Aero Precision M5 Build - Lessons Learned

[ingEneer22]

First off, a little bit about myself. I consider myself an aspiring gun nut! I have a few AR15 builds under my belt and many more ideas in the works. I am purely a hobbyist and by no means an expert. I do however find value in seeing what works and what doesn't for others in the community. So for those that are just starting, or perhaps thinking about starting, a .308 AR build, I offer you this (premature) summary on my Aero Precision M5 build.

I've had plans to build a .308 AR for quite some time and when Schuyler Arms announced they were selling Aero Precision M5 combos for $215, I jumped on the deal and it was off to the races. My initial plan was to leave the upper/lower combo in the safe and come back to it in a few months...so naturally, the next day I was ordering parts to start the build ahead of schedule!

Come to find out the .308 world is way different than that of the uniform and military specified .223/5.56. I quickly learned that most rifles fall under one of two categories, Armalite's AR10 or DPMS's LR308. The Aero Precision set falls into the DPMS category so I figured that any old lower parts kit in the DPMS style would do, wrong! Unlike AR15's, .308 parts are not manufactured to a common set of specifications. For example, parts made by CMMG may not perfectly fit every DPMS style .308. I have heard that Armalite style parts are more uniform but not near as common as DPMS. I learned this the hard way when I purchased a CMMG .308 Gun Builders LPK. (This is a great product for those of us who have no need for a gritty 40lb factory trigger and a cheapo A2 style grip). Upon assembly, I found that both receiver pins would not fit. With a little persuasion (and frog lube), I was able to get the pivot pin installed. I had to use a fine grit sand paper on the rear take-down pin in order to get it to fit. Both pins didn't protrude from the receiver like they do on an AR15 and were a bear to remove. My OCD kicked it and I ate the $12 shipping cost and went ahead ordered new pins from Aero. Much to my satisfaction, that solved the problem perfectly! Unfortunately, that was not the only issue I had with the CMMG parts. The threaded portion of the magazine catch is barely long enough to thread on to the magazine release button. I may have gotten a good 2 or 3 threads. I'm sure this will not cause a functionality problem and can be easily ignored if a solid magazine release button is used. But once again my OCD got the best of me. After scouring the web for help, I discovered that the Armalite pattern magazine catch has a slightly longer thread and will work in the Aero M5 lower. Easy fix! I have ordered one and will report back when I can confirm or deny this. The rest of the CMMG parts (bolt catch, safety and buffer retainer) all work fine. I want to stress that this is by no means the fault of CMMG or Aero Precision, just the non-standardization of .308 AR parts.

I broke my sacred Magpul relationship and opted for an Ergo Deluxe grip for this build. The AR15/M16 version fits great on the Aero. Snug and no unsightly gap between the tail of the grip and the receiver.

Thankfully, Magpul LR/SR PMags fit the DPMS style receiver and are readily available. I have heard that it is not as easy to find magazines for older Armalite pattern rifles. They have, however, released a newer model (AR10A) that does accept 3rd party magazines.

On to the upper! As you can see I still have ways to go but after the lower fiasco, I have done my homework on the upper. As I said before, the Aero M5 upper is a DPMS pattern but more specifically, a DPMS pattern with a high profile. Apparently this is the more common than the low profile design. The difference is about 1/16" on the top of the receiver. Not a huge deal until you start trying to match up a rail with a picatinny rail in the 12 o'clock position. This won't bother some but it's an easy fix if you just pay attention to what rail you're are buying. Most manufactures that make .308 rails will have a selection for a DPMS high profile rifle.

The barrel is pretty straight forward as long as you buy the correct pattern for your rifle. One word of caution, however. I've been told it's a good idea to be sure that your bolt and chamber are properly headspaced. Because of the distinct differences, not only in tolerances but specifications from one manufacture to another, it is inherently important to have a qualified individual ensure that the rifle is safe. You will find that many manufactures, such as JP Enterprises, include a headspaced bolt with each of their .308 barrels.

I'm eagerly waiting on my money tree to catch up, whenever that happens I'll finish the build and report back with any other "lessons learned!"

Additions soon to come:
Lower
-Geissele DMR trigger
-Armalite pattern magazine catch
-Magpul PRS stock

Upper
18" JP Supermatch barrel w/ bolt
JP bolt carrier
14" SLR Rifleworks Solo rail (I think)
AAC Breakout
Rainier Arms Raptor charging handle

[Mobuck]

Above is a whole list of reasons why I've not even considered "building" an AR 10 platform.
If I decide I want an AR10, I'll buy(when they're on sale from PSA, of course) an assembled upper and assembled lower.

[G.barnes]

That's why you buy receivers and lpks from the same company. For future reference when looking for 308 parts dpms and cmmg are not good choices. Don't care how they do on ar 15's. I just built one with aero precision upper,lower,lpk,and bcg. Rock river rifle buffer tube with dpms buffer and spring (not a lot of options on buffers and springs) with magpul fixed stock, and magpul miad grip. Rainier arms stainless 18" barrel (comes with a money back guarantee), syrac adjustable gas block, Midwest keymod 15" ff handgurd, and bcm charging handle. It took about 45 minutes to assemble. The hardest parts were 1. Get the pivot pin installed in the lower, and I had to clearance the bottom of the charging handle a small amount at the very back. The charging handle took about an additional 3 minutes to fix.

[Arizona Fusilier]

Is there any way a "hobbyist" can check the headspace? Special tool perhaps?

Is this not necessary for a 5.56/.223 build? Seems like a good idea.

[HKFan9]

You can check your head spacing with a set of GO / NO GO gauges sold off any gun smithing website... Midway USA, Brownells, ect ect.

The problem is a lot of AR15 and AR10 pattern rifles (since the barrel extension is permanently attached to the barrel often times don't NEED to be head spaced, and even when you try it, will fail on GO / NO GO gauges. I even had customers HK MR556 upper's fail on a GO / NO GO gauge, so they are never the best solution for AR pattern rifles.

If you are THAT worried about your build, have it looked over by a professional *NOT A BUBBA* gun smith before you pull the bang switch.

ING...

Nice looking build so far, and a good post for people interested in AR-10 builds. I even forget all the in's and outs of them. I can build an AR-15 in 15 mins, but AR-10's are a whole other ball game. Please post some pictures when you finish it up.

[ingEneer22]

HKFan9, thank you. I will post pics as I go!

[Taco-XL]

The headspace is set by the barrel extension. If all new parts are used there is really no need to worry about checking it. I have never known of good factory new parts being out of spec in headspacing.

[HKFan9]

Yup, but people still often like to check them, so I was just saying you can TRY GO / NO GO gauges, but don't be discouraged if it fails, they often do.

The biggest issue we see that people THINK is a chamber / head spacing issue is when someone builds a rifle and uses a cheap spring and buffer they ordered off discount websites or ebay (we are all guilty of it) Generally it isn't a problem, but sometimes rifles get over gassed, and the bolt will bounce off the barrel extension and seat the 2nd round out of battery and the gun will not fire.

[Duzell]

I have a current lr308 project myself

drkdragon builds

and most of its straight forward if you follow the 308 pattern your using

the issues in question with the lr308 is what fits that pattern
i have the dpms pattern, its an mk3 mod from cmmg using aero P's m5 upper(same as yours) and aero BCG (nib)


but I'll admit it was confusing at first to find parts and tools

there as stated no go and go type tools
these may also help you
http://308ar.com/tools.htm

if you need help I can assist

-duzell

[mardanlin]

You won't be sorry, a 308 AR is one of the absolute best rifles you can get for close to mid range shooting. I have a DPMS LR308 build that is a dream to shoot, holds groups much better than any of the 556s I've had and shot.

I'm also digging the desert tan color scheme. I'm pretty boring and go all black because I'm always nervous I'll over do the desert tan and make it tacky.

Here is mine, hope you get yours done soon I love to look at these things so much that sometimes I just do a Google search for them and drool.

[Sparky277]

Haven't done a lot of research on it, but is it possible to build a 308 that isn't front heavy? I've been looking at a ruger 762 but if I can build one, that's the route I would take.

[Duzell]

yes, using a fluted barrel and a better stock can make it a more balanced rifle

reason I use "fluted" heavy is mainly the improved accuracy and durability.

the concept im working with is to add a heavier stock on back to counter the weight i have up front

but the bolt does have some good weight also, that should be noted

you can order a standard design barrel
example design of a standard barrel shape
(first that came to mind)

http://www.faxonfirearms.com/p/114/2...aper-rifle-gas

[ingEneer22]

Stock is back from its paint job! I'm really digging this Patriot Brown. Looks great with the black contrast.

[HKFan9]

So your looking to sell this thing when you are done with it right?

[noonesshowmonkey]

The build looks great, and the commentary has been really well put together. Looks like you're learning alot.

This thread does a great deal to illuminate what a Technical Data Package (TDP) is, and why it is important. A TDP is, in short, a set of specifications for acceptable materials, measurements, fit ratios, etc. for a given good. The M4/M16 series of rifles famously have their TDPs which define in their way what is 'mil spec'. There has been a great deal of debate the internet wide, with the accompanying butthurt, discussing the virtues, vices, and even the ontological need for a TDP at all...

As anyone who tries to put together an AR-10, or god forbid an AK series rifle, can tell you, having a strong, abstract description of the complete rifle concept providing guidance to standardize parts makes the process considerably easier. This is why we can take an AR-15 upper from one maker, mate it to another maker's lower, then go to the range and fire the weapon to our hearts content without having to spend a drop of sweat or worry.

[ingEneer22]

UPDATE: Just traded my left kidney for the Geissele Hi-Speed National Match - DMR trigger. Primary arms has them on sale for $237 and some change if anyone is interested! I love all my Geisseles but have never owned one of their adjustable ones. Can't wait to install it and finish the lower!

[HKFan9]

Glad to see you are doing this build right! Buy once Cry once is always my motto.

What barrel are you planning on, you have a great trigger, and a great stock, hope theres a great barrel and great glass in this rifles future.

[ingEneer22]

HKFan9, I am still trying to decide that. I've got 3 in particular that I've got my eye on.

-18" JP Supermatch
-18.5" Fulton Armory (Criterion)
-18" Lilja

I was originally pretty set on the JP, no doubt its a fantastic barrel but the other two have also sparked my attention. Obviously, I want to get the most out of this rifle and I'm willing to invest some capitol where it counts. That being said, I don't want to spend money needlessly. I've heard that the Criterion barrels are comparable to the JP and cost considerably less. The Lilja barrel costs about the same as the JP considering it doesn't come with a bolt. I haven't heard too much about Lilja, but everything I have heard has been exceptional. Weight is also a consideration, I've already got a 10lb stock ! I don't want to end up with a 20lb boat anchor lol!

Bottom line, a sub MOA barrel would suit my needs just fine. I am not going lose sleep and an extra $300 to get a .2" improvement on my groupings.

Any suggestions or recommendations are greatly appreciated!

[HKFan9]

Lilja makes excellent barrels, as does JP, as does Kreiger and White Oak Armament, and Saturn.

I have heard of Criterion but never had any personal experience with them. I know Lilja and JP both have great references so I don't think you could go wrong with either of those choices (note I am not ragging on the Criterion I just personally don't know much about them.)

You build is coming along very nice, when my 7.62 Can gets here, and my Form 1 I submitted for one of my AR's is all said and done, I plan on doing a .308 build similar to yours, so I am very interested in your experiences.

Great thread.

[Sc0]

Just finished an Aero M5 build, hoping to do a function check tomorrow to tune the gas system and to sight it in. Going for 1moa or less for accuracy but will be a hunter and 3-gun rifle, or anything else I might need a compact 10lb .308 semi for.

AERO M5 upper and lower recever, Aero bolt carrier assy, DPMS LPK, Larue MBT-2S 4.5lb trigger, VLTOR AR10 carbine extension tube, VLTOR Clubfoot collapsible stock, AR10 buffer with ISMI flat wire spring, DPMS .308 charging handle. Magpul 25rd M118 magazine, CMMG 16" Nitrided barrel with rifle gas system 1:10, Nitrided Brownells gas tube, ODIN free float 12" Keymod handguard, Syrac Ordnance Gen2 click adjustable gas block, Lipski adjustable .750" clamp on front sight base, Mo's 22mm globe front sight, and Armalite AR10 Q/D A2 Sight assy

[ingEneer22]

So, the Armalite Mag catch works perfect with the M5 lower. Completely solves the problem with the short DPMS style catch. Also after weeks of going back and forth between rails and handguards, I finally pulled the trigger on JP's MK3 Signature Handguard. Figured that with many peoples .308 builds busting past the 15 lb mark, I would ensure my rifle is as fit as possible. No need for all the tacticool rails on this one. I did buy a 2" rail section for the Atlas Bipod, however.

[HKFan9]

Thanks for the update, we will need pictures shortly lol.

[ingEneer22]

Welp, went ahead with the 18" JP Supermatch barrel! I really hope it's worth the $600 price tag. I decided to go with the JP for a number of reasons. One being that it seems to be one of the best options short of a fully custom barrel. Their barrels receive quite a bit of TLC before they leave the facility. From lead lapping to cryogenic treatment, these barrels seem to be a step above the rest. One of the most appealing things about this barrel is that it comes with an individually headspaced bolt. That is how I keep rationalizing the cost lol, "at least it comes with a $200 Bolt!"

HKFan9, I am as excited to see what it is going to look like as you lol! Handguard should be another week or so for Cerakoting and then probably 2 or so weeks for the barrel to get back from Cerakoting.

[HKFan9]

Good choice on the barrel I would say. You are right it is probably the best choice (specially with the supplied bolt) for the price tag short of spending uber bucks on a custom. Realistically all things being equal I highly doubt the difference between one of the more premium barrels would be noticeable to 99.9% of shooters. Don't get me wrong here, I am not saying the custom barrels don't live up to their names, it's just usually only the highest level of shooters can harness those results, specially in a semi auto platform.

For the longest time I planned on ordering a KAC MK11 deployment pack because it is a dream gun of mine, but everyone with experience with them told me they require a lot of finesse to shoot accurately, apparently they like a death grip hold. At half the cost I can order a GA GAP-10 that is just as, if not more accurate.

[ingEneer22]

I completely agree. When I trick out a Remington 700 maybe I'll get a custom barrel but just like you said, in a semi-auto, it's not worth it to me. I'm positive the barrel will be more accurate than I am and I probably could have just gone with the Fulton Armory barrel (HEAVY THOUGH) and not noticed a difference. BUT functionality, reality and accuracy aside, we all know that to a point sometimes you just have to spend a little extra so you can make your buddies jealous at the range ! Haha