Do I dare try to do any loading with this combination or should I just pitch it into the firepit?
Hawkeye
I have a procedure where I right the load down in my book first including powder type. I then get out the powder can and check the type agains the load and tick the book. I do not place the can back where it came from but to one side. At the end when I have finished I again check the can data against the book and record a tick against it.
This is the only way I can stop myself starting bolt upright at night asking myself did I just drain VVN140 into a VVN160 can whilst I was on autopilot.
For the same reason I write down the chargeweight of every case I charge. No more (I hope) did I just put 50gr instead of 40gr.
I have to grudgingly agree that dispensing with the mixed gunpowders is the prudent thing to do. But only because the ratio of the blend is unknown. The gunpowder folks blend gunpowders as a matter of course; but deliberately and under controlled conditions. Also, don't just dump it. Gunpowder makes fine fertilizer.
As Hawkeye point out, the two gunpowders are visually identical. They are also nearly the same in other aspects. Both are single-base, extruded tubular granules. Both have nearly the same Bulk Density. Where they differ [slightly] in is potential energy content.
Given an example in published data where both are recommended for a specific cartridge, the 30-06 Springfield, a 150. gr. bullet, and a barrel length of 24 in., 48 gr. of XMR 2015 gets us around 2900 fps at a pressure of just under the 60 Kpsi SAAMI MAP. 49.5 gr. of IMR 4895 gets us the same thing.
What this tells us is that XMR 2015 is slightly more "energetic" than IMR 4895. But by how much? Using the above numbers, the energy per grain weight (E/gr.) of XMR 2015 computes to about 60 ft-lb/gr. For IMR the value become about 58 ft-lb/gr. Not a very big difference. Under controlled conditions, I would not hesitate to mix the two.
But having been involved in hazardous research and other endeavors most of my life, of which there isn't a whole lot left, I guess I'm more of a risk-taker than most folks.
Good shooting.
Robert
Regardless, the stuff needs to be vividly marked for what it is, and kept far away from the loading bench. You're lucky: for maybe $20 at today's prices, you've learned an indelible lesson of the necessity to establish easily-understood, IRONCLAD, never-changing procedures when working with powder, starting with having only one can out at a time.
I ALWAYS now label my measure as to the powder I am using in it, just in case I am interrupted, for example.
In case you didn't catch the sarcasm, I better put the straight answer in here too. Using isn't even an option. Spread it on your yard & be done with it.