any studys in accuracy between gas and piston guns?

[Ring]

say before and after groups on a free float barrel after adding a piston kit?

[larry0071]

As an ameature, this holds no real value (my thoughts). But, I can not see how a DI vs piston will change the accuracy of a barrel and bullet combination? I vote for, impossable! It will shoot just as accurate no matter the driving force applied behind the barrel and bullet interface.

[militarymoron]

i'm no expert, but i'm sure if i'm wrong, someone more knowledgeable will correct me..
anytime you have something attached to or touch the barrel can influence the barrel harmonics. with a piston system, you have a moving mass that contacts whatever the gas transfer mechanism is attached to the barrel (gas block). with a DI system, the gas just flows through the gas tube, with the moving parts housed in the receiver.
it's been discussed many times before and the consensus is that piston guns aren't as accurate as DI guns (unless step are taken to deal with that issue, like a stiffer/heavier barrel), just as (in general) rifles with free floated barrels are more accurate than non-free floated (everything else remaining the same). in general, the less moving parts or anything influencing the barrel, the more accurate the gun.

[Iraqgunz]

MM,

You pretty much spelled it out.

i'm no expert, but i'm sure if i'm wrong, someone more knowledgeable will correct me..
anytime you have something attached to or touch the barrel can influence the barrel harmonics. with a piston system, you have a moving mass that contacts whatever the gas transfer mechanism is attached to the barrel (gas block). with a DI system, the gas just flows through the gas tube, with the moving parts housed in the receiver.
it's been discussed many times before and the consensus is that piston guns aren't as accurate as DI guns (unless step are taken to deal with that issue, like a stiffer/heavier barrel), just as (in general) rifles with free floated barrels are more accurate than non-free floated (everything else remaining the same). in general, the less moving parts or anything influencing the barrel, the more accurate the gun.

[30 cal slut]

inside minute of bad guy, i haven't noticed any differences.

what i have noticed, for extended ranges (to 200 yards) is that the extra weight of a gas piston system can screw you up.

[Molon]

But, I can not see how a DI vs piston will change the accuracy of a barrel and bullet combination? I vote for, impossable! It will shoot just as accurate no matter the driving force applied behind the barrel and bullet interface.

Testing has proven your statements to be false. Whether or not the difference in accuracy is significant enough to be of concern in practical applications is another question.

[Molon]

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.

[Molon]

The highest part of the GSR-35 above the barrel on my carbine is the section on the gas cylinder just aft of the spigot. It's the shiny spot on the gas cylinder with the red arrow pointing to it in the picture below. The shiny spot was caused by the gas cylinder rubbing against the the underside of the upper handguard.









Here are some pics showing the differences between the two sets of handguards from the inside.















Today I fired 90 rounds through one of my direct impingement 16” uppers. Here are some pics showing the Smith Enterprise bolt carrier group from that upper compared to the Ares GSR-35 bolt carrier group after firing 90 rounds.













I fired an additional 89 rounds through the Ares equipped carbine without a single malfunction. When pulling the trigger on the 90th round, all I heard was the dreaded “click.” I kept the carbine pointed downrange for 20 seconds and then examined the ejection port. The bolt had failed to close completely on the round going into the chamber. The bolt carrier still had 1/8" to 1/4" of forward travel to go.

I dropped the magazine and attempted to clear the chamber by pulling back on the charging handle, several times. The action was locked up tight. The lugs on the bolt had just barely started to turn and therefore were engaged with the lungs of the barrel extension. I finally had to slam the buttstock against the ground while pulling on the charging handle to clear the weapon.

At that point, I chose to pause the testing until I could determine the cause of the malfunction. Upon returning home, a quick visual inspection of the bolt carrier group, chamber and gas system revealed no obvious abnormalities. I cycled a couple of dummy rounds through the action with no malfunctions.

I next turned my attention to the cartridge involved with the malfunction. I dropped the cartridge into a JP Enterprises chamber gauge and the cause of the malfunction became painfully clear. The cartridge failed to completely seat in the gauge. Here is a pic of a cartridge properly seated in the chamber gauge and then one of the cartridge that caused the malfunction.








Scharch case.





I checked the headspace of the abnormal cartridge using an RCBS Precision Mic. The headspace measured +0.008”. That’s 8 thousandths of an inch longer than nominal headspace for the caliber. Obviously the case had not been properly resized and that is why it failed to completely chamber in the Ares carbine. I checked the headspace on the remaining 30 rounds that I had loaded for this test session and found two more cases that were not properly resized.

Since RVO is no longer a reliable source for once-fired and resized Lake City cases, I had decided to give the once-fired and resized cases from Scharch Mfg. a try. That is the source of the cases that I had used in this test session. This is the first time that I have ever had one of my hand-loads fail to chamber.

Since I am confident that the malfunction was due to the ammunition and not the Ares gas system, testing will continue. However, I will be chamber checking all the cases before heading to the range. Here’s a pic of the bolt and carrier after a total of 180 rounds fired.

[Molon]

300 rounds


I fired another 120 rounds through the Ares equipped carbine today without a single malfunction. (I used virgin Lake City brass for the handloads this time.) Here are a couple of pics showing the bolt/carrier group and Ares gas system after a total of 300 rounds.














The inside of the lower receiver looks as if it has hardly been used. The magazines are still remarkably clean also.

Just for kicks (and to prove a point) I fired some 75 grain A-MAX loaded rounds from the Ares upper from a distance of 25 yards. The 10-shot group is pictured below. Check out the key-holing!








400 rounds

I fired another 100 rounds through the Ares upper today without a single malfunction. After a total of 400 rounds there has been no walking-out of the gas tube pin nor any movement of the JP Enterprises gas block.

Something I noticed today after doing some close range reflexive shooting drills is that the handguards seem to heat up quicker with the Ares system than with the DI system; particularly near the front of the handguards where the gas vents from the gas cylinder. I may have to invest in an infrared thermometer to determine if this is actually the case.

Here is a pic of the bolt and carrier group after the accumulated 400 rounds of firing and below that a pic showing a comparison from the individual test sessions.












One of the attractive aspects of the Ares unit is that you can easily convert back to the DI system if you so desire with no adverse affect to your weapon (and then use the Ares unit to convert another DI system to the piston system if you like.) It's too soon for me to make recomendations for the system. For example, I perceived the handguards heating up quicker with the Ares system in my recent test session. I don't know what affect, if any, this will have during extended shooting sessions or long term usage. For my next test session I plan to put a lot more rounds downrange in one outing.

I will tell you this, I definitely like the decreased fouling in the receivers and bolt carrier group. Also, while there may be a slight decrease in accuracy when using the Ares system, the accuracy is still more than adequate for my intended use. In the last test session I fired the 10-shot group pictured below from 50 yards in an informal accuracy check, using handloaded 55 grain V-MAX bullets. The group measures 0.632”. While not minute of angle, it is certainly good enough for government work.

[Molon]

550 rounds

I ran 150 rounds through the Ares upper today without a single malfunction for a total of 550 rounds. The bolt is getting fouled at this point, but I can still see shiny chrome on it!





700 rounds

Another 150 rounds went through the Ares upper today with almost monotonous reliability. That makes a total of 700 rounds through the Ares upper with no additional malfunctions since the 180th round. Remember, that malfunction was due to the ammunition.

Using the Ares upper and 55 grain FMJ handloads, I fired a quick 10-shot group from 50 yards on a 300 yard E2 silhouette target reduced for 50 yards. The results are pictured below, showing that while the Ares system might not produce MOA accuracy, it is certainly good enough for practical shooting situations even when using FMJ rounds.









Here's a pic of the bolt carrier group after 700 rounds.