Well, The weather finally colded down to below 95 degrees today so I headed out early to do a little load testing on the new 7mm Allen Mag.
Just to refresh, here are the specs of the rifle:
26.5" Shilen 1-9 6 groove stainless barrel
Fully accurized Rem 700
Fajen thumbhole sporter stock(pillared)
Holland Comp recoil Lug
Holland QD Muzzle Break
Gre Tan striker assembly
Weaver 4.5-14 Tactical Mil dot
As usual when I start load development for my wildcat rounds I am looking basically to find a working window of loads for a given powder so that I can then use that data in relationship to other powders to develope more load data.
My system is very simple a aggressive. I start a a given starting load and increase one grain for each test load until I reach roughly 105% load density.
My goal here is to find the load where the primer pockets just begin to loosen up and then I reduce the load appropriately to establish a working max pressure load for that combination of componants.
For the 7mm Allen Mag test I was using the 160 gr Accubond with a Fed-215 and AA8700. Basically because there is plenty of load data for this powder for the 7mm RUM which I used near top loads as a starting load for my Allen Mag.
I started at 100.0 gr and added one grain to each load until I reached 113.0 gr. Here are the results. Temps were in the 75 degree range.
100.0 gr............3255 fps Oily barrel
101.0 gr............3200 fps
102.0 gr............3231 fps
103.0 gr............3260 fps
104.0 gr............3323 fps
105.0 gr............3361 fps
106.0 gr............3426 fps
107.0 gr............3465 fps
108.0 gr............3427 fps ??
109.0 gr............3563 fps
110.0-113.0.........Did Not test
I learned several thing from this test, the first is that in the 107 gr to 108 gr range, there was just the slightest hint of the case being a bit sticky on extraction.
At 109.0 gr the bolt handle had to be lightly tapped to extract the case.
From this I feel that around 3480 to 3500 fps is the maximum velocity potential with this round and bullet in a 26.5" barrel. I was very curious to see what the primer pockets felt like when repriming the case so I ran back to the house and resized and reprimed the case.
There was not a loose case in the bunch!!! Even the 3563 fps load was new case tight!!
This is something I am not used to with the other Allen Mag as any of them would have blown primer pockets with this tight of a case. Of course this is why the stout 338 Lapua case was used for the parent case, almost exclusively for the strength of the case design.
It should also be noted that with every one of the other Allen Magnum rounds that were tested before I had the Full Length sizing dies topped out in what I though was high pressure several grains before what a full length sized case would produce.
For example, in the 270 Allen Mag with once fired brass only neck sized, 100.0 gr of WC872(3270 fps) is the max load and case extraction is slightly sticky. With a partially full length sized case, I am able to load up to 103.0 gr (3396 fps) with actually easier case extraction then at the neck sized 100.0 gr load.
The reason is because these case designs are so min taper in the case body.
Often I can take a once fired, neck sized case and chamber it in a rifle and then eject it without firing and it to is slightly sticky in the chamber. When the case is partially full length sized though it falls out of the chamber.
So what does this mean, well, if the 7mm Allen Mag holds true to the behavior of the rest of its siblings, the 3563 fps load should be totally usible once the Redding Full length sizing dies arrive which should be any time. We will have to wait and see??
I also realized that 8700 is slightly fast in burn rate for this bullet weight and case capacity as I was only about 90% load density at the 107-108 gr load range. This is certainly very quality load density and should be extremely consistant but I suspect WC872 will offer the 100 to 102% load density I love to get with slightly less pressures and equal velocity.
So how does this compare to other big 7mm rounds. Well the 7mm RUM has printed load data in the 3200-3300 fps range with this bullet weight in a 26" barrel. Actual chrono testing I have done results in very similiar top end performance.
Even if I have to use the 107.0 gr load at 3465 fps, basically we are dealing with +150 fps advantage over the 7mm RUM in a case that is only 2.700" in length!!!
Running some numbers real quick makes me think that very near 3200 fps may be reachable in this 26.5" barrel!!! Not to mention a much longer and much faster 3 groove Lilja at 30"!!
Lazzeroni lists his 7.21 Firebird at 3500 fps with this bullet weight in a 27" 1-12" twist barrel but I have yet to see a rifle not built by Lazzeroni and not using his specially undersized bullets in slow twist barrels come within 75 to 100 fps of his printed velocity results.
This would put the 7mm Allen Mag roughly 75 to 100 fps over the Firebird in performance which is exactly what we were expecting to get. This holds true as the Sako 7.62 Warbird rifle we have ran roughly 75 fps faster then the 300 RUM in same length barrels.
This matches the performance of the 7mm RUM compared to the 7.21 Firebird as well.
Taking into account that this rifle right now is throated so that the 160 gr Accubond loaded round has an Over All Length of only 3.595" and that production rifles will be throated to allow the selected bullet of choice to be loaded to 3.650 to 3.700" oal, we will gain even more performance. Not much really but more.
I will next be testing WC872 with this bullet weight and see how it compares to 8700 in velocity and pressure.
Then it will be onto the 140 gr Accubond for some +22-250 Rem velocites with a 140 gr bullet!!! Looking to push the 3800 fps range with this bullet in this barrel length. We will see. AA8700 may be the powder of choice for this bullet. Slightly quick burning for the 160 gr bullets, so should be a great match for the 140-150 gr class bullets.
I am also getting in some 175 gr bullets for testing as well with WC872 as this bullet weight is where the 7mm Allen Magnum should really start to perform well.
I was happy with accuracy today. Shot the 10 test shots into two, 5 shot groups which measured 3/4" and right at 1" for each with three shots in the first going into 3/8" and 4 shots in the second going into the .4"s. Not bad considering the very light barrel and all loads being different.
Will report more soon when I get the data.
Kirby Allen(50)
