This is very interesting!! I must admit that I have never seen any EVIDENCE of excessive presures in my 7mm Rem. Mag., and since I get at least 10 relodings out of my cases, all I can conclude is that my loads have proven safe, THUS FAR, for about 36 years!! So, I have no intention of making a 7X57 out of my 7 Mag.!! I will admit that the pressures may be swinging back and forth as much as 10,000 PSI, but the accuracy I get from my loads mitigates against it! (1" @ 200 yards!!) When my No.1B in 7 Mag. blows up, I'll start using my 1A in 7X57 exclusively (if I survive the blast!!) Life is just a crap-shoot anyway, and I believe I am in a lot more danger driving to and from the range than when I'm on the firing line shooting 3000 FPS 175-grain loads from the 7 Mag.!!

I ain't gonna go there with the 7-mag thing. It is for those way beyond my meager means & abilities to explore such matters.
Where I will put my $0.02 in, is on the matter of Chronographs. The Mags and factory ammo aren't necessarily alone, when it comes to busted myths about optomistic velocities. I have been the one to burst some bubbles (sometimes reluctantly) about this or that pet load. I have seen skepticisim that would rival any. Some refuse to believe the chronograph, others act like I set out to personally hurt their feelings.
Just last year, a close friend ran his favorite '06, Nos165grBT load over my chrony. It is a load worked up by another friend, that "booked" 3100+ out of his #1. I told him beforehand, that I did't think he was anywhere close to that. I also told him that it didn't matter one whit, because he has used this load, with complete satisfaction, for years.
Well, the load barely broke 2900fps. You'da thought I had kicked his dog! I told him that the truckload of whitetails he has killed with it verified it was a great load. He finally understood, but was still kinda "swole" about it.
Now, I try to do all my chrono'ing by myself!

The 7mm Rem. Mag. can easily out-perform the .280 Ackley if you have a good rifle and work up proper handloads, or even shoot Federal High-Energy factory ammunition. CASE CAPACITY STILL COUNTS! It can also equal the performance of the 7mm Weatherby. It's not as forgiving or consistent a cartridge to work with as, for example, the .300 Winchester, and sloppy handloading practices will catch up to you quicker with this cartridge than most others. And that's really the reason that I've gone to the .300 Win. Mag. over the last dozen years as my go-to, flat-shooting, all-around rifle over the 7mm Rem. Mag. The .300's just more consistent, more forgiving, easier to load for, and more predicatable. It hits stuff harder as well.

There is a WIDE disparity between various 7mm Rem. Mag. rifles in terms of what consitutes a safe and acceptable load, what doesn't, and ultimately the velocity achieved with a given bullet. That's why reloading companies have really throttled-back on published loads for this cartridge over the last twenty-five years.

I had a Remington 700 KS Mountain Rifle from Remington's custom shop that could not get to 3,000 fps. with 150 gr. bullets without showing acute pressure signs. That was the fussiest and worst 7mm Rem. Mag. I've ever owned. On the other had, one of my friends owns a very fine Remington 700 "C" Grade, also with a 24" barrel, and also from Remington's custom shop that'll easily make 3100 fps. with 160 gr. Noslers, and pressure signs are perfectly acceptable. Those two rifles showcase how much variance there is between individual rifles in 7mm Rem. Mag.

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Courtney: Thanks for chiming in with one of the issues with velocities in the 7mm RM. The bean counters at gun factories noticed a long time ago that if you start out with a bigger chamber reamer, you can get more chambers out of it before it wears down too small to make an chamber within specs. They also noticed that you can make a chamber for a belted magnum case REALLY sloppy and big, and still not have a problem with headspace since the belt will hold it back against the bolt face, anyway. Big chambers ALWAYS let even the fattest ammunition chamber, so nobody complains about "them shells won't go in my gun", and big chambers also provide leaway for overly ambitious reloaders who just have to cram in more powder than is judicious. So big, fat, sloppy factory chambers in the 7mm RM have long since become expected. Fat chambers make for less velocity.

On the "flip" side, ammunition manufacturers have become more conservative with virtually all loadings, and the 7mm RM is perhaps the most downloaded of any round. This can partially be blamed on the bean counters, again. They noticed that smaller charges of faster powders can get the same velocity (although less than optimum) as larger charges of slower powder. So they directed the product folks to start using faster powders. Now, in large cases faster powders leave some bit of air space, which is conducive to wider pressure variations. So now, the technicians are brewing loads to bean counter specifications and the nominal velocities have to be held down in order to keep the loads within pressure limitations.

I think a lot of Barsness as a writer, but he conspicuously fails to point out that the "pressure variations" with the 7mm RM don't apply when you fill the case up with the proper speed of slow-burning powder. T'aint no difference in a 7mm RM and a 7/08 or a .243 or a .458 when it comes to the fundamentals of internal ballistics: If you use powders that are faster than optimum your velocities will be limited and your pressures will be more erratic. It's just that with large-capacity rounds like the 7mm RM the bean counters can save more money with too-fast powders.

But as Dutch points out, I think it's scandalous that people would even consider firing a *&%$*@ factory load in a rifle they were serious about!

If anyone thinks there's some universal truth to the notion that the 7mm Rem. Mag. is not significantly faster than the 7X57 with bullets of the same weight, well they're kidding themselves. That's just not true; far from it, in fact.

I have a vintage, completely original and unaltered 1963 Remington 700 (24" barrel) in 7mm Rem. Mag. that provides an honest 3150 fps. with 150 Nosler Partitions, 2930 fps. with 175s, and sub-MOA accuracy with either load. The fastest 7X57 ever turned out will not come close to this kind of velocity, so don't anyone go and kid themselves about what the 7mm Rem. Mag. (or the 7X57) is capable of. Ballistic truths are only as solid as the individual rifle and load in question, but in general, case capacity will rule 'most every time in terms of velocity.

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Allen,
You missed my point. I built my 7x57 for what it is. I wanted a light, easy to shoot, efficient rifle/cartridge. I never held any illusions to try and make it a 7mm Remington Mag. I should have been more clear that my response was tongue in cheek. I've never understood need take a cartridge and then make it something it's not. I'm also not convinced velocity is the be all and end all in evaluating a cartridge. Personally, and within reason, I think caliber ranks down on the list of importance when it comes to successful hunting. It is fun to debate though.

Jeff

I don't worry too much about high velocity wiht the 7Rm..

Mine gets about 3000fps with a 160gr X bullet, about 2900 with a 175gr Partition, and about 3100 with a 140 gr Accubond, although I know for sure that I could increase the velocity of the 140's by about 100-200fps, the 3100 fps gives me the best accuracy, wiht that bullet...

If a load gives me about 3000fps with good accuracy, I'm happy with it..

I'm sure I could step up all the loads for greater velocity, but when I get .5" accuracy from a factory rifle, I usually leave it alone!

I decided to check the actual velocity I was getting with 7mm. I dug up my last 30 rounds of loaded 7mm Magnum and set up my Encore 26" barrel to chrony while finishing the .308 development. 10 were Federal factory rounds, probably 150 grain but as they were in a slip case and not the box I am not certain. Those 10 averaged 2912 with a SD of 27.76. My 20 handloads of 61.0 grains IMR4831 and 150 grain bulk Remington SP produce an average of 2885 and a SD of 23.45. Neither was especially accurate in the Encore but much work needs to be done to get it where I want it and expect I can do better in both accuracy and velocity.
Just a bit more real world data to toss about.