AR Sponsor
Posted: 10/13/2008 4:53:00 PM EDT
|
I don't know if this has been discussed before and I ask for no reason other than my own curiosity; All other things being equal (same barrel length, same ammo, same rifling, contour, muzzle devices, yakity-yak), does gas system length have an impact on muzzle velocity? For instance, an 18 inch barrel can be had with rifle length or mid length gas systems; Does one have significant differences in velocity from the other, would the differences be negligible, or would there be no differnce? |
| The results would be zip. Derrick Martin, author of “The complete Guide to AR-15 Accuracy" did a series of tests which consisted of blocking off the gas port and chronographing the results compared to with the gas port open. The results showed a higher velocity with the open gas port! The amount was small and could have easily reversed on another series of tests. FWIW |
That's funny, I thought about asking this when I first joined to see if there was a way to squeeze any more velocity out of the same length barrels, but after reading a bunch of tests and design stuff about the AR I found it didn't make any difference. I should have just asked here and got the answer much quicker! |
I highly doubt that. The projo has already exited the barrel by the time the bolt unlocks, that doesnt even make sense. Any difference would be minuscule. |
Exactly, his system is designed to delay unlocking the bolt which makes it easier on both the brass and the rifle. Edited for text/quote |
When using a statistically significant sample size, say 30 shots, there is a small but demonstrable difference in the velocities from a barrel with the gas port clamped and the same barrel with the gas port left open to the direct impingement gas system.  |
Those results don't surprise me and would be more in line with what I would expect with a larger sample size. They still fall in the catagory of "zip". I don't believe I would want to make a single shot out of my AR for that velocity gain. 
|
Really? How do you interpret this statement from straight from the product information?
Hmmmm? |
See! DI>Piston!  instead of the CWS, couldnt you just get an m16 carrier? |
He is saying that the heavier bolt carrier allows you to load to slightly higher pressures without showing pressure signs on your primers or beating up your brass too much, thanks to the slightly delayed unlocking. A small amount, but still, an amount. It does NOT mean that adding weight to the bolt carrier will magically increase velocity for a given load. Come on man, that doesnt even make sense. Think about it. |
Wouldn't higher pressures give you higher velocities? That does make sense.......... |
You arent getting what I am saying at all. Adding a heavier buffer doesn't magically increase the pressure or velocity. There will be no change with the same ammo. None. If you RELOAD, you can RELOAD the ammo to have slightly higher pressure before you see pressure signs, thanks to the slightly delayed unlocking, but the difference is slight. You can LOAD the ammo slightly hotter without beating up your brass AS MUCH. With the SAME ammo, adding a heavier buffer does NOT increase velocity. End of story. Make sense? |
|
Thanks for the info guys. I guess my original thoughts concerned timing, the amount of gas diverted to operate the rifle, etc. I was leaning in my mind towards either no difference or a miniscule one, but have been surprised on other subjects before. It was interesting to see the results with the clamped port, DI system and piston. |
No.......not when we are we talking about the bolt carrier. |
| well the buffer and BCG act as 1 unit when moving back so adding wieght to either one would have the same effect(Im not talking about the return, just the backward motion). Wieght doesnt matter because the BCG doesnt start to move back until the bullet has exited the barrel anyway, especially for light loads. Besides it wont increase the pressure, just the time the bullet is under max pressure IF and ONLY IF the lighter BCG would start to move b4 the bullet has exited the barrel AND the heavy BCG would not. |
AR Sponsor