Counterintuitive Trail Boss data


December 21, 2006, 11:34 AM
I want to experiment with Trail Boss for use in my .357 Mag 8" DanWesson for use in Handgun Silhoutte Field Pistol using .357 Mag brass.

In looking at the IMR website I find the data listed does not make sense to me. The max load for .38 Special 158 gr LSWC is listed as 4.2 gr delivering 804 fps and 13,700 CUP from a 7.7" barrel. The max load for the .357 Mag 158 gr LRNFP is listed as the same 4.2 gr delivering 865 fps and 20,400 CUP from a 10" barrel. I've been reloading for 30 years and this data contradicts my experience. Any insights or suggestions would be appreciated.

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December 21, 2006, 11:53 AM
Call IMR and ask them, You know that whole from the horses mouth thing.

December 21, 2006, 12:02 PM
Trail Boss isn't for magnum velocity/pressure.TB was/is designed for Cowboy Action Shooting,CAS.CAS shooters utilize black powder cartridges like .45 colt,44-40,32-20,.44 Spl..44 Russian etc.
Trail Boss fills these large volume cases so there is little air space/powder shift.Black powder is bulky whereas smokeless powder is not.Thats where Trail Boss comes in with its cheerio shaped donuts that help fill the case.
Trail Boss is for LOW pressure rounds using LEAD bullets for Cowboy Action Shooting.

Many CAS shooters use guns chambered in .357 Magnum because the brass is cheaper,easier to get locally,and is a low recoil round when loaded to CAS velocity.Some CAS shooters shoot .38 Spl in their wheel guns and .357 brass in their lever guns because some lever guns do not feed the .38 Spl well.

There is a 0.10 difference in case length between the .357 Magnum and the .38 Spl.Thats why the loading data is the same.

Trail Boss IS NOT for magnum pressures or velocities.You would be better of looking at H-110,W-296,Alliant(Hercules) 2400 and other powders better suited for silhouette shooting and the .357 Magnum.

Directly from the IMR site about Trail Boss:

"Trail Boss is designed specifically for low velocity lead bullet loads suitable for Cowboy Action shooting"

December 21, 2006, 12:04 PM
As I recall the 357 data uses magnum primers. That and the longer barrel probably account for the extra speed.

December 21, 2006, 12:45 PM
You're right about the magnum primers, which I didn't notice. I'm not looking for magnum velocities, that's not needed for shooting field position as the targets are smaller and the longest range is 100 meters.

December 21, 2006, 06:53 PM
my GUESS is: trailboss is a relatively fast powder, with air pumped in during manufacture to increase volume. being a fast powder, pressure peak will be reached relatively early in the burn. the jacketed 357 bullet will have more resistance to moving down the barrel, which will retard expansion of the combustion chamber, and result in higher peak pressure v.v. the lead 38spl. but, being a fast powder one does not want to use too heavy a dose; as powder charge is increased, peak pressure would become very sensitive to small changes in charge, resulting in possible overpressures. hence, the 357mag load is intentionally held to a low level.

just a GUESS

December 22, 2006, 07:23 AM
Trailboss is a fast burning powder, but both bullets listed are lead and this effect on pressure should be very small and dependent on bearing surface. The increase in pressure is 6,700 CUP or 49% in a larger capicity case which seems extraordinarily high. I recently experimented with magnum vs regular primers in a .38 Special wirh the same midrange load to determine the effect on accuracy. While there was a slight increase in velocity (I can't measure pressure) it was nowhere near the difference listed with Titegroup.

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