Piston Driven AR-15s

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Does anyone have any experience with DI AR-15s? Any advice about purchasing a DI upper?
 
Most are standard mil spec. Some of the fancier uppers have some better components and better barrels but really depends on how much you want to spend.
 
Better starting with your budget range, barrel length desire, what length handguard you want and such.

I helped my boss order a complete upper from MAS Defense last year. It came ready to install on the lower he bought and ready to use right after that. I made sure he got a good BCG and charging handle (good priced and better features). I no longer have the list that I sent him with which items to get.

If you don't have any real preferences for setup yet, IMO, it would be very helpful to figure that stuff out.
 
Maybe I'm mistaken but aren't most AR's direct impingment? Some are piston operated but those are usually described as such.

That is my understanding as well.

"Sort of."

The majority of ARs are usually called "direct impingement" but they really aren't.
Stoner himself didn't call them direct impingement either on patent documents.

That said, they are colloquially referred to as "direct impingement" but the bolt acts as a de facto piston.

To circle back to the OP's question, "DI" ARs are the most common variant. The above caveats aside, "piston" ARs are considered the outliers.

In other words, the majority of gunowners on here that have ARs have pseudo-direct impingement ARs and they represent what you are most likely to see online/in a store, etc.
 
Maybe I've got it backwards.

Probably, it's been a long day.

Piston driven is what the Captain really meant. [slap]
Piston guns usually have two advantages:
- Cleaner
- Cooler

This is due to the gas/fouling not blowing directly onto the bolt carrier, etc. The "cleanliness" generally feeds into increase reliability as well.

DI, or pseudo DI in the case of ARs, are generally mechanically more accurate as there is no slop from the piston, etc. The lack of a full size piston and thicker/larger gas cylinder to accommodate a piston usually leads to them being slightly lighter as well, compare an AR-15 BCG on a DI gun to the piston & cylinder on a FAL, AUG, or AK, for example.
 
Maybe I've got it backwards.

Probably, it's been a long day.

Piston driven is what the Captain really meant. [slap]
i always assumed, may be wrongly, that the real benefit of piston driven ones can be seen on full auto models only. with semi-auto it is hardly justified, at all.
 
i always assumed, may be wrongly, that the real benefit of piston driven ones can be seen on full auto models only. with semi-auto it is hardly justified, at all.
Some see an advantage of a piston system when running suppressed...
 
i always assumed, may be wrongly, that the real benefit of piston driven ones can be seen on full auto models only. with semi-auto it is hardly justified, at all.
IIRC if you're running a suppressor, piston driven can be an advantage. What's the chance of THAT happening in the PRM? ;) Of course, an adjustable gas block (for DI uppers) can help there too.

A lot of the piston uppers use proprietary parts in them. Where DI uppers use parts that can be easily swapped/changed out (without high costs).
 
Standard ARs are often called direct impingement, but aren't exactly... But typically they get called that so we'll go with it. DI vs piston.

If you do not want DI (standard AR) you are probably looking at a piston driven system. They are typically cleaner to run, easier to suppress, and easier to tune for SBR and pistol lengths... BUT the major downside is a lack of uniform standards (there is no "mil spec", and not even interchangeable widely used manufacturers specs, like an AR10). Smaller downsides are added weight, a lot of heat around the barrel, and of course higher costs.

A variety of manufacturers make a variety of different systems - some are more reliable than others, and some get orphaned when the manufacturer goes under. Hoard replacement parts if you invest in one system.

Some systems utilize an op rod connected to the bolt (long stroke, like an AKM) and others are an unconnected op rod (short stroke, like an SKS). Most have a spring return system in or on the gas tube (like SKS) while others utilize the receiver extension/buffer tube (this has become far less common). Almost all use a proprietary bolt, but some are a entire proprietary upper and/or barrel.

Do your homework. Olympic made some fairly terrible early piston ARs, while Bushmaster made a great early drop in kit (most drop ins were/are not good). Adams Arms uppers I have owned and loved, Ruger was OK but less than I expected from a production gun when it came to tuning. The AR18 style kits from Brownells are phenomenal (now that they have been fixed). There are dozens I have not laid hands on.

You might consider simply buying a tried and true piston gun that does not rely on an AR platform lower. If you're in MA, they are mostly AWB friendly and nearly all of them take STANAG mags. Love my ACR and have had great luck with the SCAR - there are other less pricy piston guns on the market by Kel Tec, Sig, IWI, etc.
 
You might consider simply buying a tried and true piston gun that does not rely on an AR platform lower. If you're in MA, they are mostly AWB friendly and nearly all of them take STANAG mags. Love my ACR and have had great luck with the SCAR - there are other less pricy piston guns on the market by Kel Tec, Sig, IWI, etc.
My two favorite piston rifles:
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1630629116608.png
 
I've had the Ruger SR556 piston rifle, the Sig 556 and 556R (7.62x39), the Wolf A1 upper.
The issue I had was that the front end is heavy on all of those rifles. That's good if you want to
shoot more accurately offhand, but throws off the balance of what was originally very light aluminum gun.
 
The biggest reason for my question is my son's interest in the WWSD rifle. He wants one but we will probably NEVER be able to get one in this god-forsaken state.

 
The biggest reason for my question is my son's interest in the WWSD rifle. He wants one but we will probably NEVER be able to get one in this god-forsaken state.


The WWSD rifles were never piston. They can be, obviously, if someone puts a piston upper on. But they've been using DI uppers built around a modern pencil barrel.
 
The biggest reason for my question is my son's interest in the WWSD rifle. He wants one but we will probably NEVER be able to get one in this god-forsaken state.


One of the guys at my channel works for KE. DM me and I will send you a special code to save a few bucks.

Snag a lower and put whatever upper you want on it... Piston will be mighty front heavy though. Plenty of MA FFLs will transfer it, no problem.
 
The biggest reason for my question is my son's interest in the WWSD rifle. He wants one but we will probably NEVER be able to get one in this god-forsaken state.
a polymer lower rifle - why?
 
Selling one now actually. I've fired it and the piston driven guns have a different recoil impulse than the direct impingment guns. Kind of fun actually as the .223 really doesn't have much recoil. Easy to clean as well. Only reason I'm selling is to finance a few new guns I want.

 
Piston has a role in suppressed short barrel rifles. Otherwise it’s pointless. I have an adams arms 16” upper and several long stroke PWS builds. if you’re set on a piston gun I would recommend either a PWS or an LWRC. The long stroke PWS design is very cool and functional. However nothing piston will run as smoothly as a direct gas system especially if there’s no suppressor or selector switch present.

the functionality of a tunable piston system is most realized with suppressor + full auto + short barrel. in that situation its basically a necessity. Otherwise nope. That being said as a project gun why not get into one. But look into parts availability which is a huge factor to why I dig PWS.

regarding the WWSD project, I’ve followed their build for a while now and never understood some of their choices especially the polymer lower with integrated rifle but stock. No thanks!
 
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There are aftermarket short and long stroke piston kits one could buy for an existing AR if they felt like messing around with pistons, but didn't feel like fully committing to a new complete upper. They replace the gas block and gas tube for a piston system. Some are also adjustable.

I thought really long and hard about this before my last build. The notion of running a piston intrigued me, but like others mentioned, you get the best return from suppressed and/or FA, and my MA residence and lack of credentials for FA mean that is largely wasted. So I skipped the additional expense and went standard DI.

To my understanding, the only MA return I'd get with going piston is maybe a slightly cleaner upper and arguably more reliability if I were trudging through mud pits belly down under barbed wire on the daily. On the downside, you might introduce some influence to barrel harmonics with a piston. Not saying it will kill accuracy, but adding any mechanical action attached to the barrel will do something.
 
However nothing piston will run as smoothly as a direct gas system especially if there’s no suppressor or selector switch present.
Completely anecdotal evidence but I have to disagree with this. My LMT piston AR ran flawlessly, literally never once had a hiccup. Never used a suppressor with it but had a dozen 2K round training sessions with it. You could probably make the case for the "piston kits" IMO they are garbage. I wouldn't hesitate to use another LMT piston as my battle rifle.
 
Completely anecdotal evidence but I have to disagree with this. My LMT piston AR ran flawlessly, literally never once had a hiccup. Never used a suppressor with it but had a dozen 2K round training sessions with it. You could probably make the case for the "piston kits" IMO they are garbage. I wouldn't hesitate to use another LMT piston as my battle rifle.
+1
 
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