A few weeks ago on the Borelli Consulting discussion board, a question was asked about the pros and cons of piston-operated semi-automatic rifles versus gas-operated semi-auto rifles. At that point in time I had little information about the piston-operated systems and therefore couldn't comment. A representative from Leitner-Wise Rifles jumped on the discussion board and offered some basic information. It sparked my curiosity and I had to learn more. Next thing you know, I'm at the range with the folks from Leitner-Wise, shooting a collection of rifles and learning about the piston-operated system. As I learned, there are some definite benefits to be had from the piston-operated design. They are cooler and cleaner than traditional gas-operated systems. I noted that the recoil felt different and that's apparently the result of the piston itself moving in the place of gas pressure building up. More on that below.
So, I got to the range (wife in tow) and was introduced around. The St. Charles Sportsmen's Club in Charles County, MD was our location. The club president was on hand and was very cordial and hospitable. When we arrived, the folks from Leitner-Wise had already been there for a little while and had unloaded their truck. I really didn't expect them to bring as many weapons as they did--nor as much ammunition. As you read this and look at the photos, remember that I'm a cop first, trainer second, writer third and photographer last.
The first photo is most important to our understanding of the piston operating system. I was schooled in the operation of an M16 by Uncle Sam when I was in the Army as an MP. My instruction included a section on how gas pressure built up behind the bullet and then how a portion of it was redirected down the gas tube before the bullet left the barrel. That gas pressure was used to force the bolt backward, ejecting the spent brass. The recoil buffer and spring then forced the bolt forward again to feed the next round and slam into battery for firing. There are two downsides to this operating system:
- It gets dirty fairly easily. I've heard horror stories from my older brothers and other Vietnam veterans about how the M16 would get so dirty that it wouldn't fire. "You have to keep it heavily oiled," I've heard. "Don't let any dirt or grit get inside the receiver. It'll lock up on you." Okay; we all know that we should keep our guns clean, but a combat weapon should also be reasonably expected to function under less than optimal conditions. Adding to the potential dirtiness of the weapon doesn't seem like a good idea, but that's exactly what happens with a gas-operated system. Unburnt powder, carbon, etc all can travel back down the gas tube to be deposited onto the bolt, bolt face and inside the receiver.
- It gets hot! Anyone who has shot a rifle knows how hot the barrel gets as a result of the powder burning and the bullet traveling at high speeds down the barrel. Does anyone know why the bolt gets so hot in an M16? Because of that hot gas that is being forced back down through the gas tube. The burning powder and expanding gas that heats the barrel should be expelled out the end...not recycled.
So, those are the two common problems with a gas-operated semi-auto. A piston-operated system solves them both. The piston actually takes the place of a portion of the gas tube. The gas that is in the barrel is still redirected, but instead of going back to the bolt it is spent pushing the piston back. The piston then strikes the bolt to cause extraction, ejection, and feeding of the next round. The strike of the piston is quick and sharp--which means the recoil felt is much faster. Whereas the gas-operated system has a drawn-out recoil feeling as the gas pressure builds and then bolt is moved back, the piston system has an immediate WHACK as the pistol hits the bolt and the bolt MOVES with authority.