What would cause this.

[sp6x6]

The belted dies have a relief cut in them for belt area,and die to bottom on holder

 

[Seabeeken]

I guess technically it's sort of a design flaw with a belted cartridge if you were to radius off the die more at the bottom edge it would not shave off the brass but then again it would not size that area and you would still have a bulge

I agree. This was, I believe the issue with my 7RM. The radius on the die base kept it from resizing that critical spot. Its as if there should be an extra die in the set to squeeze the body just forward of the belt

 

[Seabeeken]

The belted dies have a relief cut in them for belt area,and die to bottom on holder

Therein lies the issue. Didnt know that

 

[338 dude]

Therein lies the issue. Didnt know that

 

[Rob L.]

I have custom Lee dies for my Weatherby Mag cartridges.
Mine are neck sizing dies using a fire-formed case from the rifle to make the die. So I don't experience what looks like the shaving or broaching near the magnum belt like in your picture. But I have experienced a snug fit because my cases have swollen near the belt.

Innovative Collet Body Sizer Die is what I use now just to squeeze the part of the case just above the belt a little, so it fits the chamber easily and works! Unfortunately, I own 2 Weatherby calibers that it doesn't fit. It fits the 340 Wby and not the 240 nor 378. However, I believe this one collet does fit a whole bunch of cartridges, and may be of interest to you?

Here is a list:
"This ONE die and collet is universal and works on ALL of the popular belted magnum calibers including: .257 Weatherby Magnum, 6.5 Remington Magnum, .264 Winchester Magnum, .270 Weatherby Magnum, 7 x 61 Sharpe & Hart, 7mm Remington Magnum, 7mm Weatherby Magnum, 7mm STW, .300 H&H Magnum, .300 Winchester Magnum, .300 Weatherby Magnum, .308 Norma Magnum, 8mm Remington Magnum, .338 Winchester Magnum, .340 Weatherby Magnum, .350 Remington Magnum, .358 Norma Magnum, .375 H&H Magnum, .416 Remington Magnum, .458 Winchester Magnum, .458 Lott Magnum and several belted wildcat cartridges. There are no extra collets to buy when resizing different calibers. The U.S. Secret Service was one of our first customers to purchase this product."

And a link: https://www.larrywillis.com/mainpage.html

 

[LVJ76]

Innovative Technologies - Reloading Equipment

Our patented resizing die can reload Winchester, Remington and Weatherby belted magnums up to 20 times, instead of just 2 or 3 times and the top of the die is a chamber width gauge.

www.larrywillis.com

I have custom Lee dies for my Weatherby Mag cartridges.
Mine are neck sizing dies using a fire-formed case from the rifle to make the die. So I don't experience what looks like the shaving or broaching near the magnum belt like in your picture. But I have experienced a snug fit because my cases have swollen near the belt.

Innovative Collet Body Sizer Die is what I use now just to squeeze the part of the case just above the belt a little, so it fits the chamber easily and works! Unfortunately, I own 2 Weatherby calibers that it doesn't fit. It fits the 340 Wby and not the 240 nor 378. However, I believe this one collet does fit a whole bunch of cartridges, and may be of interest to you?

Here is a list:
"This ONE die and collet is universal and works on ALL of the popular belted magnum calibers including: .257 Weatherby Magnum, 6.5 Remington Magnum, .264 Winchester Magnum, .270 Weatherby Magnum, 7 x 61 Sharpe & Hart, 7mm Remington Magnum, 7mm Weatherby Magnum, 7mm STW, .300 H&H Magnum, .300 Winchester Magnum, .300 Weatherby Magnum, .308 Norma Magnum, 8mm Remington Magnum, .338 Winchester Magnum, .340 Weatherby Magnum, .350 Remington Magnum, .358 Norma Magnum, .375 H&H Magnum, .416 Remington Magnum, .458 Winchester Magnum, .458 Lott Magnum and several belted wildcat cartridges. There are no extra collets to buy when resizing different calibers. The U.S. Secret Service was one of our first customers to purchase this product."

And a link: https://www.larrywillis.com/mainpage.html

This

Had that issue with my 7mm Rem Mag,
the brass wasn't getting sized back enough at just above the belt, to the point it started getting stuck in the chamber and getting those scratch marks.

 

[meatyrem]

I think he's getting that die mentioned above to solve his problem. Thanks for the responses

 

[spladi]

I had a similar issue with Lee FL dies for my 300 Win Mag. I put a small radius on the circumference of the opening of the FL die which I believe ended the misalignment of the press ram and die brass shavings issue. My press is a RCBS JR. bought in 1979 and its loose so after a partial resize of a piece of brass I release the ram handle thereby letting the case self align with the die, I do this maybe twice which eliminated my shavings and shelf type cuts above the belt.

 

[BRM99]

I have custom Lee dies for my Weatherby Mag cartridges.
Mine are neck sizing dies using a fire-formed case from the rifle to make the die. So I don't experience what looks like the shaving or broaching near the magnum belt like in your picture. But I have experienced a snug fit because my cases have swollen near the belt.

Innovative Collet Body Sizer Die is what I use now just to squeeze the part of the case just above the belt a little, so it fits the chamber easily and works! Unfortunately, I own 2 Weatherby calibers that it doesn't fit. It fits the 340 Wby and not the 240 nor 378. However, I believe this one collet does fit a whole bunch of cartridges, and may be of interest to you?

Here is a list:
"This ONE die and collet is universal and works on ALL of the popular belted magnum calibers including: .257 Weatherby Magnum, 6.5 Remington Magnum, .264 Winchester Magnum, .270 Weatherby Magnum, 7 x 61 Sharpe & Hart, 7mm Remington Magnum, 7mm Weatherby Magnum, 7mm STW, .300 H&H Magnum, .300 Winchester Magnum, .300 Weatherby Magnum, .308 Norma Magnum, 8mm Remington Magnum, .338 Winchester Magnum, .340 Weatherby Magnum, .350 Remington Magnum, .358 Norma Magnum, .375 H&H Magnum, .416 Remington Magnum, .458 Winchester Magnum, .458 Lott Magnum and several belted wildcat cartridges. There are no extra collets to buy when resizing different calibers. The U.S. Secret Service was one of our first customers to purchase this product."

And a link: https://www.larrywillis.com/mainpage.html

Also works as a go no go gauge

 

[Teri Anne]

"Got cases as once fired from another source"

Bulges often occur above the belt in belted brass. No telling of dimensions of previously fired chamber that was probably cut to headspace on belt. Apparently the previously fired brass developed bulges & the Lee Die swaged the bulge out. My suggestion would be to get new brass & headspace on shoulder & continue using the Lee dies. I am assuming the Lee dies used are F/L dies. I have found my Lee dies are often tighter than others. Measurements of new brass that have been fired in your chamber might be compared to:

View attachment 319653

Edit: I noticed that my Lee F/L dies instead of having an inside radius had a sort of inside gently rounded taper having a well-defined upper edge (die screwed into press). If the OP's .300 WM dies were similar that would account for the brass shaving. I don't especially like belted cases but go with the flow considering brass availability. Never seen anything like this with a .300 WSM.

The 300 win mag has a belted case, which seems to be what you are having the issue with.
According to my information from Noser is that the 300 WSM is not belted so there would not be any issues with a belt. https://www.nosler.com/300-winchester-short-magnum-wsm.