Over-gassed vs Under-gassed

[Agnotology]

Just trying to see if I understand the concept. Under-gassed guns have issues cycling, because when the pressure wave finally gets to to release the locking portion of the action, too much gas has left the system and it doesn't have enough "oomph" to push the bolt back fully, or stovepipes. Which is to say, once the bolt is unlocked, the system functions identically to a straight-blowback system.

In an over-gassed setup, this all happens too soon, causing the bolt to get thrown back with much more force than necessary, increasing felt recoil and generally causing the gun to jump more when shot.

Am I correct in this?

Reason I ask, is a few days ago I was at the range with someone and he was shooting a mini-14, brand new, getting it sighted in and breaking in the barrel. This gun was flinging brass 20 feet before hitting the ground. Sometimes it would arc so high to would hit the rafters of the shooting pavilion. And this was all intentional, according to the gun owner. It apparently made the gun "shoot smoother". I just don't understand how it is possible.

NES, Educate me plox!

 

[PappyM3]

Just trying to see if I understand the concept. Under-gassed guns have issues cycling, because when the pressure wave finally gets to to release the locking portion of the action, too much gas has left the system and it doesn't have enough "oomph" to push the bolt back fully, or stovepipes. Which is to say, once the bolt is unlocked, the system functions identically to a straight-blowback system.

In an over-gassed setup, this all happens too soon, causing the bolt to get thrown back with much more force than necessary, increasing felt recoil and generally causing the gun to jump more when shot.

Am I correct in this?

Reason I ask, is a few days ago I was at the range with someone and he was shooting a mini-14, brand new, getting it sighted in and breaking in the barrel. This gun was flinging brass 20 feet before hitting the ground. Sometimes it would arc so high to would hit the rafters of the shooting pavilion. And this was all intentional, according to the gun owner. It apparently made the gun "shoot smoother". I just don't understand how it is possible.

NES, Educate me plox!

Correct, over-gassing doesn’t make a gun shoot smoother. More reliably operate in austere conditions and with a wider range of ammo pressures? Yes. But not smoother. I don’t tend to listen to randos at the range. Chat with them, sure. But I don’t take anything they say as truth.

There are lots of variables for this discussion. But over-gassing can also cause failure to feeds like under-gassing, just a different reason. An over-gassed rifle can cause bolt speeds to be faster than the magazine can keep up with. However, that’s less common than under-gassing failure to feeds. Over-gassing can also increase wear on parts and result in compressed maintenance schedules (for parts check/replacement).

 

[18 Ventura]

Mini 14s are notorious for sending brass into orbit.

That's just how Minis roll...

 

[Agnotology]

Mini 14s are notorious for sending brass into orbit.

That's just how Minis roll...

The brass hit me a couple of times, which I found hilarious. Watching brass get flung is entertaining to me, being the that I am

 

[pastera]

Just trying to see if I understand the concept. Under-gassed guns have issues cycling, because when the pressure wave finally gets to to release the locking portion of the action, too much gas has left the system and it doesn't have enough "oomph" to push the bolt back fully, or stovepipes. Which is to say, once the bolt is unlocked, the system functions identically to a straight-blowback system.

In an over-gassed setup, this all happens too soon, causing the bolt to get thrown back with much more force than necessary, increasing felt recoil and generally causing the gun to jump more when shot.

Am I correct in this?

Reason I ask, is a few days ago I was at the range with someone and he was shooting a mini-14, brand new, getting it sighted in and breaking in the barrel. This gun was flinging brass 20 feet before hitting the ground. Sometimes it would arc so high to would hit the rafters of the shooting pavilion. And this was all intentional, according to the gun owner. It apparently made the gun "shoot smoother". I just don't understand how it is possible.

NES, Educate me plox!

You described pusle timing or where on the barrel the gas port is located.
Over gassed - gas port is too high or port location too close to the chamber so there is much more energy than necessary pushing the bolt back. This causes the action to violently get thrown back taking a chance of ripping the extractor off the case and causing the bolt to bounce at the remost position inducing feed failures and OOB conditions.
Under gassed - gas port is too small or too far forward resulting in too little energy to fully cycle the bolt to the rear causing failures to eject and/or feed along with some OOB conditions

All of this is effected by powder type and quantity also.

A gun is a system - treat it kindly

 

[pastera]

Mini 14s are notorious for sending brass into orbit.

That's just how Minis roll...

Mine will place brass into orbit.

 

[Dench]

My Saiga 5.45 throws bass like 30 feet in front of the gun. I don't think it has any gassing problems. Probably just how the ejector is.

 

[pastera]

My Saiga 5.45 throws bass like 30 feet in front of the gun. I don't think it has any gassing problems. Probably just how the ejector is.

if you miss with the bullet, get them with the case?

 

[PappyM3]

My Saiga 5.45 throws bass like 30 feet in front of the gun. I don't think it has any gassing problems. Probably just how the ejector is.

Good point, bolt velocity is only a factor in brass ejection distance when the ejector is fixed. If the ejector is built into the bolt head and is spring loaded, then its power is agnostic of the “gassing” of the system. Provided the brass has a clear exit path.

But I think on the Saiga, the ejector is fixed, no?

The ejector on the Mini-14 is built into the bolt face, so it should eject with whatever force the spring provides, not how gassed the system is.

 

[Ultrarunner]

Sorry, I thought this was a thread about folks reaction to Taco Bell...Ill move along...

 

[Dench]

Good point, bolt velocity is only a factor in brass ejection distance when the ejector is fixed. If the ejector is built into the bolt head and is spring loaded, then its power is agnostic of the “gassing” of the system. Provided the brass has a clear exit path.

But I think on the Saiga, the ejector is fixed, no?

The ejector is fixed onto the receiver

 

[PappyM3]

The ejector is fixed onto the receiver

So in that case, for AK variants, the ejection distance will depend on how fast the bolt moves rearward.

 

[Amputee Marksman]

Sorry, I thought this was a thread about folks reaction to Taco Bell...Ill move along...

 

[Dench]

So in that case, for AK variants, the ejection distance will depend on how fast the bolt moves rearward.

Shit maybe it is over gassed. No idea. It's never had any problems. I think it has the stock gas tube on it still. The gas tubes from Saigas are a little wonky they aren't exact copies of AK tubes.

 

[PappyM3]

Shit maybe it is over gassed. No idea. It's never had any problems. I think it has the stock gas tube on it still. The gas tubes from Saigas are a little wonky they aren't exact copies of AK tubes.

Meh, that’s the way AKs are designed. Tough built components to handle the extra gas, and the extra gas to keep the system kicking with shoddy ammo in extreme cold.

 

[Mesatchornug]

Meh, that’s the way AKs are designed. Tough built components to handle the extra gas, and the extra gas to keep the system kicking with shoddy ammo in extreme cold.

...with a ham sandwich in the action just like Mikhail intended.

 

[fishhawk357]

I believe they are designed that way purposely in order to function properly with a wide range of ammo. There is a kit available for the mini that allows the user to change port size. I got the kit for my mini. There is a large port drilled into the barrel then a gas port bushing with a slightly smaller port drilled into it. Replacing this bushing with another bushing with a smaller sized port slows the speed of the action. I got mine dropping brass to my 5 o’clock not more than 5 or so feet away. Very easy to switch out the bushings to get one with a port that suits the individual users needs. I think the kit comes with 5 different sizes. It’s the Accuracy Systems gas port bushing kit.