The first prototype of the 270 Allen Mag like its smaller caliber brothers the 257 and 6.5mm are based on an extensively modified 338 RUM case with shoulder blown out to min taper and shoulder angle increased to the Allen Mag configuration.
Case capacity of these rounds based on the shorter 338 RUM case is equal to the longer RUM cases(7mm, 300, 375). In fact it is a bit more. I decided to use the 338 RUM case as the parent case because I was sick of dealing with belted cases as I could not fit the chamber as tightly as I wanted without sorting brass by belt thickness. I also wanted more horse power then the full length belted magnum could offer.
The case capacity of the 257 and 6.5mm Allen Mags proved to limit the powder in which they can use to AA8700 and WC872. No stick powders can be used in these huge cases small bore magnums because of powder bridging issues which will cause severe pressure variation.
With AA8700 and WC872 though they perform exceptionally well with bullet weights from 100 to 156 gr in the 257 and 120 to 169.5 gr in the 6.5mm.
The 270 Allen Mag proved to be easier to load for and with bullets in the 130 to 140 gr range, Retumbo and H-50 BMG and any other stick powders in these burn rates worked well.
With the heavy 169.5 gr ULD Wildcat bullets, AA8700 and WC872 are still top choices.
I tested the 338 RUM based 270 Allen Mag extensively and was impressed by its accuracy and performance being able to drive 130 gr bullets easily past 3800 fps and the huge 169.5 gr pills to 3300 fps with top loads.
I also found that this bore size when used with the slower burning powders could even accept more case capacity so I looked at the 7mm RUM case which is roughly 0.100" longer in the case body. WHat I did was simply deepen the chamber of the test rifle to accept the longer case and tested this new prototype 270 Allen Mag. Accuracy stayed the same, well under 2" at 500 yards but I gained at least a 100 fps with all bullet weights. The 130s could be driven to 3900 fps and the big 169.5 gr pills were clipping out at +3400 fps.
The best part is that a 7mm RUM case is vastly easy to form into the 270 Allen Mag compared to the 338 RUM. Also there is no annealing really needed after fireforming these brass.
This pic shows a fireformed 257 Allen Mag(left), original 270 Allen Mag prototype(center) and production 270 Allen Mag(right). You can see the increased length of the final form of the 270 Allen Mag.
This is the original 270 Allen Mag test rifle with its unfinished stock and barrel.
This is the same rifle but with the chamber opened up to the longer 7mm RUM version of the 270 Allen Mag with a Laminated wood stock much more suited to big game hunting and the rifle finished properly. Very classy looking rifle, can hardly tell its a Savage!!!
Here is a oic of the big 169.5 gr ULD RBBT Wildcat Bullets. With a b.c. of .740 they are the highest ballistically performing 270 bullet out there. They are built on a heavy tapered jacket designed for use on deer size game for big game hunting.
This certainly is not what the rifle will average but it clearly shows the potential of what this round will do even at the extremes of performance.
I do not have the loading dies for the Allen Mags yet. Redding is in the process of buiding them and they tell me I will have them by mid to late May. We will see.
If you have any other questions let me know and I will do my best to answer them on this round.