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Case neck donut

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2008 at 09:50
8shots View Drop Down
Optics Jedi Knight
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I have just bought my first inside neck reamer to remove donuts. The manual says this should be performed on fired cases before resizing. A bullet will drop through the neck of a fired case into the case with ease. So does the reamer.
Surely such a large donut as to block the reamer or bullet is impossible to form, especially on a 308 Win caliber!
My dealer confirms this is the correct procedure and case necks must only be reamed when a bullet cannot fall through a fired case neck.
Surely this cannot be right? has anyone experience with such a large donut forming?? Did I waste my money in buying the reamer?


Edited by 8shots - September/01/2008 at 09:52
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2008 at 10:49
helo18 View Drop Down
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Maybe it is just habit, and my Dad always did it, but I always have reamed the inside and outside of the neck to get rid of any roughness.  I like my cases as even as possible and with as little variation as I can get.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2008 at 17:51
Dale Clifford View Drop Down
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the high pressure gases will form the inside of the neck to the dimensions of the chamber neck, round or ellipse or whatever, inside neck reaming is best done on cases that are being wildcatted, such as .223 WSM, when the case is cut off and the neck is formed from the the lower part of the case which is usually thicker. the reduction in thickness is to allow the case neck to "spring back" after firing. thinning was done a lot when military surplus brass was used in the tighter dimensions of hunting rifles before the really good stuff that is now available. On the other hand quite often when one shoots loads a large amt. under the usual pressure for that round the brass neck will never get blown out evenly, and outside neck reaming will remove the scallops and dishes that develop over several firings (more than 10). Inside neck reaming is done to reduce dimension and will never produce the smooth dimensional necessay to the out side of the neck. It can also be necessary if the barrel is a replacement and the chamber dimensions have been specified as especially tight.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2008 at 18:45
Mike McDonald View Drop Down
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On a 308 wnchester the case can form a "doughnut" if you have turned the case neck (outside) and not allowed the cutting tool to travel up onto the case shoulder just a bit.
By stopping at the case neck/shoulder junction you will cause the case body to flow "under" the neck just a few thousandths with each firing.
 
On a rifle with a chamber cut to SAMMI spec, 0.345", the neck has sufficient room to expand so that your test method may not be valid.  With a tighter neck dimension such as 0.335" it will work.
Non turned necks would likely never form a doughnut on a  308 case.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2008 at 23:34
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Hey 8 shots
 
What kind of a reamer did you buy?
 
In my experience, you have to set up your cases so they have the right neck thickness in order to have the reamer contact the do-nut.
 
First of all you have to determine if you have developed a do-nut and whether it will have any bearing on the bullet.  If you can slide a bullet past the shoulder/body junction then you have nothing to work on.  You may in fact have a do-nut but it will not bear on the bullet.  Reference this sketch
 
If the do-nut does not contact the bullet in a fired unsized case the neck sizing will size the neck brass past the do-nut and the inside diameter of a sized neck will be smaller than the do-nut brass.  No problem.
 
In my experience you will only develop do-nuts in a custom chamber where you have minimum neck clearance on a loaded round.  For instance I develop them on my Hart barreled 280AI with a .313" neck.  Going through the math; .313"-.003" (recommended minimum clearance around the neck on a loaded round)=.310"-.284"=.026"/2 (both sides of neck)=.013" and I give it a little more and turn my necks to .0125" for a .004" clearance
 
This is as far as one of my bullets will go into my neck
 
I turn necks with a Forster hand turner and I discovered that the reamer they provide has the same size attaching stem
 
Their reamers are advertised to be .003" + larger than caliber.  So since I set my brass up to have .004" clearance around the neck, after firing that .004" transfers to the inside of the neck and the reamer will work perfectly and I can "clean up" the outside of the neck at the same time with the outside turner
 
I say "clean up" because I have already outside neck turned the new brass in order to get it down to the .0125" thickness.  It did take a little off the high spots on the outside and reamed out the inside and got rid of the do-nut
 
After reaming the neck thicknes was reduced to a very consistant .012"
 
A quick clean up of the inside of the neck with steel wool to get it smooth (or at least a lot smoother)
 
That is the way I address my do-nuts and it does make a difference
 
Most factory chambers have too much clearance around the brass at the neck to develop any problem do-nuts.  The way to check is to measure the outside of your fired & unsized case neck, then measure the brass thickness at the neck.  For example if your neck measures .340" and your brass neck thickness is .013", the math would be;  .340"-2*.013"=.314"-.308"=.006".  That would mean that you have .006" clearance around your neck and it would be unusual for you to develop a do-nut large enough to hit the bullet.  Varying neck thickness with different brass will change the math.
 
Sometimes the do-nut does not develop even with a tight clearance.  I have a 6.5 rem mag with a .292" neck and I turn the brass for a .003" clearance and it does not develop the do-nut.  Go figure.
 
One thing for sure is that you need a good way to measure and a caliper will not cut it.  You need a micrometer.  I'm a cheap bastard and this one only cost about $40.00 (some are as much as $150.00) but it is much more accurate than my caliper.  Even so it was almost useless until I got that stand, which I highly recommend
 
If you have a K & M outside neck turner you can buy a cutting mandrel that will remove the do-nut but it does not work as well as my Forster IMO.
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/02/2008 at 05:57
8shots View Drop Down
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Thank you for all the responses. Sakomato thanks for the detail you have gone into. I have a Wilson case trimmer and inside neck reamer.
I tried the reamer on 30-06 brass that has been fired more times then I can remember, It runs smoothly through the case neck, no brass to cut away. I also tried it on 300 H&H cases that has been fired at least 10 times. Same result. The reamer has no work to do.
 
The reamer will only cut brass on resized cases.  According to the instructions the reamer is .003 inches smaller the bullet diameter. So if I ream a sized case the bullet cannot be pushed in with my vingers. I still need to use the bullet seater.
 
Would it be wrong to ream sized cases? Or have any advantage?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/02/2008 at 08:25
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Reaming on sized cases is not as good as reaming on fired/unsized cases because when you size the case you push all the irregularities in neck thickness to the outside of the case neck.   IOW, depending upon which sizer you are using, the expander ball or collet mandrel will uniform the inside of the neck.  On fired cases the pressure has uniformed the outside of the neck to the chamber and all the irregularities are then on the inside and reaming will do the most good.

If your reamer is .003" smaller than caliber then the only way to have the reamer work is to have a bushing type sizing die where you can get the right bushing to give you that .003" inside neck diameter and not use the expander.  Then the irregularities will be on the inside of the neck and the reamer will take brass away.
 
IMO, inside neck reaming is not as good as outside neck turning.  If you did outside neck turn and did use a bushing type resizer without an expander to give you the proper inside neck diameter, then inside reaming could have some beneficial effects on it's own.  As long as your reamer could be set to follow the inside without veering to one side or the other.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/02/2008 at 08:42
Roy Finn View Drop Down
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I am probably wrong, but, I thought that this practice was for cases that had many firings and that the purpose was to correct excessive brass flow. I do understand sakomato's situation where he specified a tight neck, but that doesn't sound like the case 8shots should be having. 8shots, how many re-loadings are you trying to get from those cases. What brand cases are you using? As far as being able to push a bullet through a fired, but yet unsized case, that is the norm for me. Frankly, this is the first time I have heard of this problem.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/02/2008 at 23:52
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Hey 8shots
 
What is the measurement on the outside of the neck on a fired unsized case?
What is the neck brass thickness?
 
If your reamer is not contacting the inside neck brass after sizing and it is .003" smaller than the caliber, then you could take a little off your expander ball to get a smaller inside diameter.  If you are using a Lee Collet Neck Sizer then you could order a smaller mandrel from Lee for $5.00 plus shipping.  If you are using a bushing type sizer then you could order a smaller bushing.
 
That is if you wanted to inside ream.  Do you turn the outside of the neck or have a way to measure neck brass thickness?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/04/2008 at 02:35
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Originally posted by Roy Finn Roy Finn wrote:

I am probably wrong, but, I thought that this practice was for cases that had many firings and that the purpose was to correct excessive brass flow. I do understand sakomato's situation where he specified a tight neck, but that doesn't sound like the case 8shots should be having. 8shots, how many re-loadings are you trying to get from those cases. What brand cases are you using? As far as being able to push a bullet through a fired, but yet unsized case, that is the norm for me. Frankly, this is the first time I have heard of this problem.
 
My situation is this: Whenever I discuss case prep with the fundis they ask the following questions:]
Did you do ouside neck turning?
Did you ream the inside of the neck?
 
Well, I do outside neck turning.
No I do not ream the inside of the neck.
They then tell me "Well you must do that"
 
So I went and bought an inside neck reamer only to discover it does nothing. Hence all my questions.
I have a standard Remington 700 action.
I normally load say 10 times.
 
My own opinion, after reading all the comments, is that I bought a tool I will never need.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/04/2008 at 08:12
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Originally posted by sakomato sakomato wrote:

Hey 8shots
 
What is the measurement on the outside of the neck on a fired unsized case?
What is the neck brass thickness?
 
 
8shots
 
We could figure out if it is possible to have the reamer contact some brass with the answer to those questions.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/09/2008 at 17:55
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Forster says:
trim after sizing
ream before sizing
outside turn after sizing

"pressure donuts" are usually with high intensity cartridges (220 swift), softer cases (Norrma weatherby) or custom cases like Qual Cartridge.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/10/2008 at 03:48
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Fiberoptics, that is my opinion too, but unfortunately came to this conclusion after buying the reamer!!!!

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