New to AR's - sight question

[gr8gun]

Why do all ARs have the front sight pushed back as far as possible?

If the sight were at the end of the barrel, you'd have a longer sight radius. I know its ugly on AKs, but it works.

[FS2K]

They have their sights up front.

[gr8gun]

Excuse my crude photo-chop, but here's an illustration:

Why do they look like this -
http://www.xlr8nrg.com/images2/frontsight1.jpg

and not this?
http://www.xlr8nrg.com/images2/frontsight2.jpg

[sleeping dog]

The gas block diverts pressure in the barrel back to push the bolt carrier. If that was too far forward, the pressure would not be enough to work the action and eject the spent brass. Putting the front sight on the gas block combines two functions into one chunk of metal, saving cost.

You can see some "space gun" ARs on http://www.whiteoakprecision.com (http://www.whiteoakprecision.com/tubb2k.htm) as well as other places. These guns have a gas block in the "normal" place to work the action, then a separate piece, a front sight mount, way out on the muzzle, just like you describe. More costly, but better sight picture.

Regards.

[gr8gun]

Thanks sleeping dog, I'm learning as I go.

I almost asked the question once, "why aren't there any folding stocks for ARs" -- but that one I figured out on my own! LOL.

[OneInTheChamber]

You could do it that way; but you'd have to have a separate gas block where the existing FSB is and then have some sort of mount for a front sight up on the front end of the barrel.

You will see a lot of High Power AR's with sights like that.

[kwkoch]

too much clutter on the barrel to have the gas block and a front sight separate, especially on a shorty. best to go with a clean gas block (no front sight) and opt for a scope or red dot.

[MatthewVanitas]

http://www.jtk3.com/laissezfirearm/ar15diss.gif

Here's a pic of what a Dissipator-type looks like. There's a separate gas-block under the handguards, rather than being attached to the front-sight assembly like on most ARs.

The official "Dissipator" made by Bushmaster has a carbine-length gas system, but CMMG makes them with the mid-length gas system. Midlength theoretically gives you smoother recoil and less wear on moving parts.

If done w/ HBAR barrel, Dissys are muzzle-heavy. But if you get one with a lighter contour or M4-profile barrel (such as BM makes) they balance quite well.

The result: a 16" carbine with the same sight radius as the 20" rifle. I have one, and they're pretty cool. The above pic is from the "Laissez Firearm" site, and has a good article on Dissys written by Mark Penman (MHRIP). Lots of good articles on this site: http://www.jtk3.com/laissezfirearm

-MV

[hps1]

It would seem to me that, with proper engineering, the gas port and front sight on the M16/AR15 could be located further forward. The only requirement would be to have the correct size hole to deliver sufficient pressure to operate the gas system in the time remaining after the bullet passes the port and before it exits muzzle, is it not? Maybe the 223 does not generate sufficient volume of gas for this to work?:confused:

The M1 Garand gas port is within an inch or so of the muzzle and it served the US military well for 25 years plus.

I suspect that it may be more an issue of the very tall front sight being more vulnerable to damage in combat the farther forward it is located, but your guess is as good as mine.

Regards,
hps

[gr8gun]

The only requirement would be to have the correct size hole to deliver sufficient pressure to operate the gas system in the time remaining after the bullet passes the port and before it exits muzzle

I'm totally guessing, but to keep the pressure the same, the volume would have to be the same, which would mean that if it were longer, it would be narrower, and would then be more susceptible to getting fowled and clogged.

[hps1]

which would mean that if it were longer, it would be narrower, and would then be more susceptible to getting fowled and clogged.


Sounds reasonable, especially since this was a real problem in early years due to retardants used on ball powders at the time. The garand did not have the gas tube to deal with.

Regards,
hps

[kwkoch]

the front sight is pretty tough we put them through hell in the marines and remember the garand had more powder/gas/recoil. you could move you gas block out to the end of the barrel but you would be turning your semi into a single shot.

[hps1]

OK, I'm convinced, bad idea to move gas block, but hey, I can barely see the front sights on my old M1's; put it any closer and forget about it. :(

Actually, I guess there is a large percentage of M16's issued w/optical sights today so sight radius would not be an issue. I'm sure the ratio varies according to the TO&E for a particular unit, but wonder what that % is today?

Regards,
hps

[gac009]

Just get a gas block and a stand-alone front sight and then put the sight wherever you want it. They sell both online if you look.

[Lowe Rent]

The reason is quite simple and has nothing to do with gas block placement. As stated above Bushmaster Dissipators have a separate gas block under the handguards, CMMG has 3 models, one with a carbine length, one with a midlength and one with a rifle length gas system, DPMS' dissipator has the rifle length gas system. It's all a matter of tuning the action to the gas system length you want.

No, the reason is, the civilian AR-15s at least initially were semi auto versions of military models (that way companies didn't have to tool up especially for the civilian market -- no longer the case), and the military models have the distance set between the muzzle and gas block/sight tower because that's where the bayonet mounts. Simple as that. Same reason the M4 has a 14.5" barrel. It has nothing to do with performance, it's the shortest length they could get and still mount a bayonet.

[sleeping dog]

Lowe Rent, sounds good. I completely forgot about the bayonet. It goes on the far end of the rifle, right? :)

When I was in, I figured "bayonet" was a French word that means "can opener". That's about all I used mine for.

Regards.

[44 AMP]

of the gas block, and length of the gas tube are critical for proper functioning. Because it is a direct gas impingement action. If you use a gas piston, you can put it anywhere, changing the length of the op rod to compensate, like the M1 Garand/M14.

You can't do that with a direct gas action. The real shorty ARs have a coiled gas tube, so it is the same length as a standard rifle. That way the correct pressure is still delivered.

longest possible sight radius is desirable on a sporting/target rifle. The military doesn't care about iron sight marksmanship anymore, outside of a handful of specialists. M16 sight radius is "adequate", they don't need anything else. Unless you go to optics.