Hi Peter,
got your PM. I must say this cartridge is way out of usual size zone - .300 H&H Mag and 6.5-284 the biggest I've played with to date! But, nothing ventured, nothing gained.
Had a look through my many printed data sources and found what you probably did too - ie found nothing. .264 Win Mag is as big a .264 as anybody provides loads data for. Well, not quite - good old P.O.Ackley has some from many, many years back.
139gn Norma match bullet 31" test barrel:
88-90gn H202 (3,472)
88-90gn 283 (3,341)
84-87gn H870 (3,591)
Designed for 1,000yd shooting. Work by Bruce Hodgdon showed this was as big a case as you could use with the calibre even with slower burning powders.
Anyway, none of the above available now, so let's look at the QuickLOAD PC internal ballistics program. I couldn't find it at first in the cartridge listing, so played with the even larger cased 6.71 Lazzeroni Blackbird - more on that in a bit.
Anyway ......... then noticed 6.5-300 Weatherby which is what I presume we're talking about here since you mention necking down and neck-turning .300 WBM brass?
Right, try H870 first to see if a max load matches Ackley, and what people are saying here. 85gn works out at around max load for 3,255 fps with a 140gn Nosler Partition at standard COAL from a 26" barrel which all sounds right. Increase barrel length to 31" and MV rises to 3,418 fps, all in line with Ackley etc given this is just a model that makes various assumptions.
I can see why H870 should be regarded as near ideal - 85gn = 99% fill ratio at 62,546 psi with a 100% charge burn in a 26" barrel - pushes all the right buttons.
So, since you can't get H870 (I actually have a pound in my powder cupboard that I bought cheap thinking I'd find some use for it, not realising just how slow a burner it is. Unfortunately, 1lb in North Yorkshire 5,000 miles from Texas doesn't get us far.)
So ........... let's look at other powders in QuickLOAD
Hodgdon US869. 90gn, full case 3,200 fps, but only 96.5% burn - bit too slow methinks
Hodgdon 50BMG. 86.5gn, full case 3,234 fps, 93.7% burn - that less than 99% burn worries me.
Hodgdon Retumbo. 81gn, 97% full case also 3,234 fps 100% burn - looks good
IMR-7828 (long grain version). 73gn, 100% burn 90% full case 3,225 fps. Too fast I'd say.
Norma MRP-2. 77gn 3,208 fps 100% burn, 92.5% fill.
Ramshot Magnum (Big Boy). 79gn 3,235 fps 100% burn, 79% fill - I'd prefer to tun at 90% + fill ratio with a case this size over 6.5mm bore.
Viht N170. 81gn 3,186 fps 99% burn, 98% fill ratio. Looks promising despite less velocity than others. I find Viht single base powders a bit peaky in smaller cartridges, so this could be 'iffy' in this big case.
Viht N570. 82gn 3,297 fps 99.6% burn, 93% fill. This could be a good prospect. N500 series powders often suit over bore capacity cartridges.
Viht 20N29. 93gn 3,215 fps 98.4% burn, 104% (compressed) fill. Maybe a bit slow burning, but a possible good choice depending on bullet and your COAL.
All loads with the Nosler 140gn Partition seated to give 3.56" COAL and producing pressures somewhere between 62,000 and 64,500 psi.
Usual warnings apply - QuickLOAD is a computer model and so everything has to be taken with a big pinch of salt. Start 10-15% down and work up. No liability accepted thanks!
I find QuickLOAD usually pretty accurate as a starting point, but have been caught out with the occasional combination that the program said would be below max pressures - and wasn't!
If you want me to run a particular bullet at a particular COAL with any bullet, PM me and also let me know your barrel length.
Regards,
Laurie,
York, England
PS the Lazzeroni, nearly forgot it. No loads available, but the 6.71 (6.5mm cal) Lazzeroni Blackbird has an even bigger case than the 6.5 WBY (105gn water capacity v 100gn, so around 5% larger). You would have to reduce loads for the smaller Weatherby case. Just a thought - might be worth contacting Lazzeroni and asking for a powder suggestion or two. I'd bet they'd never give any loads data both on commercial secrecy and fear of litigation grounds, but they might just give a pointer as to what they've found a good powder with a particular bullet weight. Worth a try anyway!
