Quick question about dwell time:

[Straight Shooter]

Dwell Time: does a longer dwell time have ANY effect on velocity? If I HAD to make a guess-Id guess it would increase it, if only slighty. Am I right or wrong?
Just something Ive been thinking on.

[BufordTJustice]

Dwell Time: does a longer dwell time have ANY effect on velocity? If I HAD to make a guess-Id guess it would increase it, if only slighty. Am I right or wrong?
Just something Ive been thinking on.

As I understand it, dwell time is directly linked to the amount of barrel between the gas port and the muzzle and that gas system pressure returns to atmospheric quickly thereafter (with a slight amount of blow down time) once the bullet has uncorked the barrel. This dimension, along with bore diameter and gas port size, is what determines the dwell time of the system.

You can get real precise and start to calculate the volume of the gas manifold/block and gas tube, but you get the idea.

I would imagine that, if there were any effect on muzzle velocity, it would be difficult to measure above the statistical noise of shot to shot variation between different barrels and would be more likely linked to large differences in gas port dimension... but I emphasize that this would be nearly impossible to measure with accuracy IMHO. But, in my observation of various clips of high speed video, the bullet has left the barrel before any effect could be placed on it by the gas system (and before the movement of any components has begun). At least in terms of a properly functioning DI AR.

So, for barrels of equal lengths, there will be no difference.

[Straight Shooter]

Very good answer sir, I thank you!!

[Failure2Stop]

Only at the extreme would a difference be noticeable.

[Savior 6]

You can get real precise and start to calculate the volume of the gas manifold/block and gas tube, but you get the idea.

Calculation along with trial and error such as KAC spending the time/resources to find a "self-regulating gas sytem" as oppossed to an Armalite "switch block" gas regulator/block for suppressor/no suppressor use.
OR the "boring out" of 10.5" SBRs/Colts.

Straight Shooter, don't get "wrapped around the axle" unless you are super-fine tuning your AR system/combo.
Dwell time equates to the reaction time the action/bolt/BCG of a weapon has time to properly go through a weapon's cycle of action and repeat reliably.

Eugene Stoner seems to have come up with an AWESOME solution and anyone in charge of those using it keeps trying to come up with a different solution although based on user/logistic requirements.

You want short? Go Short.
You want long? Go Long.
You want average? Go Middie.
And if want velocity, approach from that angle.

[markm]

So, for barrels of equal lengths, there will be no difference.

That'd be an interesting test. Although if a slight variance in velocity was detected, you couldn't attribute it to port location.... and in any case. SEE Failure2stop's post.

[BufordTJustice]

That'd be an interesting test. Although if a slight variance in velocity was detected, you couldn't attribute it to port location.... and in any case. SEE Failure2stop's post.

Yeah. I bet one would have to get a barrel with a GP barely big enough to cycle and another so large it's on the ragged edge of early extraction just to possibly see a difference in MV beyond the measured std deviation of a few FPS.

[cemoulton]

I could imagine if you had a 16" with a pistol gas port location and a 16" with a rifle gas port location that you would possibly find a miniscule speed increase with the rifle gas simply because the gas is allowed to push nearly the full length of the barrel before any is bled off through the gas port. But I agree with what others have already posted, it probably would not be a measurable amount, if for no other reason than standard deviations in velocity of even very high quality match ammo.

[sevenhelmet]

I seriously doubt you could measure any difference in MV based on gas system length, and I would not be surprised if there IS no difference.

Simple test? Shoot several rounds through a chrono with your AR. Then shoot several more of the SAME EXACT LOAD through your chrono with a bolt-action .223 with the SAME TWIST AND BARREL LENGTH as your AR. Note any difference in average muzzle velocity between groups, taking into account the standard deviation for the load. I would bet there is no statistically significant difference, or that any difference would be overshadowed by other factors, such as variances in seating depth, machining tolerances, actual barrel twist, etc.

Has anyone actually done this type of test? The results would be interesting.

[markm]

Has anyone actually done this type of test? The results would be interesting.

I think it was always reported that 30-50 fps was lost with a gas system. I'd have to look through my data to see if I have any duplicate loads shot in the 20 inch AR and the 20 inch bolt gun too.