Part 3: (Direct Gas Impingement (DI/DGI) vs. Gas Piston Operated) Some of the problems that plague the classic AR style rifle platform have to do with reliability, especially in sandy and dusty environments, as evidenced in Iraq and Afghanistan.
There’s nothing worse than having a survival tool fail on you when you need it most and the two loudest sounds in the world are: a “click” when you expect to hear a “bang”, and a “bang” when you expect to hear a “click”.
The military and the gun industry have been looking to fix the problems associated with the reliability of the M4 carbine’s direct gas impingement system (DI/DGI) and one of the options that has risen to the top of the stack is the gas piston operated alternative. This is a very controversial topic and there are many that believe the DI/DGI is still the best option and the gas piston system introduces a whole new set of problems.
The question remains, what would be the best AR survival rifle choice. Before we get into brands, let’s look at some of the new AR gas piston rifle systems vs. the classic AR legacy rifle, direct impingement systems. One of the first factors to consider is the compatibility of parts between different AR systems.
It’s important to consider the high likelihood that if you use your rifle system, at some point something may break and need to be replaced. The fact that the new gas piston systems do not enjoy total parts compatibility between brands and that there are currently fewer on the market compared to the legacy DI systems, may outweigh many of the performance considerations when choosing your primary survival rifle.
For a look at a mechanical and performance demonstrations of each type of system, please look at the following illustration of mechanics provided by the Army Times.
HK 416 (Gas Piston) vs. Colt M4 Carbine (Direct Impingement)
There are a couple of great reference handbooks on each of the systems written by Mike Pannone as well and are worth checking out.
Let’s look at the differences (Pros and Cons) between a direct gas impingement operated and the gas piston operated rifle.
1. Run cleaner
2. Run cooler (can contribute to longer life and less breakage due to heat and wear)
3. Run (arguably) more reliably than DI/DGI systems especially when chambered with 5.56 mm NATO in SBR (Short Barrel Receivers) and running cans (suppressor/silencer).
4. Typically need less lubrication to run reliably which means they don’t pick up as much grit and run cleaner especially in dirty and dusty environments (see #1).
5. Can reportedly run a wider range of ammunition with less finicky results than a DI/DGI system.
6. Usually, everything not directly related to the proprietary piston system is MIL-SPEC and interchangeable with its DI/DGI brethren. Brand specific on whether this is standard but most of the top manufacturers seem to have this quality in common.
1. Possible Carrier Tilt Wear – The piston places torque on the gas key causing the back of the carrier to tilt down causing scrapes along the buffer tube and shearing gas keys. The original AR platform was designed as a free floating bolt carrier. Some companies have addressed this (i.e. LWRC) by installing carrier guide rails and going to solid one piece carriers and/or upgrading the buffer (i.e. PWS enhanced buffer tube) as well as some other proprietary fixes.
2. Usually heavier than DI/DGI systems (for example HK reportedly had to thicken their barrel in the HK-416 to counteract barrel flex caused by the forces exerted by the offset, reciprocating gas piston and operating rod. This system was already much heavier than its DI/DGI competitors)
3. Many parts are proprietary and unable to be changed out easily at the user level (i.e. the rifle has to be sent back in to the company to undergo barrel changes or repair/replacement on proprietary parts)
Direct Gas Impingement (DI/DGI)
1. Typically lighter
2. Some claim they are more accurate (other arguments are that the barrel is the deciding factor in accuracy not the DI/DGI vs. Piston system).
3. Enjoy more interchangeability with currently fielded military equivalents (especially when dealing with MIL-SPEC AR systems) this means replacement parts are more readily available and if you buy a certain brand of AR, even if the particular company goes out of business, you can turn around and acquire compatible parts from any number of other companies.
4. Easy and quick shooter level maintenance and parts upgrades/changes, which means you usually don’t have to send your rifle back in to the shop. In a TEOTWAWKI or a long term survival situation… you aren’t going to be sending anything to the shop… you have what you have or what you can find along the way and that’s it. If it stops working and you can’t fix it… it’s dead weight, especially if you are on the move.
5. Easy to build your own franken-rifle/M4-gery from the ground up using the wide variety and compatibility of AR parts available on the market from numerous manufacturers.
1. Usually runs very dirty due to its gases being blown back into the chamber which is what makes the rifle cycle. This system is often described as one that Sh*ts on itself.
2. Reliability when running SBR’s/Short Barrel Receiver (especially barrels shorter than 12.5”), suppressors or in very dusty sandy conditions (i.e. during a sandstorm reliability test the M4 was prone to jamming 3.5x more than the 3rd place finisher. ref link: here).
3. Require more maintenance and cleaning.
These are all important considerations to take in before buying or upgrading your Survival Carbine. There are a lot of gun manufacturers out there and most of them make a pretty good product but as you well know, sometimes you get what you pay for. It is worth noting that the AK-47 is a gas piston driven system and no one has ever questioned the reliability of that weapon system.
Continue Reading Part 4: Build Options
In the next installment we’ll look at some of the survival carbine (AR style rifle) choices from some currently available brands, both in DI/DGI and gas piston systems.
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Photo Credits: Hk-USA.com, Colt.com, Murdoconline.com, LWRC.com, DefenseIndustryDaily.com, usarmy.mil