AR-10 Build Question (AR-10 LPK vs AR-15 LPK)

SoMD_Gen4 · Oct 2, 2014

So, I am building out my buddies AR-10 lower for him. He gave me everything he bought which included a LPK labeled .308.

While taking out all of the parts, and doing a quasi dri fit, i noticed the mag catch is too small (likely got switched with an ar-15 mag catch).

This got me thinking what other parts may be switched. He has a billeted lower where there are certain pins that would be very hard to extract, if they turn out to be the wrong size (bolt catch pin is one i immediatley noticed).

SO......does anyone know of a spec sheet that shows the differences between an .308 build kit and a 5.56 build kit? I want to make sure that I identify any other accidental AR-15 parts before i try and bury them into the lower without the ability to get them back out.

Appreciate the help!

TheBulge · Oct 2, 2014

For a DPMS pattern only four lower parts should be different until you get to the buffer/extension.

Bolt catch, bolt catch screw, pivot pin and take down pin.

SoMD_Gen4 · Oct 2, 2014

TheBulge said:
Only four lower parts should be different until you get to the buffer/extension.

Bolt catch, bolt catch screw, pivot pin and take down pin.

So I definitely noticed the take down pins being longer, so those are good to go. Your saying the only other pieces that should be different are the bolt catch and pin?

How is the mag catch not differnet with the mag wells being obviously differnet widths?

TheBulge · Oct 2, 2014

SoMD_Gen4 said:
How is the mag catch not differnet with the mag wells being obviously differnet widths?

The mag catch button is long enough to make up the difference. The mag catch will only screw part way into the mag catch button.
The bolt catch usually uses a screw not a roll pin. Check to see if the receiver is threaded.

Sticky · Oct 2, 2014

The mag release parts are the same, but the bolt stop catch is much larger and beefier on a 308 and normally the bolt stop catch pin is threaded at the end to secure it in the hole, instead of being a roll pin like on an AR. The pivot and takedown pins are longer and larger in diameter than an AR15.

The lugs for the bolt stop catch should be threaded on the lug that you first insert the pin into, it should pass through that and as it enters the second lug, the rear of the pin should thread into the few threads on the first lug, securing it in place.

Some use an AR15 bolt catch, but I have heard that it isn't recommended, so I used the proper one on my 308 build.

SoMD_Gen4 · Oct 3, 2014

Thanks gents!

SoMD_Gen4 · Oct 3, 2014

So everything worked out perfectly except the mag release catch. I attached a pic for reference. Because it is a billet lower, it seems it's alot wider than normal mag wells. Does anyone know where I can find an extended mag release assembly?

I need one that's likely at least a 1/4 inch longer since the threads right now sit pretty flush to the lower (no room to screw in the mag release button).

SoMD_Gen4 · Oct 3, 2014

It's a normal size mag release at about 1"

Sticky · Oct 3, 2014

SoMD_Gen4 said:
So everything worked out perfectly except the mag release catch. I attached a pic for reference. Because it is a billet lower, it seems it's alot wider than normal mag wells. Does anyone know where I can find an extended mag release assembly?

I need one that's likely at least a 1/4 inch longer since the threads right now sit pretty flush to the lower (no room to screw in the mag release button).

That is pretty close to normal and you should be okay.. Remove the mag release lever and stud, install the button and spring and then... You need to use a pencil eraser end, or similar to depress the mag release button in against the spring, as far as it can go and this should give you enough clearance to rotate the mag release catch a few turns and engage the release button. But.... if you install the bolt catch release first, this may interfere. I always install the mag release first, then install the bolt catch release, but on a 308 it's easy to remove the bolt catch release, install the mag release and reinstall the bolt catch.

Did you try it this way? You usually cannot 'rotate the mag release button' to thread it on, you have to thread it together using the mag release bar and it needs to clear the lugs for the bolt catch pin and can't really have anything else in the way..

SoMD_Gen4 · Oct 3, 2014

Ha yeah I'm officially a dumbass, I forgot I need to go button first and screw in the release catch into it, vice the other way around. Thanks for curing the brain fart ha

Sticky · Oct 3, 2014

Here is one of my 308 lowers.. you can see, after installing, there is not as much engagement as on a 223 lower, so you have to properly install the mag release assy (first, before you put the bolt catch release together)..

0102b57c9b2e40255047548153432c2d03602357cc_zps07209137.jpg

Sticky · Oct 3, 2014

SoMD_Gen4 said:
Ha yeah I'm officially a dumbass, I forgot I need to go button first and screw in the release catch into it, vice the other way around. Thanks for curing the brain fart ha

Haahaa..

Glad to help out.. :thumbsup:

(and often guilty of that as well) :lol2:

AR-10 Build Question (AR-10 LPK vs AR-15 LPK)

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