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Gas port size question
12/28/2011 6:36:03 PM
I remember somebody who was having ADCO do some work on a barrel, and asked about optimum gas port size based on his barrels length and gas system length. I wish I knew how you can calculate that, but I don't, and have been wondering about something:
M-4 barrels, (14.5" barrel, w/carbine length gas system) have a 0.63" gas port, which AFAIK is what he optimal gas port size is for that configuration.
So a 16" barrel w/car-length gas system should have a smaller gas port for optimum functioning, but most makers drill it as large or larger than that of a 14.5" M-4 barrel.
So I wonder what size would the gas port need to be on a 16" car barrel to approximate the same functioning as an M-4 barrel? as a wild guess, I would think ~0.50", but I really don't know. How about 1mm?
M-4 barrels, (14.5" barrel, w/carbine length gas system) have a 0.63" gas port, which AFAIK is what he optimal gas port size is for that configuration.
So a 16" barrel w/car-length gas system should have a smaller gas port for optimum functioning, but most makers drill it as large or larger than that of a 14.5" M-4 barrel.
So I wonder what size would the gas port need to be on a 16" car barrel to approximate the same functioning as an M-4 barrel? as a wild guess, I would think ~0.50", but I really don't know. How about 1mm?
12/28/2011 7:52:50 PM
The only "Optimal" gas port size you will find, is if someone uses ONLY one type AND brand of ammo. Then the gas port can be adjusted to give perfect function and ejection path.
What i think is optimal, is whatever makes it WORK, with all types and brands of ammo. I don't give a rat's ass if it ejects at 2 o'clock or 5 o'clock, as long as it WORKS. That usually means error on the larger side, which will give different ejection paths for different ammo.
Have never seen a difference in port sizes from 14.5" to 16". Have seen a WIDE variance from manufacturer to manufacturer in port sizes though.
We have port sizes that we use, that through MUCH trial and error, seem to make them function pretty good (we do not freely give those out). That is not to say ours are any better than anyone else (except for the ones that don't work).
In short, if your gun works reliably, with all types of ammo, THAT is optimal. If it does not, start experimenting (i suggest a little at a time) until it does.
What i think is optimal, is whatever makes it WORK, with all types and brands of ammo. I don't give a rat's ass if it ejects at 2 o'clock or 5 o'clock, as long as it WORKS. That usually means error on the larger side, which will give different ejection paths for different ammo.
Have never seen a difference in port sizes from 14.5" to 16". Have seen a WIDE variance from manufacturer to manufacturer in port sizes though.
We have port sizes that we use, that through MUCH trial and error, seem to make them function pretty good (we do not freely give those out). That is not to say ours are any better than anyone else (except for the ones that don't work).
In short, if your gun works reliably, with all types of ammo, THAT is optimal. If it does not, start experimenting (i suggest a little at a time) until it does.
12/28/2011 8:12:08 PM
Originally Posted By PropDoc:
The only "Optimal" gas port size you will find, is if someone uses ONLY one type AND brand of ammo. Then the gas port can be adjusted to give perfect function and ejection path. True, but I was asking in a more general sense.
We have port sizes that we use, that through MUCH trial and error, seem to make them function pretty good (we do not freely give those out). That is not to say ours are any better than anyone else (except for the ones that don't work). But can you at least tell me if you've tried either a ~0.50" or ~0.40" gas port on a 16" CAR barrel, and did it work?
The only "Optimal" gas port size you will find, is if someone uses ONLY one type AND brand of ammo. Then the gas port can be adjusted to give perfect function and ejection path. True, but I was asking in a more general sense.
We have port sizes that we use, that through MUCH trial and error, seem to make them function pretty good (we do not freely give those out). That is not to say ours are any better than anyone else (except for the ones that don't work). But can you at least tell me if you've tried either a ~0.50" or ~0.40" gas port on a 16" CAR barrel, and did it work?
12/28/2011 8:25:23 PM
Ok, so hypothetical question, If somebody has a partially finished 16.5" AR-15 barrel, (yes, 16.5", an extra half inch more than usual) and what's to use the carbine length gas system because, for whatever reason, they want to be able to use the short 7" handguards, what size gas port would you recommend they drill?
And yes, this really is a hypothetical question, I don't have an oddball project going.
And yes, this really is a hypothetical question, I don't have an oddball project going.
12/29/2011 4:28:43 PM
Originally Posted By Jolkm:
Ok, so hypothetical question, If somebody has a partially finished 16.5" AR-15 barrel, (yes, 16.5", an extra half inch more than usual) and what's to use the carbine length gas system because, for whatever reason, they want to be able to use the short 7" handguards, what size gas port would you recommend they drill?
And yes, this really is a hypothetical question, I don't have an oddball project going.
Ok, so hypothetical question, If somebody has a partially finished 16.5" AR-15 barrel, (yes, 16.5", an extra half inch more than usual) and what's to use the carbine length gas system because, for whatever reason, they want to be able to use the short 7" handguards, what size gas port would you recommend they drill?
And yes, this really is a hypothetical question, I don't have an oddball project going.
If i were building a CAR gas system barrel, that is 14" to 18" long, i would drill it .065".
Edit to answer question: .040" is to small, and would give reliability issues if it worked at all. .050" would probably work, but only with very good, high power ammo.
12/29/2011 5:46:26 PM
Originally Posted By PropDoc:
If i were building a CAR gas system barrel, that is 14" to 18" long, i would drill it .065".
Edit to answer question: .040" is to small, and would give reliability issues if it worked at all. .050" would probably work, but only with very good, high power ammo.
Originally Posted By Jolkm:
Ok, so hypothetical question, If somebody has a partially finished 16.5" AR-15 barrel, (yes, 16.5", an extra half inch more than usual) and what's to use the carbine length gas system because, for whatever reason, they want to be able to use the short 7" handguards, what size gas port would you recommend they drill?
And yes, this really is a hypothetical question, I don't have an oddball project going.
Ok, so hypothetical question, If somebody has a partially finished 16.5" AR-15 barrel, (yes, 16.5", an extra half inch more than usual) and what's to use the carbine length gas system because, for whatever reason, they want to be able to use the short 7" handguards, what size gas port would you recommend they drill?
And yes, this really is a hypothetical question, I don't have an oddball project going.
If i were building a CAR gas system barrel, that is 14" to 18" long, i would drill it .065".
Edit to answer question: .040" is to small, and would give reliability issues if it worked at all. .050" would probably work, but only with very good, high power ammo.
It's interesting you mention 14-18", I remember seeing in an old magazine/catalog from 2005 that Wilson Combat made an AR with CAR-gas 18" barrel, which has always intrigued me. Even being the short-as-feasible handguard/gas system fan that I am, I admit that's probably pushing it, and it would probably be tricky to get that to work well, which is probably why they don't make it anymore, but still it interests me, and I wonder what size gas port they used for it.
