AR308 DPMS Build Issues

[Bgillette91]

Its been a while since posting, but Im back with some need of help.

A month or so ago I received the 5D Tactical AR 15 jig and started doing my own 80 percent lowers. I was so impressed by it that I also got the Ar308 conversion kit and did an Ar308 lower too. The lower is a 7075 billet DPMS gen 1 style lower that 5D Tactical machined themselves. Im about halfway done with build now but have some problems.

I bought a 20 inch Aero Precision complete upper and an Aero Precision M5 lower parts kit. I emailed 5d tactical before going with Aero to see if they have used their lowers with Aero uppers with success, and they said that they have.

Here are my issues.

1. The lower has a threaded hole for bolt catch pin and rear takedown pin detent hole. The Aero parts kit does not include these screws. I emailed 5D tactical asking what size the threads were bur they didnt specify, all they said was that they come standard in DPMS style LPKs (which apparently is incorrect). They definitely arent 4-40, because the threaded bolt catch pin from my New Frontier 9mm AR lower is too big for both holes.

2. What size length does the take down pin screw need to be? Because the detent spring is nowhere near long enough to come close to the hole. The spring is same length as AR15 detent springs, and the rear of the AR308 lowers between takedown pin and buffer threads/endplate is longer than AR15s, as we all know.

3. The pivot pin secures through lower and upper nicely, but the rear takedown pin will not go in. The holes in the receiver do not line up with the lug in the upper. I was afraid that was a possibility with this build, as Ive heard that is a common issue among different AR308 manufacturers. Do I sand down the pin? Do I lap the hole in the upper lug? Do I sand down the area on the radius of the buffer mount where the rear of the upper is making contact and not allowing it to fully seat down inside the lower?

Id appreciate any feedback on these issues of mine. And Id also like to say that if you dont own this jig kit yet, do yourself a favor and get it. It is absolutely amazing how good the lowers are coming out. I finally can own an AR pistol now without the stupid single shot crap.

Im gonna post some pictures of the rear takedown pin alignment issue so you guys can see what I mean.

Also, if there are any guys out there who have machined their own AR308 80 percent lower from 5D Tactical, please let me know.

[new shooter]

Seems like your lower is completely out of spec and 5D tactical are not offering any help or good customer service on their product.

Unfortunately I do not have the threa dimensions for your build. Though I can't imagine it wouldn't be hard to find that spare part somewhere online... atleast for the bolt catch..

As far as the rear take down pin, most .308 lowers go from the bottom up from the grip tang rather from the buffer tower like an AR15. That is why the spring is not much longer.

If that's not the case with your lower. Then the required spring for the rear pin is special for their lower and they should provide one for you.

Edit: looks like it comes from the buffer tower. The normal spring should work but the set screw to retain it should be Fairly long or it must be threaded all the way through to get tension on the spring.

Now the biggest problem of all is your lugs not lining up. If it were me, I'd send a photo to 5D and demand a new one for you to mill out free of charge. I wouldn't alter the aero upper one bit as heir stuff is pretty nice and to alter it would just be sacreligous

[Bgillette91]

The point of the chopstick is where it is making contact too early.

New Shooter, you are correct. It is the buffer tower, forgot what the techincal term was.

The problem is that I dont think 5D will send me a new one. Besides, it will probably be same exact specs. They need to completely change their CNC plotting points to correct the issue. Then again, maybe it will work with other brands of AR308 uppers. Who knows. None of it is standardized.

[baih777]

here is the bolt catch screw. I think its 6-32.

http://www.midwayusa.com/product/283473/dpms-bolt-catch-screw-lr-308-steel-matte

[baih777]

if you know someone that has a DPMS upper. check the fit.
it is possible Aero moved the holes for their AR308.

[Bgillette91]

I emailed them before ordering the upper, I wanted to be sure they knew that it would work on their lower.
This is the response:

I’d steer clear of the PSA uppers. They have their own thing going on and they don’t fit well with most other brands. The Aero upper will work just fine, you may just need to clearance the rear lug a tad. It’s typical with 308 building that things don’t fit together perfect. We are offering a 308 upper that fits our lower perfectly. It’s a stripped upper, so if you feel like doing the upper receiver build you’re guaranteed a perfect fit.

The problem is that the rear lug is going to need to be sanded down a lot more than a tad for it to work. And that doesnt fix the issue with the angled gap between the upper and lower.

[baih777]

just checked the Aero website. your right, the parts kit does not come with the screw. also DPMS 308 lowers use a different bolt catch. not sure which one Aero has in their kit.

http://www.midwayusa.com/product/215764/dpms-bolt-catch-lr-308-matte

[new shooter]

Your best option is to try and order their stripped upper receiver and transfer the aero parts onto the 5D upper.. then sell the stripped Aero upper.. I hear they are in high demand anyways

[Bgillette91]

here is the bolt catch screw. I think its 6-32.
http://www.midwayusa.com/product/283...08-steel-matte

Definitely not a #6 diameter. I tried using the one from my New Frontier 9mm lower and that one uses a 4-40 screw. So its even smaller than that. I have no idea why they would use one smaller than a DPMS standard size and then turn around and tell me a standard DPMS style threaded pin will work.

[new shooter]

Definitely not a #6 diameter. I tried using the one from my New Frontier 9mm lower and that one uses a 4-40 screw. So its even smaller than that. I have no idea why they would use one smaller than a DPMS standard size and then turn around and tell me a standard DPMS style threaded pin will work.

If it's smaller u can always redrill and retap to 4-40

[nate76239]

Your best option is to try and order their stripped upper receiver and transfer the aero parts onto the 5D upper.. then sell the stripped Aero upper.. I hear they are in high demand anyways

I agree don't waste time trying to force something that doesn't fit right. Not sure about the takedown pin detent hole, the .308 lowers I've seen had the hole on the bottom and was held on by the pistol grip

[Bgillette91]

If it's smaller u can always redrill and retap to 4-40

It is certainly within my skillset to do this, however Id rather see what 5D is going to do to remedy the situation. Ive already spent well over a grand on jigs, tooling and lowers with these guys, I hope they value my business.

[Bgillette91]

If I were to sand down the take down pin and get it to go in through the upper, wouldnt that mean there will be some wobble and vibration when shooting?

[Drew Eckhardt]

Its been a while since posting, but Im back with some need of help.

3. The pivot pin secures through lower and upper nicely, but the rear takedown pin will not go in. The holes in the receiver do not line up with the lug in the upper. I was afraid that was a possibility with this build, as Ive heard that is a common issue among different AR308 manufacturers. Do I sand down the pin? Do I lap the hole in the upper lug? Do I sand down the area on the radius of the buffer mount where the rear of the upper is making contact and not allowing it to fully seat down inside the lower?

You cut the radius because a bad job there won't affect how the receivers fit together.

As you discovered, there's no standard for .308/6.5 Creedmoor/etc. ARs. Everybody apart from Armalite, DPMS, and KAC builds parts reverse engineered from Armalite / DPMS, or does their own thing for good ($2 20 round G3 magazines in free states, small frame with a half pound less metal) or bad reasons.

My "DPMS compatible" Aero Precision M5E1 upper does not close on my genuine DPMS LR-308 lower.

[yoko]

This problem is the main reason why I always buy matched upper/lower receivers whenever I have a large frame AR project.