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So now I want a 308. Im looking at a variety of different guns. Not just ar style. Im wondering what peoples thoughts are. I wont be spending a ton but somewhere in the $1500ish range is where id like to keep it. Keep in mind im pretty new to this. Ive been shooting precision bolt guns for many years and just want to ad some variety to my range trips. I shoot anywhere from 100 to 1200+. I dont need this to be a 1000yd+ gun but if it is great. Ive always been mostly interested in accuracy (groups) but recently started doing more "tac" type shooting. (Ranging with reticles at various targets set out randomly) I also make as many trips prairie dog hunting as possible. So whats my best bang for my buck.
Looking at:
M1A
PTR91
AR-10
FN-AR
I'm sure there are lots I'm not familiar with. I'm not dead set on 308 but at least something 308 based like 243, 260, etc.
You won't likely find anywhere near the levels of what you probably deem "acceptable" accuracy with the PTR-91 series and with only a ~$1500 budget...not likely the M1A either. With high quality ammo, most PTRs in their basic config (not counting the MSG/SS upgraded rifles that are out of your budget range) are no better than 1.5MOA on a good day and they are murder on brass and expensive to work on/upgrade/etc. Great main battle rifle/clones, but not the best for "precision-minded" applications.
The FNARs can be great rifles, are pretty affordable and offer decent enough performance/accuracy, but they are generally unsupported in the aftermarket which will make tailoring the rifle to your specific likes/wants/needs somewhat more difficult than any of the various large-frame AR platforms.
Now...leaving the large-frame ARs left in the realm of consideration, your options are still pretty good for a basic rifle that you can upgrade/modify more to your liking down the road as time/money/necessity dictates.
For an off-the-rack rifle capable of precision levels of accuracy (sub-MOA out of the box), longer range use (1k or so), and in/around your budget confines, you have a couple options. One of my favorites is the Armalite AR-10T series. They are some of the finest "production" rifles on the market, featuring match, 2-stage triggers, a match, triple-lapped 20" SS heavy barrel, vented FF handguard capable of adding rails at multiple positions if you choose, etc. They can be had on the open market for <$1600.
Similarly, for just a hair more money than the Armalite, you can get into a DPMS SASS which is really their top-of-the-line production rifle. They feature a ton of "upgrades" over many stock factory rifles, including a Magpul PRS stock, Palm-shelf adjustable target grip, JP Enterprises Match Trigger group, threaded 5/8x24 match SS barrel (18"), quad-rail FF handguard, Harris bipod, Magpul BUIS, etc. They can be had on the open market for ~$1750.
In terms of building...you can build a large-frame AR in the same manner you build any AR-15, but the costs of building a large-frame AR can add up quickly as parts like receivers, BCGs, etc. are a good bit more expensive. As for building what you want...you can get a decent receiver set for ~$500 or so (depending on make/model/etc., maybe a bit less). Tack on another ~$400 for a match barrel, ~$275 for a BCG, ~$200 for a trigger, ~$75 for a LPK, etc. and you are ~$1500 give or take into a rifle without stock/hardware, grip, handguard/FF tube, muzzle device, etc. It can be done on the cheap, but to really get the most out of it in terms of accuracy and performance, you can easily get yourself into more money than a factory rifle will run you plus upgrades, but you'll have precisely what you want at the end of the day. It really comes down to what specifically you want to put into it, the options you desire, etc. as to whether the cost/benefit analysis comes out in your favor or not.
As for "alternative" calibers to the venerable .308/7.62x51...they are out there, but usually require a custom build or more than your average $1500 budget for a quality sample. I'd personally look to something along the lines of the 6CM, 6.5CM, .260, etc. class built on an Armalite pattern bolt/carrier/barrel/etc. to take advantage of the smaller firing pin which functions better than the larger DPMS-pattern FP size which is notorious for cratering/piercing primers when used on heavier pills/hotter loads versus the Armalite pattern on that class of cartridges.