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11/22/2017 10:05:29 PM
Posted: 10/6/2004 9:19:14 AM EST
I have a 16" barrel with carbine gas system... am i right in assuming that i have higher pressures since my barrel is longer but is using gas system that is designed for 14.5 barrel? Therefore my carrier is traveling rearward with more velocity than a 14.5in barrel?

Thanks!
Link Posted: 10/6/2004 10:04:49 AM EST
That's how I understand it.
Link Posted: 10/6/2004 1:16:27 PM EST

Originally Posted By jar3ds:
I have a 16" barrel with carbine gas system... am i right in assuming that i have higher pressures since my barrel is longer but is using gas system that is designed for 14.5 barrel? Therefore my carrier is traveling rearward with more velocity than a 14.5in barrel?

Thanks!



All else being equal yes. But not all else is necessarily equal... gas port sizes vary.
Link Posted: 10/7/2004 9:04:09 AM EST

Originally Posted By wyv3rn:

Originally Posted By jar3ds:
I have a 16" barrel with carbine gas system... am i right in assuming that i have higher pressures since my barrel is longer but is using gas system that is designed for 14.5 barrel? Therefore my carrier is traveling rearward with more velocity than a 14.5in barrel?

Thanks!



All else being equal yes. But not all else is necessarily equal... gas port sizes vary.



thats a good point... thanks!
Link Posted: 10/7/2004 9:24:32 AM EST
[Last Edit: 10/7/2004 9:34:56 AM EST by jmart]

Originally Posted By jar3ds:
I have a 16" barrel with carbine gas system... am i right in assuming that i have higher pressures since my barrel is longer but is using gas system that is designed for 14.5 barrel? Therefore my carrier is traveling rearward with more velocity than a 14.5in barrel?

Thanks!



If I understand correctly, with equal gas port sizes and equal port locations, pressures on the carrier are the same. Max pressure of about 55-60K psi will be achieved well before the bullet reaches the gas port. Depending on powder burning rate, max pressure can be achieved with the bullet only an inch or so down the barrel. From that point forward, as the bullet travels down the barrel, pressure falls.

As the bullet continues down to the point where it passes the port, pressure bled off through the tube to the carrier is the same -- overall barrel length has nothing to do with the pressure at this point. The only variable regulating how much pressure is bled off to the carrier is the port size, port location on the barrel, and the gas tube internal diameter. There may be a timing issue where pressure has to be applied for certain duration, so with this in mind, a 16" barrel will apply pressure for a longer duration than a 14.5" barrel, but realize the pressure being applied is decreasing over time as the bullet continues down the barrel.

Where the difference between the two barrel lengths comes into play is in residual pressure at the muzzle. The 16" barrel will have less pressure at the muzzle than a 14.5" barrel since the internal volume contained in the 16" barrel is greater. Basically, the greater the internal volume, the less the presure.
Link Posted: 10/7/2004 12:29:45 PM EST

Originally Posted By jmart:

Originally Posted By jar3ds:
I have a 16" barrel with carbine gas system... am i right in assuming that i have higher pressures since my barrel is longer but is using gas system that is designed for 14.5 barrel? Therefore my carrier is traveling rearward with more velocity than a 14.5in barrel?

Thanks!



If I understand correctly, with equal gas port sizes and equal port locations, pressures on the carrier are the same. Max pressure of about 55-60K psi will be achieved well before the bullet reaches the gas port. Depending on powder burning rate, max pressure can be achieved with the bullet only an inch or so down the barrel. From that point forward, as the bullet travels down the barrel, pressure falls.

As the bullet continues down to the point where it passes the port, pressure bled off through the tube to the carrier is the same -- overall barrel length has nothing to do with the pressure at this point. The only variable regulating how much pressure is bled off to the carrier is the port size, port location on the barrel, and the gas tube internal diameter. There may be a timing issue where pressure has to be applied for certain duration, so with this in mind, a 16" barrel will apply pressure for a longer duration than a 14.5" barrel, but realize the pressure being applied is decreasing over time as the bullet continues down the barrel.

Where the difference between the two barrel lengths comes into play is in residual pressure at the muzzle. The 16" barrel will have less pressure at the muzzle than a 14.5" barrel since the internal volume contained in the 16" barrel is greater. Basically, the greater the internal volume, the less the presure.



If I'm reading this correctly, this effectively explains muzzle blast being greater on the 14.5" vs. 16" and greater. Shorter barrel, less dwell time, greater pressures = more noise.
Link Posted: 10/7/2004 4:21:34 PM EST
16 inch vs. 14.5 inch with the FSB the same distance from the chamber:

Using the same ammunition, within normal variances, bullet will reach the gas ports at the same time.

Initial gas pulse will be the same amount of pressure on the port and the carrier.

Initial unlocking sequence will begin at the same time.

Length of gas pulse will be longer on the 16 inch barrel, as it takes the bullet longer to exit the muzzle.

The end result, with identical sized ports, will be more total energy applied over a longer time with the 16 inch barrel, which means you MAY need a larger port with the shorter barrel, or MAY get by with a smaller one on the longer one.

I'm thinking less pressure over a longer time would be a good thing. Less stress on the whole system and PROBABLY more reliable.

DISCLAIMER:

I am NOT any sort of engineer and did NOT stay at a Holiday Inn last night. This is strictly my "Armchair Commando/Engineer" opinion, and I may very well be full of it.



Lonny
Link Posted: 10/7/2004 6:04:36 PM EST
i don't know about having a smaller port in a 16"... i'd rather just run it having my carrier being pushed back a little harder than not softer... the harder the more able it'll get through grit and carbon...

i can almost bet that i won't ever have a shortstroke...
Link Posted: 10/7/2004 6:20:58 PM EST

Originally Posted By jar3ds:
i don't know about having a smaller port in a 16"... i'd rather just run it having my carrier being pushed back a little harder than not softer... the harder the more able it'll get through grit and carbon...

i can almost bet that i won't ever have a shortstroke...



Nope they won't short cycle but they will start the bolt moving backward when the pressure within the barrel is still high (higher than on a 20" rifle) and may cause extraction problems. These aren't imagine symptoms and are why the PRI fatboy gas tube, Stinger gas tube, Wolff XP extractor springs, Wolff XP action springs, H buffers and H2 buffers, LMT carriers, LMT dual extractor bolts and D-fenders and M4 HBAR SOCOM barrels weren't created. Carbines regardless of barrel length have shorter bolt and extractor lives than 20" guns. They cycle faster than the original design (20").

It's just like with a 5" 1911 any departure from the 5" original to make it smaller is a compromise on reliability.
Link Posted: 10/7/2004 6:30:43 PM EST

Originally Posted By gotm4:

Originally Posted By jar3ds:
i don't know about having a smaller port in a 16"... i'd rather just run it having my carrier being pushed back a little harder than not softer... the harder the more able it'll get through grit and carbon...

i can almost bet that i won't ever have a shortstroke...



Nope they won't short cycle but they will start the bolt moving backward when the pressure within the barrel is still high (higher than on a 20" rifle) and may cause extraction problems. These aren't imagine symptoms and are why the PRI fatboy gas tube, Stinger gas tube, Wolff XP extractor springs, Wolff XP action springs, H buffers and H2 buffers, LMT carriers, LMT dual extractor bolts and D-fenders and M4 HBAR SOCOM barrels weren't created. Carbines regardless of barrel length have shorter bolt and extractor lives than 20" guns. They cycle faster than the original design (20").

It's just like with a 5" 1911 any departure from the 5" original to make it smaller is a compromise on reliability.



Anyone use a Tubbs Carrier Weight System? It's supposed to address this situation by increasing the mass of the carrier. The bolt is supposed stay locked up a tad longer which allows gas pressure to decrease so you don't get such a quick impulse on extraction. Also, it supposedly allows case walls to shrink back some more so extraction is eased. The literature sounds convincing but I'm not really sure how effective it would be in carbine.
Link Posted: 10/7/2004 6:37:28 PM EST

Originally Posted By jmart:

Originally Posted By gotm4:

Originally Posted By jar3ds:
i don't know about having a smaller port in a 16"... i'd rather just run it having my carrier being pushed back a little harder than not softer... the harder the more able it'll get through grit and carbon...

i can almost bet that i won't ever have a shortstroke...



Nope they won't short cycle but they will start the bolt moving backward when the pressure within the barrel is still high (higher than on a 20" rifle) and may cause extraction problems. These aren't imagine symptoms and are why the PRI fatboy gas tube, Stinger gas tube, Wolff XP extractor springs, Wolff XP action springs, H buffers and H2 buffers, LMT carriers, LMT dual extractor bolts and D-fenders and M4 HBAR SOCOM barrels weren't created. Carbines regardless of barrel length have shorter bolt and extractor lives than 20" guns. They cycle faster than the original design (20").

It's just like with a 5" 1911 any departure from the 5" original to make it smaller is a compromise on reliability.



Anyone use a Tubbs Carrier Weight System? It's supposed to address this situation by increasing the mass of the carrier. The bolt is supposed stay locked up a tad longer which allows gas pressure to decrease so you don't get such a quick impulse on extraction. Also, it supposedly allows case walls to shrink back some more so extraction is eased. The literature sounds convincing but I'm not really sure how effective it would be in carbine.



In my 16" I use a M16 carrier, PRI fatboy gas tube, Wolff XP extractor spring and a LMT H buffer and to be honest I cannot tell the difference in recoil or muzzle rise between it and my 20" A4gery rifle.
Link Posted: 10/7/2004 6:53:10 PM EST
If I may go off on a tangant for a sec. Would the increase in pressure dwell time between a 14.5" and a 16" account for more Gas being released into the action of an AR and also increase Port noise? or vise versa?

My 16" carbine is a midlength so it has roughly 6.5" from gas port to muzzle
My 14.5" carbine has roughly 8.5" from gas port to muzzle

Running the same suppressor on both rifles the 14.5" has more port noise but less "Dirt" in the reciever for the same amount of ammo fired,..

Sounds like a question I know so bear with me.............Udog

Link Posted: 10/7/2004 7:03:13 PM EST

Originally Posted By underdog75:
If I may go off on a tangant for a sec. Would the increase in pressure dwell time between a 14.5" and a 16" account for more Gas being released into the action of an AR and also increase Port noise? or vise versa?

My 16" carbine is a midlength so it has roughly 6.5" from gas port to muzzle
My 14.5" carbine has roughly 8.5" from gas port to muzzle

Running the same suppressor on both rifles the 14.5" has more port noise but less "Dirt" in the reciever for the same amount of ammo fired,..

Sounds like a question I know so bear with me.............Udog




The 14.5" CAR has more port noise because the bolt is opening before that of the 16" midlength. The shorter the gas system the sooner the bolt opens unless measure(s) are made to counter the effect. Meaning using a larger volume gas tube, heavier buffer, stronger buffer spring, LMT carrier (larger volume gas chamber) etc. Simply put the longer the bolt stays closed the better. Anything to get a shorter gas system AR it to duplicate that of a 20" rifle or a slightly longer will make it work the best and have the longest bolt and extractor life.
Link Posted: 10/7/2004 7:08:46 PM EST
OK so how do we explain a 16" middy running dirtier than the 14.5"?
The Middy has a rifle length buffer and rifle length Xtra power recoil spring
The 14.5 has an H buffer and xtra power recoil spring

Oh yeah and how much wood could a woodchuck chuck if a woodchuck could chuck wood?

.............Howya doing tonight Robb?
Link Posted: 10/7/2004 7:23:22 PM EST
[Last Edit: 10/7/2004 7:31:32 PM EST by gotm4]

Originally Posted By underdog75:
OK so how do we explain a 16" middy running dirtier than the 14.5"?
The Middy has a rifle length buffer and rifle length Xtra power recoil spring
The 14.5 has an H buffer and xtra power recoil spring

Oh yeah and how much wood could a woodchuck chuck if a woodchuck could chuck wood?

.............Howya doing tonight Robb?



Your middy is most likely staying closed longer than your 14.5". Your middys rifle buffer is 5 something ounces and an H buffer is 3 something ounces. Both ARs have +10% XP springs with the rifle having a longer travel (which equates to slowler cyclic rate). The heavier rifle buffer with a stronger than stock spring and a longer than CAR gas tube is going to make it stay closed longer than a CAR thus the reason its quieter with the suppressor. Dirtyness can be because of how well the gas tube fits the gas key on the carrier, headspace, throat erosion, how well the bullet fits the barrel, gas rings etc. These are built by humans shit varies a little. Just like two identical Corvet Z06s, 1 might have 420hp and one my only have 405hp. Tolerences!

I'm good how are you?
Link Posted: 10/7/2004 7:32:57 PM EST
go to bed and quite talking about gas systems :-)... heh, just kidding
Link Posted: 10/7/2004 8:39:12 PM EST
Where's Tweak?
Link Posted: 10/7/2004 9:04:03 PM EST

Originally Posted By gotm4:

Originally Posted By underdog75:
OK so how do we explain a 16" middy running dirtier than the 14.5"?
The Middy has a rifle length buffer and rifle length Xtra power recoil spring
The 14.5 has an H buffer and xtra power recoil spring

Oh yeah and how much wood could a woodchuck chuck if a woodchuck could chuck wood?

.............Howya doing tonight Robb?



Your middy is most likely staying closed longer than your 14.5". Your middys rifle buffer is 5 something ounces and an H buffer is 3 something ounces. Both ARs have +10% XP springs with the rifle having a longer travel (which equates to slowler cyclic rate). The heavier rifle buffer with a stronger than stock spring and a longer than CAR gas tube is going to make it stay closed longer than a CAR thus the reason its quieter with the suppressor. Dirtyness can be because of how well the gas tube fits the gas key on the carrier, headspace, throat erosion, how well the bullet fits the barrel, gas rings etc. These are built by humans shit varies a little. Just like two identical Corvet Z06s, 1 might have 420hp and one my only have 405hp. Tolerences!

I'm good how are you?



Im good as well......... BTW easy on that "built by humans shit varies a little" stuff these are Dog built rifles!
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