Range report with 257 and 270 Allen Magnums....


Official LRH Sponsor
Jun 12, 2004
Fort Shaw, Montana
Well, I finally got some testing done with the 257 and 270 Allen Mag. Fist the 257 Allen.

I started testing this round with a fully accurized Rem 700 fitted with a 30" Pac-Nor Super Match #6 contour with a 1-8" twist.

During fireforming I quickly learned that the 257 AM would only be suitable for use with ball powders. The stick powders of appropriate burn rates were having powder bridging issues and premature pressure signs.

Because of this, AA8700 was tested and found to be a very good performer in the 257 AM, in fact, it may be the only suitable powder that is easily available for this very high performance 257.

The bad news is being limited in powder selection, the good news is that it performs great in this case with a wide range of bullet weights.

Starting with the 130 gr Bonded Core FBHP from Wildcat Bullets, this barrel topped out at a very impressive 3725 fps level with good case life. This compared to a 257 STW fired out of a 30" Lilja 3 groove 1-10 twist barrel that would produce 3450 fps comfortably and reach 3470 fps if it was pushed a little.

These bullets used the very accurate J-4 match jacket and as such Richard Graves decided that they would not be suitable for this velocity range. He built some prototype bullets using a dramatically heavier tapered jacket that would perform specifically int he velocity range of this big 25.

He also slightly shortened the bullet length and brought the lead core to teh very tip of the meplat. Then the heavy jacket was formed to practically a solid point with only a very small sign that the lead was even there.

This was to slow the initial expansion slightly for the velocity ranges we were dealing with. B.C. dropped very slightly to around .520 but bullet performance was dramatically improved to match this round.

Because of the very thick jacket, we also received a drop in top velocity which was expected. This 130 gr Heavy Jacketed BCFBHP topped out at just a tick over 3650 fps. Still a solid 200 fps over the STW with the thin jacketed bullets.

Only problem was that group size was larger then I expected but I also found out during the fitting of this barrel that it had a bore diameter in the .2514" range compared to .2502" for the Lilja barrels that I am used to using.

Anyway, groups were in the 1.5" range at 100 yards, far larger then what I expected from my rifles.

I also tested the 115 gr Ballistic Silvertip again using AA8700 and found that this bullet was able to be driven to 3875 fps out of the 30" barrel compared to an even 3600 fps for the 257 STW in the 30" Lilja. Still groups were sub par.

I contacted Chris at Pac-Nor and after hearing the diameter of the bore he instructed me to ship the barrel back for a replacement, no charge as their bore diameter for the 257s should be in the .250" range.

So now I was without a test barrel. I decided to take the 30" Lilja 257 STW barrel and set it back .200" and rechamber it to the 257 AM. This would be about as fair a comparision between the 257 STW and the 257 AM as I could get even though the AM would be fired in a .200" shorter barrel, nothing really.

Well, recut the Lilja and headed out to the range. I quickly found out that the tighter Lilja barrel would not allow as large of powder charges to be used and that top velocity was slightly lower. Still group size shrank to the .3" range for all loads.

The Lilja topped out at an honest 3600 fps average with the heavy jacketed 130 gr BCFBHP. Still 150 solid fps over the STW and with equal group size averages at 100 yards. I was very happy with the results.

Retesting the 115 gr Ballistic SIlvertip revealed that the Lilja barrel woudl average a bit ove 3800 fps with comfortable loads. The same barrel cut for the 257 STW drove these same bullets to 3660 fps so again, another 140 fps advantage for the AM.

Perhaps the most interesting development with the 257 AM has been a bullet that Richard Graves designed specifically for this big 25. It is a ULD rebated Boattail that weights an impressive 156 gr!!! The bullet is 1.550" in length!

Expected B.C. should be over .800 fired in the 3000 to 3300 fps range.

It has been extremely cold here so I have not yet been able to test this huge bullet much yet. I was able to run a few down the barrels and check bullet stability in the 1-10, and the loose 1-8 Pac Nor before I shipped it back.

As expected, the 1-10 Lilja made beautiful full profile bullet holes, no suprise there.

The loose 1-8 Pac-Nor did much better. Starting with 83.0 gr of 8700, and working up two grains at a step to 89.0 gr, the big 156 gr bullets showed slight nose tearing on the bullet holes with the 83.0, 85.0 and 87.0 gr loads.

At 89.0 gr the 156 gr bullet made a nice round bullet hole. Since it was -25 degrees I could not get any velocity readings. This load was still quite mild.

I loaded up four more loads, 91.0, 92.5, 94.0 and 95.0 gr and tested them on paper as well to see how they landed. This was kind of like paper tuning archery gear.

They all produced clean round bullet holes and I found that the 94.0 gr load was the top working load for this bullet which was far higher then I was expecting to get to.

This is of course a very simplistic test of bullet stability and it only shows the results of severe bullet wobble but in -25 degree weather, it was about all I was up to doing.

Personally, I do not like a bullet to go from unstable to marginally stable in the velocity range of a particular round. This tells me that we are on the raged edge of stability and in cold weather and extreme range we will have problems.

Because of this I have decided to pay Lilja to get tooled up to make 1-7 twist 257 barrels specifically for this bullet in the 257 AM.

Also, if a rifle is to be built in this round, with a shorter barrel in the 16" range, while the 1-8 twist may work for a full 30" barrel at top velocities it will probably fall short in a 26" barrel.

I have always been a far of a bit more spin then needed and that has never let me down. Again, these rounds are not designed for BR matches, they are for reaching out 500 to 600 yards with the 130 gr class bullets and hammering game up to the size of whitetail and mule deer.

With the 156 gr pill and the correctly set up rifle, we have a legit 1000 yard deer rifle in a 25 caliber.

As far as the 270 Allen Magnum goes, I finished the test rifle using a Savage M111 receiver originally set up for the 300 RUM, easy convertion even though the feed lips need to be widened slightly at the front of the mag box to allow the fatter AM round to slip though into the mag box.

The stock is a fiberglass composite offered by Brownells with a full length aluminum bedding block. There are four designs and this one was the BR/Long range target model. It is suprisingly light not being any heavier then the Boyds Laminated Thumbhole Sporter stock.

The stock comes fully inletted but unfinished. Minor sanding is needed and then primering and painting for finishing.

The receiver was fully accurized but because of some problems Savage has been having with their barrel locking nut cracking on the RUM rifles, I opted to remove the savage system and fit the barrel in the same manor as a Rem 700.

Savage increased the thread diameter of their RUM barrels and as such had to thin the locking nut as well. This is teh reason for the cracked nut I believe so instead of dealing with this potential problem, I removed it totally. Worked great and in my opinion made the Savage rifle look much better.

The barrel is another Pac-Nor Super Match stainless with a #6 contour and 1-8" twist. The first bullet tested was the Wildcat 169.5 gr ULD Rebated Boattail. This bullet has a B.C. of .740 adn I was hoping for around 3200 to 3300 fps in the 270 AM.

Unlike the 257 AM, the 270 version is a pleasure to load for. There are no problems at all with stick powders and the first powder tested, Retumbo, produced some great velocities and groups.

Looking to limit load testing as much as possible and still get an idea of this rounds potential as far as velocity was concerned, I loaded one round each at one grain heavier charges using Retumbo.

The 270 AM topped out at 3313 fps in the 30" Pac-Nor 1-8 twist barrel. There were 10 test shots fired and all were shot at the same target. The entire group measured 1.5" ctc which with the +350 fps velocity spread causing most of the group variation, I was pleny satisfied. Also, the rifle was not bedded, just bolted into the stock and tested.

I then tested the 130 gr Ballistic Tip just to see how hard this round would run with a conventional bullet weight.

Again, Retumbo was used and while 3877 fps was reached, it was determined that 3800 fps was a comfortable top velocity level with this bullet and Retumbo.

There were 8 test loadings with this bullet. I fired four into one group and then four into the second.

The barrel was cleaned prior to testing and as such the first shot out of the oiled barrel hit slightly high, The
Next three, even though they were different loads, cut a sub 1/4" group. The second four were not quite as tight but still around the 1/2" range, plus the velocity spread of the last four was greater.

So that is where I stand right now with the Allen Magnum rounds. The 257 AM is proving to be typlical of big 25 caliber magnums, a little ****y but once you figure out what powder it likes(8700) it settles right down and is easy to load for.

Performance numbers for the 257 AM are topping the 257 STW by a solid 150 fps with all bullet weights in same length barrels.

Using the 156 gr ULD, the 257 AM will give true extreme range performance to those wanting to use the 257 bore.

The 270 is also reaching all the performance goals set for it so far. There has not been as much testing performed on it because of weather constraints but they will be coming soon.

Also, I will be testing a second design of the 270 AM using the full length 7mm RUM case as a parent case instead of the 338 RUM. This case will add another 8 grains of capacity but better yet, will make this round much easier to load. Necking down a 7mm RUM to 270 will be nothing and neck annealing will not be needed either. After I test the current 270 AM I will lengthen the chamber ans test the longer version and decide which I will use for the official 270 Allen Mag.

The 6.5mm AM is also on the way, just waiting for the barrel to get in.

Dies are under contract by Redding for the full length sizing dies and I will be offering in-line BR style bullet seating dies from Redding and Forster.

I will get some pictures posted soon to show the new bullets and such.

Good Shooting!!!

Kirby Allen(50)
Fifty, Great to hear a progress report on the 257 AM, and that you are achieving your velocity goals. 3725 fps with the 130 grain bullet would certainly be a potent package, and it will interesting to see what the 156 grain ULD achieves.

I was also interested in what is the maximum length that your REM 700 long action magazine will take and still feed reliably, and was that a restricting factor when you throated the 257AM. Also, about how far below the neck shoulder junction do the 130 grain and 156 grain bullets protrude.

You mentioned that you worked up to 94 grains of 8700 with the 156 ULD, and was interested what were the maximum loads of 8700 with the 130 and 115 grain bullets. Also, what was the approximate loading density you believe the maximum loads represent.

The reason for my question is that with the 257 AM holding 123 grains of 8700, and the .250 neck holding about 4- 5 grains, it would leave about 118 grains below the neck, (less the amount occupied by the protruding bullet) and I was trying to work out what the real usable space was.

A question on case design philosophy, and not a criticism of your design. You mentioned in a previous post that the 257 AM had a neck of .250 inches, which for a case of this size to me seemed less than I would have preferred, bearing in mind that 25/06 has a neck length of .308 inches, and the .257 Roberts about .321 inches.

I realise that there has always been considerable debate on the pros and cons of neck length, and wondered whether you had any specific reason for choosing a .250 neck.

I agree that 8700 would be the powder of choice, and it is reassuring that it shoots accurately in the 3 bullet weights. However, the lack of loading flexibility with other powders is a potential concern, especially if there are availability problems with 8700.(ie.not available in OZ)I have a good supply of H870, but remember reading on Hodgdon's website that the H870 and AA8700 are not the same powder with different labels.

Although I have placed an order with Richard for some 224 and 257 bullets, I can now understand your vocal support for both he and his bullets. One aspect that impresses me, is that he continually seems prepared to make changes to the initial design until he believes he has got it right.

I look forward to hearing further progress reports, and as a wildcatter from way back, it is great to see and hear reports from someone who is prepared to push and test the existing boundaries. Good luck, Brian.

All your comments are good ones and things I have been playing with on these case designs.

The Rem 700s will accept up to a 3.690 to 3.700" OAL from one rifle to another.

I have the 156 gr ULD seated to 3.675" for the rounds I tested. This is slightly off the rifling and with a conventional thin jacketed match bullet in a big cased wildcat with a fast twist barrel this would lead to poor bullet results but with the heavy jackets Richard designed these bullets around, I do not see much problem.

I will be doing more testing here as soon as the temps get to where I can do some chrono testing. Will need to determine as well if the 1-8 will stabilize the 156 gr ULD at 500 yards and out. Will report any findings I get.

With the 115 gr Ballistic Silvertip, The 257 AM topped out in the 105 gr area in this specific 1-10 Lilja barrel. The 130 gr Wildcat Bonded Core FBHP topped out at 100.0 gr.

I would say the load density of the 115 gr loads were in the mid 90% range. The 130 gr were probably around 90% and the 156 were in the mid to high 80% range just estimating right now.

The 115 and 130 gr bullets were seated quite deep to help cushion pressure spikes by adding some freebore until I established a starting powder charge basis to work from.

The 156 gr pills were seated out further.

The 115 and 130s were seated with roughly .575" of bullet shank below the case mouth.

The 156 gr had roughly .600" of bullet shank below the case mouth.

Again, these are just starting lengths designed to allow me some cushion to control pressures during initial load development. Accuracy loads will be seated out longer, especially with the 115 and 130 gr bullets. The 156, without a stretched mag box is close to the limits of its OAL. Still it is a simple matter to fit a mag box with up to 4.00" OAL.

The actual case neck on the 257 AM is .280". I think in my earlier post I stated that I wanted at least one caliber of neck length which is where the .250" may have come up.

I would have preferred a neck of .300" to .320" long but the added complexity of case forming would not have been worth the effort. Will marginal, I feel the .280" neck length is plenty for the 257 AM. Of course the 6.5mm and 270 are longer.

The 270 AMs neck is right at .285" long.

Richard and I are discussing some very interesting bullet designs specifically for the 156 gr class bullet. One design is a double diameter bullet. Similiar to the bore rider designs. This would greatly decrease bore friction, allow higher velocities and less bore fouling. We will see where this testing takes up.

I will keep you posted on the results.

Good Shooting!!

Kirby Allen(50)

I got burned pretty bad a few years back using surplus powder. It was more to do with the company I got the powder from then anything.

I would really like to test those two powders in especially the 257 AM.

Do you have a reputable powder supplier for these two powders. I would be very interested in testing them if I knew I could get a reliable source for them.

Thanks for the information,

Kirby Allen (50)
Kirby, I usually get those powders from Kent Lomont but when he comes to Knob Creek for the shoot. He and another guy bought about a million lbs a few years back and its stored at a magazine in I think WV. Kent tells him how much to bring for his orders and the guy brings that plus some extra for sale at the show. You know how those 50 Cal guys go thru powder. However if I need smaller quantities I use Bartlett, down in Owensboro, KY..270-685-2432...Course its only about 45 miles so I just drive down to pick it up. Shipping powders can be a real pain...If we can find anybody going or coming from MT to IN, could spare you about 8# of each...I have a couple friends going to MT this Spring for PD's..... /ubbthreads/images/graemlins/confused.gif

What would you need for 8# of each, $ wise.

Have you had any dealing with Thunderbird Cart. Company? They have a few powders that would work but just do not want to giev folks load data for powder that is not going to be consistant from lot to lot. At least not dramatcially different.

As you could imaging a 257 round with a 100 gr case capacity driving a 156 gr ULD in a 1-7 twist barrel is a bit sensitive to burn rate changes!!!

Thanks for the information.

Kirby Allen(50)

Talked with a very nice lady at Thunderbird and they were having a sale on their T-870 which she said was very similiar to H-870. He have all heard such things before!!

Anyway, they were having a sale on T-870 and for every 8# kag you bought, they would ship one free. Also, if you ordered a full case shipment, 4x8# kegs, they would cover shipping.

I believer they wee selling T-870 for $86.00 per 8# so that would have been $172.00 for 32# delievered!!!

I am one of those that follow the To Good To Be True Theory but that would be one heck of a deal.

I may contact you about getting some of your powder. Let me look into the shipping charges.

Thanks for your time.

Kirby Allen(50)
Warning! This thread is more than 20 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.