At this time, most of the major black rifle manufacturers offer their own external piston rifle and most all of them are short stroke tappet designs with the piston and operating rod separate from the bolt carrier. Only a couple manufacturers have gone with the long stroke piston, which is where the operating rod and piston are connected to the bolt carrier group as one piece. The most successful two companies making long stroke piston rifles are ADCOR Defense and Primary Weapon Systems. Primary Weapon Systems (PWS) began in 2005 as AK Concepts and in 2008 they formed a new company called Primary Weapon Systems. The founder and President, Dean Sylvester, is also the lead designer of all PWS products. The early company AK Concepts, manufactured collector grade Yugoslavian variant AK-47s. The first product from that was the JTAC47 muzzle brake for the AK-47 that is still in production today. The new company, PWS, first started selling long stroke piston operated AR rifles in 2009. The Modi systems were released in 2013.
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