What are the results of over gassing an AR 15 format?

[gun'sRgood]

There's stuff that's happening that I believe are a result of over gassing the AR 15 format. Dirty mag rounds, Dirty everything, cycle time, trigger slap and such. A .300 BO and a couple of 9's are in this group. What gas port and what else should I look at as issues to consider?

 

[Mk-211]

Have you looked into an adjustable gas block?

 

[Varminterror]

Are your 9mm’s gas driven or blowback?

For your 300, add an H3 buffer and an AGB. It’ll run like a top.

 

[Lo-Profile]

If the empty case comes out and a new bullet feeds. It's good.
Keep it lubed and clean.

Or take up checkers

 

[Varminterror]

Or take up checkers

Or have higher expectations and better understanding of how the AR-15 is meant to operate.

 

[d2wing]

A problem that you do not seem to have is overgassed can cause the bolt to move too fast causing ejection issues.

 

[Laphroaig]

That pie chart gets drug out every time this topic gets brought up. I have 4 .223 AR's, and can confidently state that 3 of them throw brass into the red zone at 1 or 2 o'clock. The 4th one probably does too, but I can't remember. Two of them have been rebarreled several times and all are still running the original bolts. I like it that way. For those of us who shoot on a firing line with other shooters, my brass gets deposited in front of the firing line, not tossed into another shooter and his gear. It makes life easier when the brass call is given. I'm going to state that many, if not most, competitive service rifle AR15's behave the same way because I see most shooters up front looking for their brass with me. Every so often I get pelted with somebody's hot brass, but not that often (thank God).

I also have a 6.5 Grendel AR which is "perfectly" gassed according to that chart. I hate it. I'm scrambling around looking for brass behind the firing line that's been stepped on or tangled up in somebody's equipment., and that brass ain't cheap.

 

[Varminterror]

@Laphroaig



I make my own kydex clip on versions of these to fit through or around my mounts these days, but this was what I was shown to use to solve the problem you described when I started shooting SR. Puts the spent brass at your feet. No hunting, behind the line or in front.

 

[Lo-Profile]

Or have higher expectations and better understanding of how the AR-15 is meant to operate.

Have all the understanding I need to have in my 45+ years of shooting, building and getting paid fixing them.

If the spent shell ejects and a new one feeds .... I don't give a crap where it lands.

But I only currently have 12 in 6 different calibers, so I guess I don't understand AR's.

How about a game of checkers

 

[Varminterror]

Have all the understanding I need to have in my 45+ years of shooting, building and getting paid fixing them.

Not if you think ejection and feeding are the only aspects of appropriate operation of the AR-15 action...

 

[dieselchief]

gents where does a 6mm arc fit in with ejection chart? thanks

 

[Shawn Dodson]

Brass ejecting forward can bounce back into your face when shooting from behind or under a barrier.

 

[Shawn Dodson]

gents where does a 6mm arc fit in with ejection chart? thanks

It depends on gas port diameter, buffer weight, recoil spring weight, propellant, and bullet weight (and sometimes the finish on the BCG).

 

[Varminterror]

gents where does a 6mm arc fit in with ejection chart? thanks

The same. We’re talking about the same carrier speed (targeted, at least) and the same bolt travel, with roughly the same case weight. Rebound off of the deflector is a little different when we’re hitting the shoulder instead of the side of the body wall, but the ejection ends up the same when we get things tuned properly.

Here’s an example of the ejection pattern on one of my 6.5 Grendels I put together a handful of years ago - a neat little pile at 4:30:

 

[Varminterror]

It depends on gas port diameter, buffer weight, recoil spring weight, propellant, and bullet weight (and sometimes the finish on the BCG).

It depends on whether the action is over, under, or properly gassed for its mass - but when we hit the right cycle rate, they eject the same. I’ve built hundreds of uppers in a few dozen cartridges, they all tune the same ejection.

 

[12Bravo20]

gents where does a 6mm arc fit in with ejection chart? thanks

My Odin Works 18" with adjustable gas block (never adjusted) ejects all the cases in a nice neat pile at 3:30 - 4:00 and about 4 foot away from me. I don't have to search very hard for my empty cases.

 

[Shawn Dodson]

It depends on whether the action is over, under, or properly gassed for its mass - but when we hit the right cycle rate, they eject the same. I’ve built hundreds of uppers in a few dozen cartridges, they all tune the same ejection.

Be that as it may, I've had the same ARs change case ejection angle by using different powders, and swapping an NiB or nitrided BCG with a phosphate one, without any changes to mass.

 

[Lo-Profile]

Not if you think ejection and feeding are the only aspects of appropriate operation of the AR-15 action...

Never said it was .... But the OP was asking about ejection

I'm guessing you can't win at checkers either ... Here's you prize

 

[kcofohio]

It depends on whether the action is over, under, or properly gassed for its mass - but when we hit the right cycle rate, they eject the same. I’ve built hundreds of uppers in a few dozen cartridges, they all tune the same ejection.

Am I safe to assume that an AR10 style should have basically the same ejection pattern?
Mine is unfinished, but would like to know for future reference.

 

[DMW1116]

What are signs of excess gas in a rifle without a shell deflector or a slick sided AR upper? As I understand it, the pattern most people try for is based on the cases bouncing off the shell deflector.

 

[wanderinwalker]

I'm here to find out which 9mm AR is over-gassed, and how it's over-gassed...

 

[Varminterror]

Am I safe to assume that an AR10 style should have basically the same ejection pattern?

Yes.

 

[Varminterror]

Be that as it may, I've had the same ARs change case ejection angle by using different powders, and swapping an NiB or nitrided BCG with a phosphate one, without any changes to mass.

Because changing the powder changed the gas flow. Changing the carrier coating changed the drag on the carrier, which changed the cyclic rate…

It really isn’t so complicated.

 

[Varminterror]

I'm here to find out which 9mm AR is over-gassed, and how it's over-gassed...

That’s the part that has me the most curious here - gas drive 9mm uppers are pretty rare, so I’m intrigued to hear about this one.

I suppose it’s technically correct to say a violent forward ejecting 9mm upper is, in fact, overgassed, but we can’t tune gas in the same way on a blowback upper as we can a piston or DI. Just have to add spring and/or mass.

 

[dieselchief]

a big thanks!