Donuts, will they always hinder accuracy?
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Ronald W Schaefer
Well-Known Member
OK, I'll ask...I've been reloading for fifty years and done a lot of fiddling and experimenting and all sorts of A type personality, OCD reloading practices and I've never heard of a "donut"...please 'splain it to me. I'm astounded by this gap in my knowledge
Not hijacking but cam someone explain what a "donut" is?
Bob Wright
Well-Known Member
Many Ackley Improved cartridges and wildcats can experience brass flow during forming or resizing. The area of the neck shoulder juction will have a thicker wall causing the neck internally to be smaller in diameter. Seating a bullet into and past this choke point will send pressures up due to slower bullet release. Its not predictable no matter how the neck is sized, so erratic groups. In my case I had 4" jumps in vertical at 200 yards. First time I experienced this.
So, neck reaming and simultaneous outside neck turning removed it. On my SAAMI spec 280AI, I have to seat any bullet worth hunting with into the case.
Monitoring to see if it comes back.
It certainly can be felt at the lower part of the seating stroke.
I made it to +/- 2fps ES after correcting.
So, neck reaming and simultaneous outside neck turning removed it. On my SAAMI spec 280AI, I have to seat any bullet worth hunting with into the case.
Monitoring to see if it comes back.
It certainly can be felt at the lower part of the seating stroke.
I made it to +/- 2fps ES after correcting.
Ronald W Schaefer
Well-Known Member
Ahhh, thanks. Great explanation. So seems like reaming all new/once fired cases would solve a lot of the problem?
So are the donuts are on the inside or outside of the brass? Or both? Thanks
Mine only show up on the inside. It measures no different on the outside of the neck. I would like to know if any one has ever had them show up on the outside of the neck?
Bob Wright
Well-Known Member
Its not a bad idea to do new brass, but you need to have the right equipment to ream and turn in one step. It requires full length sizing and necking, then opening the inside neck with a specific mandrel diameter to pilot the reamer above the donut. When the cutter portion gets to the donut it will remove the bulge internally and as the neck is being turned externally. Using scrap cases to set up is ideal.
I found that I got 80% average clean up on the external neck and achieved a wall thickness of .0125 in cleaned up areas. I could go thinner if needed in a future operation. I'm monitoring it too. If I have a velocity issue on one cartridge, mark it and find out if that case has a wall thickness issue i.e., not enough/too much tension.
What what brand reamer & mandrel are you using?
Bob Wright
Well-Known Member
K&M. Bought the entire kit specific to .284 dia. and the neck cutter is 43° for the Ackley shoulder. I have a 32° for the 7RM.
It's about $330, but considering the cost of brass, eventually it will pay itself off.
I lost 30 rounds of brass due to pressure blowing open primer pockets. Just in load development, twice fired brass....
Look below Bob Wright explains it perfectly
Read Bob Wright's post a great explanationOK, I'll ask...I've been reloading for fifty years and done a lot of fiddling and experimenting and all sorts of A type personality, OCD reloading practices and I've never heard of a "donut"...please 'splain it to me. I'm astounded by this gap in my knowledge
