Dee I agree, nothing beats rounds down range.

I have a 223 7 twist Bartlien 28” long screwed on to a defiance action shoots 80.5 berger full bores right at 3k with RL 15 or varget. Lots of fun and shows no wear at all. For the amount you can shoot it cost wise nothing compares. Its my favorite rifle.

While probably not the best, I would probably go with an AR. Probably get an upper from white oak and put together a lower with the trigger and stock I liked and call it good. Probably a Burris xtr scope

if you are shooting paper, I'll go against the grain and say look for a used AI. You can change you own barrels, change caliber (same bolt face), will outlast your grandkids. Spend the rest on a scope and upgrade the scope later.
You can have long barrels, short barrels, 308, 6.5C,

Jacob at Rifle's Only changing AI barrel:

https://www.facebook.com/riflesonly...technical-barrel-change/240166359965689/

Not sure if that's the rifle but he has an AI with like 50,000+ rounds on it, multiple barrels.

This is the most correct answer on the thread so far.

I agree but would still recommend a different cartridge. As soon as he hits 600 several times, he'll start looking further and further. The cost-reward can't be beat though. This is likely why most of us have multiple cartridges. I rarely take only one rifle to the range anymore. One running, one cooling.

We've done "okay" running mass production .223 ammo out to 800 yards. Some of it went sub-sonic at 600 yards.

In my opinion you need to hand load .223 to make be a good long range rifle. You definitely have to hand load .223 A.I.

6.5 Creedmoor is the best choice to shoot long range, for the non-hand loader. Lord knows how many rounds of factory Hornady 6.5 Creedmoor I've spotted for.

A metromess SWAT Sniper team also uses factory Hornady 6.5 Creedmoor. They hit my long range steel with it, almost monthly.

600 is the area where it starts to not be as efficient as more popular options it is definitely not the limit or where it magically hits a wall and dies. I routinely take mine out well past that.

What's a good spotting scope for these long ranges?

Invest in a good rifle scope before you start concerning yourself with spotting scope.

The ultimate goal is for you to spot for yourself, through your rifle scope.

Solid advice, better the glass quality the easier it is to see the vapor trail the bullet creates. Also helps reading wind especially if you know how to properly set your parallax.

Personally I’d spend $2500 or even more on glass and throw it on a $400 rifle before I bought a 2500 gun and slapped a 400 dollar scope on it.