The 7mm Fatso - The Ultimate Short Magnum! By Greg Duley

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The short magnum craze has taken the gun world by storm, with most manufacturers now producing rifles and ammunition for these cartridges. Based on the old British medium bore African cartridge, the 404 Jeffrey, these modern beltless cartridge designs are supposed to give you 2.5 inch case length medium magnum ballistics out of a short action, compact and lightweight hunting rifle. In factory ammunition they achieve this goal by loading the short magnums to higher pressures or by using the latest progressive burning powders. Handloading ammunition to the same pressure with the same powders in the same barrel length, the 7mm SAUM falls 100 fps short of the 1962 vintage 7mm Remington Magnum while the 7mm WSM drops about 50 fps short. When comparing the 300 short magnums with the 300 Winchester Magnum, they fall further behind due to the 300 WM’s 2.62 inch case length, which is longer than the other medium magnum's.Read More...
This is a thread for discussion of the article, The 7mm Fatso - The Ultimate Short Magnum!, By Greg Duley. Here you can ask questions or make comments about the article.
 
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JeffVN

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This cartridge sounds incredible!

I have to admit that I would not have signed on to build such a beast if I had been the one trying to create the cases. The new 338 Norma Mag cases should speed up the process, but its still huge amount of work.

JeffVN
 

liltank

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So when you going into production on this rifle caliber. I like everything you had to say about. Granted it looks like a pain staking process that I don't have the machinery for, but looks like and excellent caliber. I am looking into building a short mag off of the 300wsm and mounting a 180 grn. 7mm. This is suppose to be efficiency at its best, but I like what I just read. Let us know how the Norma's work.

Tank
 

NZ Longranger

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We designed the first Fatso 5 years and built the first one 3 1/2 years ago now. Don't know much about the short 7mm Lazzeroni or when it was released. I know we're getting significantly better performance than that listed for the 7mm Tomahawk when both are loaded to the same pressures. As far as I'm aware, the Fatso is the ultimate short magnum, unless someone wants to shorten the Cheytac to WSM length, but that wouldn't fit in a lightweight hunting rifle which was the whole purpose of the exercise.
We've built a few now, but wouldn't suggest it to the average gun tinkerer until we've sorted an easier brass solution. Hopefully that's coming in a week or so with the new Norma brass!
Greg
 

KIWI AL

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thanks for taking the time to writing another artical Greg, and updating those of us who already knew of the round.
with that new norma round brass do you think the standard extractor will be ok?
cheers
 

NZ Longranger

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thanks for taking the time to writing another artical Greg, and updating those of us who already knew of the round.
with that new norma round brass do you think the standard extractor will be ok?
cheers
Not unless you used a factory 338 Lapua Remington for the build, and as that would be a long action it would kind of defeat the purpose. You can use any short action Remington or Model 7, regardless of chambering, but you will still need to fit a Sako type extractor and open the bolt face.
Greg
 

angus-5024

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Great article!! sounds like the perfect high country round round!! I dont have the capabilities to machine the brass so I doubt I'll ever build one, but It's nice to dream. i really enjoyed hearing about all the field testing and hunting. Great article.
 

Boman

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Great article, I really enjoyed the read. I'd be very interested to see how the norma cases workout. I've wanted a short seven for some time now and this might be the ticket. Keep us updated. Thanks
 

Topshot

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Sounds like everyone is waiting for the Norma Brass.

Lets hope that some rifle manufacturer will soon produce a "new" action that has a bolt head and extractor large enough to handle these sort of short fat cartridges.

Just out of interest, why do you think that Norma is producing these new cartridges when there are no rifles currently available to shoot them?
 

corey006

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In your article you claim that the .378 Weatherby is based off .416 Rigby? How did you arrive at this info.

The .378 Weatherby is a belted magnum whereas the .416 has NO belt.?

Very interesting cartridge and article by the way....
 

NZ Longranger

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In your article you claim that the .378 Weatherby is based off .416 Rigby? How did you arrive at this info.

The .378 Weatherby is a belted magnum whereas the .416 has NO belt.?

Very interesting cartridge and article by the way....
Corey,
Absolutely the 378 Weatherby is based on the 416 Rigby. Yes they added a belt and the traditional Weatherby double radius shoulder, but the 416 Rigby case was the inspiration. This is common knowledge.

The 338 Norma brass has been going real well, lasting 20 loads at 65,000psi so far. I haven't been able to kill a case yet. And it has eliminated the expanding and full length turning then necking down again case forming steps. Now it is a simple neck down, shorten, neck turn, anneal and fireform with Shotgun powder.
Greg
 
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