I went to the range today with 4 different loads using 41.0 gr of AA2520. I chronographed 5 shot strings of the following:
Speer 180 gr FN
Hornady 200 gr FTX
Sierra 200 gr RN
Speer 220 gr FN.
The weather was good when I was shooting 68 - 72 degrees, clear and calm. I shot these with the Chrony 12 feet from the muzzle. Again, all of them were loaded with 41.0 gr of AA2520. Shot with a Marlin 336RC with 20" barrel.
180 gr Speer -
Average velocity - 2251 fps
SD - 23.3
I think this is a pretty mild load with the 180 gr. I'm going to try 42.0 and 43.0 gr. If I kick out the low shot (2225) it ups the velocity to 2265. I'd like to get over 2300 with this bullet.
200 gr Sierra Round Nose.
Average Velocity - 2231
SD - 7.7
I like this load a lot. It gives good velocity with the 200 gr bullet and the SD is very low. It was extremely consistent and the most accurate of the 4 bullets out of my gun. 5 shots in under 0.75" @ 50 yards.
200 gr Hornady FTX
Average Velocity - 2233
SD - 9.4
Again this was a very consistent load and I get higher velocity out of my gun with it than I do with Hornady factory LE rounds. Interestingly this shot almost 4" higher at 50 yards than the 200 gr RN. It grouped right at 0.75" @ 50 yards. This I suspect would be a good long range load.
220 gr Speer FN
Average Velocity - 2154
SD - 13.4
This is what I consider a max load for this bullet in my gun. I didn't have any pressure signs, and extraction was good, but I don't think I'd go higher in the Marlin. I might consider bumping it up a bit in the 760, but I think I'll stay with 41.0 in both guns. This shot slightly under 1" @ 50 yards. I think this would be a great black bear load.
I was not shooting for groups with any of these loads. I had a target set up at 50 yards as an aiming point as I shot through the Chrony. I did not move the scope settings. I can tell you all 4 loads shot to different points of aim, so whichever one I decide to hunt with, I'll have to zero for that load/bullet.
I wasn't happy with the 180 gr, the velocities ranged from 2225 to 2280. I need to load it up again and do some additional shooting. I think I need a slightly hotter load. The other 3 were pretty good results, and I think I'm going to stay with the 41.0 gr loading for the 200 & 220 gr bullets. Just for my own curiosity, I think I'll load up a few rounds of 200 gr with 41.5 and 42.0 gr just to see what I get velocity wise. But the accuracy is there @ 41.0 gr.
If you look in the Accurate load data for 2520, these are all over max, so START LOWER, AND PROCEED WITH CAUTION. They work fine in my guns and gave no pressure signs.
I'm going to shoot the same loads in my Remington 760, but right now the trigger assembly is at the gunsmith getting a trigger job. Since it has a 22" barrel, I might get a bit more velocity, but I suspect not much.