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Posted: 5/11/2008 10:34:02 AM EDT
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I was reading through the thread on, "What parts break in a carbine class." - What is tolerance stacking? - Are CMMG, BM's and RR Mil-Spec bolts? If not, what should I replace to make the rifle / BCG durable enough to endure this kind of use? A complete new BCG? If so, which one/s Thanks. |
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I use Colt MP tested shotpeened Bolts or Bravo Companys that are made the same way..its a little insurance of a quality part although parts will break no matter how good..the best thing is to keep some spares on hand and when taking a carbine class either take a spare carbine or at the very least a spare carrier/bolt assembly so you can get the rifle back into the game should something go.I take an identical spare carbine. I would change your bolt and keep the old one as a spare or vice versa.Ive had Bushmaster and RRA bolts give and still giving great performance.But like I said just get parts to back up what you have.Are some parts better made than others sure..like Bushy sells their Bolts for $57 and says there MP tested but I think its like theri barrels tested by batch..Bravo Company or Colt MP tested and shot peened im not sure about LMT but they are great as well. Its hard sometimes to navagate a companys claims with the process they actualy use.Like genericaly a comapny will say we use 4150 steel when the milspec is11595E 4150 CMV steel.For me anything chromelined 4140,4150 is gonna be fine but yes there are better grades of parts and materials and you will pay for them but like I said if I had to choose between a Bushmaster claimed MP tested bolt and a Bravo known and stamped MP tested and shotpeened bolt for the same money ill go bravo company. |
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Tolerance stacking=Every item manufactured has a spec and a + and - limit to those measurements. Variances occur because of tool wear, machine accuracy, hand of fate, etc. Mostly, though, things end up somewhere in the middle of the spec (which is the target). * When you get something that is on the + side mated to something else on the + side, you get something that is tight, which may be good or may be bad. * When you get something that is on the - side mated to something on the - side, you get something that is too loose, which may be good or may be bad. * When you get something that is on the -(or +) side mated to something on the + or (- side), you get a useable fit, but replacement parts may put you into a -/- or a +/+ situation. * When you get something in the middle of the spec mated to something in the middle of the spec, you get an ideal assembly. Anything replaced on the + or - side of the spec should be close enough to work (or break in) properly. One example of +/- tolerance stack issues comes with the older Oly Plinker rifles, which were all assembled with parts that were too + or too - of the tolerance, assembled into rifles. Trouble was, when something broke (and it often did), the rest of the assembly was so out of tolerance that fitting a middle spec part was all but impossible. Another example of tolerance stack issues of the -/- variety: Every year at the All Navy (East) and Atlantic Fleet shooting competetion, Crane brings a metric butt ton of old 1911A1 pistols, properly set up for DCM/CMP shooting. They rattle like Model T Fords. Funny thing is, shooters who use them routinely WIN, as well as score Gold, Silver, and Bronze, over shooters using personally owned $1500 custom 1911's or M9's that lock up tight as a drum. As far as CMMG, RR, or BM bolts.....shoot 'em until they break, which likely they'll never do. IF they do, replace with the best available part you can get for the least coin. Argueably right now that's the BCM bolt. Don't go looking to replace parts that aren't broken, though, on a rifle that's already running. It takes quite a lot of use/abuse to kill bolts, and I've never seen or heard tell of a carrier that was "worn out" or damaged by anything other than a KB! Tom |
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