Vacek,
I have played around with Trail Boss loads in my 223 and will share what I've learned. I found that 8.6 grains of Trail Boss nearly fills the case beneath the bullet without being compressed. The following data was all derived from my H&R 223 rifle with 24” barrel and 1-in-9 twist. Brass was PMC and primers were CCI small rifle. Groups were shot at 50 yards, and chronograph was 12 feet in front of the muzzle. Different loads were shot on different days with different wind and weather conditions, so comparisons are not exact.
Powder Bullet Velocity Group
8.6 gr Trail Boss Hornady 40 gr VMAX 1935 0.8”
8.6 gr Trail Boss Sierra 45 gr Spitzer 1772 0.6”
8.6 gr Trail Boss Sierra 40 gr HP 1773 0.6”
7.6 gr Trail Boss Speer 46 gr Bee 1557 1.0”
4.5-5.0 gr Unique Speer 46 gr Bee 1520-1660 0.5”
8.6 gr Unique Hornady 40 gr VMAX 2555 1.1"
10.0 gr Unique Hornady 40 gr VMAX 2719 no data
I have shot all of the above bullets into milk jugs, and used them for limited squirrel hunting, with the following observations.
The VMAX bullet is very explosive even at 1900 fps, which is fine for varmints, but too destructive for small edible game.
The Sierra spitzer and hollow point do not expand at all at these velocities. I felt they weren’t deadly enough on squirrels, resulting in too many "clingers" and "crawlers" who would escape into a hollow to die slowly.
The Speer bullet at 1557 fps mushrooms but does not explode, and it anchors the squirrels instantly. It’s a little more destructive than a 22lr, but not by much, and still leaves most of the meat edible. Right now, its my favorite small game load for the 223.
Tackleberry inspired me to try the very light load of Unique, and it looks to be as accurate or more so than the Trail Boss load. Please note, this is far less than half the case capacity, and I can’t even see the powder in the case. Great care must be taken to avoid a double-charge. I also wonder about the effect of powder position, but tackleberry indicated that powder position did not cause any problems in his trials. The other Unique loads were an attempt to duplicate Hornet ballistics. I had met another individual who had gone up to 10 grains, so I dared to gradually go that far, but no farther. However I saw no evidence of excess pressure in the primer or in case extraction. These loads seemed safe in my gun, but I have no idea if they would be safe in others, and I cannot guarentee their safety. (Nor can I guarentee I haven't made a typo.) On the other hand, the Trail Boss loads are consistent with the loading instructions on Hodgdon's website, and are presumably safe in any gun. This is probably a very stupid answer, so take it for what its worth, which ain't much.
Duane