I would like to load some .223 ammo for a DD AR with 1-7 twist barrel. I use DD and Magpul mags.
I need to order some bullets and wonder how heavy of a bullet will function and reliably work through an AR.
I don't want to have to seat the bullet so deep in the case that the bullet takes up too much powder capacity when seated to the max case length.

Cycle & function? Just plinking, range use? Yes I realize the 1/7” twist can handle the longer bullets, but it can also handle mid weight bullets.

For me with the AR/223 loading, I’m content in the 50-60 grain range. The light end for prairie dogging, 55-60 for everything else.

If I want to shoot a 70 grain bullet, I have plenty of 243’s. Of course you could work up a combination to reliably shoot heavy bullets in your AR.

Back to the question, for the average shooter, average use, 55-60 grain bullets is meat & potato’s with 223/5.56 reloading. One can look into bullet construction depending on use.

Not long ago I used my ‘birthday’ discount at Midway, looked around for a few items. I got several 100 count boxes of Speer .224 bullets for under $11 each. For my use I think they will do just fine.

I'm looking for an accurate range load. I have a 600 meter range at the club I belong to and would like to find a load suitable for that range and anything shorter.

With a 1/7" twist and 600 yds many are using 68 to 80 gn bullets. H4895 is an often used powder, along with many others in a similar burning range. The 69 gn. Sierra Match King is an old standby.

You need a heavy bullet with a high BC to fly well to 600 yards. Understand that any 223 bullet produces less than optimal wind drift at this distance -- use the best bullet you can.

SMK 69 and 77 have been around for many years, and they work well in a a boatload of barrels. Both are fairly tolerant of jump to lands.

TMK 69 and 77 have better BCs than the SMK counterparts. They can be finicky with barrels and jump. They didn't do well for me.

Hornady 75 HPBT is good option. Like SMK, this bullet works in lots of barrels. I prefer it to SMK 77.

Hornady 73 ELDM is a good option, but can be finicky with barrels and jump. It prefers a tighter chamber.

Berger 73 is a high quality option. What little I've used so far has great results.

Some folks like Nosler, but it doesn't seem all that great in my rifles. Maybe the 70 RDF.

Do these longer bullets feed reliably in your AR?

All the 69-77 grain loads feed without issues in all my ARs. Maybe 20k to 25k rounds to date. The guys I know who shoot at distance also use the heavier bullets, often 77 SMK. They have no cycling issues. Take a look at the ammo available on any web retailer and you'll find a bunch of ammo with 69-77 grain bullets. It's not until 80-ish grains do the loads become long enough that single feeding becomes mandatory with AR15s.

Wind drift is the primary challenge with 223 loads at known & fixed distances, such as 600 yards. The following is 10mph wind drift from factory loads in my 20" AR at my location. You will experience greater drift at your altitude, due to greater air density.

Hornady 55 Vmax -- 6.0 MOA (36 inches)
Federal GMM SMK 69 -- 5.2 MOA (31.2 inches)
Federal GMM Berger 73 -- 4.9 MOA
Hornady 75 BTHP Black -- 4.8 MOA
Hornady 73 ELDM -- 4.4 MOA (26.4 inches)

I rarely get to shoot in calm conditions, so the above drift differences are significant. I also find that heavier bullets seem less susceptible to vertical wind deflection, which is a factor when the shooting location includes ridges and valleys.

I have an AR I put together with a Gibbz Arms side charging upper and a 20 inch heavy profile Shilen barrel. At 100 yards with 68 grain Hornady BTHP bullets over Varget it will group under 3/10 inch for a 5 shot group when I've practiced enough to have my trigger technique in good "tune". As for Velocity, it's an expensive barrel I don't want to burn out too quickly so 2700 fps is fine and dandy for me.

Note the Shilen barrel has a 1 in 8 twist so it's not a match for your 1 in 7 but it does point out that 68 to 70 grain bullets will likely work quite well in your barrel.

H4895 + 77 SMK

Any good boat tail 68 grains and up will work, with experimentation of course, in my 1-7" AR. I don't seat bullets long so they feed through magazines. Sierra Matchkings are the ticket. The 77 grain Matchking such as smschulz mentioned will work through AR-15 mags. I've only used the 69-grain MatchKings. I've had good luck with 68 grain Hornady BTHPs. I have 500 69 grain BTHPs from Rocky Mountain Reloading I haven't tested yet. The price is right. Their 9mm bullets have worked out nicely.

Berger is another brand worth trying for match rifle accuracy.