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Thread: Machining an AR trigger group - opinion/advice

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    Administrator Krupski's Avatar

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    Machining an AR trigger group - opinion/advice

    Gentlemen,

    I have been trying to find a 2 stage trigger group for an older Colt AR-6520 carbine that uses LARGE PINS (0.170").

    There don't seem to be any available. They are all listed as "out of stock, ETA of new stock unknown".

    I wouldn't mind placing a backorder, but most of them claim a 12 to 18 month wait!

    Wondering... could I take a trigger group and just ream the holes to 0.170? That is removing only 0.008" (radius) of metal. I looked at some trigger groups I have here at home and there seems to be WAY more than enough metal that enlarging the hole shouldn't be a problem.

    Is the distance between the two pins the same as a "small pin" lower? Are they in the same location?

    Any opinions or advice on this idea? Thanks!
    Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by Krupski View Post
    Gentlemen,

    I have been trying to find a 2 stage trigger group for an older Colt AR-6520 carbine that uses LARGE PINS (0.170").

    There don't seem to be any available. They are all listed as "out of stock, ETA of new stock unknown".

    I wouldn't mind placing a backorder, but most of them claim a 12 to 18 month wait!

    Wondering... could I take a trigger group and just ream the holes to 0.170? That is removing only 0.008" (radius) of metal. I looked at some trigger groups I have here at home and there seems to be WAY more than enough metal that enlarging the hole shouldn't be a problem.

    Is the distance between the two pins the same as a "small pin" lower? Are they in the same location?

    Any opinions or advice on this idea? Thanks!
    you could try it on a factory 1 stage trigger first those are pretty cheap and readily available.

    I bet that steel is hard as hell though.

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    Senior Member Oswald Bastable's Avatar

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    My thoughts...sell any rifle that shits in its own nest...

    But, YMMV...
    If we refuse to rule ourselves with reason, then we shall be ruled by our passions.

    He, Who Will Not Reason, Is a Bigot; He, Who Cannot, Is a Fool; and He, Who Dares Not, Is a Slave. -Sir William Drummond

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    Senior Member Oswald Bastable's Avatar

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    Seriously though, I'd talk to a competent gunsmith about which one to get, whether the hole positions matched etc. Then buy the trigger you want and have him modify it for you.
    If we refuse to rule ourselves with reason, then we shall be ruled by our passions.

    He, Who Will Not Reason, Is a Bigot; He, Who Cannot, Is a Fool; and He, Who Dares Not, Is a Slave. -Sir William Drummond

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    Administrator Krupski's Avatar

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    Quote Originally Posted by Oswald Bastable View Post
    My thoughts...sell any rifle that shits in its own nest...

    But, YMMV...
    Despite the fact than an AR shits itself whenever it's fired, mine seems to be fairly reliable. That said, if I could only have one rifle, it would be the Kalashnikov...
    Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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    Administrator Krupski's Avatar

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    Quote Originally Posted by Oswald Bastable View Post
    Seriously though, I'd talk to a competent gunsmith about which one to get, whether the hole positions matched etc. Then buy the trigger you want and have him modify it for you.
    My son bought a two stage trigger for his AR and it works great. I might get a Giessle (sp?) though, not sure yet.

    After measuring everything, I found that the pins are exactly 0.170", the holes in the receiver just a hair over 0.170 (around 0.171 to 0.172). The hole in the hammer, trigger and disconnector are larger (0.174), so I bought a solid carbide reamer size 11/64 which is 0.171875".

    This should be perfect as it's larger than the pins, but not the sloppy 0.174 of the mil parts.

    I plan to go to a local machine shop (they know me) and have them "do it right" for me (that is, in a Bridgeport, hole centers indicated and holes bored nice and straight). Since the reamer is carbide, it can't be easily used hand held since any bending stress will break it.

    Oh well, we'll see how it goes.
    Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by Krupski View Post
    My son bought a two stage trigger for his AR and it works great. I might get a Giessle (sp?) though, not sure yet.

    After measuring everything, I found that the pins are exactly 0.170", the holes in the receiver just a hair over 0.170 (around 0.171 to 0.172). The hole in the hammer, trigger and disconnector are larger (0.174), so I bought a solid carbide reamer size 11/64 which is 0.171875".

    This should be perfect as it's larger than the pins, but not the sloppy 0.174 of the mil parts.

    I plan to go to a local machine shop (they know me) and have them "do it right" for me (that is, in a Bridgeport, hole centers indicated and holes bored nice and straight). Since the reamer is carbide, it can't be easily used hand held since any bending stress will break it.

    Oh well, we'll see how it goes.
    Worth a go for sure

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    Senior Member Oswald Bastable's Avatar

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    Quote Originally Posted by Krupski View Post
    Despite the fact than an AR shits itself whenever it's fired, mine seems to be fairly reliable. That said, if I could only have one rifle, it would be the Kalashnikov...
    My go to is the SAR3...I only wish I was smart enough at the time to have bought two, so I had an extra for spare parts as needed...now they are arm.9/leg.9 in pricing...
    If we refuse to rule ourselves with reason, then we shall be ruled by our passions.

    He, Who Will Not Reason, Is a Bigot; He, Who Cannot, Is a Fool; and He, Who Dares Not, Is a Slave. -Sir William Drummond

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    Administrator Krupski's Avatar

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    Quote Originally Posted by Oswald Bastable View Post
    My go to is the SAR3...I only wish I was smart enough at the time to have bought two, so I had an extra for spare parts as needed...now they are arm.9/leg.9 in pricing...
    I've got an AKM (2001 SAR-1 from Century). I lucked out on that one... beautiful matching furniture, a straight FSB and after years of use, zero problems. The only thing that can stop it from firing is an empty mag! I wish I had bought a few more of those SAR-1 rifles, especially when they were so inexpensive. What scared me away from buying more was the "Century Crapshoot". Who knew if they would send a good one or one built by a drunken monkey?

    Interesting thing is that the SAR-1 receiver is genuine Romanian military and, although it doesn't have the evil third pin, the receiver DOES have a Y shaped indent where the hole for the pin would be. Supposedly (don't know if it's true), I once read that the Romanian military issues semi-auto only rifles to new soldiers and full auto only after they reach some milestone. I guess my receiver was meant for one of the semi-auto versions.

    I've also got a nice Norinco which is an AK-47 rather than an AKM (wide front sight). It's got the bayonet lug for those drive-by knifeings. I have a "satin" (not shiny) chrome plated blade bayonet with a dark red-brown bakelite handle from North Korea. It looks bad-ass snapped onto the rifle.

    Although I prefer Kalashnikov rifles, I have more AR-15's. One is a Colt 6520 clone (thin 16 inch barrel and skinny carbine style handguards) built with Bushmaster parts. One is a "real" Colt 6520 and one is a "Vietnam style" with a Bushmaster lower, a Colt SP-1 upper with no forward assist, triangular handguards, a duckbill flash hider, 20 inch barrel and an SP-1 style short stock (not collapsible). The Bushmaster lower is wrong for an "M16E1 lookalike", but I had it in the closet, so I put it to use. That one my younger son (25 y.o.) now "owns".

    Oh well, gotta go. I have laser diodes to press into copper heatsink housings!
    Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by Krupski View Post
    I've got an AKM (2001 SAR-1 from Century). I lucked out on that one... beautiful matching furniture, a straight FSB and after years of use, zero problems. The only thing that can stop it from firing is an empty mag! I wish I had bought a few more of those SAR-1 rifles, especially when they were so inexpensive. What scared me away from buying more was the "Century Crapshoot". Who knew if they would send a good one or one built by a drunken monkey?

    Interesting thing is that the SAR-1 receiver is genuine Romanian military and, although it doesn't have the evil third pin, the receiver DOES have a Y shaped indent where the hole for the pin would be. Supposedly (don't know if it's true), I once read that the Romanian military issues semi-auto only rifles to new soldiers and full auto only after they reach some milestone. I guess my receiver was meant for one of the semi-auto versions.

    I've also got a nice Norinco which is an AK-47 rather than an AKM (wide front sight). It's got the bayonet lug for those drive-by knifeings. I have a "satin" (not shiny) chrome plated blade bayonet with a dark red-brown bakelite handle from North Korea. It looks bad-ass snapped onto the rifle.

    Although I prefer Kalashnikov rifles, I have more AR-15's. One is a Colt 6520 clone (thin 16 inch barrel and skinny carbine style handguards) built with Bushmaster parts. One is a "real" Colt 6520 and one is a "Vietnam style" with a Bushmaster lower, a Colt SP-1 upper with no forward assist, triangular handguards, a duckbill flash hider, 20 inch barrel and an SP-1 style short stock (not collapsible). The Bushmaster lower is wrong for an "M16E1 lookalike", but I had it in the closet, so I put it to use. That one my younger son (25 y.o.) now "owns".

    Oh well, gotta go. I have laser diodes to press into copper heatsink housings!
    It's a real shame all of that fine collection was lost in the boating accident you had a while back. Those will be very hard to replace now.
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  11. #11
    Guns Network Contributor 01/2015 Altarboy's Avatar

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    There needs to be a boating safety class for firearm collectors. They seem to suffer so many losses.

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    Quote Originally Posted by Krupski View Post
    I've got an AKM (2001 SAR-1 from Century). I lucked out on that one... beautiful matching furniture, a straight FSB and after years of use, zero problems. The only thing that can stop it from firing is an empty mag! I wish I had bought a few more of those SAR-1 rifles, especially when they were so inexpensive. What scared me away from buying more was the "Century Crapshoot". Who knew if they would send a good one or one built by a drunken monkey?

    Interesting thing is that the SAR-1 receiver is genuine Romanian military and, although it doesn't have the evil third pin, the receiver DOES have a Y shaped indent where the hole for the pin would be. Supposedly (don't know if it's true), I once read that the Romanian military issues semi-auto only rifles to new soldiers and full auto only after they reach some milestone. I guess my receiver was meant for one of the semi-auto versions.

    I've also got a nice Norinco which is an AK-47 rather than an AKM (wide front sight). It's got the bayonet lug for those drive-by knifeings. I have a "satin" (not shiny) chrome plated blade bayonet with a dark red-brown bakelite handle from North Korea. It looks bad-ass snapped onto the rifle.

    Although I prefer Kalashnikov rifles, I have more AR-15's. One is a Colt 6520 clone (thin 16 inch barrel and skinny carbine style handguards) built with Bushmaster parts. One is a "real" Colt 6520 and one is a "Vietnam style" with a Bushmaster lower, a Colt SP-1 upper with no forward assist, triangular handguards, a duckbill flash hider, 20 inch barrel and an SP-1 style short stock (not collapsible). The Bushmaster lower is wrong for an "M16E1 lookalike", but I had it in the closet, so I put it to use. That one my younger son (25 y.o.) now "owns".

    Oh well, gotta go. I have laser diodes to press into copper heatsink housings!
    Those were the days weren't they? $299-329 for SAR1,2 and 3.

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    Administrator Krupski's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    Those were the days weren't they? $299-329 for SAR1,2 and 3.
    Sigh... yup, the good old days. Ammo wasn't expensive either. I could go to the range and blow away a whole case of X39 and 5.56 and not even think about it. I remember when .50 BMG was $1.00 a round and I thought that was a lot. Now, .45 ACP is $.80 to $.90 a round. It's no fun seeing dollar bills hit the berm...

    As far as the topic of this thread... I ordered a Giessle SSA-E trigger in small pin (because the large pin triggers are out of stock EVERYWHERE!). I also bought an 11/64" solid carbide reamer (0.171875 diameter) to have a machine shop ream the trigger and hammer holes to "large pin" size.

    There are two problems that I can see. One is the pin retainer wire in the hammer. If I can't take it out before machining, the carbide tool might cut it since it protrudes into the hole.

    The second problem I see is the trigger. The pivot point where the pin goes has a small cutaway half way down so that the hammer spring tails rest on top of the grooves of the trigger pin to retain it. This means that the carbide tool will be trying to initially cut into the half circle which will put a lateral stress on the reamer. I think the feed speed will initially need to be very slow and careful until it gets deep enough to be fully supported.

    I will ask the guy at the machine shop if he thinks either one will be a problem. If so, I can always install the trigger into my Bushmaster 6520 clone (which has small pins).

    I'll post more as the project goes on...
    Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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