I'm curious as to exactly which powder, with acceptable temperature sensitivity, in a barrel throated to allow seating to the lands, with decent brass life, is going to be used to push a 145g bullet 3400-3450 out of that skinny tube?
I know of some hot, hot long-barreled 6.5 WSMs that'll push a 123g Scenar 3400 with Retumbo, but'd never even come close with the 140 grainers.
In the real world, performance is measured by more than just velocity - it's safe pressures, decent brass life, stable loads at a range of temperatures...
So, the real-world performance of these cartridges will indeed be interesting...
b1g_b0re, lose the lightweight bullets and try a 190 to 220 grain bullet with high ballistic coefficient in that 300 RUM. If you can shoot it accurately - you'll have a top-notch long range slayer.
STL. Principal Consultant and Managing Partner - Association of Bifurcated Tangential Ballistic Apologists, LLP.
Long Range DT, Only thing going against you is the bullets don't have high enought BC and limited suppliers. Pac-Nor, Shilen were the the first to come up with 1/15 and 1/18 twist for the 30 cal shooter HB shooters. I've got a shilen 1/15 on a 30x44 and pac-nors on 30x47. The 30x44 will shoot 125gr,135gr and 118gr if made on the long jackets. I've never fired anything heavier than 135gr so cann't comment. I don't always agree with Kirby's thinking on some matter but he is headed in the right direction with his new mag project simply put he is getting the bullets to match the caliber and he is staying with standard barrel twist and these will be hunting rifles not varmit. I know you are looking at a higher velocity than I shot with the 30x44,30x47 but you would not believe the drift in those bullets in the wind you could be outshot by a 308 with 150gr bullets. The only reason the 1/15 thru 1/18 twist barrel came along was could shot a lighter bullet in one of the short 308 cases and not get recoil beat up like shooting a 308 and it was the HB guys who pushed for them. I say you may want velocity in the 4000fps range and being those 125gr are on a short jacket your going to over case capacity. When those fast twist barrel first came out was only acouple making light bullets now have anywhere from 112gr to 135gr. seems like the bullets are always last to follow. As to comparing your to Kirbys 25 cal I'd honestly say with what you have said so far that your barrel may not last past load testing that throat will wash out pretty quick. If you look at the 22cal bullet now have some 100gr LVD bullets there is nothing going toward the lighter bullets you can get a longer jacket and more bearing suface and say with a 112gr 30 cal by the time get bullet dia and ojive not much left for a bearing surface maybe if they did something more with a plastic tip. Just my .02 worth.
No A agree kirby's idea on the new Am's and thanks Kirby I"ll be watching ...I just had some really bad stuff happen to me over the weekend that I need to deal with before I go building another rifle heck I have one at GAP right now being built...I have to pay the rest on ...I rolled my wifes truck at the range sat hit the only damn tree in 2 miles if I hadn't it would have been a 2000yd death roll to the bottom no doubt!
[img]images/icons/frown.gif[/img] anyways still waiting on the AAA guy to call and no fixxe or yes we can! [img]images/icons/mad.gif[/img] anyways I just thought IMHO that the whole big jug of powder with the asprin on top was a silly thing .....Now the AM's thats why I said thats not a even comparison those things are a whole different beast!! and a beast it will be no doubt!and I will have one by the end of the year providing R&D works out for ya... hell even if I have to sell my .338LM it would be portable here my Lapua is not bad only weighs in at 15.7 thats with no bipod We will see..like I said before wasn't trying to call anybody on anything ...I know your for real!!! and a helluva generous guy as well!
Thanks Keith [img]images/icons/smile.gif[/img]
Ya'll might wanna look at the ballistics of a 7mmRUM fired from a 30" tube. A 176gr Cauterucio with a BC of .740 running just under 3,400fps. A 156gr scooting along even faster with a BC of .650 or so.
Do the numbers - they're pretty good. [img]images/icons/smile.gif[/img]
Please keep in mind my performance goals for my AM rounds are nothing remotely similiar to a Comp rifle or Varmint rifle where throat life is a premium.
These are Big Game rifles. They are designed to be used in a way that an experienced handloader can find a top quality load in far less then 100 yards and use the rifle big game hunting where taking a few shots at game a year should be an exciting season.
The 257 STW rifles I have built have been lasting for 1000-1200 rounds of accurate barrel life before they are either ready to be set back or replaced with a fresh barrel.
TO answer your question on powders that will be used, for the lighter to medium weight bullets in the 257 and 6.5 AM and all the bullets in the 270 AM, Retumbo will be the powder of choice. It is as temp stable as any powder out there and should be a great ballance of burn rate to bore capacity for the lighter weight 257 and 6.5 AM bullets as well as all the 270 AM loads.
For the heavies in 257 and 6.5mm, H-50BMG will be getting the go ahead. Again this powder is very stable over a wide range of temps.
The 257 AM and 6.5mm AM have roughly the same case capacity to bore volume ratio as the 30-378. Anyone see a real problem with that round in powder selection?
I assure you my loads will produce brass life in the 5 to 6 firings range. Again, these are big game rifles, this is more then enough case life for that use, hell a 100 brass should last a lifetime of big game hunting.
The 6.5mm WSM is not even remotely in the same class as the AM rounds. The AM's are more round then has been used in these calibers. Combining that with the heavy for caliber bullets from Wildcat Bullets, this is the reason these rounds will work where other big cased rounds on small bores have not.
They tried to force light bullets to hyper velocities for long range performance. The only way to get consistant long range performance is with high velocity but just as important high B.C. and for on game performance, high S.D.
The AM rounds will have a powder capacity roughly 30 gr larger then the WSM rounds. The only way this large of a case capacity will work is to use non conventional bullet weights which we are doing.
In the 257 AM, I would say 130 gr bullets are as light as I will go in my testing. One could use 115 to 120 gr pill with good results but the 130 is a good minimum in my mind.
The 257 STW gets pretty finicky with 100 gr bullets and the 257 AM would be the same way with 115 gr pills. Velocity will basically be the same with the 100 gr bullet in the STW and the 115 in the AM.
All the things you have mentioned are real problems and Richard Graves and I have taken alot of time and research to come up with what we are releasing.
Will they perform exactly how I am telling it now, I hope so and believe they will. No matter what though, if my rounds will not reach my performance goals within safe pressures, I will never use damgerous pressures just to reach a velocity for a selling point.
There is no need with the level of performance these rounds will offer, even if they miss my goals by a small margin, they will still be vastly superior to any 257 , 6.5 and 277 round offered now for hunting deer and pronghorn out to 600 yards out of a sporter weight rifle.
I also had alot of guys tell me that the #6 contoured barrels would not offer enough accuracy in the 257 STW class rounds for shooting out to 500 yards. Well, after they were built and tested and proven to produce groups in the 1 1/4" range at 500 yards, those non believers came around a bit even though some needed to see it in person to believe it.
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