Has anyone chorongeaphed any common .308 win. loads in a 2o" bbl. or some handloads.

I usually get 100 fps slower than listed loads in my 20" LTR. 168 Gold Matel match at 2625 fps or so.

I have a Rem 700 with a 20" barrel and load 45.5 grains IMR-4064 behind a Nosler 180 accubond and it clocks an impressive 2,740 FPS

A bit of caution here.....It's quite compressed (and very accurate) but beyond Hodgdon's max load data and I have no clue what the pressure is.....but there are no signs of pressure in my gun or brass!

I have a Ruger 77 RSI with 18.5" barrel. It's pet load with the 165 gr. Speer Hot-Core uses 49.0 gr. of W-760 for 2550 FPS. The same load fired in a Winchester M70 chronographed at 2610 FPS. I know W-760 isn't the best powder for most .308 loads, but that's the only one that very fussy gun will shoot worth a damn.
However, I also shot some Speer Nitrex Grand Slam 165 gr. factory ammo at the same time in the M77 RSI and velocity was about 10 FPS faster, so I feel the figures are relevant.
Granted, neither gun had a 20" barrel, but I think it shows that there wouldn't be a hell of a lot of difference between a 20" and 22" barrel. That is, maybe only about a 30 FPS loss from the 22" barrel and nothing to worry about.
I used to have a Remington 660 in .308 and it did have a 20" barrel. I didn't have a chronograph way back then (1973) but I did make the longest shot I ever made on a big Nevada Mule Deer with a stiff handload using a 150 gr. Sierra Pro-Hunter (Did they call them that way back then?) and H-335 powder. The deer was 427 paces away at the shot, was wounded by my hunting partner and was getting away. My two buddies and I all paced the distance and the average was 427 paces. I don't think a 20" barrel is a handicap on the .308, however the only way you'll ever know is shoot a few rounds over a chronograph. Only then will you have the real numbers for your gun.
Paul B.