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7mm vs. .30 cal

#8
06-24-2007, 09:10 PM
 Platinum Member Join Date: Apr 2005 Location: Alaska Posts: 4,618
Re: 7mm vs. .30 cal

Yes, Hired Gun has this correct.

We just happened to have this same discussion under the subject Stubby--Lapua in the general discussion forum, where we compared 7mm to 338 velocity. But the explanation is the same for the 7mm and 30 cal. Below I've copied and pasted the explanation from the Stubby--Lapua post.

"if equal pressures (say 60,000 psi) are generated in two different cartridges over an equal duration of time, the force exerted on the base of the bullet with the larger diameter will be greater than the force exerted on the base of the smaller diameter bullet. The area across the base of a 7mm bullet is about 0.0634 square inches. The area across the base of a .338 bullet is about 0.0897 square inches. The pressure generated by the cartridge acts against the base of each bullet. In the case of the 7mm bullet, the 60,000 psi creates a force of (60,000 lbs/square inch) X (0.0634 square inch) = <u>3804</u> lbs of force. With the .338 bullet the 60,000 psi pressure creates a force of (60,000 lbs/square inch) X (0.0897 square inch) = <u>5382</u> lbs of force.

We can see that even though the pressure is equal in each bore, much more force is applied against the base of the .338 bullet than the 7mm bullet, because the force exerted is a function of the area that the pressure is able to act on. And I think we can all agree that the greater the force acting on two bullets of equal weight, the faster the bullet will be accelerated down the bore. Which is why bullets of equal weight will always be driven faster in a larger caliber, provided that the same pressures are maintained over the same length of time. So this has a straightforward explanation."
#9
06-24-2007, 10:35 PM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,426
Re: 7mm vs. .30 cal

Thanks guys.

I knew there was a good reason, I just could not figure it out.

So now the question is how far down range the higher bc 7mm bullet has to travel to make up the differance in muzzle velocity. I wonder how that compares w/ same weight bullets, and with say 160grn accubond 7mm ultra compared to 200grn accubond 300 ultra?

Hopefully I'm not beating a dead horse.

Thanks guys, Steve
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#10
06-24-2007, 10:58 PM
 Gold Member Join Date: Jan 2007 Location: North Idaho Posts: 668
Re: 7mm vs. .30 cal

If your dead set on an ultramag stay away from the 7 ultra. Although on paper it sounds like a great idea in reality it's too much of a good thing. This is coming from a 7mm fan. If you are too stick w/ an ulra get a .300. If your looking for someting different try the 7mm stw. Personally I like the 7rm. One other thing: The higher the velocity the shorter the barrel life.
#11
06-24-2007, 11:10 PM
 Gold Member Join Date: Apr 2006 Location: Alberta Posts: 868
Re: 7mm vs. .30 cal

Hi, just out of curiosity and just not knowing much about the RUM's would you mind elaborating a bit for me.

[ QUOTE ]
If your dead set on an ultramag stay away from the 7 ultra. Although on paper it sounds like a great idea in reality it's too much of a good thing.

[/ QUOTE ]

Tks!
#12
06-24-2007, 11:29 PM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,426
Re: 7mm vs. .30 cal

I'm not set on anything, I just find this stuff facinating.

Steve
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Simply Better

To hunt... or not to hunt...? What a stupid question.

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