Posted: 9/18/2008 10:51:37 PM EDT [Last Edit: 6/26/2012 9:29:22 AM EDT by Quarterbore]



archive.ar15.com/forums/topic.html?b=3&f=118&t=285950





In a thread in the EE I saw a number of people asking for the rear plate that retains the rear take down detent spring retained when using an AR-15 pistol buffer. To be honest, I got tired of fighting with that stupid little spring with my own AR-15 pistol years ago and I thought other people knew the simple trick to tap the rear takedown detent hole and then use a small allen head screw to retain the spring. Well, in case nobody has seen this done I decided to do this to a brand new lower I bought this weekend and my local fun show...



First, the rear takedown detent hole in case someone is asking WTF is he talking about?





A 4-40 tap with a little oil... Sure wish tapping an AK trunion was this easy as Alluminum is easy! When tapping the hole, if the tap gets snagged or stops turning, back it out, clean the area and try again. You should never have to force a tap and it should cut like butter when you are using some lube.







Here is the tapped hole. Just blow it out with some compressed air when done tapping.





You need to cut about 1/8-inch off the rear detent spring. If you don't do this when you tighten up the allen screw the spring will compress to the point that the detent will not come out of the divets in the rear takedown. (If you don't cut your spring, you will see what I mean ).





1/8-inch 4-40 Allen head set screws. I got these at my local hardware for $0.10/each.





0.5mm Alen wrench. Note a handy wrench like this makes it easier to keep the spring from flying!





Set screw on the wrench.





Place the shortened rear detent spring back into the hole.





EDIT 1/12/2010 Comment Added from Page 4 of this thread by ARsRlikeLegos



Use an thick grease compound or "swak" which is a teflon-style grease for SS/aluminum apllications when installing the set screw. Aluminum will gall (stick and the threads will come out with the screw) with most materials set screws are made of when installed dry. (Stainless steel is the most common due to its low carbon anti corrosive content) Some anit-seize compounds that contain copper or other fine metal powder can be too grainy and cause damage to the soft threads when taking the set screw in and out. I am sure most of you will not be taking the set screw in and out once it is installed, but Im just throwing my .02 cents.



Screw in the 4-40 Allen head set screw.





The head of the allen head screw with a standard AR-15 buffer tube.





So, what does this do for me? Now I can remove my A2 Stock and add a CAR stock with no wories of bending or losing that spring. With my AR-15 pistol, it makes it so that I don't need to use the rear cover plate. If I want to replace the spring for any reason, I just unscrew the set screw and cut off another spring and drop it in there...



This is a 10-minute job and one I like to do on ARs that I swap stocks around on...





Originally Posted By phillyd2:

BTW, what is the purpose of that spring any way?





The rear takedown detent spring is used to hold the detent against the rear takedown pin so it does not fall out of your lower!



See



PDF page 196 to 200





Originally Posted By engineer2001:

Is the spring strong enough to not bunch up and allow the detent to hang in the threads? In other words, could the spring get compressed when changing the selector and not uncompress because it or the detent was hung on the new threads?



That and the chance I'd cut the spring too short is the only reason I can think of to not do this to my two lowers.





I only tap about 1/8-inch or so... The detent doesn't even get close to the threads... Repost as the old one is in the archives...In a thread in the EE I saw a number of people asking for the rear plate that retains the rear take down detent spring retained when using an AR-15 pistol buffer. To be honest, I got tired of fighting with that stupid little spring with my own AR-15 pistol years ago and I thought other people knew the simple trick to tap the rear takedown detent hole and then use a small allen head screw to retain the spring. Well, in case nobody has seen this done I decided to do this to a brand new lower I bought this weekend and my local fun show...First, the rear takedown detent hole in case someone is asking WTF is he talking about?A 4-40 tap with a little oil... Sure wish tapping an AK trunion was this easy as Alluminum is easy! When tapping the hole, if the tap gets snagged or stops turning, back it out, clean the area and try again. You should never have to force a tap and it should cut like butter when you are using some lube.Here is the tapped hole. Just blow it out with some compressed air when done tapping.You need to cut about 1/8-inch off the rear detent spring. If you don't do this when you tighten up the allen screw the spring will compress to the point that the detent will not come out of the divets in the rear takedown. (If you don't cut your spring, you will see what I mean ).1/8-inch 4-40 Allen head set screws. I got these at my local hardware for $0.10/each.0.5mm Alen wrench. Note a handy wrench like this makes it easier to keep the spring from flying!Set screw on the wrench.Place the shortened rear detent spring back into the hole.Screw in the 4-40 Allen head set screw.The head of the allen head screw with a standard AR-15 buffer tube.So, what does this do for me? Now I can remove my A2 Stock and add a CAR stock with no wories of bending or losing that spring. With my AR-15 pistol, it makes it so that I don't need to use the rear cover plate. If I want to replace the spring for any reason, I just unscrew the set screw and cut off another spring and drop it in there...This is a 10-minute job and one I like to do on ARs that I swap stocks around on...The rear takedown detent spring is used to hold the detent against the rear takedown pin so it does not fall out of your lower!See www.quarterbore.com/library/pdf_files/tm9-1005-319-23.pdf PDF page 196 to 200I only tap about 1/8-inch or so... The detent doesn't even get close to the threads...