New BHW 20 practical barrel
 

My new AR 20 practical (22" lw) barrel is showing a lot of vertical dispersion above 23.7 gr of Benchmark and 8208. This is with Berger,Sierra,Nosler,and Speer bullets 32-40 gr. The barrel has a 10 twist, from all the load sharing info I thought I would find a node around 25, but I have been from 22-25.7 grs in both powders and 23.4 looks best with all the bullets. I haven't chronographed any, usually that is my last testing. Like the 40 gr Nosler, hoping for +3600. Have not experienced the Wahoo, this is a great cartridge why didn't I try this sooner.

Check your bedding.

Could it be your shots climb as the barrel heats up?

Even small cals warm up some when fired.

None of my BHW barrels shot well until they were pushed. The design of the poly rifling comes into play here. They take more than conventional rifling to build pressure. My Ar 20p shot terrible until I listened to this advise. Mine also likes faster powders with the 40's class bullets. H322, 4198 etc. Good luck with your build.

greasemonkey, I been running LC brass that I purchased already formed for 20 practical. After seeing my test targets, I thought the lighter load made sense with that brass. I have been using a .201 mandrel, my neck tension is 0.003-0.0035. The loaded cartridge neck .229 ish which seems to function fine. Would commercial brass, I have Rem, Hornady, or new matching lot of Lake city be easier to tune? Would have to get a .233 bushing only have the final bushing currently. Really was hoping this would be my new night hunting coyote rifle, but inconsistent vertical is not giving me confidence.

I have several hundred rounds through an AR in 20P in 10 twist and haven't used any more than.001 neck tension with any issues. Your brass will need to form to your chamber. The second time should yield better accuracy. LC brass from the same lot would also help.

I had a 20P BHW AR barrel and like you, I started with LC brass that had already been necked down...could not get it to shoot worth a darn. Would try different loads, no good, clean barrel and start another load test and repeat...still not shooting like it should.
Changed 3 things...#1) A respected AR guru told me to quit cleaning it after every 20 rounds...#2) Installed an adjustable gas block and set it to eject brass at 4 o'clock...and #3) Necked down new Winchester brass
All my problems went away...amazingly great groups and the 20Practical is my go to night hunting gun. Use 39gr Speer and 40gr Noslers with 8208 powder.
Also as stated by someone else...don't be afraid to push it a little...they seem to like the upper end.

20 Practical loads
 

What primer ? I like Cci 450's. Try one of the 4198 powders.

I run Winchester through mine. Your neck tension should be good. I can't say about the LC brass. People have good luck with that also. I also ran adjustable block to settle it down some. Biggest improvements came when I stood on the pedal some. I'm around 3650 with 40's from 20" 10 twist. Mostly v-max seated .020" off lands. Smacks dogs hard out to ~350.

Yup, CCI450's

450's for me also