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7mm Ultra

 
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  #15  
Old 05-04-2002, 01:07 AM
Silver Member
 
Join Date: Mar 2002
Location: Southern Illinois
Posts: 397
Re: 7mm Ultra

Len,

I guess I'll give you the long version. It's been quite a ride & hopefully this will save you some of the trials & errors I've dealt with.

When I was deciding on bullets for the 7mm Ultramag (I looked real hard at the STW 1st) I spoke with Walt Berger (Berger Bullets), Jimmie Knox (JLK), & Bob Cauterucio for much needed advice. All are SUPER fine gentlemen, patient, knowledgable & helpful. I can't say enough about each.

Walt ran some RPM figures by me based on estimated velocities & twist rates & readily admitted that his 180 VLDs would be UNlikely to hold together. His bullets are made with very high quality (but very thin) J4 jackets. When my 'smith speced my barrel with Kreiger, they comfirmed it - they'd just had the same idea & the Berger 180s came apart a few yards downrange. I was disappointed because I'd used 70 & 80 grain .224 VLD Bergers almost exclusively in my service rifle for years. Bummer.

I spoke with Jimmie Knox & Bob next. Both make theirs with thicker Sierra jackets. Both hold up fine at 7mm Ultra velocities. If I remember correctly (which is a big MAYBE) Cauterucio 156s were estimated at .690BC & the 176s at .710 or higher. JLK 180s were @ .740 if I recall. That's as close as I can remember, I've slept since then!

These are very long projectiles, the 176s are @ 1.440" with long bearing surfaces to match. Since the Ultra is likely to erode the throat quickly, the length is a plus IMHO to be able to reach the lands prior to re-set.

The thicker jackets are also likely to be a plus for those interested in using them for game - they should hold up well at distance just like a Sierra MK!

I E-mailed back & forth a little with an illustrious member here - Warren Jensen. He has a 162 7mm (.788) that looks intriguing. He also was kind enough to crunch some numbers when asked regarding a theoretical 180 in his state-of-the-art contstruction. He estimates it would be near (gasp) .900 BC!!! It would need a 1:7" twist to stabilize it, but hmmmm........a .900 BC bullet leaving the muzzle at 3,300+ fps....
the possiblities. [img]images/icons/shocked.gif[/img]
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  #16  
Old 06-06-2002, 04:49 PM
Silver Member
 
Join Date: Mar 2002
Location: Southern Illinois
Posts: 397
Re: 7mm Ultra

Correction:

I spoke with Bob Cauterucio today about a different issue, & remembered the BC questions posted here. He said the 156's BC is @ .630-.640 & the 176's is @ .750 ( tested by Obermeyer) above 2,700 fps. Hope this helps.
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  #17  
Old 06-06-2002, 09:09 PM
Junior Member
 
Join Date: Mar 2002
Location: Oregon
Posts: 17
Re: 7mm Ultra

7 ultrmag loads
Has anyone developed accurate long range loads for this cartridge? I' ve heard numerous reports that accuracy does not generally rival that of the 7 STW.
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  #18  
Old 06-06-2002, 09:42 PM
Silver Member
 
Join Date: Mar 2002
Location: Southern Illinois
Posts: 397
Re: 7mm Ultra

Vinne,

I'm in the process of that as we speak. I've plinked @ 1,000... but only shot on paper out to 500. Some preliminary loads went into just over 4". Wind drift, trajectory, & time of flight are impressive - just have to shrink those groups! [img]images/icons/mad.gif[/img]

The 7Ultra isn't as 'efficient' as the STW, IMHO, lots of extra powder for a little gain, but then again you're not messing with a belt either. I have some loaded up for this weekend, weather permitting. [img]images/icons/cool.gif[/img]
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  #19  
Old 06-07-2002, 04:54 AM
daveosok
 
Posts: n/a
Re: 7mm Ultra

I have a STW with a Lilja 34 in 4 groove barrel. Throat errosion hasnt become an issue yet as I have about 500 rnds through it.
I use Berger 180 gr VLD and that is the only thing that will shoot through it. Sierras, Nosler, Hornady, and Speers wont fly at all I get shot gun sized groups when using these bullets. My barrel is a 1:9 twist.
I am getting 3100 fps with the Berger 180 gr at 74.5 grains of H1000, H50BMG is just to big of a powder to get enough in the case to see any improvement over the H1000.
In my case going to the ultra mag may allow me to use just enough H50BMG to get faster fps than the H1000. With the same load of H50BMG (74.5 grs) the fps is 2870 so its a lot lower than the H1000.
The 34 inches of barrel really help with the efficiency of this cartrige.
Ballistics of the 180 gr at 3100 is quite impressive and I still have a lot of load developement left and havnet tried JLK or LRB or GS custom bullets yet.
I have never had a Berger come apart but maybe Im not pushing them fast enough yet.
The lost river bullets in 162 gr Id hate to think what velocity I would get with them if Im pushing the 180 at 3100.
Good thing the barrel is a 1:9 twist or the 162 wouldnt work.
On another note I have a pacnor 40 in barrel with a 1:8 twist designed to use the Lost River 220 gr .930 bc bullet in a 300 ultra widlcat cartridge commonly know on this site as the 300 Tomahawk but I have changed the shoulder angle to 40 degrees and have blown it out about as much as you can go without having problems ejecting it.
It should hold about 130 to 135 grs of water and push the 220 gr at 3300 or better.
If anyone has load data that works in their 1:9 twist barrel for a stw I would appreciate it it you posted it or emailed me the info.
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  #20  
Old 10-16-2003, 07:45 AM
Bronze Member
 
Join Date: Aug 2003
Location: Missouri
Posts: 44
Re: 7mm Ultra

Just returned from Wyoming Got a nice Antelope at 250yds, Mule Deer at 300yds and about 200 Dogs from 50 to 450 yds. Great fun! Shot a 7mm RUM in a rem sendero with a 6.5-20x50 LR Leupold. This rifle shoots 140gr Nosler BT at 3460fps into .3' at 100yds. The Antelope had a 6" entrance wound and no exit wound. The Mulie had a 4" enry wound and a 1" exit wound. Both droped dead in there tracks and just hit the ground.
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