I have been giving some thought into getting an inside neck reamer for my 303 British brass because I keep hearing stories about the , "dreaded doughnut."

 I did a comparison check between a new cartridge case and a case that has been reloaded 5 times and see no difference. The inside of both necks at the shoulder look identical.  The reloaded case has been trimmed to 2.150" and when a bullet is seated, it is just above the cannelure, giving a C.O.L. of 3.085". The actual bullet to case contact area is 0.175" from the opening of the case down, which is 0.150" above the shoulder and well above this "dreaded doughnut." This puts me at odds with making this purchase because I see no benefit. I do see the potential to create a very thin case wall thickness however. To the forum I ask. Enlighten me as to the virtues of inside neck reaming.

 The pictured cartridge case is made by IVI and has been reloaded 5 times now and you can see that the bullet in no way can contact the shoulder area unless I attempt to seat the bullet well beyond the cannelure...

I became aware of this when I switched over to a bushing type FL sizer which does not use a neck expander ball. I could feel the donut as the bullets were seated into it. I could also detect it with a pin gage inserted into the sized case. With a standard FL sizer with an expander ball, you can’t detect the donut because the neck is expanded to a constant diameter. 

I did get a .223 inside neck reamer and it did remove brass right at the neck/shoulder junction. I posted this sometime last year, can’t remember exactly when. You do this only on a fired case because the neck takes the shape of the chamber. It helps if you anneal the necks so they fully expand.

I also switched over to a bushing type FL sizer for .308, but no problems with the donut with my Lapua cases that had been reloaded about 8 to 10 times. I will continue to monitor them. 

If your sizing your cases with standard dies, you can’t detect the donut. The only thing you can do is measure the case neck outside diameter on a loaded round right at the junction to the shoulder. Then compare that to a fired case and see if the loaded round has a smaller diameter or not. 

My .223 loads use 69 and 80 grain bullets which protrude into the case considerably, so are susceptible to this condition.  I’ll have to check my 7.62/.308 loads with the Sierra 168 5MKs for the No. 4 DCRA conversion. 

My 7.62x51mm Lake City brass that has been Full Length resized will need to have the neck reamed eventually. My 180grn Norma Vulkan Flatbased projectiles protrude past the neck/shoulder area as well. 

The 170grn FMJ-BT M30 projectiles that I will be using along with the 174grn FMJ-BT projectiles that are made by the same manufacturer do not protrude into the case enough to cause an issue however...

But, I’ve not detected it in .303 brass that is sized in either the Lee Collet neck die or standard FL die with expander ball. I don’t have a bushing type FL sizer for the .303. 

The pin gages come in increments of 0.0005 inches (half a thou).  Useful for measuring bullet interference with the neck to achieve a desired neck tension.

Annealing the cases helps reduce springback, so it may be that after 4 or 5 reloads without annealing, the donut will spring back from the expander ball and be detectable. Last year, I started annealing before every reload, and can’t detect it with pin gages in my .303 brass.

I did not detect the donut on the fired .308 cases using pin gages. I’ve probably reloaded these cases 8 to 10 times.  I neck sized these cases in the Lee Collet die, so unlikely to form the donut during sizing. 

I seat the 168 TMKs to 2.950 OAL to get within 0.025 inches from touching the lands. This also increases case capacity and lowers pressure. The bullet bearing surface is forward of the neck/shoulder junction, so very low risk of a donut causing any pressure issues. 

So, this seems to be a condition only associated with my .223 loads with 80 grain SMK.