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Posted: 1/7/2007 3:32:26 PM EDT
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I am installing new KNS pins in my RR. While I had it somewhat apart I decided to strip it right down to clean it real well. Anyway now that it is apart I was wondering if I should install a new FCG or parts kit. I have no idea of round count on the parts. Thanks |
Agree with this 100%. I'd put all new springs in any RR since it may have been sitting for a couple of decades. Mine needed not only the FCG springs, but the recoil spring and the bolt springs (ejector and extractor). |
| Since your doing a complete rebuild, I'd look at replacing at least the "high-wear" parts like the hammer, disconnector and auto-sear. Be careful if you keep the old ones for originality or spares, though. ATF has a opinion on how many "spares" you can have for 1 RR if you also have AR-15's. |
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If there is no noticable wear -- bright spots, deformation, etc. -- there's no point in replacing the FCG itself. I strongly suggest you replace all the springs, though: They absorb all the impact and do weaken over time. I regularly replace mine, just like I change the oil in my cars. The interval depends on what uppers I'm running, but IMHO regular spring replacement is a cheap way to ensure your RR is running at its best. It's a good idea to start with fresh springs when you get a new-to-you RR. If you are running 9mm or 7.62x39 uppers of any length, or 5.56 sub-11.5" shorty uppers, I'd suggest replacing the FCG springs every 5-8k rounds. If you shoot mostly with 16- or 20-inch uppers in 5.56, or do a lot of .22RF shooting, the springs should last over 10k. But again, with a set of quality springs selling for $10 or so, why not play it safe? YMMV. |
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Not to hijack the thread, but what do we risk by running weak springs (I'm not trolling, I really don't know!). My understanding is that coil springs, in contrast to flat springs, tend to just weaken with use. But they rarely break. My own experience over decades is consistent with this - it's flat springs that will actually break, causing abrupt failure. I can understand the issue with weak hammer springs and weak primer hits.........well.......b/c I've BTDT. Also, extractor tension needs to remain good.......BTDT, too. But I've never replaced any other springs in an AR/M16......or in an Uzi for that matter. If the big recoil/buffer spring weakens enough the carrier will bottom out hard and I'd feel that as a double recoil impulse. Or I'd start to get failures to go completely into battery. This happens with long-recoil shotguns like the Browning A5. Like trigger slap, this is recognizable if you're paying attention. So what am I missing - what should I be looking for? Sam |
True, coil springs rarely break but they do lose thier "boinginess" (for lack of a better term) over time and they will get noticeably shorter. I use "known new" springs as a guide. When the old sping is next to the new one and is 2 to 4 coils shorter, I change it out. As for hammer and trigger springs. You can use the same method by comparing the angles of the legs but that's not 100% reliable due to slight differences in material/methods from various manufacturers. Personnally, I change these at 3 years or 3,000 rounds, whichever comes first. |
As the hammer spring weakens, it no longer cushions the hammer's impact on the disconnector. This will peen a flat spot on the disconnector but, more importantly, it allows the impact to be transmitted to the trigger pin. This can either break the trigger pin, allowing the broken sections to wallow out the trigger pin hole in the alloy receiver, or simply egg out either or both of the trigger and hammer pin holes in the receiver. Of course, you can always find a talented aluminum welder to weld up and redrill the receiver holes, or you can drill them out and sleeve the holes with brass or steel bushings. Either way, your $10k +/- transferable receiver will take a serious, permanent hit in market value. Let's see ... spend $10 on new springs every coupla years, or risk $1k-$2k in receiver damage ... hmmm... As always, YMMV. 
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Tony, Thanks. Is there any quantitative way to assess the hammer spring? As an example, would I expect FTF due to weak hits to precede peening on the disconnector? Is there a quick and dirty way to assess hammer spring tension? TIA, Sam ETA: had to check for peening. Compared the one that gets the most use to the near safe queen, I see no difference in the disconnector contact points - certainly nothing peened. Moreover, no detectable difference in hammer spring tension between the two. (!) The safe queen is a nearly unfired 16A1. I've put well over 10k (probably more like 15k) on the hammer spring of the "shooter" 16 myself. Who knows how many rounds went before me. I have to admit to being surprised that there is no apparent loss of spring tension after so many rounds.  Certainly I would expect some change in a coil spring after this many cycles. Dunno. Maybe I'll change it out anyway?
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My experience -- the one that convinced me of the value of fresh springs -- came when I bought my first 9mm upper in the early '90s. It was from a Colt 635 SMG and I just slapped the 9mm upper on my minty factory lower, swapped in the 9mm buffer, bought a mag block and started shooting. I immediately experienced some trigger slap, but otherwise it ran perfectly. No FTFs, etc. After a couple of range sessions, I did a detail strip for cleaning and discovered that (a) the hammer had been impacting the disconnector, and (b) the trigger pin had snapped dead-center, and the entire trigger/disconnector unit was wobbling up and down with every shot at 750 rpm.  Now, it ran perfectly, and if I had not done the detail strip, I would not have noticed. Fortunately, the pin "stubs" had not yet wallowed open the receiver holes, and I switched first to SS pins and then to KNS pins (what I use today). This was before anyone had thought to ramp 9mm bolts to 5.56 carrier profiles, so next I examined the hammer spring. First I tried a brand new milspec spring -- it was noticably stronger than the old spring when I flexed the two by hand, and the new spring alone greatly reduced the trigger slap. Then I switched to a JP trigger and use JP's 3-pound trigger springs with their 4.5-pound hammer springs. I have no idea what the milspec pound rating is, but the JP springs (in concert with ramping my 9mm bolt) mean the trigger slap issue is gone, the new disconnector has no peening and I haven't broken any more pins. Was the hammer spring in my apparently minty RR already weak when I bought it, or did 9mm upper do all the weakening? I have no idea. The point of the above long story is that a (for whatever reason) weakened hammer spring caused a broken trigger pin, and yet the M16 still ran perfectly -- and prolly would have continued to do so while quietly egging out the trigger pin hole until receiver repairs would have been required. Given how hard 9mm, 7.62x39 and shorty 5.56 uppers are on their host receivers, it makes sense to me to swap springs in these more often. A 20"-barrelled milspec M16 would need new springs far less often -- and a safe queen, as long as it is not stored with the hammer cocked, might never need them. The thing is, all transferable MGs are now at least 20 years old. And unless you bought it brand spankin' new back in the day, you have no idea how the previous owner used your M16. (Let's hope he never used an unramped 9mm upper rig.) Starting with a complete new $10 set of springs eliminates a potential danger. I generally put new springs in almost every used gun I buy, and definitely anything over 10-15 years old. That includes $150 revolvers as well as $15,000 MGs. The disassembly and cleaning process is a good way to get to know a new firearm anyway.
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