Blog,  M1 Garand

The “Gas Trap” Garand

Newer M1 Garand rifle collectors may not be aware that the U.S. Rifle, Cal. .30 M1 with which we are all familiar featured a very different type of gas system when it was adopted in 1936.  The collector term standardized by the Garand Collectors Association (GCA) in 1993 for the first type of gas system was Gas Trap that utilized a false muzzle to deflect or “trap” the gas into the gas cylinder.  The early barrel was threaded at the muzzle and the gas cylinder screwed onto it.  The gas plug slipped down into the front of the cylinder and was held in place by a screw.  The barrel had only a single spline into which the bottom of the front sight fitted and was also held in place by a screw. This system caused accuracy problems because the plug through which the bullet passed deformed under the heat generated by rapid fire.  And the single spline was a weak point when a bayonet was mounted.

That gas system was replaced in mid-1940 by a Gas Port system in which the gas entered the cylinder through a hole or “port” drilled in the underside of the barrel.  The gas cylinder slipped onto three splines cut into the barrel and the gas cylinder lock and gas cylinder lock screw replaced the gas plug.

Approximately the first 47,000 rifles used the Gas Trap system. The vast majority of Gas Trap rifles were converted to Gas Port configuration during their normal rebuild cycle.  It is believed that less than 60 substantially original Gas Trap rifles exist.  Unmodified rifles and Gas Trap parts command a huge premium from collectors.

Photos provided Bob Seijas and the GCA.  Visit the GCA website at More information on collecting the M1 Garand may be found in our book “The M1 Garand World War II” by Scott A. Duff that is available from our website.  Autographed copies are also available.




You can purchase several of our M1 Garand books online:

The M1 Garand Compete Set

The M1 Garand: WW II & Post WW II Bundle

The M1 Garand: Owner’s and Assembly Bundle

The M1 Garand Complete Assembly Guide

The M1 Garand Owner’s Guide

The M1 Garand Serial Numbers & Data Sheets

The M1 Garand: World War II, Vol. 1

The M1 Garand: Post World War II, Vol. 2

The Guam Garands