AR Sponsor
Posted: 1/29/2017 6:32:56 PM EDT
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To level set:
"Dwell time" is the time from when the bullet passes the gas port (sending the gas down the gas tube to actuate the bolt carrier group) until the bullet exits the barrel (which lets all the remaining gas escape and stops pushing the BCG). The following are (according to my measurements), the distances between the Gas Port and the end of the Barrel (resulting in the "dwell time") based on which gas length system is used. Basically a Midlength is +2" more than Carbine and Rifle is +3.5" over Midlength. (I don't know the length for "Intermediate".) 20" Barrel (M16) Rifle = 6.75" Midlength = N/A Carbine = N/A 18" Barrel Rifle = 4.75" Midlength = 8.25" Carbine = N/A 16" Barrel (most AR-15s) Rifle = N/A Midlength = 5.75" Carbine = 7.75" 14.5" Barrel (M4) Rifle = N/A Midlength = N/A Carbine = 6.25" Using this information, I can see why the Carbine-length system was instituted for the 14.5" M4 (being a half-inch within the amount of dwell time length of the 20" M16). While the different spring/buffer between the M16 rifle and the M4 carbine doesn't quite make it apples-to-apples, this dwell time would seem to deliver gas for about the same amount of time to the M4 as the M16/AR-15 was originally designed to use. |
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Trying to put it all in perspective, my questions are:
1. How “overgassed” is the original M16/AR-15 design? Does the 32% reduction for a Rifle-Length 18” (which seems to be the shortest dwell time) vs. a Rifle-Length 20” still deliver enough pressure to reliably cycle even weak (low end .223 in low temperatures) loads? 2.How much does a heavier Buffer and/or stronger Spring cancel out longer dwell times? And where does this become too much? Obviously, these heavier Buffers, heavier Springs, and Adjustable Gas Blocks change the calculations. |
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Quoted:
You can't measure time in inches. |
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