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Discussion in 'Long Range Hunting & Shooting' started by bjlooper, Oct 24, 2007.
What is the advantage of the 7mm AM over the 7mm RUM???
My first guess would be the brass quality as the 7mmAllen mag uses 338 Lapua brass unless I'm mistaken , if it is what I'm thinking about as far as the case shape then the 7mmAllen mag will probably hold more power also. So with the combo of way better brass from Lapua able to handle alot more pressure and the higher case capacity you would be looking at higher speeds with the heavier bullets it was desgined for.
I could be all wrong but from what little bit I have looked into it thats what I remember , call Kirby and ask him and explain what it is your wanting to do
the 7mm AM is 300 fps faster with a 160 gr bullet, and the best part a 7mm AM would be built by kirby Allen, and the guy does something differnt than most smiths, his rifles shoot like a house-a-fire, and are easy to get them to do it.
I own 1/2 dozen full house custom rifles and the 7mm AM was an absolute joy to work with, shoots anything great and the stuff it likes will blow your mind.
I will admit my customers get a bit more out of my 7mm AM then I do simply because I do not load mine all that hot.
Still, The way I load mine, it will do a solid 200 fps more then the 7mm RUM with bullets over 160 grains.
With lighter bullets, the advantage will drop to around 150 fps.
For comparision numbers, this is what my personal 7mm AMs will do with relatively comfortable load levels:
Lightweight 7mm AM, 27" Lilja 1-9, 6 groove barrel:
140 gr Accubond...............3570 fps
160 gr Accubond...............3490 fps
175 gr SMK......................3380 fps
200 gr ULD RBBT...............3200 fps
Heavy 7mm AM, 30" Rock 1-8.7, thin 5R barrel
160 gr Accubond...............3560 fps
200 gr ULD RBBT...............3340 fps
These are top end velocities. My go to load in my light 7mm AM drives the 200 gr ULD RBBT to 3150 fps. In my heavy rifle, its preferred load is the 200 gr ULD RBBT at 3270 fps so just a bit off max in both.
Hope this helps some.
Please realize that there is case forming involved with the 7mm AM and fireforming. I am setting up to offer formed cases for customers in this chambering and should have that up and running this winter so soon that will not be a problem for customers. I can supply the cases or you can send me your virgin 338 Lapua cases to be formed at a cost.
Why is their a difference in FPS in the 7mm AM and the 7mm RUM, when their is almost no diffrence in the 338 edge and the 338 Laupa.
The 7mm RUM and the 338 edge are on the same RUM case, as the 7mm AM and the 338 Lapua are on the same Laupa case.
I'm pretty sure that Kirby's case desgine for the 7mmAllen mag is an improved version with alot less body taper and a more steep shoulder.
It would be more like compairing the 338Lapua to a 338Lapua improved , the improved version holds a bit more powder and is a more effecient so it'll shoot a goods bit faster
I was kind of wondering the same thing. Is the 7mm AM actually a necked down Improved 338 LM version or simply getting higher velocities with higher pressures/better brass. If someone could verify James Jones comment above It would be appreciated.
BJlooper, I believe the 338 edge gets better velocity the the 338 lapua with a 300 smk.
I think that they are about even in terms of velocity
The 7 Allen Magnum is not only necked down but less body taper, the shoulder is moved forward and angled sharper. Then after all of that you get a custom chamber and tough brass to abosrb higher pressure.
With the 200 grain Wildcat bullet at 3340 fps it will blow through a full grown bull elk at 1K like a knife through hot butter
+1 for Kirby! The man is a Rembrandt with rifles!!! He's always exceeded my expectations.
If you load a 338 Edge and a 338 Lapua up to same pressures, they will basically be identical in performance as they are within a grain or two in capacity.
If you load the 7mm RUM and the 7mm-338 Lapua up to the same pressures, again they will be nearly identical in peformance.
Case capacity of the 7mm AM is roughly 8 to 9 grains more then the 7mm RUM or 7mm-338 Lapua. Roughly 10% increase in case capacity.
That in combination with the ability to be loaded to 65,000 to 68,000 psi comfortably is the reason for the increased velocity over the RUM.
what changes do you make to the 338 Laupa case in the 7mm allen mag.
Neck down to 7mm obviously, shoulder is moved forward slightly, shoulder angle is increased singificantly and body taper is reduced to min for that case size for most case capacity yet good extraction characteristics with top pressure loads.
it is quite a difference to sit a 7mm AM, or 300 AX or 338 AX next to their parent 338 Lapua case.