The CMP conducts a number of types of competitions for rifle and pistol. For the CMP National Trophy and CMP-sanctioned EIC service rifle matches (where points are awarded toward becoming a Distinguished Marksman), the National Match (NM) versions of the Garand, M14/M1A, and AR-15/M16 service rifles are used. As Scorch said, they have to look like an as-issued service rifles, but only in a black and white photo (colors and finish don't matter). The following exceptions are allowed: They may have fine adjustment NM sights and, after the Clinton era ban on ersatz assault weapons, the rules were changed so it is also no longer required that you have a bayonet lug or a flash suppressor where those were part of the original equipment. Nor is a selective fire switch required to be present, which is why the M1A and civilian version AR's may be used in place of the M14 and M16. On the inside, where the camera can't see, the rifle may be bedded and/or shimmed and may have had a custom trigger installed or had other special accuracy work done to it such as installing a heavy barrel or using a synthetic stock or adding stock weights inside. It has to be one of the aforementioned semi-automatic or automatic version rifles. The match rules require semi-automatic fire only, though the military rifle teams often are using full-auto capable rifles. All bolt guns are now considered Match Rifles (as distinct from National Match self-loaders) and have their own separate competitions.
The CMP also conducts the CMP Game and Special EIC Matches, including the John C. Garand, Springfield, and Vintage Military Rifle (GSM) matches which are for as-issued rifles. These started with the first John C. Garand match in 1998 and are designed to encourage people who want to try match shooting, but who don't want to try it badly enough to invest $4-5K* in getting outfitted to be fully competitive in the regular Service Rifle matches before finding out if they like it? But they also need to stand a chance of winning, so the rifles allowed are more restricted as to what you can and can't do to customize them. The gun must be all original military parts or exact same weight and shape commercial replacements. For example, a barrel must be standard military weight and not a heavy weight match barrel, though you can get a standard contour barrel made by Krieger or one contoured from a Douglas blank. You are allowed to select and to mix and match these to find best fit, but not to modify them. No action bedding or shims are allowed. No parts stamped "NM" (National Match) are allowed. Sights must be original as-issued battle sights with their coarse adjustments. There are some special exceptions: The Garand rifle may have an operating rod marked NM because as-issued GI op-rods in good shape are getting scarce. The Garand barrel's gas cylinder spline may be peened to prevent the front sight from shifting position around the muzzle.
*By the time you've spent $2K on a rifle, got the Champions Shooter's Supply leather shooting jacket and pants, hat with side flaps, gloves, mat, Kowa spotting scope, Freedland spotting scope stand, range cart, and had your optometrist search out a lab to grind your prescription into a round lens for your $400 German adjustable rifle shooting glass frame, not to mention setting up to load match ammo, well then you've got that kind of money in it.
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