How do i fix my ar?

S

sgt.rock

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HI, I have a Mossberg MMR and the rear takedown pin has lost it's ball-bearing or whatever keeps it tight when it gets pulled to open the gun. The pin just falls out now and the rifle opens up during firing. How the hell do I replace the ball bearing (the pins have a groove in them that the ball bearing slides in to keep it from falling out of the rifle. The front pin is fine, but the rear one is giving me fits.
Of course there is no gunsmith here to deal with this issue, and seeing as the lower is the restricted part of the gun, I don't want to send it away as that is just a hassle. Please help me if you know how I can fix it. The AR itself is awesome, and it is THE most accurate one I've ever shot. I easily get 1.25" groups with factory ammo, Winchester white box 45 grain . BUT , the gun is useless to me if I can't get it to stay together when I shoot it!!!

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Normally the rear take down pin is secured by the detent behind the stock. If its got a A2 stock just remove the screw in back and slide the stock off backwards should see the spring. Pull back the spring, check for the detent. If no detent just replace it.

rstactical_030105b.jpg


If its not there its normally under the pistol grip ( Selector and Take down pin )
 
word to the wise on that 45gr winchester white box, it has a nasty habit of pushing the bullet into the casing while pushig up the feed ramp as the bullet is not crimped enoughn(varmit load built for a bolt gun)
 
TinkerBell said:
word to the wise on that 45gr winchester white box, it has a nasty habit of pushing the bullet into the casing while pushig up the feed ramp as the bullet is not crimped enoughn(varmit load built for a bolt gun)
Click to expand...

Yup, that load can produce really nasty pressures if the bullet sets back - and you can set the bullet back with your hand.
 
What brand of lower is it?
As RobertMcC stated the spring and detent are held in place by the buffer tube plate or in some brands like NEA it's held in place by the pistol grip like the safety detent.
It sounds like you or someone has removed the stock or pistol grip (whichever applies depending on the design of the lower) and the spring and detent fell out. It's a simple and cheap fix but you'll want to take care of that soon if the pin is wandering out while firing. Be sure to watch for small parts falling out when you take remove parts like the stock if it's a rifle buffer, the buffer tube if it's a carbine, and the pistol grip. they are all used to retain springs and detent pins.

Good luck
 
Hi, I never touched anything like removing the stock since I got it. Can't say with the previous owner. The lower is Mossberg (same as the top) stock set up as far as I can tell.
 
sgt.rock said:
Hi, I never touched anything like removing the stock since I got it. Can't say with the previous owner. The lower is Mossberg (same as the top) stock set up as far as I can tell.
Click to expand...

Well you want it fixed so. Remove the flat head screw on the back off the stock and slide the stock off enough to remove the spring and inspect for the detent. See the picture will see the spring.
 
sgt.rock said:
Hi, I never touched anything like removing the stock since I got it. Can't say with the previous owner. The lower is Mossberg (same as the top) stock set up as far as I can tell.
Click to expand...

I've never had a mossberg AR apart but I'll guess that it's the same as 98% of the lowers out there and the detent and spring are held in by the buffer tube plate if it's a carbine with a telescoping stock. You may need to order a lower spring kit.
Unfortunately there aren't a lot of retailers around that stock the parts individually. Your parts will be in this kit but there is a lot of stuff in there you'll never need. http://sjhardware.com/store/modules.php?name=catalog&file=product_info&cPath=102_113&products_id=666

You can also try calling places like Milarm, Tier One Armoury, or Phoenix in Edmonton and ask if they have the individual parts needed.

Here are a couple others I found

http://ctcsupplies.ca/collections/g...-ar-15-lower-pin-spring-kit?variant=406281077
http://ctcsupplies.ca/collections/g...unbuilders-lower-parts-kit?variant=1244641888
https://www.wolverinesupplies.com/SearchByKeyword?word=AR-15 spring#?sortValue=0&currentPage=1
https://www.wolverinesupplies.com/SearchByKeyword?word=AR-15 detent#?sortValue=0

Good luck
 
Just pulled the stock off. I have the detent still in the channel, but there is NO SPRING. Does anyone know what kind/size/length spring I need? If anyone has a spare I'd be happy to pay for it plus shipping.
 
The detent spring size is: Length - 1.15", diameter - 0.088". You may be able to find this spring in your local hardware store (take your callipers with you). Also, you may be able to find similar springs in cigarette lighters (under the flint). There are also after-market take down pins (push button types) that don't need these springs and detents if you don't mind spending some money.
 
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