Trail Boss from IMR (now owned by Hodgdon) is a new powder developed by the Australian company ADI, Ltd for the low velocity cast bullet loads favored by the Cowboy Action Shooting crowd. This powder is unique in a several ways; first it seems to be insensitive to its position in the case. Tilt the gun up, or down and velocity stays consistent. Using 50% or more of the case capacity surely helps with that.

It’s also a bit more expensive than powders like Alliant or Hodgdon. The can of Trail Boss I found was $1.54 / ounce. The last can of Unique I bought was $1.25 / ounce, making Trail Boss about 23% more expensive. Fortunately like other fast powders it goes a long ways. Depending on the caliber you can easily get 1,000+ loads from that 9 oz can.

It’s very bulky for its weight, using approximately 78% more volume by weight than Unique. It’s so bulky the common Hodgdon can only holds 9 ounces of Trail Boss.

Mike Venturino reported in GUNS magazine that even with a double charge Trail Boss won’t reach proof load pressures. That may well make this the safest powder available. With most other powders, especially spherical powders, double or even triple loads will fit inside the case without spilling over.

To illustrate how bulky Trail Boss is I filled various cases with H110, Trail Boss and Unique to see just how case filling this powder is. This is not load data, it is simiply how much powder will fit in each case.

 9mm  45 ACP  38 Special  44 Special  45 Colt 
Unique 7.5 gr 13.5 gr 14.3 gr 18.0 gr 23.6 gr
Trail Boss 4.0 gr 8.0 gr 8.0 gr 10.1 gr 13.3 gr
H110 14.6 gr 26.5 gr 27.6 gr 34.0 gr 44.5 gr

Load Data:
IMR Powder
38 Special 158gr LSWC 2.7 - 4.2gr (13,700 CUP 800 FPS)
44 Special 240gr LSWC 4.0 - 5.2gr (11,700 CUP 763 FPS)
44 Magnum 240gr LSWC 6.0 - 7.3gr (21,600 PSI 917 FPS)
45 Colt 250gr LRNFP 4.5 - 5.8gr (12,700 PSI 727 FPS)
IMRs has targeted light/low velocity CAS loads and they’ve succeeded, this is not the powder to choose if you want magnum loads.

These piles were made by putting 5.0 gr of each powder in a 45 Colt case and carefully dumping it on the table.

It’s a rather odd looking powder, almost like Cherrios. Each grain is very thin, the grains are like a small disk of construction paper with a small hole punched in the middle. I’m sure IMR designed it that way to increase the bulk without increasing the weight.

It’s certainly a light, fluffy, powder. The slightest draft that doesn’t disturb spherical powders will blow Trail Boss across the bench.

Shooting results
As it turns out the most the small powder bar on the Dillon powder measure will drop is 5.0gr of Trail Boss so that’s the charge I used for the 44 Special and 45 Colt, for the 38 Special I dropped down to 4.0gr. I suspect most Dillon users will stick with 5.0gr or lower with this powder. As you’ll see that load generates plenty of velocity, at least in my guns, so there’s really no need to switch to the large powder bar for these calibers. Those using Trail Boss in the 500 S&W, 45-70 or other large calibers will certainly want to use the large bar. These light loads have very close to 100% load density already, you wouldn’t be able to fit much more powder into the case without compressing the load.

38 Special, 4.0gr Traill Boss, Leadheads 168gr Keith, 1.506" OAL, WSP primer, Federal brass, 4" Ruger GP100
720 fps, Std Dev 24 fps, ES 63 fps

44 Special, 5.0gr Traill Boss, generic 240gr LSWC, 1.500" OAL, WLP primer, Starline brass, 4" S&W M29-2
797 fps, Std Dev 10 fps, ES 23 fps

45 Colt, 5.0gr Traill Boss, Black River 255gr LSWC, 1.650" OAL, WLP primer, Federal brass, 5.5" Ruger Bisley
832 fps, Std Dev 17 fps, ES 45 fps

Each of these went into one hole approximately 1" across shooting hand held over the chronograph at 20 feet. I was more surprised by the velocity these loads churned up. It seems IMR might be underestimating the velocity of their loads, something not often seen in powder companies load data. As expected with low pressure loads the primers showed no signs of flattening at all. Cases came out a bit sooty, but not more than I get when shooting any cast bullet. Trail Boss doesn’t seem any dirtier than most other powders, and cleaner than the old Unique.

All in all Trail Boss seems to be a decent step forward for shooters. It may not be a terrific breakthrough, but it can easily remove the dangers of double charging and do away with erratic results due to the powder position in large cases.

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