Donuts

[savagedasher]

After thinking about it for a bit I purchased a 5.7mm 2 fluted reamer type drill bit off ebay. That comes out to .2244" which is slightly larger than a bullet. I I was able to sneak in past the neck and whack the donut down on my good cases. Just using my fingers the bit was plenty sharp to cut out the excess brass buildup.

The results were good and even the cases I trimmed the neck shoulder junction down on worked okay too

Just have a chamber that lets you seat the bullet foward of the donut and don't worry. Larry

 

[m-saunoras]

That would be ideal considering I only shoot 75-80 gr bullets. The new barrel I have is throated a bit short just like the old one. Think I should have it lengthened a little before I screw it on? Probably .020-.030" would do it.

 

[fguffey]

Just have a chamber that lets you seat the bullet foward of the donut and don't worry. Larry

Ignoring the donut is one method for dealing with the donut, then it goes back to 'what causes the donut?'. And then there are flow meters when the flow is controlled by the diameter of the orifice. When it comes to hot high pressure metal cutting gas I do not want a restriction.

F. Guffey

 

[savagedasher]

Ignoring the donut is one method for dealing with the donut, then it goes back to 'what causes the donut?'. And then there are flow meters when the flow is controlled by the diameter of the orifice. When it comes to hot high pressure metal cutting gas I do not want a restriction.

F. Guffey

What causes it. Very simple answer pressure stretching of a metal with one relief area .
The neck on a case is the only pressure area with out fixed resistance . Larry

 

[fguffey]

What causes it. Very simple answer pressure stretching of a metal with one relief area .
The neck on a case is the only pressure area with out fixed resistance

Larry, thank you for your effort, we all know for the most part an answer is based on opinion. I was of the opinion once reloaders started responding to the question; "What causes donuts?" someone would come up with a better answer. I have never had a doubt about the cause; now I need to figure a way that makes it sound like it is someone else's ideal.

F. Guffey

 

[savagedasher]

Larry, thank you for your effort, we all know for the most part an answer is based on opinion. I was of the opinion once reloaders started responding to the question; "What causes donuts?" someone would come up with a better answer. I have never had a doubt about the cause; now I need to figure a way that makes it sound like it is someone else's ideal.

F. Guffey

Simple answer shoot a case without shoulder.
If you shoot a case that gets them . Don't seat your bullet in them. Cut them out internally. Larry

 

[fguffey]

If you shoot a case that gets them . Don't seat your bullet in them. Cut them out internally.

Larry, thank you again, the question is about what causes donuts. Your answer has more to do with dealing with the donut after they appear. I do not want anything to slow the escape of the gas from the chamber; but if I did I would reduce the inside diameter of the neck.

F. Guffey

 

[savagedasher]

Larry, thank you again, the question is about what causes donuts. Your answer has more to do with dealing with the donut after they appear. I do not want anything to slow the escape of the gas from the chamber; but if I did I would reduce the inside diameter of the neck.

F. Guffey

Actually a donut makes a increase the speed of pressure Larry

 

[fguffey]

Actually a donut makes a increase the speed of pressure

Larry, thank you again, but it is one of those things that we can not discuss; because of 'speed of pressure'. There has to be two parts of pressure, there must be pressure and volume, I do not want a restrictor in the case neck of the case, I do not want to control the escape of gas because I have a bullet that controls that. I want the hot high pressure out of the case, to me it is a time factor thing. A restriction has to raise the pressure in the case if the neck restricts the escape.

F. Guffey

 

[m-saunoras]

I made a better attempt at fixing my issue. The savage factory barrel I have allowed me to seat the 75gr A-Maxs out to 2.105" base to ogive which leaves the bullet out past the neck shoulder junction. The 2 shilen barrels I have will let me go approx 2.030" before I hit the lands, quite a bit shorter. I have about 1500 rounds on the first Shilen and the throat has not grown a significant amount so I decided to lengthen it a little more. I picked up a PTG uni-throater, set it at the depth of the savage and used it to cut my first Shilen.

The 75gr A-max, 65gr JLK and 60gr V-max all seat above the neck shoulder junction now. The 80gr Berger VLD is very close. If this throating job works I'll use it to lengthen my new barrel too. I was happy with the ease of use.

 

[Murray Brook]

The pic you posted does not suggest any donut. But most cases which have been in use have something of a donut, however insignificant.

I use pin gages to probe inside necks (both just fired, or just sized) and have determined that most if not all unturned case necks are tapered slightly in thickness, being thinner at the case mouth than near the shoulder junction by from .001" to .003". Look at many SAAMI chamber drawings - they indicate the neck portion can and will taper slightly towards the mouth. And the way brass cases are "draw" formed necessarily results in case walls that taper from the web all the way to the case mouth.

Assuming your unturned necks are indeed slightly thicker near the shoulder than at the mouth, if you size them using a cylindrical bushing, the neck ID will be forced to slightly conical. If you then probed the necks with a pin gage that is a slip fit into the case mouth, you typically encounter an obstruction just ahead of the shoulder junction, but it will only be .001" to .002" tighter there than at the case mouth. Is that a "donut"? I don't think so. I think it is a gradual narrowing and perfectly normal after sizing the neck. And if the narrowing there is that slight, seating a bullet past it will not cause a problem in a typical "no-turn" chamber.

I think a real problem donut will be both more pronounced, and more abrupt, than what I described above, and than what I your photo suggests.
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I know this is an old thread but I am having just this problem/situation . Used the search function and found this. The value of old threads. I don't believe it hurts anything but will have to test TKS Brian.

 

[Kracken McGraw]

I know this is an old thread but I am having just this problem/situation . Used the search function and found this. The value of old threads. I don't believe it hurts anything but will have to test TKS Brian.

Plus we got to read one of Guffey’s puzzlers above!

 

[Rat Rifle]

I know this is an old thread but I am having just this problem/situation . Used the search function and found this. The value of old threads. I don't believe it hurts anything but will have to test TKS Brian.

The solution can not be simpler. If we think they are not a problem, seat above them. If We think, or know they are a problem, use the RCBS Neck Reamer to KNOCK THEM SUCKERS out of there. JMO