How is the 11.5 has 40% more dwell time than a 10.5 calculated?
How is the 11.5 has 40% more dwell time than a 10.5 calculated?
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Sic Semper Tyrannis
Just a guess, but gas to muzzle length must be 40% longer thanks to the added overall length.
I’m not saying this to pick on you or BCM, but it’s just good marketing. The hard truth is that dwell doesn’t matter much at carbine gas length and 40% dwell time makes most people think it runs 40% better. Dwell time is a real concern at the much lower port pressure of rifle gas length.
The problem with carbine gas is that it exposes things like lack of buffer weight, weak extractor springs, damaged or poor magazines, and crazy port sizes. All things that have been figured out and are fixable, but are known even on the 14.5”. The difference from 14.5” all the way down to 10.5” is just very, very marginal if the above things are taken care of.
So is there even any difference in the dwell time between an 11.5 vs a 10.5?
If there is a difference how is measured?
You won't outvote the corruption.
Sic Semper Tyrannis
Dwell time is how long the gas port is under pressure. So from the gas port to the end of the barrel.
If the gas length stays the same, a longer barrel has more dwell. Both the 10.5” and 11.5” use carbine length gas systems, so the 11.5” has more dwell.
My position is that it doesn’t really matter, both can be reliable.
I think you should focus on getting a quality barrel that isn’t known for excessive port sizes first, the length difference second.
Yes, there's obviously a difference between the two.
One way to calculate dwell time:
take the distance from gas port to muzzle and divide by average bullet velocity
The 10.5" has 2.83" and the 11.5" has 3.83"
If you use an average velocity of 2600 fps and 2675 fps (and convert to inches), you'll get approximately
91 microseconds for the 10.5"
119 microseconds for the 11.5"
That difference is 32% more by our math, and the difference between 10.3 and 11.5 is about 44%, so perhaps the 40% number is close enough to the average of those.
Black River Tactical
BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
BRT Bolt Carrier Groups M4A1, M16 CHROME
BRT Covert Comps 5.56, 6X, 7.62
Keep in mind, one shouldn't focus on a single parameter without considering all the other related parameters.
There is no universally "correct" dwell time.
A better version of that question would be:
"Given a barrel of X length, Y cartridge chamber and Z suppressor use, where should the gas port be located for best performance?"
Black River Tactical
BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
BRT Bolt Carrier Groups M4A1, M16 CHROME
BRT Covert Comps 5.56, 6X, 7.62
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