
Originally Posted by
Eric D.
IIRC the specified cyclic rate for an M4 carbine is between 700-900 cycles per minute. There's your operating parameters and I don't think anyone will disagree that a gun operating outside that range is more likely to have issues.
Brass ejection may give you reason to suspect over-gassing but the only definitive way to tell if a gun is operating outside of cyclic rate specifications is to do cyclic rate testing with high speed photography or some other method. There is just no way to know how fast the carrier is moving by looking at the where the brass is going.
Yes and no.
Exact speeds? You're right. Pull out the do-hickeys and do-dads.
Behavioral wise though, experience shows us that, once again, with all things being equal (appropriate milspec parts, springs, etc, that are still well within their expected life cycle) that the gun will behave in certian manners that give a good indicator of bolt speed being either within spec, or outside of it.
As has already been established, under "normal" circumstances, indicators of out of spec bolt speed are in fact caused by other aspects such as worn action springs, ejector springs, fouling, loose carrier keys, etc. Meaning that simple parts replacement removes those false indicators and all is well because the bolt speed was never actually out of spec.
But, when all of those other factors are accounted for and the gun is still behaving in a certian manner, it does in fact mean that bolt speed (i.e. the cyclic rate as you mentioned) is out of spec and other issues need to be looked at. Gas port erosion, incorrectly machined chamber/throat or excessive gas port size (if on a brand new gun), etc.
I fully understand that all brass throw does under normal circumstances is indicate that *something* is mimicing either excess or under gassing, but it's a hell of a lot easier to know which end of the spectrum to start troubleshooting from by paying attention to ejection. That's all i've been trying to say this entire time.
Last edited by GrumpyM4; 10-01-12 at 00:34.
It is missing the point to think that the martial art is solely in cutting a man down; it is in killing evil. It is in the strategem of killing the evil of one man and giving life to ten thousand -Yagyu Munemori
Bookmarks