AR Gas/DI explanation

G

gizmo688

New member
I'm looking into building an AR from the ground up, but the only thing i'm not 100% understanding of is gas vs DI. I know the theory behind their operations, but how do they apply to the ar platform?
It seems DI is just a modification kit attached to the gas port on the barrel. If that is the case, does the addition of a DI system warrant "DI friendly" parts in the carrier group?
Again, if my thoughts are correct on the kit concept, is it worth the extra $?
Any explanation would be appreciated.
 
I think that you are a bit confused on the whole concept of how AR gas systems work both DI (Direct Impingement) and piston type.

I will give the "Cliff Notes" version if I can.

DI is the original gas system and what most ARs come with.

Piston operated system is the new and so called improved system that most people pay extra for and comes as a kit to change from a DI system.

I will let you google the two systems to see how they operate.
 
direct impingement is the standard for the ar platform. this is a system that captures the hot waste gas behind the bullet and channels it back to the bolt face and directly causes the bolt to be forced back to cycle the action.

it is from a engineering viewpoint a messy solution since it is allowing unburnt powder and debris that is also in the gas to be introduced inside the rifle. in the real world this is still what the army is using and has served millions of gun owners well.

a piston system functions the same basic way but a piston is put between the gas and the bolt face removing the mess from the receiver.

there are other slight benefits in a piston system such as ability to adjust for sub sonic or silenced/suppressed applications.
 
I wish I owned Palmetto State Armory, but unfortunately I do not nor am I affiliated with them, the only thing we have in common is we are both South Carolina Proud...............lol
 
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OK so I was using DI and piston interchangeably. Obviously incorrect.

Does the piston system require any special parts with the obvious exception of the piston kit? (special bolt/carrier, buffer system, etc?)
 
Yes it requires a different bolt carrier, but that is generally included as part of the piston conversion kit... or if you buy a gun already equipped with a piston kit.
 
Quite a few major manufacturers are now producing Piston AR's. I waited to buy an AR until S&W came out with their piston gun and bought one about 6 months ago. It has been flawless, super easy to clean and I have no regrets. Takes only a couple of minutes to remove the piston, wipe it off with a little Hoppes 9 and reinstall it. The bolt is just as easy. Sort of like going from a stick shift transmission to an automatic....there were skeptics then as well. :D
 
You will find the two systems are debated endlessly on each side.

DI will be cheaper.. and may require a little bit more cleaning..(were talking only a few minutes time.)

Piston will be more expensive, but will run cleaner.. but SOMETIMES you may need to tweak the system or the ammo to get them to run correctly. Not a huge deal, but it CAN happen, not always though.

I have shot both.... both run well, Piston being better for running a suppressor. However my personal AR's are all DI.

In case you were wondering the military still uses DI, but a lot of new guns that may go into future trials are a lot of piston.

Personally if your new to AR's and want to build one up yourself (its easy) I would stick to DI for now... cheaper... parts are literally everywhere... less to worry about. That will let you learn the in's and outs of the rifle... and down the road you can try a piston conversion if you'd like.
 
The only downside that I see with a piston AR-15 is the proprietary piston systems on them. Gas tube is an easy fix.

An interesting thing is Anderson Arms and their RF-85 coatings for an DI AR-15
http://www.atdmachineshop.com/rf85.htm

You clean the bolt and gun with soapy water and add no oil.
 
Apparently TimW77 doesnt like to share his thoughts with the class. PM quoted:

It's called a SEARCH, GOOGLE, manufacturers websites and READING...


"It seems DI is just a modification kit attached to the gas port on the barrel."

Depends if it is an ADD-ON or from an OEM...


"Again, if my thoughts are correct on the kit concept, is it worth the extra $?"

Depends on what you want to believe...

I've always though of it as the solution for a non-existent problem.

Also, how does adding parts and increasing complexity improve anything?

T.
Click to expand...
 
Aside from the "dirty" aspect of DI, what is often overlooked is the fact that the heat- obviously more of a factor if the weapon is used rapid-fire- from the combustion gases accelerates wear and decreases the life of the parts affected by it- the bolt, and extractor. I would extend that by saying that in extreme circumstaces that the temper of the steel of those parts could be affected as well. Heat obviously leads to dimensional changes in parts as well...

There's nothing good to be said about heat and dirty fouling, carbon, impurities, etc. in the action of any rifle.

Own two AR's- and they're both DI- just stating the facts as I see 'em.
 
Same basic system.

Another downside of AR piston systems is that is a noticeable amount of extra weight hanging out over the end of your weapon now, as well.
 
Oh. I just started a thread similar to this. Didn't mean to detract from this one. My question is why weren't they made w pistons in the first place?
 
another downside of AR piston systems is that is a noticeable amount of extra weight hanging out over the end of your weapon now, as well.

That is just a fallacy...the weight of my piston rod and spring is negligible. The weight of added lights/lasers, pistol grips, or other add on stuff to the rails adds more to the weight of the gun than a simple rod and spring. Go to the S&W web page and look at the Specs for the M&P15A and the M&P15PS...the weights listed for both are 6.5 pounds.
 
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Considering the original post, I'd say it will be quite a while before you know enough about an AR to be able to determine the difference.
 
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