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Posted: 4/9/2011 7:19:07 PM EDT
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Hey All, another question about 22lr conversions. i did a search but didn't really come up with anything.
I've seen some references to snapped hammer pins when using blowback conversions on an AR... is that really a problem that seems to be common? Is there anything that can be done to reduce the possibility of a breakage? I only have one functional lower for the time being, and I'd like to do what i can to keep it at 100% Please share any experiences that you've had with this sort of thing! |
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Usually it will happen with cheap pins. I won't mention names.
The blowback does create more pressure on the pins. I install KNS anti rotationals on all mine. You will have those that argue with the need for KNS but for $30, it's worth the insurance to me. Dave N |
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Quoted:
Usually it will happen with cheap pins. I won't mention names. The blowback does create more pressure on the pins. I install KNS anti rotationals on all mine. You will have those that argue with the need for KNS but for $30, it's worth the insurance to me. Dave N Hey thanks for the quick response. Yeah I've seen people arguing both ways for the KNS pins. I'm not too worried about the anti-rotational properties, but are the pins themselves significantly stronger than standard pins? |
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so which are the un-mentionable pins.....so we don't accidentallly get them, for those that can't break yer code  I'll take a stab at it without having to name names. If I recall correctly, USAF armorers expected Mil Spec hammer pins to last between 6000 and 12000 cycles under combat conditions and running practically dry (little to no lube), with loving care totally absent. Trigger pins seemed to last forever, but do change your disconnector spring around 20,000 cycles. From those figures you can see how a rimfire shooter could easily reach those numbers quickly, what with rounds costing pennies. So it would seem to me that any garden variety, inexpensive "Mil Spec" pins should be avoided if you expect longevity in your civilian AR. Avoid the "el cheapo's" and buy quality pins, but keep a spare on hand for emergencies. The "Two Daves" gave you two quality brands, why not start there? Ted |
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Thanks for all the great info.
Dave S: When you say "solid" pins, I'm assuming you mean that they don't have notches like the standard pins do? And a semi-thread-related question for anyone who cares to chime in: Does anyone know why/how a 22 conversion can put more pressure on the pins than a 5.56 round? I understand that the 22 is blowback and therefore not locked during firing, but it seems that even after unlocking, the cycling is much more violent on a gas AR. I can see how a 9mm or some such could cause significant pressure on the pins, but I can;t really get my head around how a 22 can be damaging. Is the bolt just moving that much faster on the 22? Anyone who can educate me on this please share. :) |
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Quoted:
Thanks for all the great info. Dave S: When you say "solid" pins, I'm assuming you mean that they don't have notches like the standard pins do? And a semi-thread-related question for anyone who cares to chime in: Does anyone know why/how a 22 conversion can put more pressure on the pins than a 5.56 round? I understand that the 22 is blowback and therefore not locked during firing, but it seems that even after unlocking, the cycling is much more violent on a gas AR. I can see how a 9mm or some such could cause significant pressure on the pins, but I can;t really get my head around how a 22 can be damaging. Is the bolt just moving that much faster on the 22? Anyone who can educate me on this please share. :) Take with a grain of salt, my two cents worth: Most rimfire ammunition requires extra hammer spring power to ignite reliably. Extra spring power equates to greater stress on the hammer pin, especially as the standard pin rotates. Centerfire guns can get away with much less hammer spring power because the cartridge primer is twice as sensitive than rimfire primers. But that isn't the whole story. Direct impingement centerfire may seem to have a more stoutly felt recoil, but the DI cycle actually produces less shock due to the very nature of gas compressibility (think of gas shock absorbers). DI guns also reduce recoil impulse by allowing the BCG's mass to travel a longer distance against a counter mass (buffer) which exerts less shock on the hammer, so less shock on the hammer pin. The centerfire hammer is drawn back in a fully dampened cycle with no undue stress ripping through the receiver. Think of it being like a tennis ball hitting a racquet, there's plenty of cushioning going on. In rimfire AR's the recoil cycle is quite violent, being pure inertia dampened only by spring pressure. The BCG is driven back a very short distance against a spring, which compresses against a plate, and that transmits a lot of stress throughout the receiver. Both as it is slapped hard against the hammer to over come the heavier spring tension, then again as it is driven by the recoil spring and slams into battery while driving a round up a steep ramp and in to the chamber. There is no dwell time in rimfire AR's (as you noted, their bolts don't lock) to delay and soften the recoil impulse, so the recoil is quick, direct, and violent. When a rimfire AR's hammer is released it slams the pin and the BC against the barrel extension so hard that the bolt actually bounces (high speed photography captures this and I wish I had a link for you), that's a lot of shock going back down the hammer and onto it's hammer pin. The rimfire hammer wiggles side to side as it travels back. You normally don't get that stress with a locked bolt. Now don't you have a new respect for rimfire AR's and the people who make them? Hope this makes sense. Ted |
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Quoted:
Quoted:
Thanks for all the great info. Dave S: When you say "solid" pins, I'm assuming you mean that they don't have notches like the standard pins do? And a semi-thread-related question for anyone who cares to chime in: Does anyone know why/how a 22 conversion can put more pressure on the pins than a 5.56 round? I understand that the 22 is blowback and therefore not locked during firing, but it seems that even after unlocking, the cycling is much more violent on a gas AR. I can see how a 9mm or some such could cause significant pressure on the pins, but I can;t really get my head around how a 22 can be damaging. Is the bolt just moving that much faster on the 22? Anyone who can educate me on this please share. :) Take with a grain of salt, my two cents worth: Most rimfire ammunition requires extra hammer spring power to ignite reliably. Extra spring power equates to greater stress on the hammer pin, especially as the standard pin rotates. Centerfire guns can get away with much less hammer spring power because the cartridge primer is twice as sensitive than rimfire primers. But that isn't the whole story. Direct impingement centerfire may seem to have a more stoutly felt recoil, but the DI cycle actually produces less shock due to the very nature of gas compressibility (think of gas shock absorbers). DI guns also reduce recoil impulse by allowing the BCG's mass to travel a longer distance against a counter mass (buffer) which exerts less shock on the hammer, so less shock on the hammer pin. The centerfire hammer is drawn back in a fully dampened cycle with no undue stress ripping through the receiver. Think of it being like a tennis ball hitting a racquet, there's plenty of cushioning going on. In rimfire AR's the recoil cycle is quite violent, being pure inertia dampened only by spring pressure. The BCG is driven back a very short distance against a spring, which compresses against a plate, and that transmits a lot of stress throughout the receiver. Both as it is slapped hard against the hammer to over come the heavier spring tension, then again as it is driven by the recoil spring and slams into battery while driving a round up a steep ramp and in to the chamber. There is no dwell time in rimfire AR's (as you noted, their bolts don't lock) to delay and soften the recoil impulse, so the recoil is quick, direct, and violent. When a rimfire AR's hammer is released it slams the pin and the BC against the barrel extension so hard that the bolt actually bounces (high speed photography captures this and I wish I had a link for you), that's a lot of shock going back down the hammer and onto it's hammer pin. The rimfire hammer wiggles side to side as it travels back. You normally don't get that stress with a locked bolt. Now don't you have a new respect for rimfire AR's and the people who make them? Hope this makes sense. Ted Wow! Thanks! That's a good explanation. I meant no disrespect to rimfire AR makers; I was just curious about what was going on to make it rougher on the FCG. :) |
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Colt put SS hammer/trigger pins in their 9mm SMGs because they were tougher and less brittle than the carbon steel pins.
I would install those, if you can find them cheap, or just use the plain KNS SS pins. I've never felt the neeed for anti-rotation or anti-walk pins, but that's just me. |
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All the pins that broke on me have been DPMS's pins that come with their lower parts kits.
I have changed out all of my pins to solid of one manufacturer or another... I could probably run the DPMS Standard pins forever in one lower, I have about 40 spares in my junk box... Dave S. |
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All the pins that broke on me have been DPMS's pins that come with their lower parts kits. I have changed out all of my pins to solid of one manufacturer or another... I could probably run the DPMS Standard pins forever in one lower, I have about 40 spares in my junk box... Dave S. And I haven't broken a DPMS LPK part yet, in close to 10 years of shooting - many thousands of rounds through several 9mm ARs (I did switch my 9's to KNS anti-rotation pins a few years ago though - just to be cool). All of my dedicated .22's have standard DPMS pins in them (probably 20+ boxes of Fed bulk through them a year) as do my .223 lowers which sometimes get the Ciener kit thrown into them (maybe 5 or so bulk boxes of Federal through the kit per year). I have to imagine there is more to the pin breakage issue than it simply being cheap DPMS pins. My best guess would be that there are just some lowers that, while they may still be in spec, may be near the edges of the tolerances, and they just have a tendency to break pins with more regularity than other lowers when shooting 9mm or .22 blowback. Or, there were some bad batches of pins that may have been problematic and broke easier than others (bad material, bad heat treat, bad ???). I don't know. I tend to buy a lot of my parts in bulk at one time though - rather than an LPK here or an LPK there - so maybe I just happened to get a good batch of 30 DPMS LPK's about 10 years ago and since I'm still using those same LPK's to build today, the lucky streak continues for me??? |
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