Custom Piston Operated M4 Project: Need Some Help & Have Some Questions

[Hungarian_Legionnaire]

I was looking to build a "Custom"-as close as I can get to a USGI Mil-Spec M4, but with a Piston System. I looked at the Colt 6920 which is Mil-Spec & as I was told by Colt: "The uses the SAME Upper & Lower Receivers as the US Military Mil-Spec M4", just with different markings on the Lower" + of course it's Semiautomatic & has a 16.5" Barrel, in place of the 14" that is standard with most US Troops.

I would like to use a Hybrid of parts but using a Stripped Colt 6920 Lower & Upper, creating a completely Custom & unique Piston Operated Colt 6920, having the looks of a M4/6920 on the outside with with an H&K 416/ M556A1: Piston System/ Barrel, Complete Bolt Group, Tungsten Filled Buffer, H&K Buffer Spring ect. "Under The Hood" of the Upper. I know this is going to cost more than just straight out buying a H&K M556A1 or Colt 6920, but I am planning this out as a project, and IMO with a project you don't buy everything at once, (In a perfect scenario), I'll probably buy a number of the smaller less expensive parts once or twice a week & 1 of the more expensive parts once a month.

The thing is, I just don't know how much MORE this specific way of building the AR I want will be, compared to buying a complete off the shelf Colt 6920, then buying a complete H&K M556A1 Upper with Piston System, Barrel, Quadrail & every other part included. Just that H&K M556A1 Upper @ HKParts.net is like $2k! & a Colt 6920 is $1,000-$1,200. I'm glad still have my Aimpoint CompM2, that I had mounted on the long carryhandle of my FAMAS F-1 back when I was in Le Legion. Basically I don't have $3K+ to build a Custom Colt M4/6920 with a H&K Piston System, Bolt/Carrier ect. Which is why I planned for an extended Project, piece by piece.

I also Note: I have NO Experience with AR's, I've shot an actual M4 in Afghanistan because many of the US Operators loved the look of our FAMAS F-1's, & would always ask to shoot/ check them out, (As they should the FAMAS in general is a VERY reliable, versatile & accurate Bullpup due to it's 19.2" Barrel & Overall Length of 29.8", it's more compact than a M4A1 W/ the Stock Collapsed & has a Barrel that's just under an inch of the M16A4's 20" Barre)

I wanted to share my idea of MY ideal M4 Piston Project & would like any input or ideas to make my project faster & less costly. Thanks

[Droppin Deuces]

So... Do you want something close to a mil spec M4 with a piston or do you want a Colt lower with an HK upper? Because there are a dozen or more ways to build the first thing, but only one way to build the second. And they aren't terribly similar.

[Hungarian_Legionnaire]

So... Do you want something close to a mil spec M4 with a piston or do you want a Colt lower with an HK upper? Because there are a dozen or more ways to build the first thing, but only one way to build the second. And they aren't terribly similar.

I basically want the Piston System, Barrel & Internals ect. of the H&K M556A1 to be placed in to a Colt M4/6920 Striped Upper & build the Colt M4/6920 lower from a Stripped Colt Lower. How should I go about this ?

[Hungarian_Legionnaire]

Bump!

[wash]

So you want an AR that looks like a Colt but uses the HK piston system?

I hope you understand that building a rifle like that is all about looks because at best it will perform just like any other gas piston AR.

As far as looks go, I don't believe Colt uppers have any distinctive markings other than on the barrel and that is under the hand guard so making a look alike can be lots cheaper if you skip the hard to find name brand parts.

I'm not familiar with the HK piston system but if the Colt is direct impingement and has oval handguards, I think there is a gas piston system that uses the standard gas block and fits under the handguard (called an Osprey I think). If that's not the look you are going for, I would have to see pics before I can give a good answer.

Performance-wise, a 16.5" barrel with carbine gas and a gas piston system can certainly work but it's not going to do anything particularly well.

I don't get the fascination of Colt marked lowers or gas piston systems installed for looks but whatever floats your boat...

[Droppin Deuces]

So you want an AR that looks like a Colt but uses the HK piston system?

I hope you understand that building a rifle like that is all about looks because at best it will perform just like any other gas piston AR.

As far as looks go, I don't believe Colt uppers have any distinctive markings other than on the barrel and that is under the hand guard so making a look alike can be lots cheaper if you skip the hard to find name brand parts.

I'm not familiar with the HK piston system but if the Colt is direct impingement and has oval handguards, I think there is a gas piston system that uses the standard gas block and fits under the handguard (called an Osprey I think). If that's not the look you are going for, I would have to see pics before I can give a good answer.

Performance-wise, a 16.5" barrel with carbine gas and a gas piston system can certainly work but it's not going to do anything particularly well.

I don't get the fascination of Colt marked lowers or gas piston systems installed for looks but whatever floats your boat...

Huh..?

[wash]

What advantage would it have over a 16" mid-length with direct impingement?

The honest answer is probably none unless your idea of an advantage is not melting a gas tube in (barrel melting) full auto beta-mag dumps.

[Droppin Deuces]

What advantage would it have over a 16" mid-length with direct impingement?

The honest answer is probably none unless your idea of an advantage is not melting a gas tube in (barrel melting) full auto beta-mag dumps.

But what won't it do particularly well?

[wash]

Anything.

I'm not sure if you are just lacking in reading comprehension but when you say that something won't do anything particularly well, it usually means that it does things normally but does not display any abnormally good qualities.

That is the way I meant it.

[wash]

You could also say an inexpensive Palmetto State Armory AR upper doesn't do anything particularly well and you would be 100% correct unless you count saving money as doing something particularly well.

[Droppin Deuces]

What's with the attacks, son? It just sounds like your statement is based on an opinion. I'm just wondering what you've experienced to help you form that opinion.
I had a 16" carbine piston upper that could shoot right with my 16" target gun using the right ammo.

As for what a Palmetto State Armory upper is capable of, I can't and won't say since i've never used one.

[Droppin Deuces]

I basically want the Piston System, Barrel & Internals ect. of the H&K M556A1 to be placed in to a Colt M4/6920 Striped Upper & build the Colt M4/6920 lower from a Stripped Colt Lower. How should I go about this ?

Not going to happen. I don't believe your parts are going to be compatible. Even if they were, your modified upper would just end-up looking like an HK upper, so why not just have an HK upper?

[wash]

So you're saying that a rifle with a 16" barrel and a carbine length gas system is always going to be super accurate?

In my opinion the gun in your example was accurate despite the carbine length gas piston system, not because of it.

The higher gas pressure, increased dwell time and mass of the new moving parts in a carbine length gas piston system all lead to additional movement of the gun before the bullet leaves the barrel and that will have a negative impact on accuracy.

You don't see gas piston ARs in long range rifle matches because there is no accuracy advantage to a gas piston.

Gas piston systems might have an advantage in reliability but on a 16" barrel a mid-length system would operate at lower pressures for reduced carrier speeds and it will just generally be smoother and that should give you a theoretical advantage in reliability.

So it's not really optimized for either...

It still could be fantastically accurate and Rolex reliable but it won't be because it has a 16.5" barrel with a carbine length gas piston system.

It will most likely shoot close enough to any other direct impingement Colt with good enough reliability that you'll never see a difference.

If he builds what he describes, I expect the performance to be exceedingly normal.

I can't put it any more plainly.

[Droppin Deuces]

So you're saying that a rifle with a 16" barrel and a carbine length gas system is always going to be super accurate?

In my opinion the gun in your example was accurate despite the carbine length gas piston system, not because of it.

The higher gas pressure, increased dwell time and mass of the new moving parts in a carbine length gas piston system all lead to additional movement of the gun before the bullet leaves the barrel and that will have a negative impact on accuracy.

You don't see gas piston ARs in long range rifle matches because there is no accuracy advantage to a gas piston.

Gas piston systems might have an advantage in reliability but on a 16" barrel a mid-length system would operate at lower pressures for reduced carrier speeds and it will just generally be smoother and that should give you a theoretical advantage in reliability.

So it's not really optimized for either...

It still could be fantastically accurate and Rolex reliable but it won't be because it has a 16.5" barrel with a carbine length gas piston system.

It will most likely shoot close enough to any other direct impingement Colt with good enough reliability that you'll never see a difference.

If he builds what he describes, I expect the performance to be exceedingly normal.

I can put it any more plainly.

So basically, you read it on the internet. That's what I figured.

[wash]

No, I have shot and assembled rifle length, mid-length, carbine length and pistol length gas system ARs and I've messed around with a few gas piston systems too (both AR and FAL).

I haven't seen too many good reasons to change an AR to gas piston. One good reason is if you have a 5.45*39 AR and want to keep the corrosive gasses out of your bolt carrier. I think they might be better on some supressed rifles but I'm not sure about that (I haven't played with supressors).

Now why don't you tell me what gas piston systems do better than direct impingement if I'm so wrong about this?