Re: 240SMK with 300 RUM
I figured I'd post some results. My rifle probably has a sloppier chamber than many (116.2 grains water capacity of fired cases) and it has a nice factory freebore but my short magazine limits loads to 3.60" OAL, so these powder charges may not be safe in many rifles even though they're pretty mild in mine. But it should give you guys an idea of the velocity potential of each powder as I have found them.
It's a 26" A-Bolt with factory barrel, BTW.
For Retumbo, I have settled on 89 grains. I have over 100 rounds of this load sent downrange already and it has proven to be the most accurate load ever fired from my rifle. Of course, I've improved the rifle since running out of my H870 load which I suspect may have done just as well in the rifle currently.
In working it up I put four shots--87, 88, 89 and 90 grains all on top of each other into what would have easily been the best 100 yd group the rifle had ever fired. But at 91 I got an ejector mark and the shot flew wide. I didn't fire the 92 grain load. I guess that was sort of a "ladder test" right there and I wasn't even trying to do one. ES and SD are ridiculously low. Here's a 3-shot string: 2852, 2851, 2855....
The only problem with this load--I chronographed it. 2853 fps. A full 125 below my old beloved H870 load. The velocity alone is enough to show up in trajectory but this time the trajectory seemed even worse than the velocity difference alone would indicate, which goes back to what I said in the other thread about BC's. In any case, a very accurate, safe load--but Retumbo is just too fast to be optimum for this bullet weight. It's giving up quite a bit of power.
H50BMG: Color me disappointed. I didn't get a substantial pressure sign until 103 grains. I loaded a bunch up at 101 grains and accuracy was pretty poor. I only chronographed one at 2923. Loaded a bunch more up at 100 grains for an average of 2899. ES and SD the worst I've seen in a while (and that's with weighed charges). Accuracy was pretty mediocre.
I've burned up nearly a pound of it and see no indications that it will approach the accuracy of the Retumbo load or the old H870 load. Maybe if I loaded it down to 2850--but then, what's the point?
So I don't see myself bothering much more with this powder. Somethin' just ain't right about it. I noticed well before all the ruckus was made of it. Man, the recoil, the muzzle blast, and yes--the heat this stuff produced were just brutal. For only 50 damn fps? And groups nearly twice as big? Life is too short. I'll use something else.
I do have some theories as to why this stuff occurs, and they do indicate those with longer barrels may have much better luck, but probably nothing I could prove in a court of law....
And so I remember so fondly my H870 load. 99 grains for 2978 fps. I do think it was a little warmer than the Retumbo load but I could drop a grain and still beat it by a full 100 fps. And it was the most accurate load I had at the time. I suspect with the improvements to the rifle it would shoot right with the Retumbo load now.
So damn. I'm thinking it's time for me to join the crowd and order up some WC872. Maybe it can be a suitable replacement. IMHO, neither Retumbo nor H50BMG are. Retumbo is great for 200's, 180's, etc. But for 240's I want my H870 back! I'm really hoping WC872 fills the void.