Aero Precision Build with Fulton Armory Barrel

[MaineMan2]

This is my first 308 AR build. Been lurking here a while and posted a couple questions ahead of time. I’m posting to share a few things that have come up.  My goal is an accurate 308 rifle, but I live in Maine so anything farther than 500 yards isn’t relevant to me.  I didn’t worry about cost as much as quality and compatible parts.

I bought an 18.5” medium weight stainless “match quality” barrel from Fulton Armory. My Aero Precision bolt would not close on a Clymer GO headspace gauge, so I called FA.  The guy there told me that Clymer gauges ran a bit long in their experience and they use Forster headspace gauges. I bought a Forster GO gauge and nope - bolt wouldn’t close. As instructed, I sent the bolt and barrel back to Fulton Armory. The man I spoke to said that my bolt would close on his Forster GO gauge, but they still reamed about a thousandth more out of the chamber and re-polished it. Now the bolt closes on both of my GO gauges. I did have to pay shipping both ways, but I thought Fulton Armory’s service was very good. Oh - I left out that their turn around was only a few days. 

if you buy a Fulton Armory barrel, make sure that you buy your gas tube from them as well. I was smart (lucky?) enough to do that and it turns out their gas tube is 1/4-3/8” longer than you might expect. End of the gas tube is just a touch to the rear of center of the cam pin cutout in the upper receiver. 
 

On to the build:

M5E1 “enhanced” receivers from Aero Precision

15” enhanced handguard, BCG, lower parts kit, and rifle length buffer tube assembly also from Aero Precision.  Make sure you buy their lower parts kit if using an AP lower. Geiselle SSA trigger.  SLR adjustable gas block. Lancer carbon fiber fixed stock (sweet!).  Ambi charging handle from Daniel’s Defense - I really like it!  Moving tabs are almost twice as thick vertically as others giving you much more gripping surface.  Not cheap though.  Likewise with the LWRC buis set that I also like a lot because of the very solid lockup.  
 

I really like the Aero Precision enhanced receiver set, with 1 qualifier. You are locked into their proprietary handguard; however, instead of attaching to a separate barrel nut or other part the handguard attaches directly to the upper receiver.  Fit and finish are excellent.  There’s a screw-in pin instead of a roll pin for the bolt catch.  The qualifier has to do with the takedown pin detent.  Instead of the spring coming from the back and being held in place by the end plate, the hole comes from below, where the pistol grip will be.  You are supposed to put the detent in position, drop in the detent and spring, then compress the spring and lock it in place with a tiny set screw.  This process is NOT fun.  There’s a lot of tension on that spring.  Both the spring and the detent got airborne at different times.  Then I remembered to do it inside a gallon ziplock bag to avoid losing small parts. I finally got the set screw in place but there was so much tension that it was impossible to push the takedown pin out.  The only solution I could figure out was to cut a couple of coils off the spring.  This was the last set of parts for the lower so it was the correct spring and the pivot pin detent was working fine (springs were identical as far as I could see and I did check before assembly).  
 

Here’s a better way to get that takedown pin detent secured with much less risk of small parts flying off into your workshop debris.  Chad from SOTAR posted a video about how to replace a takedown pin without removing the castle nut and end-plate.  It would be perfect for initial install on the AP enhanced lower as well:

note: if posting a YouScrewed link is verboten please let me know and I’ll delete it. 
 

By now I can hear the screams of “photos!  We need photos!”  Forgive me. I stopped putting pics of anything firearm related on the internet a long time ago. And yes I realize how silly that is having just typed this really long post. 

[98Z5V]

2 hours ago, MaineMan2 said:

  The only solution I could figure out was to cut a couple of coils off the spring.  This was the last set of parts for the lower so it was the correct spring and the pivot pin detent was working fine (springs were identical as far as I could see and I did check before assembly).  

 

 

 

That's exactly what I do everytime I put one of these together.  I lay the set screw out beside the spring, and cut that much off the spring, plus 2 more coils.  Makes running that takedown pin much easier. 

I've always loved Fulton Armory.  Both @Matt.Cross and I have that same exact barrel.  RIP Clint McKee. 

[MaineMan2]

On 2/4/2022 at 8:32 PM, 98Z5V said:

That's exactly what I do everytime I put one of these together.  I lay the set screw out beside the spring, and cut that much off the spring, plus 2 more coils.  Makes running that takedown pin much easier. 

I've always loved Fulton Armory.  Both @Matt.Cross and I have that same exact barrel.  RIP Clint McKee. 

I’m wrestling with another Aero Precision lower and that takedown spring is driving me nuts again. So I found this video:

They say to cut off much more of the spring than I had done.  Plus now I know why they don’t give you a shorter spring for the rear takedown pin.