I got a new APR rifle chambered in 280AI with a 24” barrel in 1:8.4 twist. I measured the chamber after having a lot of difficulty with the hornady tool. I ended up just loading a bullet into an uncharged case and used a sharpie to look for touching of the lands. I loaded up 5 rounds of each with hornady 175 grain eldx loads ranging from 56.0 grains to 60.0 grains of IMR 7828 ssc.

I have a chronograph and am would like to get to my final load fairly quickly because I want to take this rifle to Colorado elk hunting the first week of October and need to spend as much time on the range with it that I can. What is your favorite way to go about it from here? Shoot through chronograph and look at the sd es, look at the group displacement? Do you let the barrel completely cool between shots?

Thanks guys.

Finally probably going to get to shoot my 7mm08 with the same bullet this weekend if things work out at the ranch and im not too busy!

I loaded a ladder from a mild beginning load to .6 over max in .3 grain increments. I plan to shoot at 200-300 yards over a chronograph will use vertical dispersion and velocity to determine my load. I believe I will find an all season load with temps 100+.

I so want to change my 270 to a 280 AI, im jealous, Good luck both with the load and the hunt

Thin hunting barrel, 3 consecutive rounds is about all it will tolerate. If you believe you are going to be near that powder charge, you can load 3 shot groups -/=/+ from where you believe you will be. Shoot them at, at least 200 yards. Often the tightest group also has a low ES. And an ES below 20 fps is perfectly fine, when it shoots tight. A "bad load" can look good at 100 yards, thus the 200 yard minimum.

Between strings, let the barrel cool until you feel no heat in it.

This rifle has a carbon wrapped proof barrel. I’m not sure how quickly this will cool or if the carbon fiber will act like insulation and hold the heat longer.

in this heat it will be difficult to get the barrel cool, take some ice with a towel that has been on the ice, wrap around the barrel, make sure you clean and dry when you get home.

The steel will heat up quickly, and it will cool down quickly.

What Colt mentioned is a good trick, using a chamois sitting in ice water. I've done it on blued and stainless barrels alike.

Sweet looking rig, good luck with the load and the hunt!

Did you build a few rounds to sight the rifle in and foul the new barrel? If not factory announced will work fine for this if you don’t have time. Being the first time out I find this important for getting to know your set up as much as fouling and sighting in.

I always take the long road and shoot 5 rounds in .3 increments bottom to top. If I had 50 rounds loaded as you appear to and was trying to shorten time I would use one round of each in a ladder test. You need at least a 300 yard range for this. The results should give you 3 loads to concentrate on and allow you to shoot for groups with the remaining 4 bullets of each of those loads.

When you start testing be sure you have the time and patience needed for it. Otherwise your wasting your time.

Foul the new barrel with exactly the same powder and bullet the load testing will be performed with.

The lowest charge you plan to use in testing, make 9 more of them.

Shoot 3, cool, shoot 3, cool, refine the zero, shoot 3.

See there ^^^^, I learned something. Makes perfect sense, I just hadn’t thought it through.

I got some time to go to the range and shoot at 300, but I forgot my chronograph. I shot 4 rounds of each load. I circled the groups and drew an arrow to the aim point. You will see one group way off to the right because I adjusted the windage the wrong way for that group but corrected it for the next group. I didn’t adjust the elevation the entire time. I think the circles are 5” circles. I don’t know if this info is helpful without chronograph data.

57.0 looks great, minus the one shot. What happened on that round? Wind, called flier?

58 looks good

A little more information. I shot 1 round last week from each load and shot it through a chronograph at 100 but didn't have time to go to the long range and shoot groups.

56.0 2614
56.5 2693
57.0 2650
57.5 2688
58.0 2715
58.5 2737
59.0 2789
59.5 2824

Here is a pic of all the empty casings in order. I don't see any signs of excess pressure. Should I continue to go up in powder until I start to see pressure signs?

I'm not sure, I didn't have a spotter looking through the spotting scope as I shot. I shot the four shots in a row and couldn't see the impact from my scope. I would shoot 4 rounds, cool the barrel with a wet towel while I drove down to the target and wrote the info on the target.

I try to stay away from vertical stringing...those historically have been the worst consistency for me. You can typically add/subtract a .1 or two and get it to rounden up though.

I like 57-57.5 of what we see there.

No pressure that I see on any of those cases....but what's the mark on the side of the case it's on several but it looks like the top left (first one in the box) shell has it at 5pm...is that a sharpie for you to know which cases are which?

^^ This.

57.0 gr is your load.

Well I guess I don’t know much but 58 seems to be by a good margin the smallest group, is also the flatter spot in velocity. Both 57 and 58 have a flyer, one went high one went left. I’d still pick 58 backed by tightest group and smallest steps in velocity change.

After I took the picture I saw the red marks on the cases and had to figure out what that was myself. I was wearing a red shirt and it’s a reflection of my shirt.

Have you settled on a load, or reshot anything? I didn't get a chance to shoot mine lol gotta live through the fun of others for a little longer