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Posted: 8/9/2009 9:23:44 AM EDT
| I have a BM 16" carbine and in stock form the spent casing would land in the 2 oclock position with .223 spec ammo. now I've added an M16 carrier and a H buffer and my casings land at a strong 4 oclock and I'm getting heavy brass marks on the deflector, gun has not had any malfunctions in the 200rds since switching parts, but I'm starting to think maybe the .223 ammo is a little weak for this setup, I haven't tried any 5.56 ammo yet but plan on it when it isn't so dang hot out. Should I put the carbine buffer back in for the .223 loads or do you think I'm fine as is. |
Counterintuitively, forward ejection is a symptom of excessive bolt velocity - I've seen this a lot with 16" M4 carbines, especially when fitted with an AR15 bolt carrier and/or CAR buffer. When you added the heavier BC and buffer, your bolt velocity was reduced and thus the your ejection pattern moved back. Personally, I prefer my rifles to eject in the 3-4 o'clock region... if it were my gun I would run it just like you have it now (unless, of course, you encounter some actual reliability issues). In any case, as you put more rounds through it, the gas port will erode, the bolt velocity will increase again, and the ejection pattern will move forwards... the curse of the M4gery  .
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Stealthyblagga has it right.
The ejection pattern of the AR with a brass hump, given everything being equal and ideal, will be directly straight out the side, and the brass should land at least 4 to 5 feet away. The more forward the brass ejects, the hotter the system is running and the further to the rear the weaker the system is running. With the standart bolt and buffer, your system showed it was running hot. By changing to a heavier FA carrier and a heavier buffer, the velocity of the cycling bolt was reduced and thusly the ejection pattern shifted. What this means is that the gun is still running a bit hot out of the gas port, but you're now controlling this with heavier reciprocating parts that respond slightly less to the greater forces. What this also does is make for more mass on the return aspect of the cycling, meaning thatit has more force behind the bolt when it strips a new round off the top of the magazine, making for a more reliable feed system. In other words, leave the system like it is with the new heavier parts in it. M4s can be finicky, but you have one that will, all things being equal, run like a top with the new setup. Now get out there and train. |
| Order a couple ejector springs. Try setting the first one to a length that you just barely have to put a little pressure on a little to get the pin set back in place. This should give you about 2 oclock ejection. The springs just grind off easily to whatever length you want. Keep the one you have in there as a control to measure with or go back to if you need it. Tolerance on bolt holes the spring sets in can vary and sometimes they use the wrong spring. Most rifles eject at 4-5 oclock but I set mine at 2 oclock as they run best for me there and save dings. Just remember to keep you right side bench clear of objects to prevent brass bounce back. I really dont believe an m-16 carrier will shoot as good as the AR 15 carrier for felt recoil , but the H buffer will be a plus. On semi I always go lighter on the carriers to avoid the slam home affect. Which carrier shoots best for you ? |
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I don't understand your theory how shorter, weaker ejector spring will throw brass toward 2 o'clock position without hitting the brass deflector.
It has to hit something to bounce in that direction. I will buy some ejector springs and test your theory. Where should I buy them? Brownells has them. Good to go? |
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