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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
.257, 6.5mm and 270 Allen Mags, New Family or Rounds...
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<blockquote data-quote="Fiftydriver" data-source="post: 36726" data-attributes="member: 10"><p>DanTec,</p><p></p><p>First off let me say I have no illusion about the efficency of these rounds, I could really care less about efficiency.</p><p></p><p>Also, the powder capaacities I listed were amounts of H-335 filling each case to the mouth of the case.</p><p></p><p>Actual usable case volume with the proper powders will be much less.</p><p></p><p>My 257 STW is using 77.0 gr of H-Retumbo to produce 3470 fps out of the 30" barrel. I project my 257 AM will use in the range of 87-89 gr of Retumbo with the 130 gr bullet for +3600 fps performance.</p><p></p><p>I have also found in studying and researching the 257 STW over the last year extensively that with 100 gr bullets which will easily hit +4000 fps in a 30" barrel, they tend to be quite inconsistant in velocity spreads. With the 115 gr weight bullets the 257 STW tames down dramatically and with the big 130 gr BCFBHP's it is a ***** cat to load for using Retumbo and it will get extreme spreads in the low teens, not bad for such a long skinny case.</p><p></p><p>My 257 AM is slightly shorter then the STW but substantially fatter. It also has a steeper shoulder to help retain the powder in the case for a more efficent powder ignition.</p><p></p><p>As far as the 408 is concerned, this case has a larger case volume then the Fed-215 was ever designed to ignite. THis is why the big 50BMG primer works so well.</p><p></p><p>THe Fed-215 is the best primer I have found for cases with up to 130 gr capacity which my AM rounds have no where near this, in fact, non will be loaded with a charge heavier then 90 grains I would suspect.</p><p></p><p>If you compare the 25 AM with other rounds, it compares almost identically with the 338-378 Wby as far as bore volume to case volume goes and is far better ballanced then the 30-378 which has not been know for ignition problems.</p><p></p><p>Carbon fouling is a problem with any big cased round especially if they are not loaded to proper working pressures. I designed these rounds to work at 65,000 psi, standard for modern high performance magnum rounds. </p><p></p><p>At this pressure level, Retumbo and H-50BMG burn very clean.</p><p></p><p>The bore should have the powder fouling removed completely after every 20 to 25 shots anyway so this will not be a real problem from what I have experienced.</p><p></p><p>I agree if you do not clean your bore properly, you will see an increase in powder fouling but it is easy to remove if done when it should be.</p><p></p><p>I am not a fan of solid bullet designs such as the X and the other solid bullets.</p><p></p><p>I feel a cup jacketed bullet with a match quality cup is far superior in accuracy and consistancy. They are also much more forgiving as far as pressure and bullet seating depth is concerned.</p><p></p><p>Also, these are deer and pronghorn rounds. They are designed for this size game so a bolded core bullet will produce amazing results.</p><p></p><p>Good Shooting!!</p><p></p><p>Kirby Allen(50)</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 36726, member: 10"] DanTec, First off let me say I have no illusion about the efficency of these rounds, I could really care less about efficiency. Also, the powder capaacities I listed were amounts of H-335 filling each case to the mouth of the case. Actual usable case volume with the proper powders will be much less. My 257 STW is using 77.0 gr of H-Retumbo to produce 3470 fps out of the 30" barrel. I project my 257 AM will use in the range of 87-89 gr of Retumbo with the 130 gr bullet for +3600 fps performance. I have also found in studying and researching the 257 STW over the last year extensively that with 100 gr bullets which will easily hit +4000 fps in a 30" barrel, they tend to be quite inconsistant in velocity spreads. With the 115 gr weight bullets the 257 STW tames down dramatically and with the big 130 gr BCFBHP's it is a ***** cat to load for using Retumbo and it will get extreme spreads in the low teens, not bad for such a long skinny case. My 257 AM is slightly shorter then the STW but substantially fatter. It also has a steeper shoulder to help retain the powder in the case for a more efficent powder ignition. As far as the 408 is concerned, this case has a larger case volume then the Fed-215 was ever designed to ignite. THis is why the big 50BMG primer works so well. THe Fed-215 is the best primer I have found for cases with up to 130 gr capacity which my AM rounds have no where near this, in fact, non will be loaded with a charge heavier then 90 grains I would suspect. If you compare the 25 AM with other rounds, it compares almost identically with the 338-378 Wby as far as bore volume to case volume goes and is far better ballanced then the 30-378 which has not been know for ignition problems. Carbon fouling is a problem with any big cased round especially if they are not loaded to proper working pressures. I designed these rounds to work at 65,000 psi, standard for modern high performance magnum rounds. At this pressure level, Retumbo and H-50BMG burn very clean. The bore should have the powder fouling removed completely after every 20 to 25 shots anyway so this will not be a real problem from what I have experienced. I agree if you do not clean your bore properly, you will see an increase in powder fouling but it is easy to remove if done when it should be. I am not a fan of solid bullet designs such as the X and the other solid bullets. I feel a cup jacketed bullet with a match quality cup is far superior in accuracy and consistancy. They are also much more forgiving as far as pressure and bullet seating depth is concerned. Also, these are deer and pronghorn rounds. They are designed for this size game so a bolded core bullet will produce amazing results. Good Shooting!! Kirby Allen(50) [/QUOTE]
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.257, 6.5mm and 270 Allen Mags, New Family or Rounds...
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