Looking for some input from more experienced precision shooters.

Two years ago I wanted a DMR setup and the consensus I got was 308 was the way to go. So without putting much thought into it I built an Aero M5. Having owned it for awhile and doing more research I'm leaning towards selling my 308 DMR and building a SPR/MK12-ish upper after I made a few realizations:

1) I don't have access to any ranges past 300 yards.
2) I don't hunt other than ridding the world of a few ground hogs on my parent's property, typically a 50-100 yard shot.
3) I'm not thrilled with the accuracy. It does 3 moa with ball ammo and 1.5 moa with 168 gr FGMM. Not terrible but I can do 2 moa with my 5.56 10.5" SBR  from a supported position shooting m193. I'm shooting more expensive rifle and more expensive ammo to get an extra 0.5 moa?!
4) My main goal for owning a scoped precision rifle is the entertainment value of ring steel between 100 and 300 yards.
5) I have a small safe and the 308 takes up a ton of room.
6) The recoil isn't awful, especially with a suppressor, but after 100+ rounds my shoulder starts to ache a little (as does my wallet), whereas i can shoot 5.56 all day long with no issue.
7) I'm a little bit OCD and get annoyed with keeping track of all the different calibers. I have 22lr, 556, 308, 9mm, 380, and 12ga. Would be nice to eliminate unnecessary firearms and calibers.

I already have a quality AR15 lower with geissele trigger so all I need is the SPR upper. I plan to take the difference in value and upgrade to a higher quality scope.

What would y'all do in my situation?
Smart move or will I be kicking myself for selling it?

I am planning to sell the entire setup including the suppressor to my dad so I could always get it back if i sweet talk him.

Please understand that I'm not being a jerk when I say this:  If your 208 DMR only does 1.5MOA with FGMM, then you need either to improve your rifle shooting skills or your rifle building skills before you will see any accuracy gains going from a 308 DMR to a 5.56 SPR.

ETA

For your requirements, the .308 doesn't seem to make a whole lot of sense. I'd invest my effort and capital into completing your 5.56/.223. rifle, stock up on good ammo, and go to town.

Understandable, human error can play a large factor. With that said I'm by no means new to shooting for accuracy and know the fundamentals of trigger squeeze, natural point of aim, resting heart rate, breathe control, etc... As far as build quality goes almost all of the parts are Aero so not sure what else I can do to improve aside from swap out the barrel and bolt with something that is match grade. ( I don't think Aero guarentees any level of accuracy for their rifles)

From what I've read 1.5 ish MOA is pretty normal for the Aero M5.
https://www.pewpewtactical.com/aero-precision-m5e1-308-complete-rifle-review/

I certainly need to work on my shooting skills and I'm wondering if going with a SPR would help with that seeing as its cheaper to shoot and takes far less effort to manage recoil allowing for more trigger pulls per range trip.

OK, I expected more from the Aero M5.  My bad.

I have a Noveske SPR upper on a Mega lower I built with a Geissele 2-stage trigger. The SPR concept with medium-weight 18" barrel is VERY accurate, it will be a great 300y rifle if you feed it good ammo.  I feed mine Black Hills Mk262 and get 2" or better groups at 300 yards, but at $1/round I don't shoot it much

if you build an SPR, don't use a standard AR upper. Get one with a slightly stronger design, like the Vltor.

One option is to build a LaRue UU kit and get the 18" Stealth barrel option.  I have a LaRue UU kit with the 16" non-Stealth barrel option (don't remember what it's called), it's a great kit.

I built a 13.5" LMT MWS with a TR24 up top...it is a sub 500 yard gun and its perfect for that role.

I was originally thinking a BCM as they sell a complete mk12 mod 1 upper that looks nice but I also enjoy building my own rifles, plus they are usually cheaper.

you're gonna want a stronger, stiffer upper receiver to hold that barrel.  An 18" medium-weight barrel is heavy, and you don't want it to introduce flex into a standard M4 upper receiver. The LaRue and Vltor upper receivers have more material, are slightly larger in their external dimensions, making them stronger and stiffer.

One thing to think of if you do indeed ever want to shoot past 300yds the .308 does much better in the wind than 556. With more power.

But if everything is within 300yds and you’re not trying to kill big game or people hiding behind cover then the 308 is very pointless.

*laughs in Service Match Rifle*

do you disagree that a stronger, stiffer upper receiver provides a more stable platform for a heavier barrel, thus enhancing accuracy?

Even a service match rifle with its 20" HBAR could benefit from a stronger, stiffer upper receiver.

Not noticeably.

Not even close to a precision expert, but I would think a billet upper receiver would be better.  The Larue Stealth uppers come with them, have one.  I built an 18" 6.5 Grendel DMR and used an Odin Works billet upper receiver, not only for the barrel weight, but also for a suppressor attached to it.  It would give greater stiffness to the whole upper.  I don't think it's absolutely necessary, but if you are trying to increase precision, why not add one more thing to help improve it?

.308 AR rifles need close to 70 foot pounds of torque on the barrel nut as opposed to 35+ for an AR-15. At least 50 foot pounds as a minimum. There is a lot more recoil and a bigger frame.

Big frame AR's are not bolt actions. Barrel quality plays a role in group size. 1.5 moa is not bad for a AR-10. Custom handloads may improve your results.

Try 175 and 155 match ammo as well. Outback, Hornady and Black Hills. You mat find one of their loads that perform better in your particular rifle.

The only FMJ's I shoot is ammo that is gifted to me. I normally load Sierra 69's in my AR's. Sometimes Hornady's 68's. I have grown to expect 1 moa or better results on target. Even factory chrome lined barrels usually shoot my ammo around 1.25" to no bigger than 1.50" at 100.

Once the Reloading bug bites there is no going back.

69 SMK - 24.5 grains of Varget

68 grain Hornady - 24.0 grains of VihtaVuori N140

2.250" OAL both loads.

HighpowerRifleBrony is right regarding upper strength.

I only use heavy walled custom uppers for 24" to 26" long match barrels. Service rifle (1" diameter under the handguard inside a steel float tube) 20" long work great in standard uppers.

Use SS shim stock or 609/620 Loctite to eliminate any free play in the barrel extension/upper receiver fit.

There's more to it than that. Probably the most critical part of it is how the extension fits the upper, but almost no one wants to break out the torch to get their gun together.

Depends on range and what you want to shoot with it.

I shoot my LPR more than my APR, ammo is a bit cheaper, I’m lazy and not about hauling shit further out, ammo is a tad bit cheaper.

Honestly, the LPR does pretty good with mil spec/commercial n-nm ammo. Which makes it just fun.

It’s my understanding that billet uppers have material added because they are inherently weaker than forged. Thicker dosen’t always mean stronger. The Vlor may in fact be stronger, it is forged, but most billet uppers are not going to be significantly stiffer than a forged upper.  The Larue you mention is billet I believe.

I highly doubt you would see any measurable flex in a standard, or billet receiver with a 24” varmint barrel, much less in an 18” SPR. If thicker walled receivers were a real advantage I think you would see companies like WOA and Compass Lake offering their varmint and space gun uppers with thick recievers.

Personally I have 2 SPR type rifles with standard uppers and both are well under 1 MOA shooters.

To the OP, get both. I love my SPRs, they really can’t be beat for a one rifle to do everything reasonably well gun. With that in mind I still felt the need for and built a large pattern in 6.5 Creedmoor. If you are unhappy with your Aero build, I’d suggest going over the tacked posts in this forum and checking your rifle over. If you didn’t assemble the upper, I’d also suggest pulling the barrel and reinstalling, after making sure the receiver is true and shiming the barrel extension. Aero has a good reputation for parts and a not so good reputation for putting out assembled uppers. Just read the reviews on Brownells site. I’d also consider pulling the muzzle device and try grouping the rifle with that off as well as trying a few different weights of known match ammo. Worst case senario rebarrel it.

For as cheap as you can build a SPR type upper these days I wouldn’t sell the large frame to build an upper, I’d just build it. Wait a month and the black Friday prices will start kicking in. You could probably build a decent upper for $500.

I've had zero problems ringing steel at 400 yards with my 16" Criterion barrel using IMI 77gr Razorcore.

Buy a nice upper like White Oak Armament, stick your barrel in and the rest is up to you. My experience with WOA uppers is that they're tighter than skinny jeans on a man. You might need a heat gun to get the barrel all of the way in.

That's good to know. I emailed them a while back asking about exactly that, and the response was that they're 100% to print uppers with a 1.000" bore.

I've always liked Holliger's parts. His improved barrel extension is awesome.

I just shot sub-MOA today with IMI Razor Core out of my WOA-barreled Mk 12 Mod 1 upper while doing some factory load testing out of a few rifles.  It's not fully clone-tastic just yet, so since my AEM-5 is *still* in jail, I threw my YHM phantom SS 30-cal on the end of it.  The receiver didn't break or anything.  

White oak barrels plain shoot.  NOTHING comes close to them without paying well over $100 more.  And that's several boxes of Razor Core.  

I have a 16" ballistic advantage mod H in the works that was doin pretty well too with lighter stuff, but wasn't *QUITE* there with 77s.  At least not factory stuff.  I'll probably still do development with them (and 75s) though.

If you're not looking to reach out past 600, you can have just as much fun with 5.56 as you can with .308....for cheaper (especially if you reload).

Not that "get both" isn't of course the standard answer but....in your case, 5.56 sounds like the better of the two options.

I am running a green mountain barrels 223 wylde 18 inch shooting magtech 77gr. Im hitting 600 yards consistently on a 12 inch plate (depending on wind)  I keep debating on going to a grendel or valkrie so I can go out further and stay in the Ar15 platform  but ammo costs are keeping me in the 556 for now. Magtech is 65cents a round vs $1 rounds for other "match" rounds

another good consideration.  I reload and frequently forget about the constraints ammo prices can put on people.  It's easier for me to grab once-fired at the range (RSO is a really good friend so he hooks me up on occasion--just tossed a gallon ziploc full of 6.5C brass at me yesterday and all i have for that build so far is a stripped upper ) and projectiles, as i typically tend to have plenty of various powders to do load dev.

can we also spend OP's money by saying he should get into reloading too?  

I already have a RCBS reloading setup with 223, 308, and 9mm dies. To be honest I stopped reloading as I can buy ball annoying for just a few pennies more per round. I think match ammo might be a different story though.

Oh yes, match ammo is definitely a different story.  I'll buy factory ammo here and there to test various loads with new builds just to have a baseline.  If it throws things like razor core, gold medal, or other known-good stuff into 3-4 MOA, i'm probably just going to be chasing my tail everywhere handloading and end up frustrated.

Plus I just asked santa for a big blue to replace my 15-year-old (and still very much kickin) rock chucker this Kwanzaa.  Hopin he pulls thru.  

I'll still probably use the chucker for .243, 7mm-08, .308, and 6.5C (once that one's built) either way.  I shoot lower volume with those though so no big deal to run 100 rounds in a sitting.

Technically the 308 only has more brute power close in....it quickly goes to the 6.5CM after a few hundred yards.  

I do know my buddy with 140s out of his CM hits the steel at 300 with a *LOT* more authority than my 308 with either 168s or 175s.....

It's exactly why I'm now starting a 6.5 build...Can't let him have the last word now can I?  

What about 185s or 200s?

You'll be destroying your brass in a semi before you even get close to pushing them fast enough.  Hodgdon says 2450 is max on 200s for a lot of their different powders.  You're crossing a lot of manufacturers' reliable expansion threshold a *LOT* sooner than a 6.5 with 140s or 143s.

Sure it's an option, but it'll yield more money spent on brass a lot quicker.

And I say this with a .308 up in my reloading room right now and a boatload of different 30-cal projectiles.

Just realized this was the semi auto forum. Even read the OP.  200s are probably too long for a semi anyway.

Out of a bolt rifle I'm not sure the 140 6.5s ever catch up to a 185 or 200 energy wise, not that its enough to matter.  Wind and drop sure all the way.

Edit: 140ELD going 2690 has 1551ft lbs at 300m, 185 Berger going 2600 has 1855ft lbs at 300m.

yes, but they don't tend to have enough velocity out of a semi, due to shorter OAL constraints and pressure levels beating up on the brass before you get close to max velocity.

bolt rigs are a whole other story, especially if one builds a 308 on a long action.  

Don't sell the ar10.  It may prove useful later down the road or you may decide to rebarrel with a proven barrel.

I'd build an 18-20" 223 upper for what you want to do (100-300yd shooting).  Those distances are easy to shoot with a decent barrel and ammo out of a 223.

WOA, Criterion are awesome if you're on a budget.  Bartlein, Krieger, Hart, Shilen, or Lilja if you've got a little more money to spend.

Freefloat the barrel, bed the extension with some blue loctite, and slap it on the lower you already have.  An adjustable gas block is optional but recommended.

First and most important question is, what (no BS) is the purpose of your rifle? Seriously no BS! Second what is the typical distance you will be shooting, again no BS. From the sound of it you won't be shooting past 100m in practicality. If you just want to ring steel @ 300m or hit ground hogs @ 100m then just go with a 16" 556 gun with a QPQ nitride barrel (SS if you want to spend the extra money) and get a 1-6x or 1-4x quality scope (Vortex HD, Leupold, NF, US Optics) and buy or load quality ammo (testing will be required). If you want an excuse to build an SPR for 300m and in, then I personally have no excuse other than spend money for your personal satisfaction of owning an "SPR" upper.

Lots of options for SPR/ish style uppers. It makes all the sense if you're going to stick to 300 yards and in. Cheaper ammo, less recoil. Get both, if you can't then it's a no brainer. As mentioned, read the stickies on getting the most out of your upper if you decide to build, or qa/qc a purchased upper.

Reading back through this why not get a grendel?

I'm finally to the point where I'm ready to move up. I have a recce ar I can easily hit steel with at 500 yards.

I'm ready to push out past 600 and I'm thinking the grendel is my answer.

Cheap wolf is available for plinking or match grade for longer distance.

I came to the same conclusion. I’ve got a 5.56 SPR and a 6.5 Creedmoor heavy barreled AR-10. The Grendel is the perfect in between round. I’m now in the middle of a 6.5 Grendel pistol build for in between the two.

If you want the room in your safe, I'd off the 7.62 and get into a quality 5.56 upper (WOA, JP, BCM, CLE, LMT, LaRue, etc...).  If you've only got access to 300 yards, staying with the 5.56 makes even more sense.  Once you dial a load in, you'll be impressed with what an accurate 5.56 can do.