Title says it all...

I have a substantial amount of .308 ammo sitting around (mil-surp thru expensive commercial loads) but no .308 rifles.  

Time to buy one...these two are in the price range and I like both of them.

Mostly looking for the 12" steel plate at 400 yards type accuracy but it would be nice to shoot some nice 100yd groups with quality ammo (IE: sub 2 moa).

Probably a micro t1...

Seems both of the rifles have rails worked out.

I know the AR10's can be more accurate but I have never been a big fan.  Maybe the 2 that I shot were not good builds.

Do you think the two rifles I've mentioned will not cover my accuracy goals?  Truthfully I will probably shoot more open sight than anything.  The red dot tends to float around my collection to see what I can wring out of them.

Check out these vids.

https://www.ar15.com/forums/precision-rifles/PTR91FR-Accuracy-Review-Very-good-quality-vid/4-9378/

Both are good performers.  I prefer the feeling of the m1a, also will come with better trigger, sights and camouflage stock if you like.  As mentioned the ptr is hard on brass.

A scout style mount on the M1-A will allow a pistol scope and excellent accuracy (probably 2.0 moa) with match grade ammo. I have never seen a HK-91 rifle that I considered "accurate". The action is extremely violent ejecting cases 30 feet or more, not conducive to great groups on target.

Both are a nuisance to scope, both are not known for accuracy.  Handle both before you buy.   IMO they both suck pretty bad but the M1a has the steel & wood cool factor.

I reload military brass shot through my PTR brass all the time. The marks from the fluting will still be visible after sizing, but longevity is unaffected. An FAL is more abusive on brass than is the G3/PTR.

My vote is for a G3/PTR. I shoot mine with irons at IDPA-sized steel plates out to 600 with ease. The trigger on the PTR is fantastically smooth. Spare parts and mags are cheap. I recommend a brass deflector, an HK21 buttpad, and an HK21 charging handle. I also have a G3A4 collapsible stock and wide handguard that I can swap out whenever I choose. The last time I put mine on paper, I had a cloverleaf group at 50m with reloads.  Scoping them isn't difficult, though, like the M1A, your sight line will be really high. There's always the option of an integrated rail on a PTR, and Spuhr stocks are awesome to  modernize the rifle if one wants to go that route and pay the money.

It sounds like you really want to go the M1A or PTR route, but I have to tell ya I wouldn't bother with either of those and jump to an AR-10 type gun.  I spent a couple years trying to wring out accuracy from the FAL, trying three separate barrels to reach what I thought was a reasonable accuracy goal.  I spent a lot of money and time and had no luck.  (I posted my exploits on the FAL Files as "Scott S".)  Granted, I was relatively new to "precision" shooting, so my technique still needed work.  However, my third string of five shots out of a brand new DPMS LR-6.5 in Creedmoor in 2012 printed easily less than 1" at 100.  Good ergonomics, ease of scope mounting, modularity if you don't like a particular setup--these things make the AR such a no brainer.

I had a similar experience, except that I tried to wring out accuracy from an M1A Loaded.  Best I could reliably do with a 22” match grade barrel, JAE-100 stock with barrel tensioner (which required a lot of time and ammo to tune), and a number of national match components, using match ammo was 2 MOA.  And that was with a scope.  To get an M1A to reliably punch 2MOA or better requires a LOT of money.  Reliable 1MOA accuracy is almost a pipe dream for an M1A unless you have at least $5k and someone that knows what they’re doing.  There’s a reason why you really don’t see M1As in competitions outside of CMP/National Match competitions.  If you wanted an M1A that had that 1MOA accuracy, sending it to Smith Enterprises is the way to go, but be prepared to spend money because back when I was considering sending my M1A in to them for tuning and a SEI Sage EBR stock install to mimick the M14-SE Crazy Horse or Mk14 SEI, the price quote was over $5k.  And that was not including the money I already paid for the rifle.  That was also about 10 years ago, and most things generally get more expensive with time.  

Fast forward to about 2013 and my previous LE agency finally gave our SWAT snipers the go-ahead to look into buying Sniper Support Rifles (SSRs).  Basically heavy carbines or semi-auto rifles that could be used by the spotter to protect the sniper, or to make an accurate shot if needed.  We had a bunch of DRMO/1033 rifles in our armory, which included an actual HK91 and three actual M14s.  I was tasked with pricing out upgrades and gunsmithing to get the rifles to 1MOA accuracy.  Well, the HK91 was out very quickly because I couldn’t find anyone to do the work, and components like those from the PSG-1 were expensive as hell and hard to get because HK sucks (and I hate them).  After my experience with my M1A years earlier, I advised against trying to tinker with the M14s, but the chief insisted because he was a Marine and they used M14s for rifle training in his day.  The only company we could find (that we could validate as being reputable) that  would touch government M14s was SEI, and a quick chat on the phone yielded what I already knew, which was that they said it was going to be something like $3-5k per rifle, depending on what needed to be done.  So I got that idea thrown out the window and they decided to go another route.  

And if you want accuracy, you need a better package than the M1A Scout Squad, which doesn’t have a match barrel.  However, hitting a 12” plate at 400yds requires 3moa accuracy, so you may be fine with a Scout Squad.

Putting money in a .308 AR is a much better use of money.  You can build a sub-MOA .308 AR for the same amount or slightly more than an M1A Scout Squad.  The M1A is also a severely antiquated weapon system.  Reliable magazines are expensive and run about twice as much as Magpul PMAG-LR mags, which are extremely reliable.  Changing components on an M1A is difficult, and some things are not user-serviceable and require a gunsmith that knows the rifle system.  In contrast, users can do just about anything to an AR.  There is a severe lack of aftermarket support for the M1A, whereas you have an ever-growing list of companies making large frame AR compatible components.  Mounting a scope or optic on an AR is also not difficult.  With the M1A, it is.  And the M1A recoils harder than nearly any other semi-auto .308.  That higher recoil beats up the rifle and causes durability and reliability issues.  M1As are not known for their reliability or durability.

Get a port buffer. Both problems solved.

Cool.

PTR in a heartbeat.

I have 3 of the 4 major battle rifles: PTR, FAL, and AR10.

FAL was my first. It's a DSA, early 90's production, and it's the most badass rifle I've ever held.

Later I snagged a PTR on a GB deal, and it's cool. Mags are cheap, and I've noticed mine actually shoots BETTER with cheap steel cases 147 gr then it does with match grade FGMM. I'm assuming the twist rate works better with lighter pills. Input a rail on it, and 5x primary arms optic. Drilled and mounted a pic rail to the plastic forend and put a harris on it. With cheap steel case I shoot 3-4 MOA at 100.

Finally I bought a complete upper and lower from Palmetto. I wasn't happy with it it's accuracy and it didn't cycle well. Sent it back and they fixed it. Then I decided I wanted a better barrel so I rebuilt it with a 14.5" BA barrel and an adjustable gas block. Pinned a YHM QD and run a suppressor on it, and topped with a 5x primary optic. With M118LR clone it'll shoot around 2 MOA. At 100 I usually can keep my rounds in a group smaller than a small fist. It's not "precise" but for me it works, and it's the same feel and controls of an AR15. Mags are easy to get and although not as cheap as G3's, they're still affordable.