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300 wsm case capacity question.

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Old 04-15-2006, 01:16 PM
Bronze Member
Join Date: Dec 2003
Posts: 38
300 wsm case capacity question.

I had pac-nor make a barrell for my savage mbvss in the 300 wsm chamber. My obsevation is and I am new at this is that my loaded cartridge overall length from case bolt face to ogive is now 0.090" shorter than the factory barrel I removed. I no longer have the case capacity that I did have before. I was shooting H4831 @71.5C with the nosler 180 accubond and it shot .4 grps at 100yds. Has anyone run into this situation before? My other question is has any one been shooting the Berger vld bullets in the 300wsm and if so what wieght bullet and powder manufacturer and grains of powder and primer are you using and with what results. The pac-nor barrel I have is the super match 28" polygonal rifling tappering from 1.020" to 1.050" at the muzzle. Thanks for any information you may have.
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Old 04-15-2006, 03:12 PM
Bronze Member
Join Date: Dec 2003
Posts: 38
Re: 300 wsm case capacity question.

Just a correction to what I posted earlier. From case bolt face to ogive is where the bullet is just contacting the rifling and 1.120" to 1.050". Thanks
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Old 04-15-2006, 06:40 PM
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Join Date: Dec 2005
Posts: 2,114
Re: 300 wsm case capacity question.

Case capacity has often been difficult to deal with. And there's several ways it gets measured, too.

For example, a new case at minimum dimensions will have a smaller volume inside than a fired case from a chamber that's at the large limits of specs for the cartridge chamber dimensions. And after the fired case is sized, its insides will have less volume because parts of the case have had their dimensions reduced.

And depending on how case capacity is measured stirs the pot, too. Some folks measure it by filling the case with water all the way to the mouth. Others only fill it to the neck-shoulder junction.

I'm pretty much convinced that cartridge brass is about the same everywhere. So, the best way to measure case capacity is to measure case weight. Those weighing less will have less volume to subtract from chamber "capacity" or volume. Note the case expands hard against the chamber body, shoulder and neck walls as well as the bolt face. It's when the case is bulged out as far as it will go with 60,000 ppsi it its true capacity/volume realized. Measuring case capacity by other ways ain't gonna result in the real case volume when it's firing a bullet; and to me that's the volume that counts.

Which means you've only got so much room inside a case. You can fill it with different amounts of powder and bullet. I don't think 1/10th of an inch deeper bullet seating will change things much. As long as the bullet jumps the same distance to the lands all is well.

I've worn out several .308 Win. and .30-.338 Win. Mag. barrels and a .264 Win. Mag one. Through their life their throats eroded such that the bullets needed to be seated out at least 1/10th of an inch to still touch the rifling when chambered. Accuracy was excellent throughout the barrel life. I knew when the barrels were about to go bad when I needed about one more MOA elevation on the sights at 600 yards on the same range with the same load due to muzzle velocity getting lower with more throat erosion but accuracy was still great.

I don't think your shorter loaded rounds will cause any problem. If they don't shoot as good I think something besides case volume is the culprit. Who knows; they may well shoot better.
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Old 04-15-2006, 06:52 PM
Gold Member
Join Date: Dec 2004
Location: Black Hills,South Dakota
Posts: 661
Re: 300 wsm case capacity question.

There was a very interesting article in PS about varying the 300 WSM seating depths.If I can find the issue I'll scan it for you.
The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms -Samuel Adams
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Old 04-15-2006, 07:38 PM
Silver Member
Join Date: May 2004
Location: MD.
Posts: 225
Re: 300 wsm case capacity question.

When the 300WSM came out I had one built in a 24" sporter. That rifle had a long throat. It was built on a 700s/a and with a 180 NBT loaded to the lands I couldn't fit in the Mag. I think OAL was just over 3" I recently had one built on a 700s/a from LongShot Rifles 25" 12.5 LB Rig. I currently shoot 175 SMK's over 65.0 of H-4350 at 3050fps. This rifle has a much shorter throat than my last. At .10 off the lands loaded rounds fit in the HS Box. Some say they are stuffed too far in the case and this hinders accuracy. After shooting this rifle I know that it's not a problem. It is probably the most accurate rifle I own. It shoots around an inch at 300 and the first time on paper at 1K it went 6.1" for 5 shots prone.
So it doesn't bother me if they are in the case a little.
If it was built for strict 1K BR I would probably throat it longer for the heavy bullets and load single, but this one is for hunting and for me it's about perfect.
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Old 04-15-2006, 08:47 PM
Platinum Member
Join Date: Feb 2005
Location: USA
Posts: 2,598
Re: 300 wsm case capacity question.

Rimfire is correct,I have seen him shoot his 300 WSM and it is plenty accurate
range it,check the wind, dial in correction, aim and only one shot
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Old 04-17-2006, 07:07 PM
Bronze Member
Join Date: Dec 2003
Posts: 38
Re: 300 wsm case capacity question.

I wanted to thank you all for your helpful and sound information. I am not concerned now about the throat being shorter. I appreciate your help and experience very much. Stephen
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