One more "Another donut question".

[Dr. Matt]

I've got donuts to the point where the bullets will not fall thru the neck of fired cases. Seating force went from 30-50 pounds to almost 100 pounds on the AMP press.
After using a cutting mandrel in the neck turner, the bullet will fall thru the neck, but the donut is only about half gone. The plan is to use the cutting mandrel then put a .025 shim under the neck bushing, so the donut area does not get resized. Any thoughts? Safety concerns? Am I reinventing the wheel?

 

[Straightshooter1]

I've got donuts to the point where the bullets will not fall thru the neck of fired cases.
After using a cutting mandrel in the neck turner, the bullet will fall thru the neck, but the donut is only about half gone. The plan is to use the cutting mandrel then put a .025 shim under the neck bushing, so the donut area does not get resized. Any thoughts? Safety concerns? Am I reinventing the wheel?

I think you should use a non-bushing FL sizing die before reaming with a cutting mandrel. This is what I recently did with my 6.5 PRC Lapua cases that had a substantial donut on them after 16 firings. It took a couple extra steps additional to my normal brass prep to do that, but the donut is nicely taken care of and the brass it good to go again, for a while.

 

[rwj]

When seated, does the bullet contact the neck/shoulder junction where the donut is located? If no, there is little/if any benefit in removing it. If yes, as @Straightshooter1 noted above, its removal will be temporary.

 

[Dr. Matt]

I have been thinking about making a guide that would let me ream the neck while still in the sizing die so nothing moves.

 

[Dr. Matt]

When seated, does the bullet contact the neck/shoulder junction where the donut is located? If no, there is little/if any benefit in removing it. If yes, as @Straightshooter1 noted above, its removal will be temporary.

Yes, the 90 gr does but I have been switching to 62 gr when the donut shows up and they do not seat into the donut. Is there something in my loading process I can do to prevent them from forming?

 

[Dr. Matt]

This all started the first time I let the brass dwell in the die for a minute while I trimmed the previous case to length. Is this a coincidence?

 

[rwj]

Is there something in my loading process I can do to prevent them from forming?

When sizing the neck, some of the material moves radially inward, some moves axially in the same direction as the bushing - towards the neck/shoulder junction. This material cannot “turn the corner” into the shoulder and forms the donut. It can be removed by cutting the neck ID, but the donut will start forming again during the next neck sizing operation.

Can you use a 90 grain bullet having a boat tail configuration?

 

[6MMsteve]

A diff bullet maybe or just make your freebore .050 longer or what is needed to get the bullet away from the donut..I'm not a gunsmith just kinda a shadetree guy, or keyboard warrior

 

[Dr. Matt]

When sizing the neck, some of the material moves radially inward, some moves axially in the same direction as the bushing - towards the neck/shoulder junction. This material cannot “turn the corner” into the shoulder and forms the donut. It can be removed by cutting the neck ID, but the donut will start forming again during the next neck sizing operation.

Can you use a 90 grain bullet having a boat tail configuration

Will the amount of shoulder bump affect the rate at which these form? I only bump .002.
I use the Hornady A-tip, it has a boat tail

 

[rwj]

Will the amount of shoulder bump affect the rate at which these form? I only bump .002.
I use the Hornady A-tip, it has a boat tail

Doubtful that shoulder bump has much, if any, effect on donut formation.

If you examine a loaded round, you should be able to visually see a small bump on the case neck that indicates where the bullet’s pressure ring is located. Unless you’re seating very deep into the case, it will likely be above the donut and not pose an issue. If your chamber has a short free bore, it may not.

 

[Dr. Matt]

Doubtful that shoulder bump has much, if any, effect on donut formation.

If you examine a loaded round, you should be able to visually see a small bump on the case neck that indicates where the bullet’s pressure ring is located. Unless you’re seating very deep into the case, it will likely be above the donut and not pose an issue. If your chamber has a short free bore, it may not.

 

[Dr. Matt]

Empty brass
This is the graph with out addressing the donut ( top 2) and a full neck resizing. The bottom 2 have enough donut removed that the bullet doesn't touch and the bottom .020 of the neck no resized. I seated them much deeper than normal. Normally seating depth would have stopped at .15.

 

[Sandstorm]

Just seat above the donut and forget about it. I never worry about it and its going to happen
no matter what you do. No issues here.

 

[ChrisA]

Just seat above the donut and forget about it. I never worry about it and its going to happen
no matter what you do. No issues here.

Kinda hard to do with certain configurations such as a Model 7 chambered in 6.5 SAUM shooting 140 gr bullets. Choose your battles I guess.

ETA: ya I know, you could use as a single shot if throated properly