7 wsm vs 7 rsaum-- that is the ?

[buzzgun]

[ 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

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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.......

 

[1doug]

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

 

[uncleB]

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

 

[uncleB]

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

 

[uncleB]

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

 

[uncleB]

[ 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

 

[.25AOD]

[ 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

 

[.25AOD]

[ QUOTE ]
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

[/ QUOTE ]

Take the Nosler #5 manual... average the velocities for the top 3 loads in the .280... then average them for the .280 AI and you see an increase of around 3%. This is right inline with the math supplied for us on this very post (and made famous by John Barnsnes), velocity increases (3%) at 1/4 the increase in capacity (12%). Do it again with the .30-06 AI data, and the .22-250 AI data in the same manual and you'll see the same trend. This data was shot in a lab, using SAAMI pressure specs for the given standard cartridge. You do see slightly more than 3% as bullet weight increases... but it's still around 100fps. Now, given this data it's hard to believe that simply lengthening the throat would enable one to reclaim enough powder capacity to generate AI type gains. I love my AI... and I see significant gains in velocity... but I always tell folks it's because I'm able to shoot the round at higher pressure due to the benefits of AI case design... not because I can fit a little more powder in it. Again, I don't doubt that you see the kind of velocities you do... I just doubt that you're within the same pressure limits, and I doubt that the extra couple of K/PSI really matter in the whole scheme of things. But, I think we should just call a spade a spade and recognize that it takes higher pressure to make stuff go faster out of the same case... regardless of the throat length (within reason). Oh, and what barrel length/make do you shoot in the custom 7WSM with the LONG throat? ~JT

UB: I truly enjoy discussions like this... they're both informative and educational. I appreciate the fact that you read the article I mentioned before responding, and I like the "bottom of the birdcage" line... I ask your permission to use it at work.

 

[buzzgun]

[ QUOTE ]
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

[/ QUOTE ]


Actually, the math is absolute......the formula for potential velocity increase may not be absolute, but the math is either right or wrong.......

I don't doubt that you are seeing the velocity you claim......but I don't believe you are getting there by simply seating the bullt out farther......seating the bullet out farther would actually decrease the internal pressure in the case which would lower velocity.......I suspect you believe that seating the bullet out farther allows you to increase the powder charge.....and, to a certain extent, it does, but I believe you have increased the powder charge beyond the point that would compensate for the longer OAL and you have now increased the pressure to the point that velocity has increased.......