KNS Adjustable AK Gas Piston

By Alton P. Chiu

Avtomat Kalashnikov, a storied and proven rifle, is adored by both militaries and citizens alike. However, its propensity for vigorous cycling and ejection can cause complications with sound suppressors as well as induce premature wear and tear even when unsuppressed. The KNS adjustable gas piston mitigates this overgassed condition that factory rifles commonly arrive with.

Principle of Operation

Unlike an AR-15 gas block, the AK’s is interference-fitted to the barrel and requires a shop press to remove. Although aftermarket adjustable gas blocks exist, they cannot be easily installed at home. The KNS adjustable gas piston changed that as it only requires one to field-strip the rifle; installation can be accomplished by hand tools. No permanent modification is necessary, so there are no qualms partnering it with a collectable parts kit.

A hole at the tip of the KNS piston channels excess gas to a vent further back on the piston, whereby it makes its way out of the gas tube. The size of the piston vent hole is regulated by a collar in order to soften the recoil impulse and facilitate controllable rapid fire. The collar moves axially along the piston by threading around it like a nut.

KNS produces variants with different thread pitches, hole distances and working lengths to fit the AK family (including but not limited to AKM, Arsenal, Yugo, Krinkov) and even its extended cousins (e.g., Valmet, Galil). For this article, the AGP-A-20S model was evaluated on an Arsenal SLR106F chambered in 5.56x45mm which sported a 16-inch barrel.


The rifle was field stripped and the bolt carrier, sans bolt, was removed to a vise. Note that the bolt carrier is hollow, and the vise jaws should be applied to the piston to avoid damage. The author then searched for the rivet securing piston to carrier with a good light source in order to remove the OEM piston. During installation at the factory, a rivet was bucked on both sides into the countersunk holes on the carrier. The excess material was then ground down and finish applied over. The one on the Arsenal ran side-to-side...

This article first appeared in Small Arms Review V23N1 (January 2019)
and was posted online on November 16, 2018


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