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257 Allen Magnum progress continues to another level...

 
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  #8  
Old 12-17-2004, 08:41 PM
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. In past tests the STW proved to produce about 47 fps more velocity p

[ QUOTE ]
. In past tests the STW proved to produce about 47 fps more velocity per inch of barrel length. .

[/ QUOTE ]
I'd be a little bit cautious about total V increase projections, as my graph Differential Vel Gain shows. I'd embed the graphic here but this [img]/ubbthreads/images/graemlins/confused.gif[/img] [img]/ubbthreads/images/graemlins/wink.gif[/img] software has an absurdly low limit on URI length.

The data comes from a Program Daniel Lilja wrote. He sent me the code to modify (because alot of 50 guys are shooting out of 18" barrels) - so I will be extending the length from 18" to 48"

The graph clearly shows the diminishing returns of FPS - and the curve is pretty steep around 28"
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  #9  
Old 12-17-2004, 08:45 PM
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Re: 257 Allen Magnum progress continues to another level...

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What is the parent case for your .257 AM? Looks to be a RUM case knecked to .257 and then improved????

[/ QUOTE ]

IIRC, not just any RUM, but the 338 which is 1/10" shorter than the other RUMS. Now why did Remmington make that case shorter? ans: Just for Kirby [img]/ubbthreads/images/graemlins/smile.gif[/img]

What does improved mean? (shorter shoulder/steeper angle)?
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  #10  
Old 12-17-2004, 10:18 PM
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Re: 257 Allen Magnum progress continues to another level...

Sako 7STW,

IT is built on a modified 338 RUM case. Full length, necked down to 257 with the shoulder angle sharpened and body taper blown out.

Admittedly this case is far to large for the 257 bore with conventional bullet weights. A 100 gr ballistic Tip would be about worthless over a 100 gr capacity.

It is for this reason that Wildcat Bullets has designed several new bullet to perform in this very large case. THe light weight pill is teh 130 gr Bonded Core FBHP. It has a B.C. of .550 and a S.D. of .281.

Substantially more B.C. then a 180 gr .308" Accubond and a S.D. exactly the same as a 225 gr .338" bullet. Performance goals are to drive thsi bullet to at least 3600 fps.

The other bullet weights are a 145 gr FBSP built on a very heavy tapered jacket and a 145 gr ULD rebated Boattail HP with a B.C. of .738!

There will also be a 150 gr BCFBHP and possibly a 160 gr BCFBHP.

I used this case because it has proven to be stronger in the case head then the STW case as well as not having to deal with the inconsistant belt thicknesses with the STW in a tight chambered rifle.

Not to mention the 16% larger case capacity which should offer at least 125 to 150 fps over the 257 STW with same bullet weights.

Good Shooting!!

Kirby Allen(50)
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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: www.apsrifles.com

allenmagnum@gmail.com
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  #11  
Old 12-17-2004, 10:30 PM
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Re: . In past tests the STW proved to produce about 47 fps more velocity p

B1g_b0re,

I would agree that this 47 fps gain per inch of barrel length is alot. I got this from actually shooting three rifles I built this summer for customers. All three used Lilja #6 contour, 3 groove, 1-10" stainless barrels. All were chambered for the 257 STW using the same reamer for all three.

The only difference was barrel length, one was a 27", one a 28 and one a 30" barreled rifle.

Using the 130 gr Wildcat Bonded Core FBHP with the same load each, 76.0 gr Retumbo over a Fed-215 adn all seated to the same over all length, the results were as followed: This was for five a five shot string

27" barrel
3317 fps

28"
3368 fps

30"
3455 fps

I also tested the STW with the 100 gr Bonded Core FBHP and these were the velocity results with the same load:

27"
3853 fps

28"
3910 fps

30"
3955

I do not know what the velocity increase would be over 30", I know it will drop dramatically past this point but from what I actually got testing the 257 STW, +45 fps per inch of barrel length is the norm going from 26 to 30".

The 257 AM has an even larger case capacity and will be using significantly slower burning powders for the 145 and 150 class bullets so I am predicting around the same velocity increases.

We will have to see though what happens when the bullets get in the air!!! [img]/ubbthreads/images/graemlins/smile.gif[/img]

Good Shooting!!!

Kirby Allen(50)
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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: www.apsrifles.com

allenmagnum@gmail.com
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  #12  
Old 12-20-2006, 12:46 PM
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Re: . In past tests the STW proved to produce about 47 fps more velocity p

anything new on the 257 AM front???
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  #13  
Old 12-20-2006, 11:32 PM
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Re: . In past tests the STW proved to produce about 47 fps more velocity p

Blygy,

Its been up and running for a couple years not and is performing very well. It is a bit of a finicky round but it does have nearly a 100 gr capacity under a 1/4 more bore diameter!!!

Best loads I have tested have been with WC872 under a 156 gr ULD RBBT loaded to a comfortable 3300 fps. It will do near 3400 fps in a 30" pipe but there is no real good reason to do so other then shorten barrel life more then it already will be.

Have run into some issues with powder selection. Can only use the ultra slow burning Ball powders such as AA8700, US869 and WC872. Any stick powders, even if they are of appropriate burn rate will cause severe powder bridging issues and cause severe pressure spike.

With the slow ball powders the round performs very well and the heavier the bullets the better.

I tried to see if the 7mm RUM case necked down to 257 and fireformed would work with the 257 AM design but case capacity is simply to large being about 8-10 grains more powder volume then the original 338 RUM based 257 Allen Magnum. Performance was identical as far as velocity limits. Seems thats about the top of the pile for volume with a 25 cal bullet.

Kirby Allen(50)
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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: www.apsrifles.com

allenmagnum@gmail.com
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  #14  
Old 12-21-2006, 03:49 AM
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Posts: 733
Re: . In past tests the STW proved to produce about 47 fps more veloci

Hi Kirby when you have formed your brass you should run the reamer in the full length of a 300 ultra case and just see what the velocity diference with thw 130gr projectiles is it could be surprising it may be more with the slow powders but it would also be fun to see the diferences. I do relise the base will be slightly oversize but it would still be safe and great to hear if it worked.

Cheers Bill
Australia
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