7mm RUM help

[jlvandersnick]

I have a custom 7 rum that I bought on this forum about 2 1/2 years ago. Shooting 85 grns Retumbo and 180 VLDs. According to what I was told when I bought it ...it now has about 150 to 175 rds through it. Recently I started getting one flyer out of a three shot group at 800 yds. The flyer is usually about 12 inches under the other two, which are typically about 3-4 inches apart.

So it seems that I need to tweak the load a little ? ? are there any "usually s" that would apply here. Like "usually if you just move the bullet a little closer to the barrel" or "many times just reducing or increasing the powder charge".

I know some of you guys have a lot of experience with the "big sevens"...any help would be appreciated.

Also, thinking about changing to the new 195 VLDs, how much should I reduce the powder charge from 85 grns retumbo?

 

[dok7mm]

The first thing that comes to mind is consistent neck tension, but there are several possible causes. Need more info to offer any kind of help. Die setup, brass history, loaded neck dia, chamber neck dia, are you annealing?, and change in distance to lands.

 

[jlvandersnick]

The first thing that comes to mind is consistent neck tension, but there are several possible causes. Need more info to offer any kind of help. Die setup, brass history, loaded neck dia, chamber neck dia, are you annealing?, and change in distance to lands.

The purchase came with four plus boxes of loaded rounds. Supposedly, all were once fired brass from the same gun. I could tell that about 10-12 were virgin brass. All remington brass. All that I shot were rounds from the same batch which at first grouped well then started throwing the fliers. Thinking that maybe there was a quality issue with the loads, I then reloaded some of the brass I had shot. still getting fliers I bought some new rem brass and loaded some of them, still the fliers. Not annealing.

Dies are redding competition full size with neck bushing. Bushing size allows for bullet to expand the neck about .002 about 2/3 of neck getting sized. Concentricity gauge showed minimal variance about 1-3 on most. I sorted the best to shoot groups.

I checked the chamber and throat with stoney point setup. Seating depth is into the lands just a few thousands. I didn't change anything from the original loads. Set and confirm seating depth with collet.

I guess I was thinking the throat had been burned out some. Seller said velocity was 3350, although my crony reads about 3200....but my crony isn't what I'd call "quality". I did discover that Seller was "less than honest" about several things. So can't confirm round count with certainty....and some of the loads included with gun were of very poor quality...split necks etc. I do know I'd would never deal with this particular seller again.

I have two other long rangers (25-06 and 7mm mag) that will shoot consistently under .5 out to 1000. I shoot mostly at 800 for convenience. But I am definitely not what I'd call an expert..... I got into the long range game about 2 1/2 years ago, but have been reloading for about 15 years.....
any thoughts appreciated. Thanks

 

[dok7mm]

If you are in the lands on a 7RUM, it is definitely a custom chamber/throat. Most have a .300 to .500 freebore to deal with high pressure. I recently worked up loads in my son's rifle. Used Berger 168 Hybrids to deal with the long jump. Main problem I had was having to size neck from .322 (fired nk dia) to .313 (loaded nk w/ .002 tension). Neck sizing in one step gave very erratic neck tension and large ES on velocity. Changed to using .317 bushing and then a .313 bushing and problem solved. 90.5 gr retumbo w/ 168 berger classic hybrid @ 3188fps and 9 SD, 1/2 moa. Seating into lands, consistant CBTO measurement of your loads is critical to accuracy as pressure can change dramatically. Without knowing everything about your set-up, I can't say for sure what the problem is. I would give the bullet some jump to start with and perhaps do my own load work -up. Good luck

 

[jlvandersnick]

If you are in the lands on a 7RUM, it is definitely a custom chamber/throat. Most have a .300 to .500 freebore to deal with high pressure. I recently worked up loads in my son's rifle. Used Berger 168 Hybrids to deal with the long jump. Main problem I had was having to size neck from .322 (fired nk dia) to .313 (loaded nk w/ .002 tension). Neck sizing in one step gave very erratic neck tension and large ES on velocity. Changed to using .317 bushing and then a .313 bushing and problem solved. 90.5 gr retumbo w/ 168 berger classic hybrid @ 3188fps and 9 SD, 1/2 moa. Seating into lands, consistant CBTO measurement of your loads is critical to accuracy as pressure can change dramatically. Without knowing everything about your set-up, I can't say for sure what the problem is. I would give the bullet some jump to start with and perhaps do my own load work -up. Good luck

thanks for your input. I'll double check everything. thanks again

 

[Lefty7mmstw]

Couple of things here... I wouldn't load a bullet in a 7rum jammed if I had to. There is simply too much case volume for the bore diameter. I load my 7rum with 180 sierra pills and retumbo in rem brass with a 215 lighting the fire. The coal max. is north of 4" and I'm loading at 3.770" coal... I'm getting ~1/2 moa accuracy in a bone stock lss lh rifle at 89 grains of retumbo.

I would look at having your rifle throated to the normal dimensions if you can't back up to a decent jump at your current throating.

A note on the 195; I would hesitate on the 195 berger unless you have an 8" twist barrel. I am using the 195 berger in my 7stw (8"twist Shilen barrel) with rl33... We've shot it in a couple of 9" twist barrels and it didn't fare as well as in my 8" twist barrel.

 

[Doublezranch]

The whole beauty of the RUM can be its freebore. I agree with Lefty that there is no need to be in the lands with all that horsepower. My son Zayne shoots a sendero 7 rum with 190 grain matrix and 102.5 gr of 33. We are off the lands a better part of 50 thou. I would like it to be more but that's where the sweet spot is. One thing I would try, and I'm sorry if someone said this already, but I would shoot a group of 3. Then I would run a dry patch through the barrel. Then I would shoot a round, run a dry patch, shoot, run a patch, then shoot one more. If they all fall into place, then you know it's a fouling problem.

 

[WildRose]

The purchase came with four plus boxes of loaded rounds. Supposedly, all were once fired brass from the same gun. I could tell that about 10-12 were virgin brass. All remington brass. All that I shot were rounds from the same batch which at first grouped well then started throwing the fliers. Thinking that maybe there was a quality issue with the loads, I then reloaded some of the brass I had shot. still getting fliers I bought some new rem brass and loaded some of them, still the fliers. Not annealing.

Dies are redding competition full size with neck bushing. Bushing size allows for bullet to expand the neck about .002 about 2/3 of neck getting sized. Concentricity gauge showed minimal variance about 1-3 on most. I sorted the best to shoot groups.

I checked the chamber and throat with stoney point setup. Seating depth is into the lands just a few thousands. I didn't change anything from the original loads. Set and confirm seating depth with collet.

I guess I was thinking the throat had been burned out some. Seller said velocity was 3350, although my crony reads about 3200....but my crony isn't what I'd call "quality". I did discover that Seller was "less than honest" about several things. So can't confirm round count with certainty....and some of the loads included with gun were of very poor quality...split necks etc. I do know I'd would never deal with this particular seller again.

I have two other long rangers (25-06 and 7mm mag) that will shoot consistently under .5 out to 1000. I shoot mostly at 800 for convenience. But I am definitely not what I'd call an expert..... I got into the long range game about 2 1/2 years ago, but have been reloading for about 15 years.....
any thoughts appreciated. Thanks

If I were you I'd start with a thorough, and I do mean thorough cleaning and having a good gunsmith give it a look with a borescope since you have apparently good reason to suspect it's had more rounds down the pipe than the seller told you.

Anyone buying a used overbore barrel eater like the 7mm Rum should make the sale contingent upon such an inspection.

Have the inspection done by the seller at your expense and have the gunsmith provide pictures.

 

[bdpayne2000]

If I were you I'd start with a thorough, and I do mean thorough cleaning and having a good gunsmith give it a look with a borescope since you have apparently good reason to suspect it's had more rounds down the pipe than the seller told you.

Anyone buying a used overbore barrel eater like the 7mm Rum should make the sale contingent upon such an inspection.

Have the inspection done by the seller at your expense and have the gunsmith provide pictures.

I agree with Wildrose. In addition I had a buddy with same gun in 300 Rum that exhibited same behavior and the fix for him was action torque tightening. I can't remember the spec but it seemed pretty high to me. Fixed his.

 

[drags]

A top long range gunsmith told me that the 7mm RUM is good for about 700 rounds, but he really liked it for long range hunting. I agree with Wild Rose and with a factory barrel they tend to foul more than a custom. Even if you clean it real good it will foul quickly, my guess is that the barrel has more rounds than stated and is probably shot out or near being shot out.
Joe

 

[jlvandersnick]

A top long range gunsmith told me that the 7mm RUM is good for about 700 rounds, but he really liked it for long range hunting. I agree with Wild Rose and with a factory barrel they tend to foul more than a custom. Even if you clean it real good it will foul quickly, my guess is that the barrel has more rounds than stated and is probably shot out or near being shot out.
Joe

that's what I was thinking

thank you all for your input