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I don't think the slight increase in throat length is responsible for the 150fps gain there... heck, going from standard to AI gets you about 150fps. Furthermore, the VLDs are usually seated into the lands, or very close to them... so the only advantage is not having as much bullet in the case. You think that .25" less bullet can increase case capacity enough to get 150fps... I think not. Increased pressure, twist rate, moly, fast barrel, barrel length, good load... a lot of things could contribute to the extra buck-fifty... but to attribute it to the slightly longer throat would be a real falacy. ~JT
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.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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As I go back and read the article the chamber that was cut with a +.250" lead OVER SAAMI spec was 116fps SLOWER that the SAAMI spec chamber with 180 grain accubonds!! So, in the Nosler Ballistics Lab... the LONGER THROAT WSM was SLOWER with equal weight bullets. Now that being said... the barrel was 2" shorter(The SAAMI barrel was 26" while the +.250" lead [that's the longer throat] was a 24" barrel), so we can knock-off 60-80 fps, and pressure was slightly lower in the +.250" chamber (although by less than 1k psi). By the numbers in this article I think you would be hard pressed to gain 50fps by shooting a longer throated WSM... let alone 150-200!!
By your line of reasoning it would be easy to duplicate the performance of the .280 AI by simply lengthening the throat of a standard 280 Rem. Is this the case?
To quote Chub Eastman at the end of the article: "Theories and logical reasoning sometimes go down the drain when you actually pull the trigger and RECORD THE RESULTS"
Now for those who have shot the longer throated 7mm WSM and achieved higher than normal velocities... I don't doubt that you did. However, those differences can be attributed to other factors like a longer slick custom barrel, VLD style bullets and such. But, more than likely it's attributed to higher than standard pressure. It's tough to argue with the Ohler Model 83 in a very reputable ballistics lab.
For those interested in the article it is on page 60 of the May 2005 issue of "Rifle" magazine and is titled "3 Inch, .300 WSM". ~JT