Home Forums Hunting & Shooting Ask The Gunwriters Reloder 15.5 in the .375 H&H and .338 Win Mag

A few months ago I was able to pick up a couple of pounds of the new Reloder 15.5 powder online. I was interested in this new temperature resistant powder because my son and I have a hunt for buffalo and plains game in Mozambique coming up in late September, and I know it gets hot in Mozambique at that time of year. My last African hunt was in Zimbabwe and I used factory loads, but I wanted to use my own loads this time. I had worked up a load for my CZ 550 .375 H&H with Reloder 15 and it shot well, but I thought a bit more temperature resistance might be a good thing on hot afternoons.

Based on the information Alliant has released, Reloder 15.5 is supposed to be between RL 15 and RL 16 in burn rate, but they list no data for cartridges larger than 30-06. I called Alliant to see if I could get more information, but the guy I spoke with basically said they had no other data and that RL 15.5 was "for wildcatters." That was not encouraging, but I decided to look at the data for RL 15 and RL 16 and try to work up a load based on what I could extrapolate from that.

There is no data for RL16 in the .375 H&H, but Alliant does list data for both powders for the .338 Win Mag with 210 grain bullets, so I decided to start by working up a .338 load with RL 15.5 and the 210 grain Nosler Partition since I had a supply of those. The powder charges Alliant lists for RL 16 and the 210 NP are considerably more than those they list for RL 15. So I decided to be cautious and begin close to the starting loads listed for RL 15. Since Alliant data doesn't show starting loads, I looked at the Nosler 8 manual and based my starting loads on that.

What I found was that RL 15.5 charges seem to be very similar to those for RL15. I ended up getting 2920 fps with 66.0 grain of RL 15.5 and a 210 NP. That seemed to be in the ballpark for velocity, but I got a bit better accuracy with 65 grains for 2860 fps. I saw no evidence of traditional "pressure signs" like hard bolt lift or cratered and flattened primers, but I know that Mule Deer says those often don't appear until PSI readings are over 70K. So I don't think I will go higher at this point. Besides, that's plenty of velocity for my purposes.

Next, I followed the same process of beginning near the RL 15 starting loads using Reloder 15.5 in the .375 H&H with 300 grain TSX bullets. I worked up to 68.0 grains of RL 15.5 for 2465 fps. I might be able to go higher, but that seems like a reasonable velocity and is certainly enough for buffalo if the bullet is placed correctly.

I am interested in feedback from Mule Deer and other knowledgeable reloaders on the process I followed, and whether my loads sound reasonable and safe based on the limited information available.

For plains game, we are also taking a 30-06 for me and a .308 for my son, but there is lots of load data for those, and I had no problem coming up with good loads for the 168 TTSX and H4350 in the 30-06, and the 150 TTSX and TAC in the .308.

So have at it! This is the first time I have worked up loads without having any data available from the manuals.

Nothing to add since I’ve not seen any 15.5 yet, but it looks like you have a few great loads.

Good luck on the Buffalo hunt!

I'd quit right there. In both my 375s, I need 74gr of RL 15 to get me 2500 plus w a 300gr TSX. I need to find some of that stuff

Quickload shows R 15 and 15.5 max charges to be within 1/2gn of each other w/375 H&H and 300 TSX.

CFE223 is a good choice in the 375 H&H.

Thanks! That's basically what I'm seeing, although I didn't fully explain my process and haven't actually used TSX bullets yet. I did my initial workup with Hornady 300 grain DGS since I also need some solids and they are not only cheaper but I have quite a few. My experience with Reloder 15 is that with the same charge I get about 10-15 fps more with a 300 grain TSX than with a 300 grain DGS. So the 68 grains of Reloder 15.5 should put me at about 2475-2480 fps with a TSX. My next step is to verify that.

I have been loading CFE223 in my 375 H&H. Haven’t found anything better.

I should also mention that I seem to be getting slightly higher velocities for a given powder charge using the same bullets with RL 15.5 vs RL 15. In some cases it's about 50 fps higher.

Care to share Velocity and load, accuracy.

The basic question I was asking was whether you can be reasonably sure that loads developed with a new powder with no pressure tested data are safe, by working up the loads based on results from a similar powder that has published data. In this case, I had already worked up loads with the same bullets using RL 15 in my M70 Classic .338 WM and CZ 550 .375 H&H, so I had a pretty good reference point. Based on the chonograph results, I'm feeling good about the way this has worked out so far, but this is a new process for me.

I'm hoping Mule Deer will comment on the process I used.

Bowmanh,

I have yet to encounter any RL-15.5 anywhere, but have tested the newer temp-resistant powders such as RL-16 enough at temps from zero to 100 to know they work as advertised.

Your work-up procedure makes a lot of sense, and have yet to see a buffalo that didn't die pretty quickly with a good 300-grain bullet in the right place at even lower velocities. My friend Berit Aagaard has done it both on Cape and water buffalo with handloads at 2400 fps, with no problems.

Thanks John! I appreciate the feedback!