Is (7) RUM really THAT much of a powder "waster"???

[Max Heat]

I fired the 1st dozen rounds out of my new stainless 700 SPS yesterday. But the chrono #s were considerably lower than what I was expecting, and the chrono didn't pick up 4 out of the 12 shots. The 25% increase in powder charge over the standard 7 rem mag just wasn't panning out, in terms of the 10% increase in velocity that would verify the bullets' energy being 25% higher. I shoot the (7mm) 120gr nosler ballistic tips. The powders tested were RL22 (85 to 95gr), and RL25 (90 to 97.5gr). I cleaned and let cool for about 10 minutes after EVERY shot. Interestingly enough though, the barrel never really got more than warm after each shot, compared to how hot the 7mag barrel would get, while burning 25% less powder! And I'm not sure what this means, but when I cleaned after the 1st shot, the brush brought out a bunch of tiny little silver-colored specks, some of which can still be seen laying on various parts of the receiver/action. Is that normal for the 1st time a rifle is fired??

I started with the RL25 rounds, with the top load of 97.5gr producing 3619fps, and that one was the only one where I recall seeing a fireball through the scope. So I really wouldn't expect a higher charge than that to produce any significant gain in velocity. But I AM going to go up to 100gr today, just to see where the velocity actually is, when topped out on RL25.

For the RL22, my hottest load (95gr) failed to register on the chrono. The error# was 9, if I recall correctly. The 92.5gr charge registered 3622, while 90gr registered 3526, pretty much exactly the same as the 7mag does using only 75gr of THE SAME POWDER! I hope somebody can explain that one to me, because I sure in the hell can't figure it out. Today I'm also going to work RL22 up to 100gr, in 1gr increments from 95 to 100.

Originally, I wasn't going to consider trying RL19 in the 7RUM. But that thinking has now changed, considering yesterday's ****-poor results using slower powders. I'm going to try 75gr, which produced 3680 in the 7mag, but WAS too hot for it, at least with the loose HS that it has. I'm also loading up 77.5 and 80gr charges of 19 for the RUM, and see how things go, up to that point.

Yesterday I didn't see jack, in terms of pressure sign. The rem 7RUM takes about 8lbs of force to lift the bolt, if the firing pin spring needs to be cocked, with NO round in the chamber (about the same for the sav 7mag). NONE of the shots that I fired with the RUM yesterday showed ANYTHING above than that. I'll be checking it after EVERY one of today's dozen shots (and again, cleaning after every shot). I want to first come up with a load (or loads) that is/are acceptable to me, in terms of performance. Then I'm going to work towards obtaining the best possible groups.

 

[J E Custom]

Most of today's magnums are over bored and can be considered powder wasters unless the correct
bullet weight and barrel length is used.

The reason for bigger cases is to propel larger bullets faster than with smaller cartriges.

Your velocities are impressive but not as high as can be reached with the big 7mm.

With today's new powders this is achievable with the big cases and longer barrels.

So unless you have a 26"+ barrel you will find that the shorter barrel cannot burn all of the
powder with the light bullets (The silver flakes are unburnt powder).

Today's bullets have problems with velocities much over 3600 ft/sec depending on there type
and construction and in my experance I have found that if a cartrige/rifle combination can
exceed this I increase the bullet weight to slow it down to a reasonable velocity while maintaining
near max pressure and velocity.

For any given cartrige there is an optimum bullet weight that will produce the optimum velocity,
trajectory and energy.

Example: A 7/08 optimum bullet weight would be 120 to 150grains . A 7 Rem Mag would be 140
to 160 grains and the 7 RUMs optimum bullet weight would be 160 to 190 grain bullets to get the
most of the case capacity but would need a 28" or more barrel.

So "waste" is a by product of Big cases with big bullets and long barrels if velocity is one of the
main goals for long range hunting and shooting.

A larger powder charge needs a longer barrel and a heavier bullet to burn more efficiently and
reduce some of the throat erosion related to unburnt powder exiting the barrel.

Look at some of the loading data and you will see the optimum bullet weight for a given cartrige,
that has the best combination of energy at the POI best velocity(Not the fastest) and drop.

Is the 7 RUM nessary ? probably not. but it will do more with heavy bullets than any other factory
7mm.

Just my opinion.

J E CUSTOM

 

[highridge1]

I would be shooting 160's in a 7mm ultra to see the big gains over and 7mm rem.I don't see a point in shooting bullets less the 150 in a 7 ultra it shines with the heavier bullets and reloader 25. But in all bullet weights the 7mm ultra will outperform the 7 mm rem.

 

[Varminator 911]

I don't own a 7 RUM and not likely I ever will. But agree strongly with previous posters. A 120 gn bullet in 7 RUM is a recipe for erratic powder burn and highly variable velocity. Only use for that cartridge in my mind is for 180 or 190 gn Bergers in a long barrel. Much more uniform SD and ES and way better at long range. Even there I'd rather have the 300 RUM with a 230 Berger or the 338 RUM with a 300 Berger. The larger calibers have longer barrel life and with even higher BC, heavier bullets, more downrange killing power.

 

[Lefty7mmstw]

like the others said, use a 140 or 150 as the minimum weight for the 7rum. I shot out 1 with 95 rl25 and a 140 sierra doing 3500 fps even. I know of one doing nearly 3500 fps with a 150(my brothers rifle with retumbo). Don't play with light bullets in the 7rum, stay to mid or heavy.
If you really want to see what your top speed is, though, try aa8700 or similar. I got a 120 sierra to 4000 fps with it, but the groups were mediocre. I just wouldn't shoot anything worth eating with a 120 in a 7rum.