Myths About Gas Piston Systems
By Cory O'Connors
My experience with gas piston systems comes from working for and with Osprey Defense through more than three years of research & development. Working very closely with a group of engineers (you know the ones, the “rocket science type”) that were way smarter than I. The task given to us was to apply the KISS (keep it simple stupid) principle to the gas piston system.
MYTH #1 : CARRIER TILT
In the beginning there was a substantial problem with carrier tilt in most piston systems. To be clear, carrier tilt is when the rear section of the carrier dives into the buffer tube and gouges it severely.
Most of the people posting nowadays saying they have carrier tilt are just showing minor finish wear on the inside of the buffer tube, and panicking thinking they have a carrier tilt issue. This is not an issue and should not be confused with the destructive characteristics of true carrier tilt. Minor wear on the inside of the buffer tube is not uncommon, particularly with the carrier that has “skis”.
Carrier tilt was most prevalent with systems trying to use a bolt-on gas key. Engaging the carrier from the op rod at a position that far forward caused the rear end of the carrier to dive down into the buffer tube causing the severe damage. A large portion of the issue was resolved with the application of solid carriers, which moved the point of engagement rearward. Some manufacturers have chosen to beef up or add "skis" to the rear of the carrier for extra insurance, but there are drawbacks as the extra mass can cause a tight fit and excess drag.
There are still occasions where carrier tilt is experienced on newer systems. Usually, but not always, it can be attributed to a misalignment or improper installation of the buffer tube. It’s generally presumed, however, not always the case, that all uppers and lowers align per mil-spec, but there are many items on the market that do not adhere to the true specifications. Sometimes the solution to this is as simple as adding an Accu-wedge to help align an upper and a lower receiver.
One other potential cause of problems is over gassing a piston system by enlarging the gas hole through the barrel. Typically the enlarged hole was done prior to the gas piston system installation to overcome the shortcomings that may have occurred with the previously installed D.I. gas system.
MYTH #2 : PISTONS ARE LESS ACCURATE THAN D.I.
Once again, early piston systems did not have the technical advantages available to us today. Today we have the ability to test and balance volume and flow of gas entering the piston chamber and its timing to the milliseconds. Not having the proper balance of gasses and trapped volume caused timing issues.
Sometimes pistons would engage the bolt prematurely prior to chamber pressures diminishing, releasing the cartridge from the chamber and causing op rods to bend and cartridge rims to be ripped from cases. Mechanical parts moving prior to the bullet exiting the barrel adversely affected accuracy and reliability. Timing was the key to curing these issues, and most major manufacturers have overcome these issues making the piston driven AR very accurate and reliable.
MYTH #3 : EXTERNAL VALVES ARE BETTER THAN NO VALVES
This one could go either way. External valves are used to adjust the gas allowed into the chamber, which allows use of a wider range of cartridges and suppressed or un-suppressed fire without significant variance in cyclic rate or wear on the receiver. Units without an external valve still need to meter the flow of gas into the piston somehow, and typically the bypass allowed around the piston is to some extent self regulating; the higher the pressure, the more bypass is allowed. Therefore high pressure and low pressure cartridges, suppressed or un-suppressed, the piston exerts similar force against the bolt carrier eliminating the need for manual adjustment.
MYTH #4 : GAS PISTON SYSTEMS EXHIBIT EXCESSIVE HEAT IN THE HAND GUARD AREA
Piston systems do extend more heat into the hand guard area. This is unavoidable due to redirecting the gas from the bolt carrier to the piston located in the forearm, but generally it is not excessive. It is proportionate to the heat removed from the bolt carrier assembly, but this is a small sacrifice for a bolt and carrier that stays significantly cooler and cleaner. Generally speaking, more open forearms such as rails that allow for faster heat dissipation, greatly compliment piston systems.
Cory is the newest member to the AR15.com team. His official title is 'Director of Product Development', but he is also our technical expert. Each month he will answer some of your technical questions and address some of your product ideas here. You can email Cory at firstname.lastname@example.org.
"Proelium Comminus Auctoritate" "Sometimes the light at the end of the tunnel is a muzzle flash."
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