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GAS CHECK MAKER KITS

Photo of Gas Check Die

Corbin GCM-1 Gas Check Maker Kits are available for the Series II Press (Model CSP-1), Hydro-Mite (CSP-1H), Mega-Mite Press (CSP-2), Hydro, JR. (CSP-2H), and the Hydro-Press (CHP-1). (Select the photos to see a larger, more detailed photograph.)

The kits produce high quality copper gas checks using .030-thick 1-inch wide strip (available from Corbin in 5-lb bundles Cat.No. CU-5, and in 100-pound coils Cat.No. CU-100). Other materials such as aluminum or brass of the correct alloy and thickness can also be used (not every alloy and temper is suitable).

There are two versions of the GCM-1. The GCM-1-S is for the Series II and Hydro-Mite. The GCM-1-H fits the Mega-Mite, Hydro, JR., and Hydro-Press. The main difference is in the size, strength, and alignment method. Both can make good quality gas checks. The -H type kit is faster to operate over a longer period of time, since it can be operated in a semi-automatic mode (hand-fed but power stroke, timing, and ejection).

Copper Strip is available in bundles of 5 pounds (cut to approximately 18 inch lengths, about 42.5 feet), or a 50-pound coil. Each gas check requires a piece of copper to be cut out of the strip, using the first die of the two-die kit. The round disc punched out of the strip will be the caliber plus twice the gas check wall length in diameter. Thus, a .357 gas check with walls of 1/8 inch height would require a disk of approximately .3570 + .125 + .125 = .607 inch diameter.

The disc-cutting die has a slot in one side, through which you pull the strip of copper as the press pushes the punch up and down, cutting out discs like a cookie cutter, and pushing the disks up and out the top of the die. By staggering the holes in the strip, you can run one set of holes down one side, turn the strip over, and put another series of holes down the other side, thus using more of the strip than if one single row of holes were punched closer together. The standard width of strip is 1 inch, and only a little more than half its width is taken by each disc.

Gas Check Die Photo In .45 caliber the gas check disk will be .452 (for pistol) or .458 (for rifle) plus .25 for the two walls of the gas check, or about .702 to .708 inches in diameter. A .50 caliber gas check would be .510 + .25 or .760 diameter. All of these calibers are practical for a 1-inch strip. Larger calibers can be made using the -H die set only, because of strength and physical size limits of the -S system.

After cutting a number of discs, the second die is put into the press along with its spring-loaded guide punch. The disc is placed into the top of the punch, where it is centered and held by the spring-loaded guide bushing. The punch is then run up into the CUPPING DIE, where the bushing edge contacts the die allows the punch itself to move upward, holding the disc in perfect alignment so that the edges are evenly curved into a cup shape.

The punch and ram are lowered, another disc inserted into the top of the punch, and the process is repeated to produce a number of finished gas checks, which emerge from the top of the cupping die, ready to use. The precision of these gas checks rivals anything turned out on mass production machinery.

Gas checks can be used in a conventional manner on cast bullets, or they can be inserted into a swaging die along with the undersized lead core, and formed in one stroke to the bullet base as the lead is swaged. An alternative to the gas check is the Corbin Base Guard (TM), which has a small hole in the center and no side walls. It forms a scraper edge that cleans the bore of all lead fouling, when the bullet is fired. Base Guards (TM) cannot be used with a conventional cast bullet, but are only suitable for swaged bullets, since the pressure of swaging is what forms the rivet head of lead in the center of the bullet to attach them. The Base Guard disc is purposefully made smaller than the caliber, and in a conical shape, so it will expand and become the exact size of the bullet with zero tolerance when the bullet itself is formed (swaged).

Gas Check Maker Kits (GCM-1-S or GCM-1-H) are available in all calibers on special order (custom tooling fee applies) but are made for the standard price in these diameters: Gas Check Maker Photo