Re: help on .257 project
Well, for ease of loading the 25/7mm Rem Mag, 257 STW and 25 RUM will all be about the same as you are taking a 7mm neck down to 25 cal.
Of the three, with the heavier bullets, I would say the 257 STW will be the highest performing with the easiest to load for personality. THe 25/7mm Rem Mag will get you exactly what the 257 Wby will get so thats alot of fuss for factory performance.
The 25 RUM will be the highest performing of the three but when you get to a level of this case capacity in this bore size things really can get touchy load wise. My 257 Allen Mag has slightly more capacity then the 25 RUM but its a bit shorter.
My Allen Mag is on the 338 RUM case instead of the longer 7mm or 300. I did try a version on the longer case but I did not get any more velocity with it then I did with the shorter version so I would say the current 257 Allen Magnum and 25 RUM are about as large as is practical with the powders we have available today.
They are the most consistant with the heavy bullets so you are on the right track there. THey do shoot pretty well with the lighter weight bullets but in my experience the light bullets have never held a candle to the heavies for load consistancy and accuracy at long range.
Twist rate recommendations would be 1-8 to 1-9 for the 142 gr pill and 1-7 for the 156.
The 142 will handle the 1-7 twist but I would highly recommend getting one with a thinned land in a 5 or 6 groove. I tested these bullets in my 1-7 257 Allen Mag and at the highest velocity potential I had occasional bullet dusting but I am sure that is due to the high RPMs and wide 3 groove barrel with the J-4 jacket.
With a 6 groove I suspect you would not see that problem.
The 156 gr bullets are built on a slightly heavier jacket and I have not seen this problem with them at all with velocities up to 3300 fps which is the load I use in my 257 Allen Mag and would expect you could get very close to that with the 25 RUM.
Pros and cons, well any time you get into the class of 25 cal rounds where your dumping nearly 100 grs of powder in each case you will have a squirrelly little monster on your hands. Heavier bullets help tame the beasts but you need to realize these are EXTREME, extreme chamberings.
Kind of like a 1000 horsepower big block V-8 in a 68 camero. Can be a challange to get pointed in the right direction but once you do, watch out!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]
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