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Posted: 6/28/2025 10:10:18 AM EDT
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I have a set of chinesium alloy anti-rotation pins. Apparently they are decent quality. Should I stick them in my SP1 conversion? I know what they are supposed to do, but the questions is - is what they do actually useful? I just shoot 223. I probably will pick up one of those delayed rotary bolt 9mm uppers eventually. |
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I have captured pins in my gun with a cartridge trigger (AR10 - CMC trigger), but I have regular pins in everything else. The springs go into grooves in the pins, and I've never had one back out. I think anti rotation pins are a response to people thinking that the pins moving will wallow out the pin holes. I seriously doubt that's a thing, but maybe it could be an issue with full auto guns. |
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Originally Posted By StealthyBlagga: Anti-rotation (as opposed to anti-walk) pins are cheap insurance for a registered transferrable M16. insurance against what? I'm not trying to be a pain, I'm just wondering if they actually do anything has there been cases of damage that they would have prevented? what was the motivation to invent them? |
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Originally Posted By sleestakwhisperer: insurance against what? I'm not trying to be a pain, I'm just wondering if they actually do anything has there been cases of damage that they would have prevented? what was the motivation to invent them? The pin holes in the receiver can potentially egg out. Damaging your $35k investment. |
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Originally Posted By StealthyBlagga: Anti-rotation (as opposed to anti-walk) pins are cheap insurance for a registered transferrable M16. If you need them to keep your pins from walking then you have an issue with correctly installing your trigger group. Get some one that knows to teach you how to do it. As for anti rotation well its a made up issue. I've had 2 open bolt M16 LMGs and never had pin wear issues and those are the ones every wannabe internet gun nub swears that they damage the pin holes in receivers. |
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First, this is the M16 subforum, so I assume we are discussing use on a transferable M16 lower as it relates to preventing wear/egging out the fcg pin holes. There are several responses that are discussing use on semiautos, which is not really applicable to use on a transferable MG. I stopped using KNS non rotating fcg pins upon noticing that the external arms burnished the anodizing after around a decade of use one of my transferable Colt M16s. I now use Geissele SSF with their factory pins on my M16s and have never had any issue with fcg pins walking out. In addition, if one had a KNS non-rotating fcg pin fail, it is highly likely it would go unnoticed and be more likely to damage the receiver. I adiosed my KNS pins and haven’t looked back. |
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Originally Posted By KitBuilder: I still shoot Colt M16s from the 1960s and their FCG pin holes are fine. Standard USGI parts or Geissele parts. The hammer pin rotating doesn’t hurt anything. Originally Posted By KitBuilder: I still shoot Colt M16s from the 1960s and their FCG pin holes are fine. Standard USGI parts or Geissele parts. The hammer pin rotating doesn’t hurt anything. This Originally Posted By sgthatred: Except there has been damage receivers from the pins breaking but because of the stupid shit to keep them from rotating or walking out the pin holes got seriously deformed. If you need them to keep your pins from walking then you have an issue with correctly installing your trigger group. Get some one that knows to teach you how to do it. As for anti rotation well its a made up issue. And this |
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Originally Posted By JoshNC: First, this is the M16 subforum, so I assume we are discussing use on a transferable M16 lower as it relates to preventing wear/egging out the fcg pin holes. There are several responses that are discussing use on semiautos, which is not really applicable to use on a transferable MG. I stopped using KNS non rotating fcg pins upon noticing that the external arms burnished the anodizing after around a decade of use one of my transferable Colt M16s. I now use Geissele SSF with their factory pins on my M16s and have never had any issue with fcg pins walking out. In addition, if one had a KNS non-rotating fcg pin fail, it is highly likely it would go unnoticed and be more likely to damage the receiver. I adiosed my KNS pins and haven’t looked back. ^THIS!!! I ditched them after one broke and I was unable to tell it was broken which could lead to real problems. The one KNS pin I believe is worth running is their anti pivot sear pin which is a perfect fit in SP1 conversions. |
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This conversation is pretty much what you see everywhere the argument boils down to people who say it's a good idea and prevents damage, and people who say it's not needed and could cause damage. the thing that's missing is evidence. Truth is determined by measurement. some guys report that their anti-rotation pin broke, and was not noticed. That's hard data. And a strong vote against using the device. Is there anyone who can attest to the actual "egging" of pin holes? I guess the thing to do would be to ask a gunsmith who fixes those sort of problems. I did a google search, and all of the actual cases of egging I could find seemed more like fabrication errors than due to shooting. Like a guy with an 80% lower that he finished and has 1000 rounds through it, saying that his trigger pin hole is egged. You kind of suspect that his Craftsman drill press walked a little on him. I saw one guy say that said the sear hole on his colt SP1 conversion had egged, but again, that might be a fabrication error. He said the other two pins were GTG. The reason I don't just go ahead and put the gizmos on my gun as a belt-and-suspenders thing is because for all I know, they might actually make the problem worse. It's really not clear. |
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I run straight OEM on my Colt M16a1. What I heard (all second hand except for a warning from my dealer) about FCG pin breakage/damage was that it was due to firing direct blowback 9mm on full auto. Again, I heard (all second hand), that the CMMG RDB along with a hydraulic buffer, has solved this supposed problem, but the CMMG RDB has problems with extractors I think. I don't run a 9mm upper as I have a transferable RR MP5. Amphibian could probably expound more on this. RCA |
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Originally Posted By sleestakwhisperer: Is there anyone who can attest to the actual "egging" of pin holes? I have an Olympic/Fleming RR and it's always had standard GI parts in it. It's fired about 66,000 rounds. The trigger pin holes, hammer pin holes, and auto sear holes have slightly enlarged, but are still round in shape. Not egg shaped. Tony Rumore Tromix |
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Originally Posted By kingoftheriver: I run straight OEM on my Colt M16a1. What I heard (all second hand except for a warning from my dealer) about FCG pin breakage/damage was that it was due to firing direct blowback 9mm on full auto. Originally Posted By kingoftheriver: I run straight OEM on my Colt M16a1. What I heard (all second hand except for a warning from my dealer) about FCG pin breakage/damage was that it was due to firing direct blowback 9mm on full auto. Again, I heard (all second hand), that the CMMG RDB along with a hydraulic buffer, has solved this supposed problem, but the CMMG RDB has problems with extractors I think. I don't run a 9mm upper as I have a transferable RR MP5. MP5's shoot to fast for me to consistently pull singles and doubles at will for SMG matches as I demonstrate in this video in which I have my 9mm CMMG RDB setup tuned to run at around 550 RPM. I I also prefer the ergonomics of the AR/M16 platform, LRBHO, complete ambi, better trigger etc...  Single - Double - UZI - MP5 - Phase2 I find it smoother than my MP5's. Amphibian could probably expound more on this. RCA |
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Regarding using the anti-rotation pins or not, below is a high speed video of my 9mm setup again but notice that I'm using an MGI (now Hydra weaponry) modular lower. Notice that you do not see the hammer pin as the magwell goes over the hammer pin so it can't fall out. So can't really use an anti-walk or anti-rotation pin. I used to shoot a lot of straight blowback 9mm with the MGI lowers 20 years ago as well as a lot of full auto 7.62x39 using their AK magwell using unmodified AK mags and drums. One day, I had an AD where the hammer pin broke and thank God I had the muzzle pointed in a safe direction. This was with 7.62x39 when the AD happened but I have no idea if the pin was fatigued from a lot of 9mm as well or if it was just the 7.62x39 that killed it. I was using a standard hammer pin which has the groove in the middle to interface with the J-spring of the hammer. Ever since that happened I use a 'trigger' pin which has NO middle groove and I have yet to break one again.  DissentHybrid I bring this up because many of us use our RR's, RDIAS', RLL's in configurations that the M16 / AR15 were never designed for which may be more abusive than a typical 556 configuration. These days, I just do crazy stuff with the RDIAS. I use my RR for 22LR and my tuned 9mm CMMG RDB setup as after reviewing all my high speed footage, I'm sure it is softer than any 556 setup I have. |
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I broke a hammer pin with 20+ years ago shooting a 9mm upper. The first set of anti-walk pins I bought had a bar bell looking connecting rod between them, broke that hammer pin as well on 9mm. My current anti-walk pins are 20 years old and are much heavier duty and have been fine. I've pretty much stopped shooting 9mm as that duty is now handled by my MAC. Shooting just 5.55, I wouldn't buy them. |
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I been doing this for a long time. And this subject will always have people on both sides. IMHO the anti rotation SEAR pin is a good idea, the trigger hammer pins do what you think is best, but realize with the captive pins, there have been documented situations where the pin can break, but gun still functions because the captive pins, and it ends up causing damage. |
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