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The Best 556 Piston Gun Kits

Ruger's SR-556 is a semi-automatic rifle that accepts AR-15 rounds. The weapon comes in four models (5905, 5909, 5902, 5904) all in different calibers, weapon weights, and clip capacities. For example the SR-556 model 5905 has a 5.56 millimeter round, 30 round capacity, and weighs 7.4 pounds according to Ruger. There are a number of upgrades for the gas piston autoloading feature of the weapon.

Retrofit Gas Piston System
- The Retrofit Gas Piston System (RGPS) offered from Adams Arms Inc. offers several advantages to the autoloading system standard with the SR-556. Among these advantages are improved accuracy of the round, less recoil, and increased performance of the weapon. There are eight different models of the RGPS to fit different model weapons. The kit has been reviewed by Small Arms Review, according to Defense Review, and the rifle performed well with only a few rounds not loading properly.
Addax Gas Piston Upper
- The Gas Piston Upper (GPU) by Addax comes in a variety of sizes but offers a kit for the 5.56 NATO caliber used by most of the SR-556 models. The kit offers a better wear protection, easy cleaning, fully machined parts, and a five-year limited warranty. Addax worked with Primary Weapons Systems (PWS) to create the kit and is highly rated on Military Morons.
Considerations
- There is some debate as to whether gas-piston autoloading systems are superior to the direct-gas impingement systems (DGI systems). According to Defense Review, the DGI systems tend to make for a lighter weapon with better accuracy and more durability. The advantages of the gas-piston systems is that they allow for a shorter gun barrel and are easier to clean.

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