Gas Pressure 14.5" vs. 10.3"

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Bart212

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Will having a shorter gas tube on my AR affect the blowback pressure on the bolt-buffer-spring-buffer tube? As the gas port will be closer to the chamber. I'm changing my AR to a 10.3" and am wondering if I'll need a heavier spring.
 
With C77/M855 fodder, carbine length barrels (10.5" barrels to 14.5" barrels) operate at 26,000 psi out the gas port. Midlengths (14.5" to 16" lengths) run at 17,000 psi at the gas port and about 13,500 psi with a 20" barrel.

I doubt you'll find an AR recoil spring of varying power, but you can compensate for any erratic behavior or dwell time with a heavier buffer and/or a heavier carrier.
 
ESQ said:
Both have carbine length gas tubes....
Click to expand...

They're the same length but aren't the gas holes on a 10.5 larger?

I use both a 14.5" & 10.5" on the same lower and both operate fine with the same buffer and springs, both also use FA carriers.
 
41 Colt said:
They're the same length but aren't the gas holes on a 10.5 larger?
Click to expand...

It is.

Colt uses a .093" for their 10.5" barrels and .063" for 14.5". The pressure difference between the two lengths and hole sizes is negligible.
 
Do you know what LMT runs for the 10.5s? IIRC they are a bit smaller than the colts.
 
ESQ said:
Do you know what LMT runs for the 10.5s? IIRC they are a bit smaller than the colts.
Click to expand...

LMT does use relatively small gas ports on their 10.5s ( about .071" ) . I have measured my Noveske 10.5 and WOA 10.5 to .079 / .080 for comparison
 
So does anyone have a manufacturers chart which compares cyclic times between:

Hole Size;
Tube Length;
Tube Size;
vs.
Carrier Weight;
Buffer Weight;
Gr. Weight of bullet;
Spring Resistance (if there is a difference).
 
re

LMT specifies that some of their bolt carriers are specific to barrel length (not to be used with less than 14.5" barrel length). This has to do with dwell time,etc. They offer an "enhanced" bolt carrier that deals with this issue. I have run into issues with my 3 LMT AR`s. I swapped out BCG`s with my 10.5" and 14.5" and had some double feed and stove pipe stuff going on for abit. Swapped `em back again and problem solved. Some guys have had no problem at all doing the same thing that gave me issues? Go figure.....
 
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