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Old 12-03-2010, 06:28 PM   #11
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My Ar's are built with Double Star uppers, and I have been nothing but impressed with them so far. My rifle will only have about 150 rounds put through them in the course of a day. My current squirrel sniping rig is a 24" bull barreled gun, but what is your take on the same set up with a 20" barrel or even a 16" barrel? Will the difference in effective range and accuracy be noticeable taking into account that I am going to be shooting at a 4" target at a maximum of 300 yards away?

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Old 12-03-2010, 06:48 PM   #12
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Squirrel_Slayer
Your 24" gun will make it to the outer maximum range of the weapon, and you will notice a significant change in accuracy as you reduce the size of the barrel. The 16" barrel of the M4 was intended for close quarter battle, when being able to get your target in your sights quickly was crucial. We are currently training with reflex fire, where we only take the time to use the front sight post for close range targets, less than 50 yards. If you are walking through a field or rows of crops, and a varmint pops into view at close range, it is easier to bring a smaller barrel to aim than a longer barrel. If you have taken a position to snipe the critter at his hole, it may be advantageous to use a longer barrel.
SF operators in Afganistan are using a back up 24 inch barrel for their M16's to take long shots. This gives them the ability to extend their range without being conspicuous as snipers. Just trying to give you the perspective to make your decision.

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Old 12-03-2010, 09:51 PM   #13
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Wait a minute. You can get pistons for your AR? WOW that must make it really fast.

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Old 12-03-2010, 09:59 PM   #14
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Pistons? How many? Better be a V-8...none of that four cylinder crap!

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Old 12-03-2010, 11:50 PM   #15
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Originally Posted by Squirrel_Slayer View Post
Informative stuff in this thread, I like it. I will pay close attention to this one as I am going to be building either a 16" or 20" bull barreled AR here in the very near future. The rifle will be used for target shooting and varminting by the little woman, so it is going to be a DI gun for sure. Rate of fire will be very slow, most of the guns life it will be single fed. My question is, why would you lose accuracy or range simply because of installing a piston system?
Squirrel_Slayer, fsted2a already explained this but it might help to picture how the direct gas impingment system works. The gas pulse from the gas tube is directed right into the bolt carrier and the bolt causing those parts to become a "piston" themselves. The real beauty of this system is all the forces are in the same plane with the barrel (so it's not jarred off target), not offset like most piston designs. If you look at piston rifles the piston and rod have to be offset from the barrel and then the rear of the rod hits the bolt carrier high, all of which causes more movement/barrel rise - and carrier tilt in worst cases. True, the gas tube is also offset from the barrel but the dynamics of gas flowing through the tube don't cause the same off axis barrel movement of the piston system.

Really we're not talking that much loss of accuracy and the piston certainly does have advantages in some cases, especially short barrels and with compensators.

fsted2a and I may disagree in the value of a piston in most AR applications and whether the military will invest millions in the near future to dump perfectly good DI M4 uppers for a marginal improvement but I believe we respect each other's opinions. I also am a veteran so know the military does crazy things but I hope our tax dollars aren't wasted on replacing perfectly good upper receivers! I know people will say the money is worth it if it saves one life but I counter that the same money could be better spent on better training and other equipment and replacing worn parts - which would save more lives. The M4 AIN'T broke.
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Old 12-06-2010, 01:28 PM   #16
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Squirrel_Slayer,
On some issues, Quentin and I are in agreement. One of those is the value of the DI impingement system. It sounds like you won't be burning through several hundred rounds a day playing with your gun, so you will probably be better off going with the gas tube instead of a piston. They are more accurate, and unless you are getting your firearm inspected after shooting, a quick cleaning immediately after shooting before the carbon hardens is all you really need. Just stay away from the bargain basement parts, and stick with the brands you are more familiar with. There is a good deal of crap out there being sold as "milspec". That usually turns people against the AR to start with.

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Old 12-06-2010, 01:54 PM   #17
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"fsted2a and I may disagree in the value of a piston in most AR applications and whether the military will invest millions in the near future to dump perfectly good DI M4 uppers for a marginal improvement but I believe we respect each other's opinions"

Quentin is right about respecting each other's opinions. One thing that I didn't mention about the Army switching to pistons is that the M4 is also being considered to replace the M249 Squad Automatic Weapon (SAW) in the future as they use the same ammo. The SAW is an open bolt machine gun that shoots the same 5.56mm ammo as the M4. The SAW has a quick change barrel and a piston. The configuration being considered for the M4 will have a sear that when the selector is moved from semi to auto will also change from closed bolt to open bolt to avoid cookoff rounds. The piston system will make the quick change barrel a possibility as well, as the gas tube takes longer to replace than the piston parts. An advantage of the M4 over the SAW is not having to deal with link ammo-the firer can simply change 100 round Beta mags.

Eugene Stoner's Soviet counterpart, Mikael Kalishnikov, designed a gun that would fire when buried under mud, run over by tanks, submerged in water, and through many of the worst possible conditions that a firearm will have to go through. And the piston configuration he designed made that happen. But he sacrificed much to gain that advantage. The weapon is much less accurate and heavier than the AR. It has about 30 percent less range than the same ammo shot out of a DI rifle. This is why our military personnel are able to hit the enemy well outside the range of the AK. That and they are trained to be better marksmen.

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Old 12-06-2010, 06:01 PM   #18
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Thanks for that information, fsted2a! Good stuff from you as usual.

In regard to the AK, of course around 1974 the Soviets began switching from 7.62x39 to 5.45x39 in hopes of better matching up with the ballistics of our 5.56 AR. As usual the success of this conversion is hotly debated, much like when we began relacing the 7.62x51 NATO. When I got an AK clone I went with the original caliber though the price of surplus 5.45x39 sure is tempting.

I don't know about lesser range of 5.45 from an AK vs. 5.56 from an M4/M16 but you're probably right. And no doubt our DI rifles are more accurate.

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Old 12-06-2010, 06:33 PM   #19
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Quentin,
Due to the efficiency of the operation, the DI accuracy and range is very close to that of a bolt action rifle. It only uses about 1/8th of the gas of the AK, and could probably cycle the lightweight bolt carrier through the fire control group with less than that. It was originally in 7.62 x 54 mm (AR 10), and a lot of police snipers are currently using that caliber. When I had to do a research paper, I had a timeline on both the M16 and AK 47.
In 1984 Colt came out with an open bolt M16A2 called the Light Support Weapon (LSW),
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and had a batch of them made, but the Army went with the FN SAW. Seems like a version of that is coming full circle.
The Army is merging the M4 and aspects of the M249 to create one weapon without increasing exponentially the number of new parts it has to maintain.

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Old 02-01-2011, 07:02 PM   #20
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Quote:
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fsted2a and I may disagree in the value of a piston in most AR applications and whether the military will invest millions in the near future to dump perfectly good DI M4 uppers for a marginal improvement but I believe we respect each other's opinions. I also am a veteran so know the military does crazy things but I hope our tax dollars aren't wasted on replacing perfectly good upper receivers! I know people will say the money is worth it if it saves one life but I counter that the same money could be better spent on better training and other equipment and replacing worn parts - which would save more lives. The M4 AIN'T broke.
I beleive part of this is to push to consolidate the M4 and M249 into a single platform, instead of having 2 weapons. Big Army is always looking to consolidate parts, and if they can make one weapon perform the task of assault weapon and light machine gun, then they will.
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