Dealing with donuts

NamibHunter

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We all know donuts are a real pain to deal with. Have tried to summarize what (little) i know about the topic, and curious to learn what tricks you guys have tried!

Detecting donuts: Have recently tried gauge pins to feel for a donut, and it works pretty well. Some cases get donuts earlier than others, for some weird reason. A regular inspection every 5 firings is probably a good idea. Btw: You just need 3-4 gauge pins, and they are very cheap ($3-$5), worth getting. Or get a full set for like $70.

Have tried to deal with donuts in multiple ways, like neck turning slightly into the shoulder, or using bushing dies which does not resize that part of the neck, like a Redding Type S followed by a mandrel die in a standard press, or an LE Wilson neck sizer die using an arbor press, followed by a small base die in the large press.

Neck turning: The theory is that post firing, that gap you cut on the outside will move to the inside of the case, and you will have a “negative” donut, csing a slightly thinning of the neck-shoulder junction, which can absorb any brass growth in that area. Does not really work like that: After every firing and FL sizing step, the brass has stretched and the case gets 2-7 thou longer (also every case has somewhat different length), and that gap moves forward of the neck shoulder junction a few thou every firing. A donut eventually appears behind the gap you created. Maybe it helps for the first 4-6 firing, but i doubt it is a real solution to the problem.

Neck sizing avoids the case stretch, and maybe/probably slows down donut growth, but before long your bolt won’t close or the bolt “clicks” when you try to exteact a fired round (bad sign). So not really a longterm solution either. You could potentially neck size twice and then full length after third firing, but speed will be a little different, so you might need to tweak your powder charge (two loads) to stay in the node. Have not tried this.

Have an LE Wilson lathe type cutter that i used for trimming cases to length. Nice kit, but pricey. You can also buy an inside reamer from them. Have used it on brass after 10 firings and again after 20 firings, but it makes the inside of the neck a little rough post cutting. You can polish the turning marks out with fine steel wool imbedded in a bronze brush and a high speed drill. Extra work and your AMP machine hates magnetic material that finds its way inside. Makes the anneal inaccurate, and interferes with the operation of the machine. I also found that springback is not the same close to the case mouth and near the neck shoulder junction. The Lapua grain structure is intentionally varied from from neck to the case head, the Finns getting all clever and sophisticated on us. I suspects that contributes to the springback differences. Result is that the inside neack reamer takes more material off near the case mouth, and the brass thickness is not the same afterwards, as post neck turning. It does cut out most (but not all) of the donut, which obviously helps. But 5 firings later a small donut has formed again in the same spot, and the donut you cut back previously has just moved forward…. [Maybe I should do inside neck reaming more frequently than i do now, but it is a real PITA, and it has undesirable side effects that move your neck thickness and bullet grip. Maybe the long case life of Lapua SRP brass has some negatives too?]

The K&M carbide neck turning tool plus mandrel also helps: It has a carbide cutter on the tip of the mandrel and a carbide blade on the outside cutting the neck to a smaller diameter. You turn the outside of the neck, and cut the donut on the inside, all at the same time. Works well enough, but a small portion of the donut remains.

0D2DA945-3C83-49FF-A0C7-299C0C518DE5.jpeg


I just load the bullets long, with fairly small jump, and keep the pressure ring (thicker part close to the boat tail, for better gas sealing) well above the donut area. That initially limits your bullet choices. Trade-offs everywhere! I wait for the lands to move forward (typically when i get past 1,000 rounds on the latest barrel), then i switch from 140 gn to 147 and eventually to 156 gn bullets. Seems to work better.

I know some competitors buy new Lapua brass, use it once, and then sell it for like 70% of the new price. That is probably the only solid way to avoid donuts. Pass the problem on to somebody else who has more patience! 😊

Hope this helps…
 

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NamibHunter

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Some Teslong pictures from the inside of a fired case (no case prep other than corn cob tumbling) - after inside neck reaming:

Most of the cut occurs close to the top of the neck:

915D5A11-9CBB-4707-8406-1BF60FA2C5B2.jpeg


You can see the bevel at the edge of the neck where the VLD chamfer tool cut at an angle.

Any ideas why the neck area is smaller?
 

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NamibHunter

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The picture below shows a bright ring mark at the neck shoulder junction, where the cutter encountered a significant donut. The smaller pin gauge also got stuck there:

D97F35F0-956C-4305-81E3-7306EE50EEF6.jpeg


After inside neck reaming, the pin gauge goes through easily.

Below is a partial donut (different case) after cutting most of it out:

D6EE4036-55A5-4526-8765-F20AA83DEF0E.jpeg


Pin gauge did not pick up this very minor donut. Note the pins are 0.5 thou apart in OD, so the measurement technique has limited resolution.

Note that the cut does not go right around the neck/shoulder junction, in this case it seems one side of the donut was thicker than the other side.

Some cases had thicker donuts, some were partial, some had none. [Probably a good recipe for inconsistent neck tension, if the bullet is touching the donut.]

Also note the “negative donut” (what looks like a hollow groove) just ahead of the cut mark. This was intentionally created during neck turning (K&M tool), by cutting into the shoulder. Clearly it did not help for more than 2-3 reloads. The new donut forms just behind the groove. [The Teslong bore scope gives something like 20x magnification, so don’t be alarmed by the depth of the groove.]
 
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XLR308

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    I pretty much neck turn most of my brass to achieve approximately 90% clean up but have never seen what you posted.
    I have some reamers but never really needed any of them except in 270win when i had to seat below the neck shoulder junction.
    Your pic looks like the case mouth is belled open, i think you need a properly sized mandrel before running the ID reamer.
     

    NamibHunter

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    I pretty much neck turn most of my brass to achieve approximately 90% clean up but have never seen what you posted.
    I have some reamers but never really needed any of them except in 270win when i had to seat below the neck shoulder junction.
    Your pic looks like the case mouth is belled open, i think you need a properly sized mandrel before running the ID reamer.

    It does look that way. No flaring of the neck: The perspective and the Apple photo editing software makes it look that way - the case is fire formed, so chamber dimensions. [LE Wilson inside reamer is designed to work with fired cases.]

    BTW: The chamber is good. MPA match 6.5 CM chamber (which is a min spec chamber), gun does 0.15” to 0.35” groups at 100, depending on load.

    92A4CB8A-91DB-416C-8977-F8E9D80A41B0.jpeg
     
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    XLR308

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    Trick of the light i guess.
    It looked belled when i first looked at it.
    Unless you have a short freebore i cant see any reason to seat bullets far enough down that the donut would be a problem.
    Mine is the SAAMI .199" that Kelblys chambered and all of the bullets i have used so far ranging from the 123CC to the 150smk are seated above the neck shoulder junction.
     

    NamibHunter

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    The poors don’t have donuts. They use cheap dies with cheap brass and toss it before donuts form. Nursing Lapua brass to 40+ firing is a first world problem.
    Yep that is a fair point! Just double checked the new-ish 4x fired Lapua batch, and the pin gauge says “no donuts today”…

    About first world problems and budget deficits…. I do try to reload for quarter inch accuracy (and not always getting there), but overall aim for the best “bang for the buck”, so i am actively looking for ways to save money. Need to save up my pennies to buy a new barrel soon.

    Did the calcs, and SRP brass works out cheaper per fired round, compared to (for example) low cost Hornady brass - but only if you can get adequate accuracy after 20-25 reloads. I prefer to use SRP brass because it gives good case life, and have seen 25-30 reloads before on Lapua and Alpha. Not yet achieved 40, but who knows, it might be possible! Premium brass is nice, but have recently started using a batch of cheaper Starline SRP brass…. Looks like food brass, but will have to wait and see how they hold up.

    But if the brass becomes donut infested after 15 or 20 reload, then that cost saving is of no value, if you are loading for minimal jump and the chamber is short.
     
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    NamibHunter

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    One trick is not to size all the way down to the neck shoulder junction, using bushing dies and then opening up the neck slightly with a mandrel die, e. g. the Redding Type S or the Wilson arbor press die.

    Another idea that i learned from a hide member is putting this thin washer in place when you use a Lee neck sizer plus small base die to avoid sizing the entire neck, to ensure the donut is not pressing against the bullet when seated deep:

    1F85D29A-42CE-460D-B941-010B15F93C12.jpeg

    5956230D-4809-48E0-A500-4819A65DB049.jpeg


    Both approaches mean you have two sizing steps, instead of one. That will slow you down a bit.

    General idea being that if the bullet is not touching the donut, then the donut cannot do you any harm.

    Edit: Some folks on AccurateShooter apparently use this sizing trick to leave the donut area at a larger diameter compared to the rest of the neck, then use an outside neck cutter to carefully remove a small amount of material from the donut region only, thinning that part of the neck by 2 thou or so, then go back to normal sizing.

    It seems the problem with inside reaming is that the reamer pushed the inside donut partially to the outside, and only cuts out part of it. This trick seems to remove slightly more than required. Will give it a go and report back at some point.
     
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    XLR308

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    I was using a 21st century turning mandrel after sizing innitially but eliminated that since i neck turn my Lapua brass and it didnt seem to be doing much if anything with a .289 bushing in a Type S FL die.
     

    918v

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    RCBS makes an inside ream die that allows you to ream the neck with a reamer on a t-handle going in from the top. Furthermore, you can request a custom neck size. So if you’re good at math you can figure out what you need to have the die slightly compress the neck and body while you ream. That way, as shoulder brass flows into the neck, you can ream it away and always have the same neck. If you neck turn first, the reamer will cut dead center down the neck.

    But that’s a lot of work.
     
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    NamibHunter

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    Trick of the light i guess.
    It looked belled when i first looked at it.
    Unless you have a short freebore i cant see any reason to seat bullets far enough down that the donut would be a problem.
    Mine is the SAAMI .199" that Kelblys chambered and all of the bullets i have used so far ranging from the 123CC to the 150smk are seated above the neck shoulder junction.

    Fair point. That is what i have been mostly doing the past 5 years in my target rifles. This is one of the main benefits of “modern” cartridge designs with longer necks and a very long COAL specification, like 6.5 CM and 6.5 PRC, or 300 PRC.

    I’m trying to figure out how to deal with bullets that have to be seated deep. My hunting rifles in 308, 300 Winmag and my favorite lightweight hunting rig (a Howa 30-06) all force me to load the bullets deep, way past the neck shoulder junction. Especially the Barnes TTSX needs to be seated very deep. So curious how best to deal with that.

    MPA arrived new with a short freebore, throated for the 140 ELDM factory match ammo. I could not load a 147 ELDM or 156 Berger EOL, because it forced me to seat the bullets deep enough to intrude significantly into the powder column, and go beyond the donut region. So gave up on that idea.

    The first barrel is now past 1,500 rounds, and the lands have moved forward quite a bit. Will soon try these long bullets again, and i expect they will now fit above the donut area.

    When the replacement barrel arrives in a few months, i would like to shoot the long high BC bullets at 1,000 to 1,500 yards - even though the throat length is not optimal for these projectiles.
     
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    NamibHunter

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    RCBS makes an inside ream die that allows you to ream the neck with a reamer on a t-handle going in from the top. Furthermore, you can request a custom neck size. So if you’re good at math you can figure out what you need to have the die slightly compress the neck and body while you ream. That way, as shoulder brass flows into the neck, you can ream it away and always have the same neck. If you neck turn first, the reamer will cut dead center down the neck.

    But that’s a lot of work.

    Neat idea!

    This looks like the best way forward for the hunting ammo, did not know anybody made such a die, very much appreciated!
     
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    XLR308

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    Fair point. That is what i have been mostly doing the past 5 years in my target rifles. This is one of the main benefits of “modern” cartridge designs with longer necks and a very long COAL specification, like 6.5 CM and 6.5 PRC.

    I’m trying to figure out how to deal with bullets that have to be seated deep. My hunting rifles in 308, 300 Winmag and my favorite lightweight hunting rig (a Howa 30-06) all force me to load the bullets deep, way past the neck shoulder junction. Especially the Barnes TTSX needs to be seated very deep. So curious how best to deal with that.

    MPA arrived new with a short freebore, throated for the 140 ELDM factory match ammo. I could not load a 147 ELDM pr 156 Berger EOL unless you allow the bullets to intrude significantly into the powder column. So gave up on that idea. The first barrel is now past 1,500 rounds, and the lands have moved forward quite a bit. Will soon try these ling vullets again, i expect they will now fit above the donut area.

    When the replacement barrel arrives in a few months, i would like to shoot the long high BC bullets at 1,000 to 1,500 - even though the throat length is not optimal.
    I had the same issue with 270win and certain bullets so bought the RCBS reamer just for peace of mind.
    K&M also makes a good reamer.
     
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    NamibHunter

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    Had a look: It seems RCBS stopped making those dies and the inside reamer. Old links are all broken and Midway says “Discontinued”.

    Found a company selling tool steel reamers of almost any size you could wish for:



    Presume i could buy such a reamer that is 2.5 to 3.0 thou under bullet diameter and use a standard FL die with the sizing button assembly removed (assuming the FL die sizes the neck 2.0 thou under bullet diameter), attach reamer to an electric drill and hope for the best….

    The LE Wilson inside reamer works fairly well too on fired cases, if the brass is first neck turned. It supposedly self-centers in the case, so concentricity is not really guaranteed. Apparently in order to reduce costs, their shell holders are not drilled perfectly concentric with the outside profile of the cylindrical case holder, but the cutter has some slop in the mini lathe, allowing it a small amount of float, so it can mostly self-align with the inside of the case neck. Workable but not perfect.

    0A1EBBCA-117A-4416-A7AF-320E3CFB0704.jpeg
     
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    918v

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    Had a look: It seems RCBS stopped making those dies and the inside reamer. Old links are all broken and Midway says “Discontinued”.

    Found a company selling tool steel reamers of almost any size you could wish for:



    Presume i could buy such a reamer that is 2.5 to 3.0 thou under bullet diameter and use a standard FL die with the sizing button assembly removed, that sizes 2.0 thou under bullet diameter, attach reamer to an electric drill and hope for the best….

    The LE Wilson inside reamer works fairly well too on fired cases, if the brass is first neck turned. It supposedly self centers in the case, so concentricity is not really guaranteed. Sadly, their shell holders are not drilled perfectly concentric with the outside of the case holder.

    Well that sucks. Maybe they can make you one if you call them directly. The last one I had made was years ago. It was a pain in the ass.
     

    NamibHunter

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    Well that sucks. Maybe they can make you one if you call them directly. The last one I had made was years ago. It was a pain in the ass.

    Ebay may still be an option, and i guess i could watch the buy&sell section on the hide more diligently.
     

    918v

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    Back in the day you‘d call them in Oroville and they would transfer you to a guy who did not answer his phone. You’d leave your info and he’d call back and tell you what sizes/dimensions he could make. Then you’d wait three to six months and the die would arrive. The die was $80 something and the reamer about the same and they could do custom neck sizes for a little extra.
     

    NamibHunter

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    Have now read most everything i could find on the topic of case donuts. Trying to summarize below what appears to be the consensus opinion. [Please correct me if i got any of this wrong, just trying to learn more]:

    Definition: A donut is a small portion of thicker brass that builds up inside the case neck, that gradually moves forward with every firing, and after a number of reloads, will be located in the neck-shoulder junction area, and will have a smaller inner diameter than the neck ID.

    Main Cause: Brass slightly stretch with every firing and subsequent FL resizing operation, gradually thinning the case wall below the shoulder. For virgin brass, the brass gets gradually thicker from the top of the neck to the case head where it is at its thickest. The brass thickness is tapered from case mouth to web area. The brass in the neck is therefore naturally thicker on the shoulder compared to the neck. As the case stretch and get longer, periodically requiring the case to get trimmed back to SAAMI length, the thicker shoulder material will move forward and enter into the bottom of neck, causing a thicker ring that will have smaller inside diameter (ID).

    Result: The resulting thicker ring of carbon located at the neck-shoulder junction will require significantly more force to propel the bearing surface of the bullet (and the pressure ring at the heel of the bullet) past this point, and neck tension/bullet grip will increase significantly. High but variable neck tension will cause higher ES, and large vertical dispersion at longer distances. The change in speed can also push an optimized load out of the powder node (the flat spot in the speed vs. powder curve), and interfere with positive compensation (a load optimized via seating depth where bullets launched at different speeds, within a specific range of speeds, impact at the same height at long range).

    Case Design: The main problem is clearly that most case designs (for example 308 and 30-06, and many others) from the previous century have very short SAAMI freebore specs, and the bullet is intended to sit very deep in the case, where it will be touching any significant donut that might have appeared after 5-7 firings. This increases neck tension, and bullet speed can go up. Also, it creates significant inconsistency in bullet grip/effective neck tension, as some cases will have minimal constriction and others will have thick donuts, leading to a large ES, and can push the load out the powder node. Can also contribute to a loss of bullet concentricity (total indicated runout), but this is less problematic than neck tension changes.

    Modern cartridge design: cases like the 300 PRC ensures that the neck is long, and the bullet is seated well above donut area, so a donut will have minimal effect, aa it does not touch the bullet shank. However, a very thick donut can still restrict the flow of gasses and powder kernels through the neck, changing the pressure trace, and causing more speed, but this is rarely seen.

    Neck turning: This can help to make the neck tension/force exerted on the bullet more consistent, for the first 1-5 reloads. But it also makes the donut more pronounced, as the neck thickness reduction cannot be accomplished over the shoulder area. This leads to a fairly abrupt change in brass thickness, even if the cutting tool blends the cut into the shoulder. Virgin cases from a good batch that have relatively concentric thickness as measured at 6 spots around the circumference with a ball micrometer should probably not be subjected to neck turning. Cases that are not neck turned should last for more reloads before the donut is significant enough to cut out, but eventually a donut will appear, regardless of neck turning.

    Nr of Reloads: It is rare to see donuts that are thick enough to matter before 5-7 reloads. A microscopic donut will be present from rbe first firing oneards, but initially has minimal effect. Some older catridge designs with a 23 degree shoulder angle form donuts faster than an Ackley Improved case with a 40 degree shoulder or a modern case design with a 35 degree angle. If the primer pocket of the batch of cases survives beyond 10 firings, all case designs will eventually have some donut at the neck-shoulder junction. This may or may not be a problem.

    Solutions: Easiest way to deal with donuts is to dump the brass before the donut gets fully developed. Good quality LRP brass rarely survives beyond 10-12 stout reloads. Maybe it is not a sound idea to baby your brass to survive for 30 reloads? It is a consumable after all.

    Cut out the donut: You can do a light skim cut with a neck turning tool every 5 reloads, cutting slightly into the shoulder. Best is first to run a mandrel die through the inside of the neck to push (most of) the donut to the outside. Springback will ensure that the entire donut is not removed (a ring of brass about 1 thou thick will remain). The use of a mandrel can help to mitigate the inevitable microscopic donut that remains.

    Alternative: Inside reamers like K&M or LE Wilson can be used, but will only remove a portion of the donut (springback or elastic bending will occur so only a portion is removed). A part of the donut will be pushed to the outside of the neck by the reamer, due to plastic deformation. Best approach is to hold the case in an FL die that has already pushed the entire donut to the inside of the neck via the sizing step, then cut it out from the inside, like the RCBS FL die plus inside reamer setup mentioned above. Sadly, this device has been discontinued.

    Summary: You can mitigate (but not eliminate) the effect of donuts by:

    1) Loading long, so the bullet does not touch the donut.

    2) Start with shorter lighter bullets that can be loaded to a short jump, and still be above the donut area. Switch to longer heavier bullets as the lands move forward.

    3) Pick calibers where the bullet does not intrude deep into the case.

    4) Retire LRP cases at 7 reloads.

    5) Think carefully if you really need to do neck turning. If so, then skim cut the neck (minimal neck turning, around 30%) and cut slightly into the shoulder. Avoid taking off 2-3 thou of material from the neck.

    6) For SRP brass like Lapua, inside ream and skim cut the outside neck a second and third time, about once every 7 reloads. Use fine steel wool wound around a brass brush to polish the inside neck smooth again. Do this work outside, and avoid getting fine steel fragments into your AMP machine (it could malfunction, same as forgetting a stainless pin inside a case after wet cleaning). Use a small magnet to remove the steel wool debris from the inside of the case.

    7) Or sell your new Lapua brass after one firing…. And keep buying new brass! 😊
     
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    NamibHunter

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    One thing I’ve noticed is I haven’t had donuts since I started using a body die and Lee collet.

    Interesting observation, thank you for the contribution. This is valuable information.

    Will give it a try!
     

    NamibHunter

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    It’s the magic midget inside the collet die. He make donuts disappear.

    I like your sense of humor sir! 😁 You are a very funny dude. No sarcasm intended!!

    I guess you are skeptical if this combo will work? I can see how the Lee neck sizer will “smudge” the sharp edge of the donut and make it less pronounced.

    And a small base die should cause less case stretch. So i am willing to suspend judgement and try it…. But i expect it will delay the donut problem, and perhaps not completely remove it.

    Have you tried it? Any other approaches that have worked for you?
     
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    918v

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    I’m not skeptical at all as I have been an early adopter and promoter of the Body Die / Lee collet neck die combination. I haven’t seen donuts since.

    Lemme tell you guys a story:

    I once got some brand new Lapua 308 brass. I loaded up some test rounds right out of the box and shot most of them at the range. The rest I brought home and pulled apart. Now all the neck tension was gone so I neck sized them in the LCND. I noticed something funny about the neck after I sized it. It was longer and not uniform anymore. Apparently the brass was soft enough to extrude under the pressure of the collet against the mandrel. It wasn’t a lil bit. It was 20-30 thou. That die generated enough pressure to squirt brass out the collet.

    So donuts either don’t have a chance to form or are squished out or both. It’s a good system. Too bad they don’t make this die for all calibers or maybe a universal neck die system of some sort.
     
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    Barelstroker

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    I’m not skeptical at all as I have been an early adopter and promoter of the Body Die / Lee collet neck die combination. I haven’t seen donuts since.

    Lemme tell you guys a story:

    I once got some brand new Lapua 308 brass. I loaded up some test rounds right out of the box and shot most of them at the range. The rest I brought home and pulled apart. Now all the neck tension was gone so I neck sized them in the LCND. I noticed something funny about the neck after I sized it. It was longer and not uniform anymore. Apparently the brass was soft enough to extrude under the pressure of the collet against the mandrel. It wasn’t a lil bit. It was 20-30 thou. That die generated enough pressure to squirt brass out the collet.

    So donuts either don’t have a chance to form or are squished out or both. It’s a good system. Too bad they don’t make this die for all calibers or maybe a universal neck die system of some sort.
    I also use the LNCD but I haven't measured neck or bullet runout.
    Have you been able to measure runout of your cases after sizing with the LCND?
    Regards...........Barelstroker.
     

    918v

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    I also use the LNCD but I haven't measured neck or bullet runout.
    Have you been able to measure runout of your cases after sizing with the LCND?
    Regards...........Barelstroker.

    Yes, and it was low. On once fired unturned brass it’s within .003” TIR. It’s so boringly low I stopped thinking about it.
     
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