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Old 08-30-2008, 10:33 PM   #11
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No problem Smitty - We have several members here that are willing to help, not just myself.

The gas recoil system is based on the gas "power" generated by the cartridge, in most cases the 5.56NATO round.

Now, if you look at it base numbers to base numbers, if you fire the same round through both a long barrel, long tube/gas system & a short barrel, short barrel/gas system - you are obviously going to get more gas, per cubic, in the shorter barrel than in the longer barrel.

This could be construed as "lighter" recoil in the long barrel version, or "more aggressive" recoil in the short barrel version, but that is where your gunsmith, or parts, play a key factor.

If you want a smoother recoil, and you want smoother bolt stroke, you just have to retard the gas system a bit in a short, versus a mid length, versus a long barrel configuration.

Your barrel length should give you an ideal configuration for either a long, mid, or short fore end grip when you buy it - but that doesn't mean it has to stay the same as when you purchase it. There is an extensive aftermarket for just such "wants".

JD

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Old 08-31-2008, 12:47 AM   #12
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Dillinger can you explain this to me: "If you want a smoother recoil, and you want smoother bolt stroke, you just have to retard the gas system..."

Would installing a gas block be one way of doing this?

Im not to familiar with what a gas block exactly does.

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Old 08-31-2008, 01:04 AM   #13
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Essentially, the gas block is merely a valve, at the end of the barrel, to re-direct some of the gas, back down a return line, into the chamber to cycle the bolt. This will eject the spent round and load the next round from the magazine.

If you think about it like a straws for a Super Big Gulp - if you have a decent size straw, like the one that comes with it, you get a lot of soda per sip. If you use the kind of mini straws used for mixed drinks in bars, you get a lot less per sip.

The gas recoil system is the same way. You retard the system, for a shorter barrel version, and get the same amount of pressure in the chamber per shot. Use a full lenth gas block system, for a less than full length barrel system, you get too much gas coming back into the chamber and get a more aggressive recoil. Tailor it to the length of barrel for the weapon you are building, you get exactly what you are looking for.

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Old 08-31-2008, 02:56 AM   #14
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"If you want a smoother recoil, and you want smoother bolt stroke, you just have to retard the gas system a bit in a short, versus a mid length, versus a long barrel configuration."

Above is something that should be taken to heart. I have seen guys throw ridiculous amounts of money at AR's to fix something that is simple and 99 times out of 100 the only problem: gas system.

If your goal is smoother bolt cycling and and the benefits offered by a longer gas system, do not try to affect that system by mechanical means. I wouldn't add heavier buffers or extra power buffer springs as some recommend. This does work in an F/A rifle to reduce cyclic rate, but that is because the carrier and hammer interact (doesn't seem like the right word) differently during cycling.

Go with JD's words and TUNE the gas system with an adjustable block to your needs, don't try to add resistance here and lessen it there to speed up or slow down your dwell and cycling. After tearing your hair out and spending money you don't need to, you'll get frustrated enough to put everything stock again and start from scratch.

I had a table somewhere with figures showing the distance of gas tube holes to muzzle between the rifle and carbine. It also had pressure levels for each. Basically, if I can remember this right, the distance to the muzzle once the gas has exited the gas tube hole into the gas tube determines dwell time. By shortening this with a CAR barrel (less distance from hole to muzzle) the gas pressure increases. I think the pressure in a standard CAR system is twice that of a rifle length system. Anyhow, that accounts for "more aggressive" recoil. This has been engineered by guys with more brains and a lot more money than I have, and counter acted accordingly with proper weight buffers and correct buffer spring rate in relation to gas tube and barrel length. So by changing these, we end up back to where we were in my third paragraph. The gas pressure needs to be regulated, not the forces opposing that pressure.

In short, the mid length gas system is a solution to a problem that wasn't really a problem. It is basically an in between for rifle and carbine systems. And finally, the aggressiveness of the recoil and the smoothness of bolt cycling between the two is barely noticeable anyhow, making the mid length nothing more than an in between. Like owning three fast cars with only a two horsepower difference in power from the most to least powerful. I am not good with analogies, but you get my drift.

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Old 09-01-2008, 05:53 AM   #15
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Thanks Slo, I like this idea of a low profile gas block under the midlength handguard. Will the midlenth handguard be long enough to fit over it?

Would it be better to get an adjustable low profile gas block? This would allow me to tune the gas system for smoother cycling and operation correct?

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Old 09-01-2008, 04:08 PM   #16
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Adjustable low profile gas blocks are not necessary, but they are cool.

Usually low profile gas blocks come with rail mounts on top for a front site or other such product and goes right in front of the fore end tube.

As to the front hand guard being long enough to cover it, I am honestly not sure, I haven't done one like that yet. One of the keys to the adjustable block is to make adjustments on the fly, should you choose to.

If you cover it with the handguard, that kind of takes that ability away, unless you mil an adjustment slot into the bottom of the handguard. While that would be cool, it would be a bit more work. Nice idea though...

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Old 09-01-2008, 06:22 PM   #17
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Quote:
Originally Posted by jeepcreep927 View Post
"In short, the mid length gas system is a solution to a problem that wasn't really a problem. It is basically an in between for rifle and carbine systems. And finally, the aggressiveness of the recoil and the smoothness of bolt cycling between the two is barely noticeable anyhow, making the mid length nothing more than an in between.
So if I shot a gun with a car gas system and one with a midlength gas system, but i didnt know which was which, i probably wouldnt be able to tell the differece?

One guy said that it made a differnce in whether his young son would shoot it or not. His son didnt want to shoot his CAR because he said it hurt his shoulder only after a few shots, but he got a midlength upper a couple weeks later and his son shoots it with no problems and no complaints. So there must be some degree of less recoil.


If I cant find a middy like I want then I am just going to have to go with a CAR with the gas block under a mid-length handguard if it will fit.

Has anyone here put a low profile gas block on a 16inch carbine under a midlength hanguard?
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Old 09-01-2008, 06:34 PM   #18
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smitty - Is the concern the recoil? Or is it the performance?

Because if recoil is the only concern, installing a stock with a recoil pad, or installing a simple recoil pad on your existing stock should tame any sort of recoil that could be a problem for you.

Several companies make slip on recoil pads or ones that can be screwed on or glued on to your existing stock.

Another thing that might be considered, if the recoil is a problem, is a muzzle break. I can't remember if you have any restrictions on your build, there are so many going on right now I am having trouble keeping them all straight, but if you can legally own a muzzle break, that would also ease the felt recoil on your end of the firearm. It will, however, add to the noise at the muzzle, so keep that in mind.

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Old 09-01-2008, 07:34 PM   #19
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It is really more of a performance thing. Wouldnt less recoil mean less movement at the end of the barrel which in turn would lead to faster target aquisition on the following shots?

I really appreciate everyones patients and cooperation in answering my questions. I really dont have any experience with ARs so I want to obtain as much info as I can before making a purchase.

Is there anyone in here that has experience shooting ARs with both a midlength and car gas system? Which one did you prefer and why? or did it really not make that much differece?

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Old 09-01-2008, 08:00 PM   #20
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I have both a shorty and a mid length. But, the shorty has a long flash suppressor front end to make it to minimum length under the law, so there is addtional front end weight.

I don't consider the 5.56NATO round to be that much of a recoil concern, especially in an 8 pound gun, which is about what my 17" variant weighs in at with optics.

As far as function, both my weapons perform fine, cycling exactly as they are supposed to.

Now, part of that could be argued that I work part time in a gun shop and have access to a gunsmith that others might not. However, if you are going to purchase a gun, you should be buying one that was built with these same thoughts in mind.

Quite frankly I would say you need to shoot both a CAR length and a mid length for yourself and see what you like.

At the end of the day, it's going to be your money. You need to buy what you think is the best weapon for you, and your needs, and not what the folks here, or the guys from the range, think is the best choice, regardless of how well intentioned the advice that was given.

JD

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