Today I was able to take two of my Extreme Sporter rifles out and do some testing with the 257 Allen Mag. One rifle is a 1-8 twist and the other is a standard 1-10.
First up I tested a prototype bullet designed by Richard Graves of Wildcat Bullets. This is simply one of the most impressive bullets I have ever worked with and that includes the 300 gr ULD .338" bullets and the 50 BMG pills.
The bullet in the middle is the 156 gr ULD RBBT prototype bullet. On teh laft is the 130 gr BCFBHP Wildcat and on the right is a 100 gr Nosler Partition.
The 156 gr Wildcat is built off a heavy tapered jacket designed specifically for big game hunting. IT weights 156 gr and is a rebated Boattail design with a B.C. in the +.800 range. Have not done quite enough testing to get an accurate B.C. but I am thinking it will be in the .820 range.
Anyway, with a load of 93.0 gr of AA8700 over a Fed-215 primer and the bullet seated 0.010" off the lands the fist shot out of the freshly cleaned barrel impacted about 2" high and center. The next three landed roughly 1" above the first in a three shot group that measured .274" ctc at 100 yards. Extremely impressive for an extreme length bullet like this at this short range.
I was hoping for a velocity in the 3200 fps range and had determined that a load of 95.0 gr just started to loosen primer pockets so I dropped the powder charge two full grains and determined this was the max working load in this rifle.
I was a bit concerned how the 8700 would perform as far as velocity consistancy but the chrono reading showed the following for these four shots:
3370, 3357, 3360, 3372 fps for an average of 3365 fps and an extreme spread of 15 fps. Still this is only for four rounds but it looks like with a little seating deptth tinkering, E.S. numbers will be in the single digit range.
I will next test this load at 500 yards and see how the bullet performs as far as stability is concerned. Then I will decide if I want to stay with the 1-8 twist used here or go with the 1-7.5" twist for a little added stability insurance in cold weather or at extreme range.
Still with a velocity in the 3350 fps range and a B.C. of +.800, this 1/4 bore magnum will have few peer as an extreme range deer and pronghorn load as far as trajectory and wind drift are concerned.
My 338 Kahn will match this bullet in B.C. but not in S.D. or even close in velocity. We will see how she does at some longer ranges.
Next up is a bullet for those that love speed. This is teh 100 gr Bonded Core FBHP Wildcat Bullet. This little pill still has a B.C. of .500 so it shoots supprisingly flat for a 100 gr .257 bullet.
The test rifle used to be a 30" 257 STW and as an STW, it would drive these same bullets to 3950 fps with a max load and group in the .3's and .4's at 100 yards.
I rechambered the barrel to the shorter and fatter 257 Allen Magnum which needed the barrel to be shortened by .250" to clean up the old STW chamber.
I loaded up test loads with 8700 starting at 104.0 gr and stopping at 109.0 gr.
Here are the velocity results for each powder charge:
104.0...................4224 fps (oily barrel)
109.0...................4076 fps ???
It is clear to see that after 106.0 gr, there was no meaningfull velocity gains. Even at this level, the 257 Allen Magnum is topping the 257 STW by nearly 130 fps.
Obviously the light 100 gr bullet is not offering enough resistance to the powder to get any velocity gains over a certain charge level.
Still, the 257 AM is producing 4100 fps class performance. The 257 STW has been falsely advertised to be able to do this with a 28" barrel when in all honestly, the STW will only generate around 3850 fps with a 100 gr pill in a 28" pipe.
I shot these test loads into two three shot groups, the first three in one and the second three in another, here are those two groups:
The 109.0 gr load is the high impact on the right group. I am not sure why the shot fell out of the group or why the velocity dropped, may be a result from a bad case.
Still, if I had shot all six at the same target, the total group size would have only been .662" ctc for all size shots. Not to bad figuring they were all different loads.
Next I will load up test groups at 107.0 gr and again at 109.0 gr and see how they perform on average in groups and in velocity consistancy. If there is no real velocity advantage with the heavier charge, there is no reason to burn more powder just to do it.
Richard Graves is also building a very heavy tapered jacketed 100 gr pill for use in this round which will do a couple things. First off it will handle the impact velocity much better then this thinner jacketed model designed for the 25-06 and 257 Wby.
Second, the thicker jacket will offer more resistance to the powder charge and will help improve powder burn at the higher charge levels.
4100 fps with a .500 B.C. 100 gr bullet will be pretty darn flat shooting out to 500 yards for the ultimate pronghorn rifle.
I will repost how the velocity variation tests go with the 100 gr pills and how the big 156 gr ULDs do at 500 yards.