Velocity between 16" mid length and 16" carbine

[Oakland Tactical]

I’m looking for information on identical twist, length and brand barrels (any brand). The information is in regards to a velocity difference, if any, between a mid length and a carbine gas system for a 16" AR barrel?

It would seem on the surface that the mid length would have a slightly higher velocity. I don’t need to know this for a purchase, just out of curiosity.

 

[battlestick]

Re: Velocity between 16" mid length and 16" carbine

With non-adjustable gas systems, in theroy (IMO) you are right. But there may be someone along with with some facts to prove us both wrong.

Interesting question, I am curious to see the replies.

ETA: With factory ammo......With handloads on the top of end of pressures, IDK. More velocity means more pressure, which means you start getting pressure signs with less powder charge in a middy gas system.

 

[varmint53]

Re: Velocity between 16" mid length and 16" carbine

I think that you will get a longer gas pulse with a carbine length with the shorter distance from port to the bolt,where with a middy your port is farther from the bolt,and the cycle won;t be as long with the middy, Does that make sense.

 

[Oakland Tactical]

Re: Velocity between 16" mid length and 16" carbine

My thought is that the carbines pressure drops as the bullet passes the port. Then the additional bullet travel after the port is loosing potential pressure for the rest of the barrel. You have a longer time frame from the bolt to the mid length which seems to allow less gas to bleed off.

 

[varmint53]

Re: Velocity between 16" mid length and 16" carbine

Are you saying that you will get less gas or more with the mid,,cause I'm thinking that with a carbine you will get more gas ,,because of the amount of time the bullet will remain in the barrel,,compared to the mid being a shorter time. yes-no

 

[Oakland Tactical]

Re: Velocity between 16" mid length and 16" carbine

I am thinking you will get more gas volume, not pressure, with the mid. Because you will have more barrel for gas expansion before th bleed off of pressure takes place at the gas port. The gas is clearly expanding after the port but a portion of it is being bled off.

The carbine has more barrel in front of the port to back pressure the port so it seems that more volume of gas flow back through the carbine gas system instead of driving the bullet.

I am not trying to argue right or wrong. I just thought if the mid had a higher MV it would point in that direction.

 

[varmint53]

Re: Velocity between 16" mid length and 16" carbine

No arguement here I'm just not sure witch way it will go need more imput from ot5hers I guess.

 

[MX124]

Re: Velocity between 16" mid length and 16" carbine

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Re25</div><div class="ubbcode-body">I am thinking you will get more gas volume, not pressure, with the mid. </div></div>

This^

 

[SSSamurai]

Re: Velocity between 16" mid length and 16" carbine

I would think that a mid-length would have a fraction more velocity, but it would be very little. It has more time for acceleration before the gas port, when the pressure drops off. Also, it will depend on port size. Different manufacturers use different port sizes for what they believe is optimal.