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Posted: 6/10/2013 6:25:49 PM EDT
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Having read this article- http://www.defensereview.com/the-big-m4-myth-fouling-caused-by-the-direct-impingement-gas-system-makes-the-m4-unreliable/ - and many other sources regarding carbine length gas systems and heavier buffers, I am considering adding a heavier buffer and spring to my M4-forgery.
My rifle has a 16" "mil-spec" barrel with a carbine length gas system riding on a MKII CAV-15 lower, currently with a generic carbine buffer and Brownell's stock action spring. It has given me some extraction issues where it fails to extract the round from the chamber, usually with steel cases, but sometimes with brass. I found some of this was due to a weak extractor spring and replaced this with the BCM extractor spring and insert (I left out the o-ring for now). But the last time at the range I ran about 20-30 rounds of steel case then got a stuck brass case due to the extractor ripping clean through the case rim. Started the range session with a clean chamber. The case fell out by lightly dropping a cleaning rod down the barrel; it was not really that "stuck". I think this may be a good example of an "over-gassed" carbine system. With the stronger extractor, the harsh extraction is ripping through the case rim rather than slipping off as it appeared to be doing previously. The rifle also seems to have a fairly harsh recoil pulse, but maybe this is just the lighter weight of the plastic receiver. So therefore I'm considering giving an H2 buffer and a Springco blue spring (as recommended in the Defense Review article) a try. However, much of the ammo I shoot are handloads that are probably lower pressure than military ammo. Some examples of loads I've been running, all with 55 grain FMLBTs- 24.5 grains TAC 26.2 grains W748 25.1 grains Benchmark So I wonder if the heavier spring and buffer would be too much resistance and cause short-stroking issues with the these load recipes. Since the extraction issues have occurred, to one degree or another, with all these loads, I suspect the rifle is over-gassed with any moderate load, and could therefore still benefit from the heavier Springco action spring and H2 buffer. Your thoughts, ideas, experiences much appreciated, thanks! |
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If you are getting fail to extracts where the extractor is ripping the lip off the brass case, then after locking back the bolt carrier assembly to the rear you are able to remove the empty casing with little effort, this sounds to me possibly like the bolt is unlocking too early before the chamber pressure has started to drop. If it were my rifle, I would try a heavier buffer, and possibly a heavier tension action spring (buffer spring). The heavier buffer and/or spring will add more resistance behind the bolt carrier assembly, which in theory should cause the bolt to unlock slower. The Springco springs are a nice addition. If you go too heavy with the resistance, you will most likely then see a fail to eject. If you are still getting fail to extracts after the heavier resistance has been added, then I would look at a possible machining issue with the bolt, barrel extension (lugs), or combination of the two (stacking).
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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The 14.5" M4 carbine barrel has the same 'dwell time' as a 20" rifle barrel which is 7 inches of barrel after the gas port to muzzle. Also, as in the article check to see if your gas port is 1/16th of an inch. As for ripping apart a cartridge, as others have mentioned; if your gas timing is off then the extractor is trying to pull the cartridge out before the cartridge unseals itself from the chamber wall due to cartridges' swell for a split second. With the weapon's gas timing off this can cause the bolt to unlock before the cartridge shrinks back down; which the extractor is now trying to force the cartridge out.
Here's an article that helped me in understanding the DI gas system. http://www.ar15barrels.com/prod/operation.shtml |
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Thanks for responses guys. I also read the article on AR15barrels.com about the DI system, and it seemed to support the idea of a heavier buffer for a carbine gas system. My thinking is pretty much the same as yours, that the rifle is beginning the extraction cycle while the chamber is still under pressure, and I need to slow the down the extraction timing slightly.
Do you guys think I should jump directly to the H2 buffer or start with just an H buffer? Also, should I try the heavier buffer alone before adding the Springco spring? |
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Quoted:
Thanks for responses guys. I also read the article on AR15barrels.com about the DI system, and it seemed to support the idea of a heavier buffer for a carbine gas system. My thinking is pretty much the same as yours, that the rifle is beginning the extraction cycle while the chamber is still under pressure, and I need to slow the down the extraction timing slightly. Do you guys think I should jump directly to the H2 buffer or start with just an H buffer? Also, should I try the heavier buffer alone before adding the Springco spring? Since you already have a standard buffer, then pick up a H3. The three internal weights sizes of the two buffers are the same, just the standard buffer used standard steel weights, while the H3 uses heaver tungsten weights, and between the two buffers and swapping weights from each other, can make a H1 though H3 buffer instead. To change the weights, just punch out the buffer bumper roll pin to pull the bumper and weights. As for needing the extra tension spring, if you have to use a H3 buffer with standard ammo, you have larger problems on your hand, and the rifle/parts needs to go back to be corrected instead. |
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