338 WM and Accurate MagPro powder

[BurnOut]

Well, over the weekend my latest build hit a snag of sorts; I am having a T/C Icon chambered up in 338 WM, and it has an internal box mag with a length of 3.5", so I need my rounds to be a bit shorter than that. I am building the gun around the ability to shoot the Berger 250 gr Elite Hunter projectiles; based on Nosler's load data (https://load-data.nosler.com/load-data/338-winchester-magnum/), I was planning on running 71.5-ish grains of H4831 and running the projectile at 2800-2900 FPS out of my 26" (to Nosler's 24") barrel.

Well, last week, I received the dies that I ordered, and over the weekend went to load up some ammo. Being a semi-cautious sort, I decided to start with 70 gr... uh, Houston, we have a problem. More specifically, we have a severe shortage of space. With 70 gr of H4831 in the case, I couldn't come anywhere CLOSE to being able to seat the 250 gr Berger to my desired (3.43) OAL. Shit. I was able to work it down to 3.54, but the load was already compressed at that point, and was still over mag length. Double shit. So I started looking for alternate powders, looking at burn rate charts, and realized that even if I find a powder with a "smaller" charge (in terms of charge weight), I had no idea how much room in the case that charge would occupy. So I started looking for a way to quantify the "bulkiness" of various powders only to find that I was of course trying to reinvent the wheel... there are existing powder bulk density charts (https://www.google.com/url?sa=t&rct...m/powder.pdf&usg=AOvVaw1q2ZVU6VeeHMPpDVBEu_LI) that list the weight-per-volume of various powders. Thaaaaaat's more like it.

So, looking at the density chart, I see that Accurate MagPro is noticeably more dense than is H4831... and that at a given weight, I would see about 8.5% less space occupied by the powder if I use it instead of H4831. So, off to the store to locate some MagPro... and was able to find some at Cabela's of all places. In any event, looking at load data for MagPro powder (which burns noticeably slower than H4831 (it's closer to H1000 than H4831), I started at 68.0 gr and moved up in half grain increments up to 70.0 gr, then .2 gr increments up to 71.0 gr.

The barreled action is still a couple of weeks out, so it'll be awhile before I can get any results... but I also picked up some H414 and may build a similar set of stepped loads in order to run them through and check for pressure signs.

 

[BurnOut]

Update- using some powder charge settling techniques that I read about on 65guys.com, I was able to work up to 72.0 gr of H4831 SC into the case, seating my projectile such that my COAL is 3.43x. I may be able to get a *little* more in there, but I'll need to see how my existing loads shoot (and see if they show pressure signs).

I also have a can of Ramshot Hunter powder on the way, which has a burn rate closer to H4831 (than does Magpro), but is a bit more dense (than H4831).

I'm feeling more confident that I can salvage my original goals for this rifle, between the powder compaction techniques and the other powders that I've found.

 

[BurnOut]

'nother update- I received my can of Ramshot Hunter, and loaded up a pressure testing ladder from 69-71 gr in .2 gr increments. Something I'll note about this powder... watch your charges CAREFULLY if using something like an RCBS Chargemaster. I tweaked mine per the instructions that Hide user orkan provides on his website (https://www.primalrights.com/library/articles/re-programming-rcbs-chargemaster-combo), including the straw mod, and found that with this powder I'd get over-throws of up to a full grain.

This certainly isn't the fault of the powder, the Chargemaster, or the modifications/tweaks made to the Chargemaster (which work quite well with other powders that I've tried), but rather a compatibility issue between all of the variables involved. Unfortunately, the Chargemaster simply makes a single beep once theset charge weight has been reached (as normal), and the only indication of an over-throw is a smallish triangle on the display above the "over" label on the front of the unit. If you simply grab the powder pan and charge your case without first waiting for the display to time-out the charge count (the number of times it has dispensed that set charge weight), you'll never notice that you're pouring a hot charge. Bad shit. It'd be swell if the unit would provide an audible alert of some sort if there is an over-charge (three short beeps instead of a single long beep, for instance), but it is what it is.

Thankfully, I caught it on the 6th charge of the ladder I was building, and only had to hammer apart 5 completed rounds to re-charge them (I did not measure the charges that they ended up with; I just recycled the powder). What I ended up doing was setting the Chargemaster to get me within 1.5 gr of my target, then using a manual powder trickler to get the charge weight where I wanted it. With the RCBS unit set to stop 1.5 gr short, sometimes it ended up right on target (at the set charge weight), but most of the time it was .3-1.0 gr over. The trickle button on the Chargemaster would sometimes dump just a few kernels of powder, and other times it would start a little avalanche and dump half a grain or more (thus my use of the manual trickler to get the charge weights right).

So... to make a short story long, if you're planning to use Ramshot Hunter powder, keep a close eye on and double check all your charges.