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Rear takedown spring diameter size


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I'm finding out it is impossible to buy a lower parts kit (bought the kit and 80% lower from American Made Tactical) and expect every part to fit.  My rear takedown pin set up consists of a 4-48 allen (not in the kit, had to buy separate) and a .087" diameter detent.  My lower kit came with a .101" diameter spring and its too large.  I need a spring that is close to the .087" diameter.  Does anyone know where I can find a spring within a few thousands of .087?


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I realized I goofed in my post.  I bought the 80% lower from American Made Tactical but the lower kit from Ground Zero Precision. More than half of the lower kit GZP sent doesn't fit the AMT lower.  I'm having to buy springs, take down pins etc separately.  Even the Elftmann drop in trigger didn't fit.  I bought a Geissele SSA-E and it fit perfectly.  

Thanks for the response, Survivalshop.  I contacted Brownells last night and they have the spring I need.  For those of you running into the same issue, they sell a dpms detent spring with a diameter of .090" and is 1.090" long (item #231-000-094).  This should fit since its only 3 thousands larger than my takedown pin detent.

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I really don't know who is to blame.  This is my first 308 build and from what I've gathered in various forums there is no standard/mil-spec for 308's so one company can differ from the next when it comes to producing 80% lowers.  I have to admit I'm actually enjoying hunting down each piece.  The only bummer is you're not going to spend $4 on a few springs and then $5 for shipping so you end up putting more poop in your cart than you really wanted to.

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All 308AR spring sizes in the lower receiver are the same as AR15 spring sizes, minus a few, rare, weird ones in the takedown-pin/spring area.  Recoil springs are NOT included in that statement. 

They should be just like this:


AR Spring Sizes.png

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8 hours ago, Shawn120 said:

Nice!  I guess I do have a weird one though. The set screw for the rear takedown detent is 4-48 instead of the usual 4-40. My lower has all kinds of variances from the norm. 

I only run the 4-40s when a manufacturer has already tapped that hole.  If I have to tap them myself, I do it at 6-32.  Easier to to, with the larger diameter and coarser thread.  Some 4-40 setups I even cut right out of there and go straight for 6-32, anyway.  Aero gets it right, but the threading from some other manufacturers is jacked.  So, it goes, and 6-32 replaces it.

Edited by 98Z5V
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