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.257, 6.5mm and 270 Allen Mags, New Family or Rounds...

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Unread 10-30-2004, 09:49 AM
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.257, 6.5mm and 270 Allen Mags, New Family or Rounds...

Well, anyone that reads my response to sscoyotes question about wildcat bullets will know the cats out of the bag.

Richard Graves of Wildcat Bullets and myself have been working on a new family or rounds that are based on the 25, 6.5mm and 270 calibers for the initial members of the family.

I am not giving any specifics on case design or dimensions at this time but will say that they will take these three calibers to ranges and performance levels they have never seen before.

I wanted to design a round built specifically for deer and pronghorn hunters that would allow 500 yard shooting with conventional bullet weights without hardly any sight adjustment from the muzzle to 500 yards, at least not having to aim off hair much.

I wanted this out of a rifle weighing around 9 lbs so it could still be portable and recoil levels had to be tame enough for the relatively light rifle weight.

Richard is designing the bullets for the project and has also helped a good amount in the actual designing of the case.

The 257 Allen Magnum will be the first of the family to be released. This round will be designed around the Wildcat Bullets 130 gr Bonded Core FBHP, the 145 gr FBSP and the 150 gr FBSP.

The 130 gr FBHP's have a B.C. of .550 at a velocity of 3500 out of my 257 STW and the 257 AM should add another 150 fps to this level of performance.

The 145 gr bullet should be in the .6 range and the 150 gr bullet should be in the low to mid .6's.

Richard is also designing a prototype 145 gr ULD RBT bullet for the 25 which will have a B.C. in the .7 range.

The 150 gr FBSP and the 145 gr ULD may require a 1-9 twist but the others will stabilize in a 1-10 barrel at the velocities the AM round will produce.

In fact the 130 gr version is printing groups in the .3's out of my 257 STW and 1 1/4" three shot groups at 500 yards.

The 145 gr pills are nothing more then the 130 gr HP's with the addition of a filled lead tip and SP configutration so they are roughly the same length as the 130s.

These are the performance goals with the three rounds and some of the bullets that Richard will be or has designed for them. These are for a 30", #6 contoured Lilja three groove barrel:

257 AM
115 gr 3750-3800 fps
120 gr 3700-3750 fps
130 gr BC 3550-3600 fps
145 gr FBSP 3400-3450 fps
150 gr FBSP 3350-3400 fps
145 gr ULD 3400-3450 fps

6.5mm AM
120 gr 3750-3800 fps
140 gr BC 3400-3450 fps
142 gr ULD 3375-3425 fps
180 gr ULD 3150-3200 fps

270 AM
130 gr 3600-3650 fps
140 gr 3500-3550 fps
150 gr 3450-3500 fps
170 gr ULD 3300-3350 fps

These are conservative numbers for a 30" barrel with this case design but I would rather predict low then on the high side.

The 6.5mm will probably be the next developed and Richard is busy getting tooled up to build the 180 gr ULD. This bullet will probably hit the .8 range in B.C. and will compete directly with rounds such as the 30-378 class with 240 gr bullets and the 338-378 class of rounds with the 300 gr VLD bullets.

Anyway, the 257 AM reamer is being built as we speak and should be here in less then 3 weeks.

The case roughly spits the case capacity difference between the STW case and the RUM case.

When filled to the mouth with H-335, just used that because it settles evenly, the case capacities are as follows:

All cases necked down to .257"

STW: 104 gr
Allen Magnum: 120 gr
RUM: 126 gr

These three rounds certainly do not need 126 gr capacity to reach top performance, even with the very heavy bullets.

There are several reasons I wanted to get away from the STW case.

1. I have always found the cases to be a bit weak when loaded to full tilt pressures. The parent case used for the AM rounds has proven itself to be much stronger with higher pressure loads.

2. I chamber my rifles to very min specs and with the standard belted Magnum case, I find that 15 to 20 percent of the cases are to long from the rim to the forward surface of the belt and result in a case bind in the chamber and fliers can result.

The AM rounds are a non belted case so that even if they are tight in the shoulder area, which they will be in the fireforming process ala Ackley's crush fit design, once fireformed they will be perfect fits to the chamber with no reason to sort brass because of this problem with the standard belted magnum.

The case body of the AM rounds is blown out to minimum taper and the shoulder sharpened.

Still the design should produce good feeding characteristics for the big game hunter.

In the single shot mode, this case still offers about the max powder capacity usable in these calibers using H-Retumbo and H-50BMG.

As far as game taking ability, Richard has covered that extremely well with his prototype bullets.

The 130 gr BCFBHP has a S.D. of .281! Compare that to big game bullets in the 7mm and 30 caliber families and it become clear that these bullets will flat out penetrate, especially with the bonded core design.

Then the 145 gr version has a S.D. of .313.

Now we are talking that is compared to the 250 gr 338 class of bullets and even better then the 300 gr 375's!!

The 150 gr pill has a S.D. if .324 which is rivaling the 500 gr .458 bullets.

I am by no means saying that these are heavy game rounds, they are not, they are designd as the ultimate in deer and pronghorn rounds used in ralatively light rifles.

The high S.D. is simply a result of the bullet design as well as the high B.C.

Anyway, I will keep youall posted on the progress of the 257 AM as it should be up and running by this winter.

I am also designing a fourth member of the AM family which will be the 6mm AM. This round will use a shorter case design and will be loaded with the 110 gr and 115 gr bonded Core FBHP's from Wildcat BUllets as well.

Good Shooting, I will keep you posted on the developments of these new rounds.

Kirby Allen(50)
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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    Unread 10-30-2004, 12:41 PM
    Join Date: May 2001
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...

    Very interesting. I'd like to do a recoil calculation. How much powder do you expect to use with the .257, 145 grain bullet to get 3400 fps?
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    Unread 10-30-2004, 01:15 PM
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...


    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 pussy 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)
    Kirby Allen(50)

    Allen Precision Shooting
    Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

    Farther, Faster and Flatter then ever before.

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    Unread 10-30-2004, 01:20 PM
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...


    I am predictiong the 257 AM will use around 87 to 89 gr of Retumbo under the 130 gr BCFBHP.

    For the 145 gr pill I would say that the top load would be in the 82-84 gr level with the same powder.

    The 150 gr bullets will probably around 78-80 gr of Retumbo and probably around 88 gr of H-50BMG but these are just guesses as I have yet to test the 145 and 150 gr bullets for any solid data.

    Will be soon.

    When I say relatively low recoil, let me state that I am saying compared to other rounds that will deliever this level of penetration and trajectory. This would be at the level starting with the 7mm RUM with 160 gr bullets and up to the likes of the 30-378 and 338-378 depending on bullets used.

    Good Shooting!!!

    Kirby Allen(50)
    Kirby Allen(50)

    Allen Precision Shooting
    Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

    Farther, Faster and Flatter then ever before.

    Web Page:
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    Unread 10-30-2004, 02:10 PM
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...

    I want one! I have always liked the .257" since I got my first 25-06. I have been saving here and there, but still nowhere near enough to get anything custom built, but I can still think of the possibilities. I was thinking of necking down the .300 RUM to .257" and calling that good. Maybe blow it out to 40 or 45 degrees. It is a beltless case as well. I would also want a 30" Lilja but have it fluted so that it would weight close to that of the 26", but get a little more velocity yet out of the 30". Someday I will have one. I want it for the same reason you do, LR deer and antelope. With a click system it should be good foor deer out to 800+ I would imagine. I wish the factory would come out with a hot .25, I would buy one then. I love the idea of spitting out a 100g at 4,000+fps. I was thinking of shooting the 100g swift, or 100g xlc as fast and accurately as I could get them. I am personally hoping for something around 4200fps with a 100g and 3700-3800fps with a 115g. It would just be plain awesome for deer, I can just imagine. Anyways, If I had the money, I would definately have you build one for me, but for now I'll just have to stick with my 300 RUM or 25-06 for deer.
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    Unread 10-30-2004, 02:29 PM
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...

    I am not very skill in 0.257 caliber but I have make a lot of test and trial in 0.264 ( closest caliber of the 0.257 )

    I have start with 264 WIN mag 139 Scenar and get 3250/3300

    after to make some test in 6.5/300 wea I have get 3450 fps in long barrel

    I have redesign the 264 WIN mag by lengthening th eneck and put a parellel throat the cartridge is 6.5/300 DTC Yuma I use 264 win mag die andcase are made in 300 win mag to get longer neck

    my question is with the 264 WIN body I get enought romm to load at full density 50 BMG powder ( slow BMG powder use in 50 and 20 mm ) to reach top velocity as 3400 fps ( at safe pressure )

    so my question is with 90 grain of powder load you ahve still room in your case , does this romm is a improvement or do you can you load at full density because I always design case /cartridge to be at 100/102% ( slighty compressed load ) of the slowest powder I can use

    if your 257 bullet ULD work that can be very sweet solution in 257 WE

    good shooting

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    Unread 10-30-2004, 05:48 PM
    MOA MOA is offline
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    Re: .257, 6.5mm and 270 Allen Mags, New Family or Rounds...

    This sounds like a winner, I want one. I assume that this isn't based on a necked case-- who will be making the brass and how much will it cost? How much will the custom bullets run? What bolt face size will the case be compatible with? I have a 25-06 sendero now that would be an excellent donor if the bolt would work. It's about time someone came up with a fast mid-caliber cartridge.
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