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Tom Roster’s March/April Shot Talk column ("Inside Sub-Gauge Inserts") gave us a good feel for the capabilities of each type of insert and its price/benefit tradeoff. However, the GaugeMate people, in California, were in the midst of their own independent testing when Tom's article was written, and now that the results are in, it seems appropriate to summarize them. I was tapped for this because in its go-to-market run-up the company picked my brain, which doesn’t take long, and provided me a couple of pairs of GaugeMate Gold inserts. So much for disclosure.


Once we get past the functional issues of loading and extracting cartridges from GaugeMates which with the proper ammunition is easy and quick, what remains are questions about velocities and patterns. Intuitively, it’s beyond question: Launch a small thing (such as a 28-gauge round) through a big tube (such as a 12-gauge barrel) and the Velocity" title="Velocity" target="_parent">Velocity will drop — just think of all that propellant gas blowing by! And how could we expect decent patterns? Won’t a small shotcup full of ejecta tumble, like a .222 bullet from a .30-06?

GaugeMate hired Sherman Bell — no doubt a naughty boy who blew up stuff when he was a kid but who turned his black arts to good use as an "adult"— to test products. (Bell and Tom Armbrust, dba Ballistic Research, of McHenry, Illinois, have done a tremendous amount of research into internal ballistics, especially in double guns.) Bell fired 20- and 28-gauge ammunition through GaugeMates in a 12-bore gun, and 28-gauge ammo in a 16-gauge gun; all were Winchester AA or Remington STS shells. With strain gauges and an Oehler Model 43 ballistic laboratory, he recorded instrumental velocities four and six feet from the muzzles and combustion pressures just beyond the ends of the chamber inserts (not at the chambers, which are reinforced by the inserts). Bell factored in air temperature and pressure and calibrated with SAAMI (Sporting Arms and Ammunition Manufacturers Institute) reference ammunition. The data came from a string of 10 rounds fired for each test.

The numbers (see table, p.16) show increases of roughly 100 fps for 20s and 28s shot through 12-gauge guns; 28s in 16-bore guns also exceeded nominal manufacturers' velocities, but to a lesser degree. Speculation is that reduced friction between a small payload and a big barrel is the cause — that and, presumably, little or no gas blow-by, as the shot wad expands under heat and pressure to fill the bore. (Bell also tested GaugeMate Silver adapters and found "no ballistic significance" between the two models in performance.)

12-20 GaugeMate Gold (7/8 oz No. 7 1/2 lead)
AA (1,200 fps nominal): 1,324 fps and 7,800 psi averages

12-28 GaugeMate Gold (3/4 oz No. 8 lead)
AA (1,200 fps nominal): 1,285 fps and 8,400 psi averages
AA 2nd lot: 1,318 fps and 8,200 psi averages

16-28 GaugeMate Gold (3/4 oz No. 8 lead)
STS (1,200 fps nominal): 1,215 fps and 5,100 psi averages
AA: 1,252 fps and 5,800 psi averages

And patterning? A series of shots at 30-yard targets fired with the same ammunition and adapters in a variety of guns showed no degradation of patterns whatsoever.

All of which helps explain why I had such a fine time shooting driven pheasants last fall with 28-gauge cartridges in a 12-bore gun. And why I'm really looking forward to shooting my Italian 24-bore as a .410 this season.


—Silvio Calabi
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