New and Improved 6XC
Donut Cutter
Updated 6-23-06,
Updated 6-27-06, Updated 9-29-09
The things you
do while waiting for your Tubb gun. I picked up one piece of four
or so times fired 6XC brass from a friend that started to have some
sticky bolt issues with his rapid-fire load. I took the case home
to measure and everything seemed okay. Right after my initial
check of the 6XC case, there was somewhat of an outcry on a couple of
the competition message boards about donuts in 6XC cases. I when
back and check the 6XC case and sure enough there was a big fat donut
at the base of the neck. I first checked the fired case using a
6mm bullet to find the donut. I then got my pin gages out and
found that a .242-inch pin gage would pass through the donut
hole. The fired case neck ID measured .245 inches using the pin
gages. So now, I have a 6XC case with donut that needs to
removing, however I do not want to disturb my present donut cutter
set-up using my K&M Neck Turner for 308 cases. Click
here for
article on how to use the K&M fluted neck tuner mandrel to put a 15
MOA taper on the inside of the case neck at the neck to shoulder
junction.
Click
Here to see a short mpeg video showing how to use the K&M
Fluted
Mandrel and remove donuts.
Click
Here to see a short flash video showing how to use the K&M
Fluted
Mandrel and remove donuts.
Therefore, after getting my 6mm flute mandrel out and looking
at it for a while, I
noticed the nice little shoulder at the base of the 6mm portion of the
mandrel. Now could I find a washer or spacer the correct length to rest
on the cutter shoulder and position the fluted cutters to cut
an inside case neck taper?
First some quick measurements to determine spacer length
Cutter shoulder to end of cutting flutes = .690"
Cutter shoulder to start of cutting flutes .640”
Length of side cutting flutes = .690” - .640” = .050”
6XC case neck length = .305”
End of side cutter should be past case shoulder junction about .015”
Spacer length = .690” – (.305” + .015”) = .370”
Now .370” should be close enough to .375” to work. I think that
.375” or 3/8” may
just be the standard length for neck bushing. Sure enough, I have
an unused .244” Redding bushing. Pop it on the end of the K&M
fluted mandrel and now I have inside neck donut cutter that will work
just like the one in the above mention article.
Next, I take
that 6XC case and secure it on the end on my DeWalt 400 rpm cordless
screwdriver using a Sinclair shell holder and driver. Stick the
fluted mandrel with the Redding neck bushing spacer into the case neck
and go for a spin. You have to hold or give the mandrel some
yawing, twisting, or cockeyed motion so the little flutes on the end of
the cutter have pressure against the base of the case neck to cut the
taper. After an initial cut, I checked for any donuts using my
.245 pin gage and the donut was gone. I rechecked the case neck
ID and found that now a .247 pin gage would pass freely inside the
neck. (No big surprises here) The very end of the case neck
may not always expand fully to chamber diameter during firings.
However, the .247 pin gage was stopping on a donut. So after a
couple more spins using on the donut cutter the .247 pin gage passes
free through the donut area. One must use the largest pin gage
possible to check for donuts in fired cases. Just using the
bullet is good and that will tell you if you have a serious donut issue
to consider. However, using the largest pin gage to check for
donuts and check the donut removal process along with this method, may
just keep the donut away for a few firings. At least it should on
6XC rifles with chamber that have .276” necks.
I believe that
this case will now be good for four to six firings before any donut
will reappear and be detected using a bullet. I have found that
you must check for donuts using the largest pin gage possible and
correct so that the largest pin gage will pass through. Think
about it, if you have a .247 neck ID with a restriction or donut with a
.242 ID and just open it up so a .243 bullet will pass through, you may
still have .244 restriction or donut in the .247 neck just waiting to
reappear after next firing. The cutting process is easy, just
turn the case somehow in the 400-rpm range and wiggle and cock the
cutter around to force the little flutes up against the donut.
So above, is a
picture of my new and improved 6XC Donut Cutter after I installed a
little wooden ball for a handle. I actually like this set-up of
using a spacer on the fluted mandrel better than my previous set-up
using the complete K&M neck turner and a piece of Plexiglas to
position the flute cutters correctly at the base of the case
neck. Good news is for all 6XC people, the standard neck bushing
just happen; to the correct length to make an inside, case neck
tapering tool using a K&M fluted neck turn mandrel. The
standard bushings are too long for 308 necks and too short for 223
necks. I figure I need a spacer that is .354” long for 308 case
necks and one that is .455” long for 223 case necks.
Therefore, I
have made more little bushings for my fluted mandrels. I am now
ready for any 22 caliber and 30 caliber donuts.
I spin the cases using my Sinclair shell holder and driver or with my
K&M Case Driver. My Sinclair driver is a Fred Sinclair
special without
the little steps for primer pockets. This allows me to use it on
cases with primers and with my Lee Trim Gauges.
The
little wooden add on wheels to the shell holders make for easier
locking and unlocking. I think this bushing setup is the way to
go so I made a bushing for 30 caliber and 22 caliber.
It seems that I always do better on the second one. After doing
the bushing for my 30 Caliber, I remembered that I might need one for
my 221 Fireball. I got that hole more in the center.
Bottom line on
my friends above sticky bolt is back the load off one more grain. The
bullet is well forward of the donut area with his rapid-fire
ammo. Also having a little donut well behind the bullet should
not affect anything, unless you are race engine nut and you have
polished and ported some intake and exhaust manifolds. If this is
your case, then having any size or type of donut will surely keep you
awake at night. (Or you got nothing else to do while waiting for your
Tubb Gun)
More than you
wanted on donuts
Note: In the
sketch above that, line B is slightly longer than line A. If any
of the case neck material along line B should move forward, it would
certainly start to create a donut.
In all of the
cases that I have turned the necks on, one thing remained constant,
i.e. the case neck were always slightly thicker at the base of the neck
than at the case mouth. The two thirds of the case neck may be
only 50% cut while the back one third was 100% cut during the turning
process. So normally, the back end of the case neck is slightly
thicker than the front end. This is why it is possible to get
donuts without turning the necks. However, this may never be an
issue or detected using a bullet with standard neck chambers.
Donuts can happen for a numbers of reasons, what I find is most
important is just having a good way to find them and removed them if so
needed.
If the brass just behind the shoulder moves forward any on firing, the
thicker wall section will form the donut.
Larry Medler
anyrange@comcast.net
Any Questions or
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Released -
June 14, 2006
Revised - September 29, 2009
