Hi there,
I posted a similar thread sometime ago, as I am interested in trying Retumbo in my 270Weatherby. I did not receive a single reply. The only thing i can suggest is trying a reloading software program, such as quickload, I believe it is called. I have a hunch that Retumbo in the 270 wby especially with heavier bullets, might be pretty good. I would think that it would work even better in the 257 "bee". Hope this helps a little, anyway!
Thanks for the reply...unfortunately being up here in Greenland i don't have access to one of those programs. I'm with you on Retumbo looking like a good powder for both the 270/257 Wby. I use it in my 7mm STW pushing a 160 AccuBond and it is a total deathray.
I would assume that you should be able to start with the retumbo data for the 7mm STW using a 160gr bullet. I don't know but if you are looking to shoot a 150 gr pill i would think the data for the 7mm STW/160 gr. would be a safe place to start considering the case capacity is about the same for both and have similar operating pressures. 75.0 gr would be the starting load. i would do this for the 257 but i really can't think of what cartridge would be comparable...if there was such a thing as a 25 WSM i would figure i could start there.
I don't think that there would be any pressure problems due to the "low pressure" qualities of that powder...but with that being said i, personally, would be worried the 1st time i corked off the reload. if you had a pressure strain guage then you could really find out what your pressures are doing without just pouring powder in until you get pressure sign...the way i see it is with these highly overbored calibers you can get incredible pressure spikes with very small increases in charge weights and by the time you start seeing pressure signs you could very well be way over max.
I just looked at a powder burn rate chart and found that Retumbo is just a shade slower than RL25 so i would think that you could use the RL25 data to get you started. It looks like my previous recomendation might have been a little high. i found data for RL25 starting at about 63.5 going up to about 72. I couldn't get on alliantpowder.com to see the data off their site but i found those #'s on steve's reloading page.
Going to add the standard warnings of this is just a prediction of quickload and not a pressure tested loads. Please use at yourown risk and work up carefully
Cartridge : .257 Weath. Mag
Bullet : .257, 120, Nosler PART SP 35643
Cartridge O.A.L. L6: 3.170 inch or 80.52 mm
Barrel Length : 26.0 inch or 660.4 mm
Powder : Hodgdon Retumbo
Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !
Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms
Brad,
Thank you, I think that would at least give me a good starting place!
Also, Yeayow-thank you for your input as well.
I might just have to invest in the quikload software.
Something else I am thinking of: I would like to compare total case capacity(in grains water) with the bore diameter of the 257 and 270 weatherby(s) with that of the 7mm and 300 RUM's -cartridges that evidently do very well with Retumbo. I have a hunch that the capacity/bore diameter ratios would be very similar. Not that this necessarily would indicate success, but might give another approximation of what one could expect.
