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Posted: 1/19/2011 6:19:28 AM EDT
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i have an M&P 15 OR carbine. all stock including the buffer. I'm going to get a BCM 20 inch rifle upper (if they ever come back in stock). do i need to change or should i change the buffer if i put it on the M&P carbine lower?
if i should change what do you suggest going with? |
| Carbine stocks take carbine buffers. The difference between a "carbine buffer" and a "rifle buffer" is its length and weight-carbine buffers are obviously shorter and typically about 1 to 1.5 oz lighter than rifle buffers. It's likely that your 20" upper will run fine with a carbine buffer. While the carbine buffer is lighter than a rifle buffer, your upper's "rifle length" gas system will provide a later, gentler gas impulse to the carrier, which should counteract the effect of the lighter buffer. |
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That depends on the malfunction. If the carrier slams back to hard and bounces (which can cause failures to feed), you need a heavier carrier. If it doesn't consistently cycle all the way back (which can cause incomplete extraction/ejection) then you need a lighter one. In most cases a heavier buffer is only needed in high cyclic rate applications, not in semi-auto rifles. The Canadian Forces C7A2 is a 20" upper on a carbine lower; it uses an H2 buffer. For comparison, here's a list of buffers and their weights (accumulated from a variety of sources...)
CAR std 3.0oz CAR H 3.8oz CAR H2 4.6oz CAR H3 5.4oz RRA 9mm 5.6oz Rifle 5.1oz (obviously this won't work in a carbine lower) You can go crazy trying to figure out what "perfect" buffer to get, or you can start out with a standard carbine buffer and change if you feel you need to. I'd go with a standard buffer and change only if there were real problems. |
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