I've been loading pistol ammo for a while now and am ready to take the next step and reload some of the .308 brass I've been accumulating. The only .308 I own is a GA Precision GAP-10 with an 18" barrel. It shoots great groups with various factory ammo I've tried and I want to try to replicate that. My initial plans were to try to reverse engineer some of the best shooting bullets. What I mean is, take a myriad of measurements, pull bullets,  and try to duplicate the round dimensions. Is that a legitimate way to approach creating my initial test rounds? Of course I would do a ladder test since I have no idea what powder the factory uses.

The most accurate rounds I've fired with it are: Black Hills 168g & 175g Match HPBT, Nosler Custom Competition 168g & 175g, and Copper Creek 175g SMK Gas Gun.

I know the set up is a little different for auto loaders than it is for bolt guns. Is there anything specific I will need to be aware of?

I've already got a box of 175g SMK HPBT bullets and a whole bunch of once fired brass. I still need to get primers and I'm going to start with some Ramshot TAC if I can find it. I also plan to hunt with this rifle some day. I'm a big Barnes fan and will probably work something up with their game bullets. Maybe some SGKs or some Noslers. I'll be getting Dillon dies for my 550 and all the other accessories I'll need.

Any help would be greatly appreciated.

Set up your Full Length die and size a few"Fired" cases.  Make sure they chamber and extract with ease.  Then select a powder, a bullet and start low and work up.  Pretty much the same as a bolt action, cept that all cases need to be FL sized enough to chamber with ease.

If you are using Military 7.62 brass check case capacity for proper powder reduction.

You can duplicate factory ammo much easier if you have access to a chronograph.

A chronograph will tell you a whole lot about your rifle and ammo.

Do you have any shooting buddies that own a chronograph?

The only thing a Chrony is going to tell you is if your handloads are running at the same of close to Factory ammo velocity.  It will not tell you if your load produces the same barrel time, barrel harmonics, etc.etc.etc.  Velocity is only a small factor in what constitutes an accurate load.

Well the OP was posting about pulling bullets and trying to duplicate factory ammo by weighing powder charges from factory ammo, so "buy a chronograph" was the first thing that popped into my head over his idea.

Thanks for the info fellas! How about crimping?

Personal preference.

Load  a few dummy rounds with your desired bullet and OAL.  Measure the OAL of each round and record.

Cycle the rounds through the action.  Measure OAL again, if OAL made significant changes, you may want to crimp with the Lee Factory Crimp die,if not you are GTG.

Too much thinking! You will make cartridges more precise than these factory loads right off the bat (you will see no flyers!)... I think you can forget taking a lot of useless measurements, those once fired cases have done the work for you and are fireformed in your chamber. Do as another poster suggested and do minimal resizing but make certain the empty cases chamber. You just need to go shoot your gun and see what load works best. After doing this, you can come back to this forum and pontificate about harmonics, concentricity, muzzle velocity, extruded vs spherical, Hornady vs Sierra, match grade primers and everything else.

No crimping. [/Edna Mode]

Again, thanks for the gouge fellas! I think I'm ready to get started. I got a little loading info from one of the bullet makers.

I found slower loads were more accurate with my LR-308. Also bullet, brass and powder each had noticeable affects to accuracy.

I've been loading for my AR-10 for 4 yrs.  I size to push my shoulder back .003".  I reduced the diameter of my expander to get .003" neck tension.  This was a biggie.  My Hornady die as delivered gave me barely .001" of neck tension and bullets were moving when they hit the feed ramp, even when crimped with the Lee FCD.  I've found that neck tension works better than crimping to hold bullets.  If you want to crimp though, the FCD is the way to do it.  I use Lanolin/isopropyl for case lube and leave a thin film on the case to aid extraction in the gas gun, it's easier on the rims.  Your seating depth choices are limited due to magazine  length.  You ought to be able to do really nice things loading for your GAP.