To begin, I've worked in firearms engineering for a number of decades, at Colt's on the M-4, at Smith and Wesson on the M&
15, and at CMT/Stag arms. I designed the left handed upper for Stag, helped clean up the early in-house production problems on Smith's M&15 (the first 50,000 were made by Stag), had some input on Mack Qwinne's remarkable Hydra up at MGI (a real honor to work with the best damned living designer in the business), and designed most of the gaging used by Colt's on it's production and vendor inspection lines. Various kudos and bitchings from former coworkers are available on LinkedIn. Mostly kudos, I'm happy to say. I think I'm reasonably qualified to comment, so I will. First, S7. Love it, and I'm using it on a .50 BMG/.338 Lapua semi-auto I'm working on. With modern tooling and coolants it becomes a lot more versatile, and less subject to warpage than it used to be. Is it needed on an AR? Probably not, but what the hell.
Next, bolt breakage. It simply doesn't happen with a well made bolt (think CMT or Microbest), but it does happen with junk bolts, many of which I have seen on brand name rifles. After heat treat and case hardening, the bolt lug faces HAVE to be ground or hard turned. At S & W, we had several thousand bolts from a big name manufacturer that came in at near maximum headspace, with only partial bearing on two or three lugs. Calculate what happens when you eliminate 80% of load area and concentrate all that shock and compressive load on a few sharp points. Needless to say, we had some words for said manufacturer, and bought somewhere else.
On bolt canting, I have to call B.S. On the Kalashnikov series of rifles, certainly. The lug pushing on the top of the bolt assembly cams the bolt down into the overlarge magazine well on every shot. The almost non-existent receiver with it's huge ejection port cutout and scant right rail, combined with the over camming effect of the bolt design, is what causes the AK's to spray their groups rather than cluster them in anything resembling a proper group on target. The receiver on AK's flexes so badly that many of the milled receivers crack across the front of the magazine well or even blow completely in half.
The primary advantage of the stamped AKM receiver is that it flexes rather than breaks. Whatever reliability the AK has is provided by the sheer weight of the bolt assembly slamming back and forth inside a constantly twisting receiver, and even that is blown well out of proportion. AK magazines are often lousy, and if you haven't seen what's coming out of Ishevzk arsenal lately in the way of supposed rifles, then you haven't seen crap as bad as what the Japanese were producing the last few months of World War Two.
On the AR/M16, the gas is piped down into the expansion chamber in the center of the bolt carrier, where it works against the fixed piston (the back of the bolt, that's what those gas rings are for) , forcing the carrier off the piston/bolt, and camming it 22.5 degrees to unlock it. Then it vents out the ejection port through the two ducts in the right side of the bolt carrier.
The amount of lateral load on the bolt key is quite minor because of the center line gas system, literally no more than the small side load engendered on opposition to the cam pin rotating the bolt. I've seen uppers that have burned out several barrels, call it 30,000 or 40,000 rounds, and they still had the baked on dry film lube intact along the side of the key track.
As far as a super coating on the carrier and bolt, why not? Is it needed? No. The bolt carrier is .994 in diameter, and the minimum inside diameter of the receiver in 1.000, so the carrier doesn't even touch the receiver except at the two little ski pads either side of the magazine, and on the wear pads either side of the gas key on top.
For maximum reliability, simply dab a touch of lubriplate on the tail of the bolt, on the bearing belt around the bolt (half way up, behind the locking lugs), slightly moisten the ski ramps on the bottom of the carrier, the cam pin,and the sides of the gas key. Nothing else bears on the inside of the receiver, so run it dry and all the residue will blow out the ejection port. Or, you can grease it up and turn it into a crap magnet, your choice.
So, if you want a shiny bragger bolt, buy one. If I was spending the money, I'd put about half as much into a Stag or Microbest bolt, and grab a bolt carrier from Varsk Machine up in New Britain CT.
发表于 2015-7-14 20:43
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千斤顶
楼主
。nib-x的雖然黑了，表面還超光滑，應該暫時沒影響。其實就用phosphate的也不影響，多擦擦就行。
