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BCA 6.5 build


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Hi all. Just found this forum and thought I would do a quick intro and see what the masterminds here think about the direction I am taking. Little background on me is that I spent a few years in the mil and now am in the LE sector. I've shot a ton of rounds through M4/M16's and even trained in the MO shooting the M110 rifle. I learned to love the M110 and have craved owning a AR10 style long gun for many years and finally decided this is a good time to do a budget build. I am not looking to be the next Carlos Hathcock but I would like to have a rifle that can hold a solid 1-1.5 MOA and ethically take white tails without an issue. I also just finished my first AR build which was a P80 lower with BCA 16" 223 Wylde upper. My honest max range would maybe be out to 500yds but the timber in my state is so thick I doubt I would ever have the chance at shooting a deer at that range. So it's basically just for me to know that I can easily shoot at 200yds.

My Build:


  • P80 Warthogg
  • DPMS LPK with trigger
  • Tacstar Grip
  • Luth AR  AR-308 Rifle length buffer tube with spring and buffer
  • Magpul PRS stock


  • Bear Creek Arsenal 6.5 Creedmoor side charging upper w/ 22" heavy barrel
  • Monstrum 6-24x50 scope
  • Cheap bipod

I milled the lower out Saturday night and had a hell of a time getting the trigger to cycle reliably. Still doesn't work well. After I got it the best I could I finished the lower assembly and got real excited when it came time to install the upper. Then got disappointed. The upper doesn't line up very well despite both products claiming to be a DPMS gen 1 style. The front take down pin is fine but the rear is a bear to get in and requires a light hammer strike to get it through the upper and locked down. Add in that the rifle doesn't cycle worth a crap when function checking it AND that the bolt catch can't even move up to catch the bolt because the upper hits it and I have a lower that isn't going to work for me. Bottom line I'm looking for a new lower. Going to check out the Aero M5 lower at a LGS tomorrow and going to bring my upper to make sure it will fit. There are a couple reviews on BCA's site that say they should so I have high hopes. Just to be clear I knew nothing was actually standard when it comes the AR-308 world but I hope that someone like me will find this in the future and save them from trying the same thing. Take a look at the picture and you will see what I mean.


Edited by brapp-attack
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Went over to the LGS today and test fit the Aero Precision M5 lower on my BCA upper. The two fit together pretty well with the knurled screw in place that goes into the charging handle channel. After removing the screw they fit together really well and the take down pin holes line up perfect. I imagine with a typical rear charging rifle this is not an issue. My plan is contact BCA and confirm I need the screw there to have the rifle function correctly and if I do need it I'm going to take a little bit off the flat side with the mill bit to create the clearance I need. As for the LPK the LGS didn't have the Aero one in stock so I'm going to order the kit minus the grip and FCG. I'll use my existing FCG from the DPMS kit and Tacstar grip I have. I'll check back with what I find out about the knurled screw on the upper.

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Adding in another update on the build. Since this is supposed to be a budget type build I poked around on the forum here and found what appears to be a trigger that I can "get behind". I decided to go with the LaRue Tactical MBT-2S. I got wild and ordered three of them so I'll have one for this build, one for the 223 Wylde build, and one for the inevitable next build.

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Well I'll be able to swap the trigger out on my 16" wylde build this weekend to get a feel for it which is nice. They shipped my order out pretty quick which is rad.

On another note I talked to a person over at Bear Creek yesterday and they said that the screw I had been wondering about at the rear of the upper is in fact needed for the rifle to run properly. As it turns out they call it something fancy like "charging handle gas plug" or something like that. Without it the gas that is used to cycle would just be blown out the back and into the shooters face turning the rifle into a single shot. I told the woman it appears I'm going to have to mill or file down the flat side of it to make it clear my lower all the way and she said that my plan sounded good. Now back to the waiting game for my LPK and the new trigger. LPK hasn't shipped yet so unsure as to how long I will be waiting but as to be expected with the whole pandemic thing.

I also lost my mind and ordered everything minus the optic for a 7.5" 5.56 AR pistol build last night. Guess I found a place for that third LaRue trigger. Shucks

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10 hours ago, brapp-attack said:

Without it the gas that is used to cycle would just be blown out the back and into the shooters face turning the rifle into a single shot.

So if the screw worked loose it could be propelled at your face when you fire? Not sure I would care for that arrangement.....for sure be using loctite and checking it regular!

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26 minutes ago, jtallen83 said:

So if the screw worked loose it could be propelled at your face when you fire? Not sure I would care for that arrangement.....for sure be using loctite and checking it regular!

the plug replaces the space filled by a charge handle ie. side charge. there is a flat edge on the plug the rests on the top of the lower receiver.


23 minutes ago, shooterrex said:

Please post pics of what you are talking about. This doesn't make a whole lot of sense.




Edited by sketch
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3 hours ago, jtallen83 said:

Then I am not following how the gas used to make the rifle function would come at your face, some residual gas yes but how would it stop function?

Right on - it certainly shouldn't, not at all.  If that's the case, I'd Rock-Sett that bastard in place.  No Loc-Tite at all, straight to Rock-Sett.

But that explanation from BCA still doesn't make any sense, at all...  No sense at all...

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Ok it is taking the place of the charging handle in the rear of the receiver. It needs to be removed to pull the bolt carrier out of the upper. Yes a little bit of gas comes out the back that's why there is a "Gas Buster" charging handle. I would find a plug the proper diameter and threads that takes a torx bit so I could screw it in flush.  Locktite it in but removable with a torx bit. Or grind off what you need to get it to close. But a plug flush with the rear would be cleaner looking.

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Honestly looks like a fucked up design from a company that made a side-charger.  Why would they even machine that into the upper at all, if it was a true side-charger?  There's no reason for it to be there, in the first place.

They put the Band-Aid on the wrong cut, here...  

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My upper looks identical to the pictures. After thinking about it more I agree that it might not make the rifle function incorrectly but I do believe them that there is going to be hot gas coming out out of that hole if not plugged. I never even thought about plugging it with something else. I really like the idea of installing a flush mount torx or allen head screw in place of the thumb screw that it comes with. My best guess would be that they are using the thumbscrew because as stated it needs to be removed in order to remove the bolt when it comes time to clean the upper assembly and it just makes it easier to do that without any tools. I do remember the tech person saying that with the side chargers it is necessary to clock the plug which is nothing more than turning it in all the way and backing it out until it's flat side down. With that being the case I'll be sure to not get too long of a plug. Once I get one I'll make sure to post up a picture.

As far as it being a dumb design I'm no AR expert so I don't know if there is a better way to accomplish the side charging or not. My AR15 upper I bought from BCA is a side charger and it is really nice to not have to have a scope on a offset set of rings that's raised up to clear the rear charging handle. Is it a deal breaker to have the optic up another 1/2"? No it definitely is not especially when I'm just using the guns for plinking. But it is nice to be able to have a lower over all profile. After shooting my AR15 I really wish we used them in our squads because charging a rear charger while driving to call is kind of a pain one handed.

This is a great convo to have. Really glad I can maybe help some others out. Thanks for all the reply's so far!

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Got another update for this. Made a trip to the hardware store to "get propane" and just so happened to bring that thumbscrew with. Found the proper set screw to replace the thumbscrew and ended up getting two to put one in my AR15 upper too. Definitely like the look way more because it is way more clean. Put a little blue loctite on them and they should stay in place. 


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Well I found time last night to get this build ready for zeroing. Everything installed nicely in the Aero M5 lower except for the rear takedown pin retainer spring with the provided threaded plug. I had to cut the spring down just a little to be able to tighten the plug in enough to get it flush. Also for anyone else using the Aero M5 LPK it does come with that little 4-40 threaded plug. The LaRue trigger went in perfect and is seriously amazing. Really like the take up and breaks so clean. Fun fact is they don't play nice with the P80 AR15 lower I just milled last night. 

Anywho I'll check back in when I get to shoot the CM. 



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Good update, and good job, man.  :thumbup:

Yeah, those 4-40 set screws - you have to shorten the spring the same length as the screw, and if you force it all together, there will be so much spring pressure on the detent that you'll never get that takedown pin to move.  Another side to that - if you feel it's really tough to get that takedown pin going - pull the spring, clip off another coil, and try it out.  Still tight?  Cut another coil, etc.

I use 6-32 set screws, too.  You just have to ream the hole size up a little, then tap it.  If you have the 4-40 tap,you can just run it (tap) the standard hole straight away, no reaming required. We've been doing this for 10 years here for the takedown pin, before lowers were ever threaded for that. Aero was actually the first company to start offering that, and it was on their AR15 lowers.

Edited by 98Z5V
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