257 Allen Magnum progress continues to another level...

[Fiftydriver]

The reamer for my 257 Allen Magnum showed up Friday of last week so I got busy and chambered one of the fireforming barrels for this round because I had to see what the round looked like fireformed.

To be honest, they look pretty nice with that sharper shoulder and much fatter shoulder.

I measured the case capacity of the fireformed cases and it holds 123 gr of AA 8700 filled to the case mouth. This is compared to 104 for the 257 STW filled the same way and they both have a neck of around .250" so the AM is roughly 16% larger then the STW.

I have only used 8700 to date with the 130 gr pills out of the short 25" fireforming barrel but even with the short barrel and a powder that is a bit to slow for this bullet weight it is still topping the 257 STW when it is fired in a 27" barrel(three groove Lilja). I will be trying powders in the burn rate of Rl-25 and Retumbo. I like the looks of RamShots Magnum powder as it is said to have a burn rate very similiar to these other two powders but in a ball powder form which will be a bit easier on the throat.

I have not been able to post any pics on the new board so if some one could offer some insight into posting pics on this new sytem I will give you all a peak of this new hot rod.

Have a good one. One interesting thing, the 257 AM accepted up to 99.0 gr 8700 under the 130 gr BCFBHP for a velocity of 3400 fps in the 25" barrel. The 257 STW has been gaining about 50 fps per inch of barrel length above 26" so I feel the 3650 fps goal is well within range. Especially since the 257 STW was loaded with Retumbo which is much faster burning then 8700 or the likes.

The advantage with the 145, 150 and 160 gr pills should be even more dramatic as it will allow the use of these ultra slow burners with a more efficent burn under the heavier bullets. We shall see.

The Pac-Nore Super Match stainless 30" barrel showed up today. It is in a 1-8" twist for testing the 145 gr ULD and the 150 and 160 gr BCFBHPs. Got to get some other work done before I fit this barrel to an accurized 700 and see what this round will really do.

Anyway, any information on posting pics again would be great.

Good Shooting!!

Kirby Allen(50)

 

[robbor]

Didn't I see you post something about a 115 grain wildcat bullet, I have not been able to find the thread and richard has not gotten back to me yet. I have decided on a RUM based wildcat but still in the drooling stages, I will hopefully get the savage bought this next week.

 

[Fiftydriver]

The 115 gr Wildcat is just an idea at this time. We have to see how the 130 gr Wildcats do in this huge case first and then go from there.

SO at this time there is not a 115 gr Wildcat to my knowledge, just the 100 gr Bonded Core FBHP, the 120 gr and the 130 gr.

Good Shooting!!

Kirby Allen(50)

 

[Hired Gun]

[ QUOTE ]
I have not been able to post any pics on the new board so if some one could offer some insight into posting pics on this new sytem I will give you all a peak of this new hot rod.

[/ QUOTE ]


First upload your pictures to a picture hosting site like http://www.imageshack.us/ or http://www.hunt101.com
Once they are hosted just copy and paste the image address to the text and make sure it has

on the ends with no spaces. The periods are where the image address goes.

You can also use the image Instant UBB Code button down below and put you image address in the window that it opens.

I'd love to see that new 257AM.

 

[5Redman8]

Send the pic to me and I will post it.

Kyle
[email protected]

 

[Fiftydriver]

Well here goes.

This pic shows three fireformed and annealed 257 Allen Magnums loaded with the 130 gr BCFBHP with a 25-06 round on either side for comparision.

This pic compares the 257 Allen Mag with the next hottest round, the 257 STW. The fireformed 257 AM holds 16% more powder them the 257 STW. Currently, the 257 AM is matching the performance of the STW with the 130 gr BCFBHP bullets when the 257 STW is fired out of a 28" 3 groove Lilja at 3340 fps.

The 257 AM is getting this same velocity out of a 25" A&B fireforming barrel. In past tests the STW proved to produce about 47 fps more velocity per inch of barrel length. This will at least be true for the larger AM so 3600 fps with a 30" barrel should be well within reach and with the proper powder burn rate, I am hoping for 3650 fps.

The 257 STW will top out at 3450 fps with this bullet in a 30" barrel.

This pic shows the shoulder detail of the two rounds. Even though the 257 AM is 0.100" shorter then the 257 STW, it holds much more powder by use of a fatter shorter case.

Good Shooting!!

Kirby Allen(50)

 

[Sako7STW]

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

 

[ricka0]

. 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 /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/wink.gif 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"

 

[ricka0]

[ QUOTE ]
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 /ubbthreads/images/graemlins/smile.gif

What does improved mean? (shorter shoulder/steeper angle)?

 

[Fiftydriver]

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)

 

[Fiftydriver]

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!!! /ubbthreads/images/graemlins/smile.gif

Good Shooting!!!

Kirby Allen(50)

 

[blygy]

Re: . In past tests the STW proved to produce about 47 fps more velocity p

anything new on the 257 AM front???

 

[Fiftydriver]

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)

 

[Wild_Bill]

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