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# 7 wsm vs 7 rsaum-- that is the ?

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#15
05-18-2007, 10:14 AM
 Silver Member Join Date: Aug 2006 Posts: 164
Re: 7 wsm vs 7 rsaum-- that is the ?

[ QUOTE ]

.25AOD,
I dont mean to flame you on your two posts, but you could not be more wrong if you went out of your way to try.
The longer throat is exactly what gives this round its added velocity.
In my opinion the problem with WSM and SAUM is that the SAAMI spec O.A.L. is very short so your bullet is taking up a great deal of powder capacity, with the chambering that fiftydriver did for me the bullet is not taking up any powder capacity because it is in only the neck. the SAAMI spec O.A.L for a 7WSM is 2.860" the O.A.L. for my chambering is 3.230 making a difference of .370" if you add in bullet diameter of .284" ,that is a lot of powder capacity. I will let some mathematical genius figure out how much.
UB

[/ QUOTE ]

Area of a cylinder= 3.1416 (pi) x radius squared( .284" divided by 2) X length (.370")

A=3.1416 x (.142 x .142) x .370

A= 3.1416 x .02016 x .370

A= .02343 cubic inches ( not accounting for the boat tail which reduces the area......in other words, a boat tail bullet doesn't displace as much powder capacity as a flat base bullet).....

If bore size, bullet weight and pressure are constant, potential velocity increase varies at one fourth the percentage change of the case capacity.

To precisely figure the potential velocity increase, we would need the capacity of the WSM case with the bullet seated at 2.860" and at 3.23".....

However, we can do some rough calculations and gain some insight......if you divide the base velocity (let's say 3000 fps) by the reported velocity increase (150 fps), you get .05% velocity increase......plug that into the formula and we can determine that, with everything else being equal, you would need to increase the case capacity by 20% to achieve the 150fps increase in velocity......does seating your bullet out an additional .37" results in a 20% increase in case capacity?? If not, then your velocity increase can't be credited solely to the longer OAL.......
#16
05-18-2007, 06:47 PM
 Gold Member Join Date: Feb 2005 Posts: 628
Re: 7 wsm vs 7 rsaum-- that is the ?

Theres a lot of guys pushing the 180 bergers @ 3000 fps out of a standard( not a 7-270 wsm) 7 wsm in 26 inch barrels.

uncle B's 2895 is a accurite statement since the 300 and 270 wsm are @ .100 shorter to the shoulder than the 7mm wsm.

d-a
#17
05-18-2007, 07:36 PM
 Gold Member Join Date: Aug 2005 Posts: 558
Re: 7 wsm vs 7 rsaum-- that is the ?

25AOD,
I scoured the internet and found the article you refered to.
Chub Eastman is as respected as anyone you will find in the industry, with that said this article and the data that it provided is little more than a liner for the bottom of a bird cage they used 2 different barrels 2 different throat lengths 2 different barrel lengths and the same load for all.and they only changed the OAL .180".
the only valid point you have is "custom barrel" yes it does make a difference.
UB
ps no you wont get the AI effect from a 280Remington long throat because the bullet does not go nearly as far past the neck as it does with a 7WSM
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#18
05-18-2007, 08:10 PM
 Gold Member Join Date: Aug 2005 Posts: 558
Re: 7 wsm vs 7 rsaum-- that is the ?

buzzgun,
awesome work, this is exactly what I was looking for. mathematical equasions are great for forming a solid basis and are essential, but on the otherhand they are not absolute and do not account for variables such as efficiency and other factors. (most AI cases claim 150fps velocity increase and the case capacity is only increased from 8 to 12%). the bottom line is you have to study things out ballisticly,mathematicly then go shoot it through a chronograph to filter out the feces.
UB
__________________
Attitude:
It takes 43 muscle's to frown and 17 to smile, but only 3 for proper trigger pull.
#19
05-18-2007, 08:20 PM
 Gold Member Join Date: Aug 2005 Posts: 558
Re: 7 wsm vs 7 rsaum-- that is the ?

remingtonman_25_06,
I wanted to try the 168gr VLD but they have waaaaay too short of a bearing surface for my chamber, in a stock chamber Walt is right try the 168 first.
UB
__________________
Attitude:
It takes 43 muscle's to frown and 17 to smile, but only 3 for proper trigger pull.
#20
05-18-2007, 08:22 PM
 Gold Member Join Date: Aug 2005 Posts: 558
Re: 7 wsm vs 7 rsaum-- that is the ?

[ QUOTE ]
Theres a lot of guys pushing the 180 bergers @ 3000 fps out of a standard( not a 7-270 wsm) 7 wsm in 26 inch barrels.

uncle B's 2895 is a accurite statement since the 300 and 270 wsm are @ .100 shorter to the shoulder than the 7mm wsm.

d-a

[/ QUOTE ]
thanks,
UB
__________________
Attitude:
It takes 43 muscle's to frown and 17 to smile, but only 3 for proper trigger pull.
#21
05-18-2007, 10:46 PM
 Silver Member Join Date: Feb 2007 Location: Northern CO Posts: 142
Re: 7 wsm vs 7 rsaum-- that is the ?

[ QUOTE ]
ps no you wont get the AI effect from a 280Remington long throat because the bullet does not go nearly as far past the neck as it does with a 7WSM

[/ QUOTE ]

Yeah, I could see how that extra .1" in neck length could make 150fps difference... whatever.

It's higher pressure, period. The brass may not show it... but a pezzo would, I guarantee it. Higher than standard velocity = higher than standard pressure. I'm guilty of it too, I know I shoot my .25-06 AI at higher pressure than I could get away with in a standard case... that's one of the benefits on minimal taper and sharp shoulders. But I don't attribute the gain to simply larger case capacity... I know my AI is running in the 65K PSI range. It has to in order to gain the velocity. The math is above, and you read the article... yet you would rather nit-pick and insist that .03 cubic inches of case capacity (that's a generous .5" lead!) will make 150fps difference in performance. I think you're under too much PRESSURE! ~JT
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