K&M Doughnut Cutters, do they really work?

Having been a subscriber to Precision Shooting for around twenty years now, I have read many articles mentioning the “Dreaded Doughnut”.  I being a more realistic standup silhouette shooter, this doughnut thing is probably something that I will never encounter.  Wrong but a little more history first.  Over the years, I have enjoyed the bench rest articles in Precision Shooting.  Many of the articles gave me an idea or tip that I could use for silhouette shooting.  Would they actually be of any benefit is another story.

Back in the early 1980’s, Precision Shooting Magazine had many articles and discussions on shooting 30 caliber bench rest rifles by some real stool shooters.  Therefore, in my stack of old Precision Shooting Magazines are some with yellow post-its® sticking out and flagging a 30-caliber article.  In the event, I ever replaced my factory barrels, those flagged articles were my future references to barrel and chamber dimensions.

That day did come a few years ago.  Now I have new Hart barrels on my two standard silhouette (308) rifles.  They both have chambers with a 0.340-inch neck diameter.  I wanted 0.338 but my choices at Hart were 0.335 or 0.340, I opted for the 0.340.  The older Precision Shooting Articles indicated that the recoil lovers were using tight necks around 0.332 to 0.335 range and the 0.335 neck seemed to be most popular for the 30 caliber.  One fellow silhouette shooter had a silhouette rifle with a 0.335 neck and considered it a pain in the butt for silhouette.  He did not enjoy neck turning and would not do it again.  So I went with the 0.340 neck, even though my old pile of lake city brass, which in the process of cleaning up the necks, I had turned the neck down enough to fit it the 0.335 chamber.  A new barrel deserves new brass.  Especially after twenty years of silhouette shooting with hand me down army brass, it was about time I broke down and bought some new brass.

I opted for the IMI Match Brass based on good reports from some local high power shooters just before they all got wimpy and started good scores using AR-15’s.  In addition, the IMI Brass weight was very close to the Lake City brass weight.  I was also hoping that the IMI Brass would have neck walls thick enough and actually require some neck turning to fit the 0.340 neck.  Close but no cigar.  However, better to error on the side of safety, I will turn the necks and have a 0.340 bushing around to test the loaded rounds.

When should one turn the necks, after resizing or after fire forming with some sort of a filler?  With 1000 IMI cases to do, easy decision, after full length resizing.  First I full length re-sized all the cases to around –0.004 to –0.005 on the RCBS Precision Mic scale and trimmed cases for over all length.  Then I turned or just cleaned the necks on the IMI Brass.  I set the neck cutter for a 0.015-in. neck wall thickness.  I set the cutter on my neck turner using an old Craftsman automotive point feeler gauge.  Last time I used those feeler gauges was on my 1967 Cutlass Supreme – Turnpike Cruiser.  Anyway, using a 0.015 wall thickness, 0.015 + 0.015 + 0.308 = 0.338, I was still able to salvage something with a 0.338 dimension even if it is only the loaded round neck size.  The neck wall uniformity on the IMI Brass appeared to be very good.  The case turning effort was minimal and felt uniform all around the case neck.  Turning the brass for a 0.015 neck wall thickness, produced an extremely light cut on the neck area which seemed to be only removing the tarnish or annealing stain.  I was pleasantly surprised on how many cases completely cleaned up all the way around the case neck with such a light cut.  Only about 80 of the 1000 cases seemed to cut somewhat harder on one side, I segregated these cases from the lot.  I also set the neck turner so it would just cut the neck area and try not to go too far into the case shoulder.  Since this was new brass, the trimming operation did not trim all the cases.  Therefore, I figured that this operation may be repeated anyway.  In addition, this neck turning operation was not actually required because the IMI brass would fit the 0.340 chambers.  Therefore, it made no sense to be very aggressive in the shoulder area, only to over cut some with shorter necks at this time.  So all the case prep and initial loading went just fine.  Barrel break was a breeze.  Now just re-set the scope knobs and off to the silhouette matches and the world of stand up shooters.

Everything was just fine until one day I struck a bullet in the fired case.  As shown in Figure 1 (Doughnut.jpg)

and describing the cases from right to left side is as follows.  First is a typical loaded round with a moly coated 175 Sierra MatchKing.  Next is a fired case with a regular 175 Sierra MatchKing placed in a fired case and resting on the little case neck doughnut.  Then there is an unfired but prepped case, which I am trying to show the amount of neck turning done during the original case preparations.  Last and the case on the far left, is a case which had some of the neck and shoulder filed away to show the little bright ring where the doughnut was removed.

Actually, I was hoping that a bullet would not fit into the fired case neck at all.  I was hoping that the two thousandths of clearance between the loaded round and neck chamber would be small enough and allow the brass to spring back like the bench rest cases.  As it turns outs, the cases are partially this way.  The bullet easily slides into the case mouth but will not go completely through the neck and into the case either.  Also the loaded round may easily slip into the 0.340 neck bushing.  So is this the dreaded doughnut?  Do I have bench rest type doughnuts?  Is there a doughnut club I can join?  I did not think I cut enough off the case necks to get a little cheerio let alone to get a full fledge doughnut.  However, the pressure ring or boat-tail shoulder in my case, comes to rest at the neck to shoulder junction.  Do boat tail bullets have pressure rings?  I have heard or read that only flat base bullets have this pressure band or ring.  My 175 Sierra HPBT MatchKings appear to have one.  Also if I put the bullet upside down into the case, the bullet will also come to rest on the same pressure ring which leaves the base of the boat tail bullet just below the top of the case neck.

Therefore, I guess my new 308 cases have doughnuts.  How many dozen do you what?  I can not see the little doughnuts in the case neck but can only detect them by placing a bullet into a fired case.  About 90% of the cases used in one of my rifles are indicating the doughnuts.  The boat tail shoulder of the bullet will come to rest at the base of the neck just in front of the case to neck shoulder, as shown in Figure 1.  The bullet fits into the fired case like a shaft going into an air bearing.  It even compresses the air in the case.  In fact if I hold the case horizontally, I can lightly tap the bullet into the case and the air pressure build up will pop it back out some.  Now I have a better understanding of why I am getting the same muzzle velocity with 2.0 grains less powder with the 0.340 verses a 0.346 neck.

The bullet just seems to hit a little ridge just above the shoulder top in the neck.  I have not been very concerned about the little doughnut since I have been using the new Sierra 175 MatchKings.  As shown in Figure 2 (175mk.jpg),

the 175 MK boat tail shoulder comes to rest well above the doughnut area, and is one of the reasons I switched from the 180 to the 175 grain MatchKing.  I now have five firings on the brass and little doughnuts have been something to talk about and demonstrate.  However, after seeing many ads and reading an article in the September 2000, Precision Shooting Magazine, about the new and improved K&M Neck Turner with the built in doughnut cutter, does it appear to be exactly the tool I need to rid me of my doughnuts?

My reloading procedure, for the five reloads, has been to bump the case shoulder only using the Redding competition body die.  My fired cases measure around +0.002 using the RCBS Precision Mic scale.  I have been resizing the brass with a Redding body die, which does not touch the neck.  I am also using the Redding competition shell holders.  These shell holders allow me to leave the case about +0.000 on the RCBS Precision Mic scale.  My press is the Redding UltraMag, which I really like.  I firmly tighten (with channel locks) the body down on the shell holder with the ram in the up position and then tighten the locking ring.  I am resizing all of the cases with very little deviation.  I also have my Redding competition neck sizing die with a 0.335 bushing set so I do not resize the last 0.028 inch of the case neck.  It appear to me that the bullet will come to rest in the fired case just above the neck shoulder and well below the point I stop the neck re-sizing operation.  Again, I did not think I removed enough brass on the necks to cause any doughnut to form.  Nevertheless, the doughnuts are there, so lets order one of those doughnut cutters and see if it actually works.

Actually, my first assault on these little doughnuts was going to be with an inside reamer.  I order a 308 inside reamer from Forster Products.  Cute little reamer but it would not fit into the fired case.  Funny that a 308 bullet would fit but a 308 reamer would not.  Therefore, this reamer has been pigeon holed, lost, and found over the past few years.

The second assault on the not so dreaded doughnuts came as a result of reading Mr. McPherson’s article in the September 2000, Precision Shooting Magazine.  The article by Mr. McPherson on doughnut formation, doughnut harm, and doughnut cutters is the root cause for this article.  After reading Mr. McPherson’s article, I just had to get me one of those little K&M Fluted Doughnut Cutters.  Mr. M. L. McPherson’s article gave me the impression that using this tool is a no brainier.  Just follow the simple directions and no more doughnuts.  After all if Mr. McPherson can make it work, it should be safe and easy enough for even a silhouette shooter.

My K&M Neck Turner System came with a little note stating that I may need an Expandiron if the inside diameter was not correct.  Well that’s it for instructions and seems very simple to me.  So, let us stick one of my doughnutized cases on this K&M Doughnut Cutter and see how it works.  Well the 308 K&M doughnut cutter is too small and misses the doughnut.  What is going on?  I get a 308 reamer from Forster and it is too big.  The Forster 308 reamer will not fit into a fired case neck hole that a 308 bullet has suddenly vacated.  Then the K&M 308 Fluted Pilot Doughnut Cutter is too small and can not find the doughnut that the 175 grain Sierra bullet can find.  Now what?  I have to refresh my thinking on this whole doughnut subject.  Okay, just how, where, and when are doughnuts formed?  Formed during the neck turning process or during the firing process?  My understanding has been that this happens during the first firing process after an improper neck turning operation.  I can live as an improper neck turner.  After re-reading the Mr. M. L. McPherson’s article, yes the doughnuts seem to be formed during the firing process and any type of neck turning or neck turning tool will not produce a doughnut.  So if doughnuts in the case neck are produced only after firing, just how does this K&M Doughnut Cutter work?

Since the fluted pilot just slips right through and never even sees the doughnuts, do I need to re-size the case first?  Maybe that is the proper procedure Mr. M. L. McPherson’s article mentioned.  So musts I full length re-size the cases and then use the neck expandiron so the fluted pilot will fit correctly.  The size of the inside of the case neck must be correct per K&M for the fluted pilot.  If I re-size the case and then expand the neck where will the little doughnuts be?  This action will force the doughnuts back on the outside of the case neck.  Right where any normal neck tuner will trim cut them off and the flutes on the K&M will be just cutting air or scratching up the inside of the necks.  If I re-neck size using a 0.339 or 0.338 bushing I may get the case neck inside diameter correct for the K&M fluted pilot.  Nevertheless, using a neck bushing it would be very hard or even impossible to re-size the very corner of the neck shoulder where my little doughnuts have formed.  This is the area where the little doughnut lives.  So is the K&M fluted pilots on the neck turning tools such a great idea?  It is appearing that if the K&M fluted pilot works for you, you are one lucky person.  Somehow, you got a fluted pilot with a diameter that is perfectly sized for your case neck wall thickness and neck chamber, now go buy a lotto ticket.  However, I still got my not so dreaded doughnuts and they are starting to upset me for no known reason.

How may I rid myself of these little doughnuts?  Use the K&M fluted pilot?  Is it also an inside reamer?  Only that this fluted pilot appears to be too small to function as a 308 Doughnut Cutter.  However, may I still be able to use it somehow?  Can the fluted pilot cutters be positioned in the case somehow, then also be forced to cut the doughnut.  Answer is YES.  Is this the proper K&M procedure?

How to position the case neck on the fluted pilot so that the fluted cutters can attack the doughnut area.  See Figure 3 (Cutter.jpg),

this shows the K&M flute pilot inside the notched out case, the small straight portion of the cutter flutes must be positioned correctly in the case.  My first attempt, I held the fluted pilot by hand so the flutes on the pilot would contact the doughnut area inside the case.  Then turned the case and pilot in opposite directions by hand.  I was able to cut away the doughnut.  The main part of the pilot is just a mandrel without any cutting teeth.  This part of the pilot or mandrel may contact the upper part of the neck inside and will not scratch or cause any harm to the case inside surface.  The little flutes on the tip of the pilot, this is where the cutting action takes place and where the cutting teeth are located.  Just the tip of the fluted pilot must contact the case in the neck to shoulder area to remove my not so dreaded doughnuts.  Then comes the hard part, how do you force the pilot tip to ride on one side of the case neck wall so that the cutter portion will cut into the doughnut area?  I did it on one case by hand. May I do it again?  Yes I may do this by hand, but not for another 800 or so cases.

The case must be position so that short flat cutting section of the fluted pilot aligns with the doughnut area inside the case.  In order to do this, I just added some washers around the base of the fluted pilot, which was stuck in the wooden block.  I also found a rubber grommet that fit onto the K&M 308 Fluted Pilot.  See Figure 4 (Position.jpg),

this pictures shows the rubber grommet on the K&M fluted pilot for positioning the case correctly to attack the little doughnuts.  What this procedure ends up doing is cutting a taper on the inside of the neck at the shoulder.  The angle for this taper is small.  My 308 necks are about .300 in. long.  If the pilot or mandrel was 0.002 or 0.003 in. smaller then my neck inside diameter, which would only allow the mandrel to angle at a 2 - 3 to 300 rate.  Expand that to 2 to 3 ft for 300 ft. or 24 to 36 inches at 100 yards, and the angle is around 24 to 36 minutes.  Therefore, this turns out to be a very small angle.

Must get some power into this operation.  Somehow, I have to get my 3.2-Volt Skil electric cordless screwdriver involved.  This led to mounting the K&M case holder on my cordless screwdriver.  Now I may slowly power turn the case.  Next, how to position the case’s neck, so the cutters on the tip of the fluted pilot will align with the doughnut.  I need some sort of a positive alignment.  Therefore, I mounted the K&M Fluted Doughnut Cutter Pilot onto a small wooden block.  Drilled a hole in block to fit pilot and even added a setscrew in one side to hold the pilot in place.  The right combination of washers along with rubber grommet was used to position the case on the fluted pilot so the small reamer like cutter would align with the doughnut area.  See Figure 5 (Block.jpg),

picture showing fluted cutter mounted on block with washers and rubber grommet to position the cutter.   Now the case may be power turned using the electric cordless screwdriver in one hand, while holding the small wooden block with the fluted pilot.  Next, force the doughnut area of the case neck into fluted cutter.  The thumb on the hand holding the block may perform this little function.  Now, the doughnut area inside the case neck is being power reamed.  This was easy to do.  On some cases, I would tilt the cordless screwdriver a little to force the cutting action.  The final no/go test is to have a bullet pass in and out of the case by gravity action only.  Because of the close fit it takes a second or two for the bullet to settle into the case and a couple of extra seconds for the bullet to back it’s way back out.  Therefore, I repeat the cutting action until the bullet goes in and out by only gravity.  The process is not the best, but it works.  So my bottom line is, I made the K&M Fluted Pilot Doughnut Cutter work.  I do not think this is or ever will be the recommended process by K&M.

This whole doughnut thing has been very interesting.  I am not about to offer my opinions to the pile of opinions on the formation of doughnuts.  However, I do have them.  For example, my two silhouette rifles with the same specified barrel act as follows. One rifle (Old Red) has doughnuts in 90% of the cases after five firings and the other rifle (Blue) has doughnuts in 10% of the cases after three firings. Two guns and differences in doughnut percentage, Red 90% and Blue 10%.  Red: Fired case headspace equals +0.002 and resized case equals 0.000 using the RCBS Precision Mic scale.  While Blue: Fired case headspace equals 0.000 and resized case equals –0.001 using the RCBS Precision Mic scale.  Both rifles have 0.340 necks and I can not measure any difference using fired cases between the two rifles.  All brass prepared the same, at the same time for both rifles.  In fact, I sorted the brass by weight after all the brass preparation was completed.  Four hundred cases for each rifle.  Red got the lighter half and blue got the heavier half.  The only difference is the brass for old red as stretched, expanded, or flowed an extra couple thousands of a inch on the first firing.  The little doughnut I have looks much like the doughnut in Mr. McPherson’s article.  His doughnut was on a 6 PPC, which had a lot more brass, removed around the neck than my 308 cases.  Both his doughnuts and my doughnuts were right where the shoulder turns into the neck.  Very hard spot to deal with.  The way I ended up removing the doughnut, may actually be a better way?  Re-sizing cases using die with bushing can you actually resize that last little portion of the neck?  The brass spring back in the corner of the shoulder and neck or doughnut area is going to be different then the other portions of the case.  This difference should appear during both resizing and firing.  Does not matter how the doughnuts got there, they are there, and should be dealt with.  Using the K&M fluted pilot as I did may be one of the easy ways to rid yourself of the dread doughnut.

When is the dreaded doughnut actually a problem?  Well I do have an opinion on that; there are safety-related doughnuts and accuracy-related doughnuts.  First safety-related doughnuts, these are the, I want to say larger type, that can cause interference’s with the bullet, case, and chamber.  The amount of interference required to become a safety issue is not an area I can really comment on.  However, if it only required the slightest amount of interference, I think you would see this problem very often.  In addition, any level of interference type doughnut should be easy to detect.  A loaded round may be hard to chamber due to this interference.  Loaded cases may be measured and compared to chamber dimensions.  Bullets fitting into a fired case only part way, this also indicates some type of interference.  Cartridges that were partially neck sized maybe checked after loading with a neck sizing bushing, one, which is the same size as the rifles chamber.  There may be other types of doughnut out there which do not cause any interference, however it may affect accuracy.  In my case, if the chamber were 0.341 instead of 0.340, I would never have found the doughnuts.  Then again they may have never formed.  Let us say there are some, how would you know if you had one?  Normal sized bullet would pass right through and everything appears to be correct.  If I had an oversize bullet, 309 verses a 308, then I may find them.  I am just trying to make a point and start some of the readers thinking.  It appears to me that having a set of pin gauges to check the case neck size and look for doughnuts may not be such a bad idea.  After all it also appears to me, that even after following all the correct procedures you may still get a small doughnut right at the shoulder to neck juncture.  I was lucky that I could use my bullets as a pin gauge and look for little doughnuts.  If I turned the brass down another 0.0005 in, I would not have seen the doughnuts.  Would I have noticed this small doughnut during bullet seating?  I do not think I would have using my press.  After re-sizing the neck, the normal neck area would offer more resistance than the little doughnut at the base of the neck, which I would not have re-sized.

K&M make a nice case mouth reamer with a depth of cut stop.  They also have a great case neck turner which only needs an additional cutting stop guide to become a great inside case shoulder to neck reamer also.  The fluted mandrel can not be one size fits all as a prefect doughnut cutter, however the current design, may allow it to double as a shoulder to neck reamer if used as I used it.  I think the size for a prefect doughnut cutter would have to be one that is sized for the spring back inside neck diameter which would still hold the bullet in a tight neck chamber.  However, this dimension will vary still by user and the number of case firings.  However, the amount of variations from different spring backs maybe down to less than one thousand of an inch.  So maybe the K&M designed the fluted mandrel this way and it was just a tad small for my doughnuts.  Therefore, the fluted pilot must be somewhat sub caliber sized so it will fit into any tight neck fired case without scratching up the inside of the neck.  This is the only way the fluted pilot mandrel may check for or remove any doughnuts without re-cutting the outside of the case neck.  On the other hand, make your own cutting guide stop and just put a little taper on the inside of your cases at the case shoulder to neck area just for good measure.

How much accuracy is affected by hard to detect doughnuts?  All I know is this is not something I have to lose any sleep over in my silhouette game, however, maybe this is something that should keep a few bench rest shooters awake.  Some of you do sort your cases by firing, right.

(If you read this though, you may have noticed that I have done a 360 or a full turn around on the K&M fluted mandrel for their neck turning system.  It works, or it maybe made to work.  Using it is not as straightforward as one expects it to be.)

Part Two: Found some more doughnuts in my 221 Fireball Cases.  The Fireball Barrel for my Contender has a match chamber, which only really means the case necks must be turned to fit the 0245 neck.  Checked some fired cases with a flat base bullet and sure enough, doughnuts.  Same little critters as were in the 308 cases.  So tried the doughnut cutting procedure by hand and doughnut was gone.  Bullet slips into and out of the case by gravity.  Second generation idea, the .22 caliber fluted mandrel was in the K&M neck turner.  I was leaving it set up for the final cut on the fireball cases.  The little cutting teeth on the mandrel stick out past the edge of the turner housing.  I cut off a small piece of 1/8 inch thick Plexiglas (screen door stuff) the same size has the housing and drill a .221 diameter hole in the center.  Placed it over the fluted pilot and reamed the hole to fit.  See Figure 6. (PlexiglasK&M1.jpg)

The Fireball Case stops at the correct point to taper the inside of the neck at the shoulder junction.  Best of all, all the neck trimming settings were not changed.  Holding the K&M turner housing was easier than the wooden block.  K&M should consider this and supply a small aluminum plate the same size as the housing with hole for the flute mandrel.  The fluted mandrel maybe adjusted in and out to place the flute flats right on the case neck shoulders.  That would make the system a first class doughnut cutter.

Notice a couple of things while doughnut cutting away on over 100 Fireball Cases.  I am mentioning this only as some thought starters.  First, while cutting the doughnut on some of the cases, it felt like I was hitting something hard on one side of the neck inside.  Felt different than just a heavy cut on one side.  No visual signs of anything on the outside of the case to cause it.  I had about half dozen cases do this.  Next, while checking the cases by letting the bullet slide to and out of the case by gravity only, I noticed on a couple cases that the bullet would yaw some.  The bullet would yaw some just as it was released from the upside down case.  Looks like I need to re-crown a couple of cases.  Additionally, on a couple of cases, the bullet was tight at the mouth.  I appear to have a little bur or doughnut inside the neck right at the end of the lead in taper.  Mentioning these items because of the article on the Secrets of the Houston Warehouse by Dave Scott some time back, in that article something was mentioned about sandpaper and cases.  Article never really explained anything about using the sandpaper other than indicating that it was something like the final tuning step for those 0’s groups.

Larry Medler

Rifle Silhouette Shooting

Silhouette Ballistics

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February 11, 2003