Ares Defense GSR-35: gas system retrofit range report.
Since I personally have never had any reliability issues with my direct gas impingement system AR-15s, my interest in a gas piston system is due mainly to curiosity. (Isn’t that what killed the cat?) The possibility of having to spend less time cleaning the bolt carrier group and upper receiver is also rather appealing.
Proponents of the gas piston system for the AR-15 claim it is more reliable than the direct impingement system, (which seems rather ironic since the gas piston system not only adds more parts to the overall system, but adds more moving parts as well.) Opponents of the gas piston system state the AR-15 does not have reliability issues as long as proper cleaning and maintenance procedures are followed. They also claim that the gas piston system causes a decrease in the accuracy of the AR-15.
There are a few different gas piston systems for AR-15s on the market, but most of them are proprietary affairs. The allure of the Ares Defense GSR-35 is that it is user installable on your existing AR-15. The GSR-35 kit comes with everything you need to convert your existing system to a piston system, including a set of modified M4 handguards.

You use the bolt from your existing system but remove the gas rings to run with the gas piston system. I chose to use a Smith Enterprise chrome plated bolt as this would more easily show the fouling on the bolt for comparison. I also chose to use a 16” HBAR for my testing and evaluation of the GSR-35 with the rationale that a heavy barrel would be the least likely profile to show a decrease in accuracy (if it actually did occur). If a substantial decrease in accuracy was found using the gas piston system with an HBAR, there would be no point in even testing the system with a government profile or light-weight profile barrel. The 16” HBAR I used for the conversion is a new chrome-moly barrel (not chrome lined) of uncertain pedigree. (I think it was made from a Douglas blank, but it’s been sitting on my spare parts shelf for so long I’m not sure.) The barrel is stamped as having a 5.56mm chamber and a 1:9” twist.
Upon removing the GSR-35 kit from the box, I was disappointed to see that the gas spigot was bent. It was only slightly angled away from the gas cylinder, but you would think Ares Defense would hold a higher level of quality control on such a crucial piece of their system.
The Ares defense literature states their gas system is designed to work with “mil-spec” AR-15s. I decided to deviate a bit from the “mil-spec” by using a JP Enterprises adjustable gas block, for three reasons.
1.The JP gas block uses an extra long roll pin to secure the gas tube/gas spigot. I thought this would help to mitigate any problems with the roll pin walking-out during firing, (as has been reported.)
2.The JP gas block is secured to the barrel using set screws. I wanted to see if a set screwed gas block could withstand the additional forces applied to it by a gas piston system.
3.The JP gas block is adjustable. I thought this might prove for some interesting experiments if the gas piston system proved useful. (The gas adjustment was left “wide open” for this evaluation.)
Before installing the GSR-35 system on my carbine, I performed some informal accuracy testing from a distance of 50 yards using the direct impingement gas sytem. The forearm of the rifle was placed on a sandbag resting on a wobbly table. There was no support for the butt-stock (nor for my elbows.) The ammunition used was one of my hand-loads, using Sierra 52 grain MatchKings and VihtaVuori N135 powder. As well as being an extremely accurate load, this load has functioned flawlessly in every AR-15 I own.
I fired three 10-shot groups in a row that measured, 0.558”, 0.408”, and .570” for an average group size of 0.512”. The targets are pictured below.

Dennysguns has done a great job of describing the installation of the GSR-35, so I’ll not go into that here. As I mentioned earlier, the gas spigot from my kit was slightly bent. When installed on the carbine, this caused the gas cylinder to angle very slightly to the starboard side of the barrel. This in turn caused some very slight binding at the juncture of the gas cylinder/gas piston/connecting link.
before conversion

after conversion


I began function testing of the newly converted carbine by loading and then firing a single round at a time from a magazine for the first ten rounds and then 3 rounds at a time for the next several magazines. I experienced multiple failures of the bolt to lock back after the last round of the magazine was fired. I don’t know if this was do to the slight binding of the mechanism I mentioned above, or if the system just needs a little “breaking in.” After approximately 30 rounds the bolt began to lock back consistently. There were no further malfunctions during testing.
I performed informal accuracy testing with the GSR-35 system installed on the carbine in the same manner as described above. The three 10-shot groups that I fired from 50 yards measured, 0.677”, 0.501” and 0.879” for an average of 0.685”. (targets pictured below) This does demonstrate a decrease in accuracy (larger average group size) using the gas piston system compared to the direct impingement system, albeit a rather small one at approximately 0.35 minutes of angle with this 16” HBAR.

I fired a total of 90 rounds for this first test session of the GSR-35 and here is what the bolt and carrier looked like afterwards; (pictured below) not nearly as much fouling as would have been present with a direct impingement system. Below is a picture of the inside of the upper hand-guard. This is where the fouling goes with the gas piston system. I was pleased to note that the JP gas block had not shifted forward at all during testing; nor was there any sign of rotational shifting. Also, the roll pin securing the gas spigot held tight.


Over the next few months, I plan to fire 1,000 rounds of ammunition from the GSR-35 converted carbine without cleaning the gas system. If there are no further malfunctions/problems, I will be doing some formal accuracy testing of the system from 100 yards. If the results from that testing are acceptable, I’m going to repeat this course of testing with a GSR-35 installed on a 16” government profile barrel.
Here’s a pic of my GSR-35 carbine.
Last edited by Molon; 04-13-09 at 21:19.
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