Disclaimer: The following loads listed were safe in my rifle. They may not be safe in your rifle. Always use starting loads 10% below the maximums listed in reloading manuals. I am not responsible for typographical errors. Always refer to reloading manuals before reloading any cartridges.
While the .357 Maximum is not the most common round these days, there is still a fair amount of loading data available. However, finding data that gives velocities for the Max out of a rifle length barrels is rather limited. This is a large part of why I decided to post a site on the subject. I do not claim to be an expert, but I can tell you I am very thorough in my research and testing. Also, I only report factual information that I have experienced first hand. All of the bullet velocities reported were actual measurements taken from my “Chrony” chronograph.
While I was waiting on my barrel, I purchased 100 new Remington cases and a set of Lee .357 Magnum dies. As stated on the instruction sheet that is included with the dies, these will also load .357 Maximum cartridges. The seating stem that is in the bullet seating die is designed for blunt bullets like semi-wad cutter and hollow points that are commonly loaded for the .357. To keep from deforming the exposed lead tip on my pointed bullets, I had to modify the shape of the seating stem. A sample bullet with a check for $12.00 was mailed to Lee Precision. In less than 2 weeks, a new modified seating stem that matched the shape of my bullet was in my mailbox. That is very good service, in my opinion! Meanwhile I deburred the flash holes on the new brass to assure consistent ignition. Fortunately the new Remington brass was very consistent in overall length and ranged from 1.598” to 1.600” after running all of the cases through the carbide sizing die. I felt that this eliminated the need to trim cases. I gave each case a slight bell at the mouth, for easy bullet seating, using the Lee flaring die. I then primed each case with a Remington 7 1/2 rifle primer. It is important to understand that the .357 Maximum requires the use of small rifle primers. The maximum pressure for the Max is 48,000 cup. This pressure is higher than that of the .357 magnum, so the heavier constructed rifle primers are a must for safety sake. I found that there were a number of powders that would work well with the Max. For my own testing I decided to start with Hodgdon Lil Gun and use Accurate Arms 1680 as a second choice. Hodgdon 110 was also a powder I would try if the first two did not work out.
I have always had good luck with Hodgdon powders. It has been the preferred choice in my varmint rifles as well as my shotgun loads for skeet and sporting clays. I decided to start with Hodgdon’s Lil Gun. Even though this powder seemed to work well in my friend, Bill Novy’s Handi-Rifle, it proved to be a disappointment in my Encore. After cautiously working up to 22.0 grains of Lil Gun I was achieving 2138 fps but my extreme spread was 87 fps. My groups were averaging 2.0” at 100 yards for 3-shots center to center. The impact on my targets could be correlated with the velocity that the chronograph was showing. Most dispersion was in the vertical direction. Also, I could never get rid of the soot on the outside of the cases, which made me think that my primers were not hot enough. I tried CCI 450 small rifle magnum primers and a heavy roll crimp but still experienced the inconsistent velocity and groups that were in the 2.0” range at 100 yards.
Next up was Accurate Arms 1680. Groups immediately begin to tighten up with this powder. 100 yard 3-shot groups were averaging in the 1.30” range with 26.0 grains. Even though I was experiencing some soot on the cases as I did with the Lil Gun powder, my velocity spreads were much less. The Accurate Arms loading manual lists 26.5 grains as a top load with the Hornady 180 gr. SSP bullet. However, they show the pressure at 41,000 c.u.p. while SAAMI specs list the maximum pressure for the .357 Maximum at 48,000 c.u.p. I found this puzzling. I carefully loaded more rounds up to 28.0 grains of AA1680 and achieved 2205 fps for a 10-shot average with an extreme spread of 49 fps. Furthermore, the soot I was seeing on the cases seemed to disappear. Extraction of cases was good and I could not find anything indicating that pressures were too high. These test loads were loaded with CCI 450 primers and bullets were seated .010” off the lands. The velocity was identical on a heavy roll crimp versus no crimp but the accuracy was better with the rounds that had a heavy roll crimp. I generally do not exceed maximum loads listed in the loading manuals. However in this case, I felt confident that I was still within the pressure window from what I read in the Accurate Arms loading manual. To be certain, I emailed Accurate Arms and received a prompt email from Ballistician, Johan Loubser. Johan told me that they stop loading at a given density limit. Since 1680 is really verging on being too slow burning for the .357 Maximum I could safely compress more and the chances of over pressure is virtually impossible. Johan estimated the pressure of my 28.0 grain load to be 43,000-45,000 psi and well within the caliber’s envelope and the T/C gun I am using. Hallelujah and please pass the powder! It was refreshing to hear straight forward answers based on scientific data rather than diluted down attorney influenced chit chat. Kudos, to Johan and Accurate Arms Powder for being upfront and producing great powder!