Home Forums Hunting & Shooting Ask The Gunwriters Mule Deer 7mm Remington Magnum

69 grains Reloader 26 and a 162 ELDX gets really close to 3k out of my Tikka.

The 7mm Weatherby has similar case capacity. How’s the pressure variations with that cartridge? I’m guessing it’s not a problem, but it’s only a guess.

I never had an issue with my 700 7mm RM, by the way. But I’m not into maximum velocities in my rifles, prefer instead to get tiniest groups, even with the rifles meant for large game.

Good morning to you. I don't shoot 7mm RM but this I an interesting thread.

I would think that there were/are things that were/are correlated with these unpredictable pressure readings that a consumer can leverage.
1.) Are the issues more prevalent with heavy for caliber bullets? eg. are there pressure issues seen in, let's say, 140gr bullets not seen in 175gr bullets or vice versa?
2.) How about bullet form factors? Were more problems seen with boat tail bullets vs. flat based bullets? How 'bout bullets with the lead core exposed ( like a Partition ) vs an Interlock? Perhaps bearing surface plays into this?
3.) Are powder burn rates, within a bullet weight, mitigating factors? For example, a relatively fast burn rate powder for a given bullet weight vs a relatively slow burn rate powder.
4.) Seating depth considerations? How much free bore is given to a particular bullet? Does this matter?
5.) Your last paragraph is interesting. Obviously design spec's for the 7mm Rem Mag are not going to change but it looks like there are some things with this cartridge not well understood.

I may have to go out and buy a 7mm Rem Mag just to set up some DOE (Design Of Experiments) whereby an ANOVA ( Analysis Of Variance ) will shed some light on this...... nope I'll stick with my Boomer/Fudd 30-06, 270 WCF, and 6.5x55 cartridges.

Good point re the Weatherby Mag.

Pretty sure it's not a case capacity issue. I'm to lazy to look it up, but I assume the 7mm WM has a longer neck, I know it has a different shoulder angle/shape.

A few more comments:

First, SAAMI lists three piezo pressures for rifle cartridges. The one most handloaders pay attention to (if they pay attention to SAAMI specifications at all) is Maximum Average Pressure, or MAP.

The other two are Maximum Probable Lot Mean (MPLM) and Maximum Probable Sample Mean (MPLSM), which basically indicate the variations in pressure.

The concern about the pressure variations in the 7mm RM involved the possibility of individual rounds exceeding what are considered "safe" pressures. These tend to be somewhat on the conservative side, because that was one of SAAMI's original intentions when it was organized in 1927, to make sure all commercial ammunition of a certain type/designation would be safe to fire in any commercial rifle chambered for that round.

Before then, ammo and firearms manufacturers basically made what they wanted to, so there were variations not just in pressures but dimensions of factory ammo and chambers. (Here it should be noted that adhering to SAAMI specifications is NOT mandatory for members, but voluntary. There's still occasional "experimenting" by members, though not nearly as much as there was before 1927.)

The SAAMI MAP for every commercial American 7mm "magnum" cartridge EXCEPT the 7mm Remington Magnum is 65,000 PSI--which is the maximum MAP allowed for any cartridge by SAAMI. The MAP for the 7mm RM is 61,000--due to the wide variations seen when piezo testing started becoming the industry standard. (It should also be pointed out that these variations also included individual rounds with considerably LOWER pressures, but obviously SAAMI wasn't concerned about those.)

The 7mm Weatherby Magnum doesn't show the same pressure variations as the Remington round, even though it has a very similar shape and powder capacity. This is probably due to the Weatherby "freebore," essentially a longer-than-average chamber throat, which tends to "flatten" the pressure curve, resulting in less variation in pressures.

But the other commercial American 7mm magnum rounds that also have a MAP of 65,000 PSI include the 7mm Remington Ultra Magnum, 7mm Short Action Ultra Magnum, 7mm Shooting Times Westerner and 7mm Winchester Short Magnum. You can look at the chamber drawings on the SAAMI site to find variations in throat dimensions to see if you can "solve" this pressure-variation mystery, but it has been well-documented for around half a century. (Here's a link to that part of the SAAMI site: https://saami.org/wp-content/upload...CFR-Approved-2015-12-14-Posting-Copy.pdf)

I will also note that one of the many pressure-lab people I've interviewed over the years, the head pressure guy at a major American ammo company, said the .243 Winchester shows the same sort of wide pressure variations--but only with heavier bullets, in the 100+ grain range, not with lighter bullets. In fact, he also said more .243 barrels have been "blown off" pressure-lab receivers during testing than with any other cartridge.

Well if it easy to figure out…

Short necks like on the 350 RM and 300 Savage don’t seem to cause a pressure problem. Sharp shoulders on various cartridges don’t seem to be an issue.

Why the 243 and not the 22-250 or the 6.5 C. or the 260 Rem? (I always knew the 6mm was a better cartridge than the 243 by the way .)

Sometimes trial and error is the solution.

The test lab at Illion, shot bushel baskets of 350 Rem Mag before Remington released that cartridge. I wonder what tests are run on rifles chambered with cartridges being released in general.

One case characteristic the .243 Winchester and 7mm Remington Magnum share is a shoulder angle which, combined with their short necks, concentrates hot powder gas in front of the case mouth--where it causes quicker throat erosion than most other rifle cartridges, including the 6mm Remington, which has both a steeper shoulder and longer neck than the .243.

And contrary to what many shooters believe, the early stages of throat erosion tend to INCREASE pressure, instead of reducing it, due to the rougher throat. This has been demonstrated many times in piezo labs.

OK ..... since MV is a function of the pressure curve, are the hand-loaders out there reporting more MV variation when working up a load?

BTW here is a good thread from a few years back on this topic.

https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/1662047/1

Yeah, there has been a bunch of "discussion" on this subject before. Which proves nothing about actual pressures--because it often involves stuff like primer flattening, which has been proven many times to be pretty much irrelevant--unless a primer blows.


Bugger, I don't know why you might believe cases like the .300 Savage and .350 Remington Magnum might apply to "magnum" of much larger powder capacity with much smaller bores.

Throat a 7MM RM so it can breath. This has worked in every single one I’ve done that in. Velocities are where they are expected to be. ES and SD’s are good. Case life is good and accuracy is exceptional.

Strange thread because the 7mm as the 7mm Rem Mag is pretty proven.

I had good luck with it.

Grizzly at 620 yds.



Elk at 350 going away.



Bull @ 800yds single shot.



7MM is a good caliber and when loaded in the Rem version it pretty close to the best big game round.

That said I prefer a 1/2 MM less diameter if given a choice but I can make the 7MM work pretty well.

I could never understand how long range hunters prefer 6.5’s while long range guys that shoot for score pick 7’s.

Interesting... back in 1986 I traded for a BAR in 7 RM with a Leupold scope. It was a special order that was never picked up by the client. I commenced handloading for it right away using mostly 150s, but also some 175s. I didn't yet own a chronograph but used book loads. It appeared to me that the "book loads" I'd gotten from RIFLE magazine, that was used in a 7 RM BAR, were overly "hot". The ejected brass was literally so hot that I coldn't pick them up with bare hands! But far worse was the fact that all fired cases didn't need resizing as the necks had never expanded!

In reading the lengthy article in RIFLE on the BAR in 7 RM, the author (don't recall his name) had the same experience with "his" BAR, or the one being tested! He went on to explain in some detail that it was a common fault with early made 7 Rem Mags (not only in the BAR) due to different spec reamers being used in manufacture. From that he said SAAMI reduced MAP for the 7 RM. I recall the article well... anyway I returned the rifle to the dealer and he gave me a new .300 Win Mag M70, + the best scope he had in return.

Since that experience, I purchased my first chronograph and have never been without one since. But I've also owned a few more 7 Rem Mags (not semis), the best of which (in my view) was a Ruger #1 with a 26" barrel that would shoot a 175gr Partition right at 3000 fps over a good dose of RL-22. Also, I've owned a Rem Classic in 7 Wby Mag with a 24" that would equal the 26" Ruger #1 in firing 175s at 3000 fps using the same powder.

That's a FWIW.

Bob
www.bigbores.ca

150 NBts in front of 69 gr of RL 26 print groups down in the .4s from my(GASP!) 2019 mode 700 BDL. the handful of Deer and black bear I've taken with it have given me no reason to denigrate it

Yep that's a great load.I shot this group with 69.0grs of Reloader 26 with a 150gr Nosler Ballistic Tip out of my Remington 700 Stainless Steel Long Range 7mag.


67.5grs of Reloader 26 with a 160gr Accubond out of the same rifle was good too.

John,

As I noted, the wider pressure variations with the 7mm RM have been well-established in numerous pressure labs.

That does NOT mean, however, that they occur with every powder and bullet. But it's why the SAAMI MAP is only 62,000 PSI.

John

I've also wondered about this. It must be like the Ford Chevy thing.