AR15 gurus. Difference between DI and piston

[GrensVegter]

The other thing I have thought about is spares, almost all the piston systems are propitiatory so if you do need to get spares you will have to source the parts from the manufacturer or their distributer. A DI gun if made to spec can be fixed with any spec part regardless of manufacturer.

 

[Hitzy]

Can people explain pws long stroke system like in the ak47 ? what the difference between between it and piston or DI

That's not a bad question really. Would take some modding to the upper, where a lot of the piston stuff is designed to drop in to the existing platform which seems to have limitations.
I wonder if having the piston directly attached to the carrier would solve some of the accelerated wear issues we see with piston uppers short stroke system.
Gas block, gas tube, and piston bolted to carrier in place of gas key....3 parts proprietary.

 

[Ed The 3rd]

I'm really enjoying this thread. I've learned a few things. And to whoever asked, the difference between short stroke and long stroke piston is short stroke just smacks into the BCG and long stroke is attached to it. its a much longer piston, heavier system that allows for more reliable extraction (according to some) but a helluva lot more recoil (according to others). Its also used in the XCR. Just learned that the other day.

 

[Gunnerlove]

The way I see it is that they both break in different ways.

The big question is: At how many rounds and at what firing schedule does the system fail? Failure means the weapon ceases to function.

The other way of asking the question, does it pay to buy a "reliable system that wears out within a known period of time" or a "system that lasts a long time but it will fail fast once it is used beyond its limit".

Let's look at it this way, if the receiver of a piston gun receiver progressively wears out in 20,000 rounds and a DI bolt has a high probably of snapping in under 6000 rounds under an intensive firing schedule, it is better to toss away a piston gun ( or send it back for overhaul) every 20,000 rounds than snapping a bolt without knowing when it will happen. If I am running a SOF kind of organization, that is a pretty good trade off for a small fleet of weapons.

On the other hand, for a large organization who does more traditional infantry or LE enforcement with a less demanding firing schedule, parts are not changed until they are broken and the entire inventory is maintained as a "fleet" on a set schedule. In this scenario, a good DI gun will probably last a long time and it does not pay off to buy a piston gun and pay for the weight penalty. If you look at it this way, you get more bang for the buck with DI guns due to the scale of economy in both upfront cost, lower maintenance skill needed, and parts replacement. The number of failure due to excessive usage can be predicted based on organization history and as a project manager you will just factor those incidents into the total life cycle cost.

For a regular joe weekend warrior, there isn't really a need to buy a piston gun. And for those who shoots a lot, buying a 90 dollars bolt every 6000 rounds or until failure is still cheaper than buying an expensive HK piston or LWRCI gun. On the other hand, if I am in an organization where I need to fire fast and furiously and it must be reliable/durable only in a predictable a set number of round count(more than 6000), I will be exploring some other options other than DI guns.

But if you really like a piston gun, buy it. It is not a choice of economy - I buy guns because I like guns. And deep inside everyone loves good "fit and finish" even if we deny it in the forum.

I fully agree, a rifle that runs like a sewing maching for 20K and dies has its place. The problem is no one is making one.