It pains me to post this. On the bright side it was an easy fix, and it taught me to reel myself in especially when it's late and I should have slept on it.
Yesterday I cleaned a bunch of rifles and pistols I took to the range this past Saturday. I also have four stripped AR15 lowers in the safe. I had ordered a couple of build kits last week, and the big brown truck dropped them off yesterday evening. Since the safe is open I start building them around 11pm last night while watching The Force Awakens with my son. I'm farting around, beating in time, and finish them around 12:30. Get my son to bed, and go back to take them downstairs to put in the safe and I notice the rear takedown pin won't move on one of them. Strike one is that I didn't function check that one after I installed it before staking the castle nut.
What I first noticed was that the takedown pin was not flush to the lower in the "in" position, and I couldn't move it by hand in. I've had a few takedown pins in the past that were a little sticky and tighter that needed a little "persuasion" to move. I've already staked the castle nut so I don't want to take it off, bugger it up, and make it look like crap. I'm tired and just really wanting to go to bed as yesterday was just a hell of a day. Oh yeah, I really should have taken that castle nut loose!
Since my punches and hammer are still lying there I figure I'll just tap it and it will move. Tap it once, nah doesn't budge. Tap it twice, nope still won't budge, tap it a little harder for a third time, and now I'm pissed. I know I've assembled it properly, and figure it's a bur or something in the detent hole not letting it move so I hit that sum bitch pretty damn hard and this is the result. This is where my "learn from my mistake" comes in. If you have a REAL tight rear takedown pin, don't lay into it's ass with a hammer and punch. Just bite the bullet and remove the castle nut off the receiver extension and take out the detent spring and detent because if you hammer the hell out of it then it'll look like this...
I had never seen this type of damage before, and thankfully I'm not the first one to do it. The good news is there is a simple, cheap, easy fix, and I did not ruin the lower receiver as I thought I had. I used my Google Foo, and came across a couple of threads which one gave me the fix idea. The second link involves using a drill press, and that's something I don't own. I'll post it in case someone has the tools to fix something like this that way though.
So, armed with this knowledge I sleep on it. I get up this morning and go to my local fastener store looking for 3/32 drill rod. They don't stock it, but tell me Lowe's carrys it. I go to the hardware section at Lowe's, and find this. It's not called drill rod, but I can't bend it. It also doesn't list the size, but I can tell it's close by looking at the bolt sizing tool. The largest size is a perfect fit. So, I spend $2.98 and tax and take it home with me.
Basically the long and short of it is that I just made a longer takedown detent since there's still a large portion of the hole remaining to keep the detent in place. The detent I made doesn't flex, is solid and there's not sponginess. I had to use my bolt cutters to cut it that's how hard it is. I could not cut or dent it with regular cutter pliers. Hand sanded the tip and the back of it to make it straight, slipped it in the lower and viola it works like a champ. I was seriously ****ting bricks when it happened last night. Moral of this story, don't be like me and hammer like a gorilla as you will most certainly break something. Of course it would have been simpler and easier if I had just removed the castle nut. The red you see is a little grease in the takedown pin channel. I always grease them to keep abnormal wear down. I also had to cut down the detent spring to compensate for the longer detent. I ended up using the shorter one as the longer half still made it bind up. Yep, I function checked it after hand tightening the castle nut.
The silver lining is that I was trying to close the takedown pin. Hindsight being 20/20 I'm glad I wasn't trying to hammer it open. Could you imagine how bad it would look if that were on the outside? Yeah, I'm still a little pissed off at myself, but it could have been so much worse.