7mm UM Loads

[Mike Liane]

I'm looking for some ideas on load development for a 7mmUM in a 700 Sendero with a factory stainless flutted barrel. I'm thinking of starting out with the 162 A-Max. I picked up some Retumbo. Has this powder turned out to be the optimum for this caliber? I know there were some delays in it's release last year. I am willing to compromise and sacrifice a little speed if it will mean a longer throat life, but I want to play at 1000 yards or slightly more. I won't use it much beyond prarie dogs or coyotes. Should it have a run at the lands? I've heard of problems seating too close to the lands and a short run. Any tips that may speed up my load development would be appreciated. Mike.

 

[Al8095]

Well this probably won't be much help but I shoot a sendero 7mm ultra also. I have only been shooting for about 6 months so I am no professional, also I have been shooting different bullets. I have been shooting 160gr sierra gamekings with Retumbo at .010 off the lands. I have only shot about 80 of them and loads with only 89 grains have shot better than the faster loads. I can shoot a 6 inch group at 500 yds with them. I just got some 168 matchkings I'll be trying now. I'm still searching for a good load too, I may want to try the A-max also.

 

[dwm]

FYI, Hodgdon publishes an annual reloading manual for about $12. The 2004 version has loads for almost all of the new Ultra/WSM versions. For a 7MM RUM with a 24 inch barrel and 162 AMAX using Retumbo as a powder it shows:

Start: 89 GR - 3009 fps (162 Hornady Spire Point)
Max: 95 GR - 3223 fps

The AMAX likes to be seated into the lands. I would use a Stoney Point seating depth gauge, a magic marker, smoke from a candle or whatever works for you and find a seating depth of ~0.005 into the lands for your chamber.

Then I would start with loads using 89 grains of Retumbo and work up using the ladder method. (You can find the ladder method on this web site by doing a search.)

My 7MM RUM is doing quite well with 92.5 grains Retumbo and Federal Gold Match 215 Magnum primers.

Yours may be different so start low and work up, especially if you seat them into the lands.

Doug

[ 03-29-2004: Message edited by: dwm ]

 

[dbhostler]

I too am shooting the same rifle. For high speed I load 140gr NBTs at 3500fps with I-7828. Have just begun to load for 162 A-Max. My SF Sendero doesn't like 168 SMKs at all. Want to load some VLDs too.
db

 

[dwm]

Had some fun at the range last week. Was shooting 168 SMKs at ~3350fps out of my 28 inch - 11 twist 7MM RUM barrel and stuck two in the same hole at 200 yards. There couldn't have been much over .1 to .15 between them. I about went home after that. The third one went about 3/4 inch from the other two. Not to bad for me at 200. Maybe it was the new bubble level I was playing with.

Not to get off topic, the load was 100 grains of WC872/FEDGM215M primers with the 168 SMK into the lands a bit. Again, I would start low and work up to loads like this.

Doug

 

[JustC]

94gr retumbo behind the 162a-max in the same rifle showed us well under .5moa with only a trigger job and a break. We did however collapse a case (caliber specific problem) due to the slow nature of the powder and the overbore case coupled with HUGE factory neck diameters. We have considered necking down 300RUM brass to see if that thickens the neck and eliminates this sporadicaly occuring issue.

 

[dwm]

JustC, please explain about the collapsed case. My 7MM RUM has a custom chamber with a tight neck, so maybe I won't see this problem.

Did you guys get some of those Federal 300 RUM cases that were being discussed a couple of weeks ago?

Doug

Sorry for going off topic. Should I have started a new thread?

 

[JustC]

dwm,...you will not see this!!!! My smith has chambered (in his estimate) 40 barrels (with HIS reamer)in this caliber with not one single problem. In his opinion,..the large throat (factory),..coupled with the overbore nature of the case,..and SLOW powders show this exception. The neck of the case just can't expand fast enough to seal,..and some of the gasses are reverted back past the shoulder,..which when the neck does seal,..compresses those trapped gasses,..and they collapse the case. The collapse marks look like you took a pair or vice grips and crimped the case 1/4 way. The collapse marks are ~.3" long and about .25" deep, right at the body/shoulder junction. This has been observed on a buddies sendero as well as a Mcmillan in the smiths shop. The smith has stated that with his reamer,...and the subesquent tighter tolerances,...this is a non-issue. You are good to go,...try the 94gr load at/into the lands with the 162gr a-max. You may find the sweet-spot lower as I am sure your throat is shoeter. But in the sendero,.,..it shot beautifuly.

[ 04-01-2004: Message edited by: JustC ]