7 RUM velocity

[WeiserBucks]

I should be able to get out and start load development this week. I've got a few rounds loaded with H1000 and Retumbo. Will be using the 180 hybrid and book loads to start.

My manual shows max velocity under 3000 FPS with a 26" bbl . However, I keep hearing reports of guys getting 3200 . Is that realistic or just people exaggerating? What should I realistically expect?

Running some numbers through a ballistic calculator, looks like anything over 3000 will be pretty impressive.

 

[J E Custom]

I should be able to get out and start load development this week. I've got a few rounds loaded with H1000 and Retumbo. Will be using the 180 hybrid and book loads to start.

My manual shows max velocity under 3000 FPS with a 26" bbl . However, I keep hearing reports of guys getting 3200 . Is that realistic or just people exaggerating? What should I realistically expect?

Running some numbers through a ballistic calculator, looks like anything over 3000 will be pretty impressive.

Depending on barrel length and free bore of loaded cartridge, you should be able to get 3100 ft/sec safely if you use the slowest powders (Like 50 BMG)

The 7mm RUM will really propel the 160 weight bullets and give up very little BC with extremely good trajectory's and velocities.

J E CUSTOM

 

[WeiserBucks]

My bbl is 26" and has more free bore than anything I've ever seen. I have a box of 180 hybrids , a pile of Retumbo and a lb of H1000 so I figured I'd give them a try .

If I'm not successful, I'll move on to lighter bullets first and other powders as a last resort. I hate having rifle specific powder , I like to keep powder on hand that works well with multiple cartridges.

 

[J E Custom]

My bbl is 26" and has more free bore than anything I've ever seen. I have a box of 180 hybrids , a pile of Retumbo and a lb of H1000 so I figured I'd give them a try .

If I'm not successful, I'll move on to lighter bullets first and other powders as a last resort. I hate having rifle specific powder , I like to keep powder on hand that works well with multiple cartridges.

I hear you, but unfortunately most cartridges have a preferred powder and bullet combination
and in order to get the best performance you have to find them. (the reason we re-load)

Large overbore cartridges need to use slow burning powder and long barrels to get maximum velocity. Accuracy Is a different matter, Accuracy in normally obtained somewhere below maximum velocity so the use of faster burning powder may work well.

A 26'' barrel is perfect for most cartridges and can achieve good hunting velocities, But at some point it will not burn all of the powder and efficiency will be lost by seeking more velocity. Also depending on the barrel contour, it may not shoot the heavy bullets well.

Try what you want to but keep this in mind if you run into trouble getting accuracy and velocity.

J E CUSTOM

 

[WeiserBucks]

Good velocity and accuracy are the #1 priority for all my rifles. I don't need to break any velocity records , just watched to get what the cartridge has to offer.

I don't see any reason the RUM shouldn't offer respectable velocity with any bullet used . I also have zero experience with the cartridge at this point , all advice is appreciated.

 

[MudRunner2005]

For what little velocity gain you will get with the RUM, when you rebarrel, you might consider the 7mm STW or .28 Nosler as viable options. They produce nearly identical ballistics as the RUM, but with nearly 20 grains less powder, and much better barrel life.

One my 7mm STW's was built off an old 7RUM Rem 700 CDL action. The RUM would group like a softball at 100 yards. Had a beautiful (and repeatable) pinwheel cold-bore shot, but shots 2 and 3 looked like a few buckshot pellets managed to hit a target at 100 yards...They were completely unpredictable. I had a spare STW heavy barrel sitting in the safe, my smith lives 15 munutes away with a week or 2 turn-around time, so why tolerate poor accuracy, when you can do something about it quickly and inexpensively.

 

[Rich Coyle]

For what little velocity gain you will get with the RUM, when you rebarrel, you might consider the 7mm STW or .28 Nosler as viable options. They produce nearly identical ballistics as the RUM, but with nearly 20 grains less powder, and much better barrel life.

One my 7mm STW's was built off an old 7RUM Rem 700 CDL action. The RUM would group like a softball at 100 yards. Had a beautiful (and repeatable) pinwheel cold-bore shot, but shots 2 and 3 looked like a few buckshot pellets managed to hit a target at 100 yards...They were completely unpredictable. I had a spare STW heavy barrel sitting in the safe, my smith lives 15 munutes away with a week or 2 turn-around time, so why tolerate poor accuracy, when you can do something about it quickly and inexpensively.

I rechambered a 28" barrel 7STW to 7RUM. By trying several powders I gained 25 feet per second. Now that I have some US869 it might get more velocity. But I traded it off so it's too late to try.

 

[Lefty7mmstw]

I should be able to get out and start load development this week. I've got a few rounds loaded with H1000 and Retumbo. Will be using the 180 hybrid and book loads to start.

My manual shows max velocity under 3000 FPS with a 26" bbl . However, I keep hearing reports of guys getting 3200 . Is that realistic or just people exaggerating? What should I realistically expect?

Running some numbers through a ballistic calculator, looks like anything over 3000 will be pretty impressive.

I'm running 3100 fps with my 7rum (lh lss 7rum) using the 180 sierra hpbt and retumbo fired by a 215 in remmy brass... I can look up the charge if you want but it's actually a good bit down from the top load. The load will dump three in an inch at 200 and is so repeatable it's boring. It is a bit longer than mag length but if you want a few in the mag simply sub in the 175 hdy interlock as it shoots the same (poa and accuracy) to 200 and is just as accurate as the 180.

 

[WeiserBucks]

I'll be happy if I can get 3050 or so without too much pressure. If I can get there , I'll let the bullets B.C. do all the work and not be too hard on the brass . Thanks for the advice

 

[Lefty7mmstw]

I'll be happy if I can get 3050 or so without too much pressure. If I can get there , I'll let the bullets B.C. do all the work and not be too hard on the brass . Thanks for the advice

I looked at an ammo box a few minutes ago; it's 89 gr. retumbo... I'm at 3.770" oal with the sierra 180 hpbt, so a bit stretched from normal...

 

[WeiserBucks]

I'm still waiting for the weather to clear! I've got several rounds loaded to mag length as follows:

84-85-86 grains of Retumbo, 3 rounds each

80-81-82 grains of H1000 , 3 rounds each

These are the lower end book loads , I like to start low with any new rifle/ammo combination. For you guys with 7 RUM experience, does the pressure build slowly and predictably like most rounds ? Or does it come on all at once like my STW?

 

[Lefty7mmstw]

I'm still waiting for the weather to clear! I've got several rounds loaded to mag length as follows:

84-85-86 grains of Retumbo, 3 rounds each

80-81-82 grains of H1000 , 3 rounds each

These are the lower end book loads , I like to start low with any new rifle/ammo combination. For you guys with 7 RUM experience, does the pressure build slowly and predictably like most rounds ? Or does it come on all at once like my STW?

It doesn't usually come on fast, but you are right to take it slow on the run up if you aren't that used to your pipe. I've never killed a rum casing (7mm or 300) from an overload, but a few do have mild shiners on the back that have lived past a barrel or two...

As to charge, you likely have a few grains left on the retumbo... I'm not sure on h1000 as I haven't used since I tossed 190-200 grain slugs from my 300win a couple decades ago...

 

[WeiserBucks]

The rifle and cartridge are new to me , not sure what to expect yet . Just trying learn all I can without wasting to much powder and bbl life.

 

[WeiserBucks]

Finally fired the rifle today. Shooting conditions were terrible, the wind was blowing very hard . My Retumbo loads performed much better than the H1000 loads . Both shot right at 1" , which isn't bad considering the 30+ mph winds.

The heaviest charge of Retumbo got me 3100 fps with an ES of 9. No pressure signs at all , I'll continue testing this load in better conditions. Hopefully it will be a good combination of accuracy, velocity and brass life. I think I could push it much harder, but I'm not going to.

All 3 different charges of H1000 were under 2900 fps, I'm not going to pursue this powder any longer.