One other consideration; from lessons learned in combat, it has been found that the M4, with it's 16 inch barrel has more cycling problems than the longer 20 inch barrel of the M16. This is due to the shorter gas tube having less room to dissipate some of the gas pressure, which in turn causes a quicker cyclic action. This translates into a cyclic speed of 900+ rounds per minute verses 750 rounds per minute. This results in the bolt arriving at the next round before it it completely seated correctly in the magazine. Best case scenario at this point is that you have a stoppage, and you have to eject the round manually and manually cycle the next one. Worst case scenario is catastrophic failure of an accidental discharge, and your weapon blows up in your face. You have three options to resolve this issue, depending on how much you fire your rifle. 1. Cheapest is to put an 0-ring under your extractor, which will force it to strip the next round out of the magazine. If you fire a lot of rounds, this is not a viable answer as you will end up with a broken extractor before long, which ends up as a projectile coming out of your ejection port 2. More expensive (and safer) solution is to swap out your milspec buffer with a hydraulic buffer, which will last about as long as your barrel, and if it fails, will not cause any damage to other parts of your rifle. If you fire your rifle once a month or more, this is a reasonably priced option, running about 70-80 bucks. 3. Most expensive, but longest lasting solution, is to convert to a piston system, which can run $300 and up, depending on which brand you get. If you can change a gas tube, you should be comfortable with installing one of these systems. They not only slow down the cyclic action, but they are significantly less time consuming to clean. They also keep the heat out of the bolt carrier group, which reduces the opportunity for accidental discharges due to a cookoff if you are firing a lot of rounds. Hopefully some of this information can help out. May you have many successful days at the range.