult if a member of our group had not taken the precaution of carrying the package of extra rings in his pocket.

A tube of Super Lube is included with the set, and the instruction manual recommends that the O-rings be greased before the insert is placed in the chamber. Aligning the ejector on the insert with the ejector on the firearm was a simple matter, and the tubes were easily pushed flush with the edge of the chamber.

Removal of the inserts was another simple matter, using the brass tool designed to hook the front end of the insert to allow it to be pulled out of the chamber. The 20 and 28 gauge inserts were no problem, but because of its additional length, the .410 tubes were a little more difficult to hook and pull out.

Concerning patterning performance, both the inserts for the 20 and 28 gauge shells provided nearly identical results. Both the Improved Cylinder and Light Modified chokes provided solid patterns at 30 yards, with the same 50-50 spread as the 12 gauge. As with the Briley inserts, there was an average of seven 3-inch holes in the patterns for both the 20 and 28 gauge Seminole tubes.

Results with the .410 were more disappointing. The number of 3-inch holes was 17 with the Light Modified choke and 20 with the Improved Cylinder. Different ammunition may have produced different results, but this number of target-escape points could mean fewer broken targets and lighter game bags, in our view.

This patterning performance was repeated on the clay target course. No difference could be determined in target breaks at various ranges between the 20 and 28 gauge inserts. However, the performance of the .410 remained disappointing. Naturally, with a reduced number of shot in the .410 shells, the results were not totally unexpected.

Our test group found that while close targets were handled with no problems, any shot beyond 35 yards resulted in inconsistent results. Some targets were only chipped or broke in half at the longer ranges. It should be noted that most of the holes in the Seminole’s .410 pattern were on the fringe of the 30-inch circle, so some of the misses could be attributed to shooter error.

Gun Tests Recommends
• Briley Manufacturing Side Kick Chamber Inserts, $239 per pair in 20 and 28 gauge; $279 per pair in .410; or $600 for a three-set package. Our Pick. Although the performance of both brands of inserts was nearly identical, the snug fit of the inserts in the chambers, the color coding and the price difference for the three-gauge set gave Briley the advantage in a head-to-head match up.

• Seminole Gunworks Chamber Mates, $240 per pair in 20 and 28 gauge; $290 in .410; or $650 for the three-set package. Buy It. The target breaking ability and patterning performance of the 20 and 28 gauge inserts were very acceptable, but two blown O-rings and some ejection problems caused concerns with our test group. The .410 inserts would be good for skeet targets, but shooters should experiment with different loads and tighter chokes to find acceptable longer-range ammunition.