Donuts

[fdshuster]

Discovered donuts in brass that has never been outside neck turned. One of the cartridges in question is a Hart barreled 223, chamber cut with my reamer, .253" no turn neck, .074" of freebore. Brass is Lapua used as-is, right out of the box. Recently took a box of 20 that had been loaded 5 times, and tried to drop a 80 gr. SMK into the as fired, unsized case. The bullet stopped at close to its loaded o.a.l. Then checked the other 19 cases & the same bullet stopped at the same location. Took my Stoney Point Gauge and measured the length from the case head to the bullet ogive & got 1.996". Then took the same measurement with a loaded round, same bullet & that measurement is 2.005", so I'm .009" in front of the donut. No problem. But if that bullet were to be seated deeper, like with a .020" jump, then it would be seated on top of the donut. Not good! I always thought donuts were caused by not making the cut close enough to, or slightly into the shoulder, but from these findings that is not necessarily true. Then checked some Lapua 6BR brass, also no-turn at .272" & found donuts there also. Might be a problem there since my reamer is a zero freebore & with the longer, flatbase bullets, like the 80 gr. Berger Varmint, they are also contacting the donut. Another learning experience for me. Check your as fired brass for donuts by trying to drop a bullet into the case. If it hangs up, there are donuts there. Interesting to me also that when measuring those 20, 223 Lapua, the lengths as mentioned above were exactly 1.996" for all 20. I'd be interested to hear if anyone else finds donuts in unturned brass. :-\

 

[jonbearman]

The only time I get donuts is when using bushing type sizers or when I go to dunkin,LOL It seems the standard dies are less prone due to being the exact shape of the cartridge to begin with.

 

[artbosco]

Discovered donuts in brass that has never been outside neck turned. I'd be interested to hear if anyone else finds donuts in unturned brass.

NEVER. But, I use Lapua exclusively.

 

[Eddie Harren]

Jon, don't confuse the "step" left on the neck when using a bushing die, to the real doughnut, on the inside of the case, at the neck/shoulder junction.

 

[mikecr]

I always thought donuts were caused by not making the cut close enough to, or slightly into the shoulder, but from these findings that is not necessarily true.

You'd also find this because it's just opposite of reality.
All cartridge brass irregardless of brand has a built-in donut. It's because they taper in thickness from the webs all the way to the mouths. But it's not always a problem.
You didn't say how you neck size, but if you FL size the necks you can force the thicker brass nearest the neck-shoulder junction to the inside. This is dependent on your die though, as many FL dies would have a tapered neck per cartridge design(SAAMI).

If it's a non-tapered neck chamber or non-tapered neck die, then the best solution IMO is to partial NS with a bushing die(if a tapered neck chamber), or turn the necks to uniform thickness.

 

[fdshuster]

The responses raise another question. Yes, the brass in question is all out of the box Lapua, and they are all being sized with the Redding Type S FL neck bushing dies. I understand the bushing leaves a small area at the neck/shoulder junction that is unsized, whereas the conventional die will size all the way to the neck/shoulder junction, but it seems to me the donut would then be even more pronounced since this "excess" ring of brass is being moved to the inside of the case. Incidently, I have also re-attached the carbide neck expander button to the decapping rod, (something I never normally use) attempting to force the donut to the outside of the case, but the donut(s) remain. The restriction is a very minimal amount, probably only .001" to .002" smaller than the case inside neck diameter. I can see it with my borescope. It's so slight that sometimes a case will fall past it, fully into the case & I'll have to tap the bullet out with the impact bullet puller. This is especially strange to me since I've never found donuts in my 22BR, 6ppc , 6BR & 6 BRX Lapua brass that has been outside neck turned.

 

[fdshuster]

mikecr: Posted the last msg. before seeing yours. Just checked my reamer print drawings (PTG) for the 6BR and the 223. Both show non taper chamber necks, the BR at .272" and the 223" at .253", same dimension front to rear. Then tried to measure the Redding bushings, but all I have is a Starret dial caliper & as crude as that is for trying to take a small inside diameter dimension, cannot see any difference between the numbered side and the unnumbered. I do suspect that the brass flows forward with each firing and maybe (?) collects at the neck/shoulder junction. I would expect none of this to be an issue as long as one is aware of the possibility & either removes the donuts or seats the bullets accordingly.

 

[mikecr]

This is especially strange to me since I've never found donuts in my 22BR, 6ppc , 6BR & 6 BRX Lapua brass that has been outside neck turned

That's because neck turning uniformed the thickness.
This donut issue is one of the reasons for neck turning.

Your die is not causing any problem here. Your non-taper chamber neck is. Your fired necks measure the same OD from mouths to near shoulder junction right?
That means the neck IDs vary with datum down the neck -because your brass is not turned uniform.

There is another action related messing with reloaders; measuring neck thickness variance.
Every ball mic out there has no stop to set datum of measure. This would cause any user to get greater variances than actual, because depth of measure is then also a variance.
The fix for this: An adjustable stop:

 

[mikecr]

LOL, I just overposted you too

Brass does not 'flow' anywhere. When it moves, it's being moved by sizing(up or down).
FL sizing IS the culprit to this, but it's unlikely to be so consistent as you've described.
A contributor only..

Turn it away

 

[fdshuster]

mikecr: I have not yet loaded those 20 cases so could outside neck turn but it would have to be just a light cleanup cut. Anymore and I'll be creating too much clearance. Chamber neck is .253", loaded round is .250" unturned. Will also outside neck turn 20 new 223 Lapua & watch it over the course of several loadings.

 

[mikecr]

I think Boyd was going to try higher neck clearance with a 6ppc to see if it's performance improved a little. Haven't heard the results, but you never know, it might help!

Personally, I don't see the built-in donut as an issue when I'm not seating there.
I partial bushing NS and watch seating forces with a gage.
What I would notice, is variance or new formation of donut thickness, because it would cause tension variance even though not a sized area.
FL sizing of necks could amplify this greatly, and I would never do that.

Good luck with it. Hope a slight turn helps(or doesn't hurt).

 

[6BRinNZ]

fdshuster - for what its worth with my 6BR lapua brass unturned I get donuts....I have found the donuts grow. Found the issue as I was shooting 88 Bergers and after the third firing i had seating depth issues...tracked it down to donuts same way as you mentioned.

I use redding bushing dies and FL size every time.

These are my findings so far;

(unturned lapua brass)

1./ 1 firing no donut detectable using the bullet drop method
2./ 2 firings small donut forming detectable on some cases using the bullet drop method
3./ 3-5 firings strong donut on all cases
4./ 3-5 firings the Sinclair expander will push donuts out - the "pop" is noticeable along with feel when using the expander
5./ A slight outside neck turn clean up on cases that have been expanded show significant (relative) brass removal in the donut area.
6./ The size of the donut and placement of the donut is the same as the unsized portion using bushing dies.

After my issues with the 88s I always ensure that I am loaded above any potential donut area and typically use BT bullets now....not because of this issue but the type of shooting I do.

I don't believe the brass manufacturer has anything to do with the issue and have believed it related to the fact that the bushing didn't size all of the way down the neck.

I do wonder if the bushing sizing method is similar to having a piece of cloth and constantly pushing it in one direction with say an iron....the material will "move" in that direction and will flare towards the edge that the motion is towards. With a brass case something similar may happen but it meets the neck shoulder junction so can't move any where so it "builds up/congregates" in this region, this effect combined with the small portion that isn't sized may produce the donut....anyways just conjecture.

Good luck.

 

[artbosco]

Discovered donuts in brass that has never been outside neck turned. I'd be interested to hear if anyone else finds donuts in unturned brass.

NEVER. But, I use Lapua exclusively.

Let me clarify a little further with this statement: I've never found donuts in unturned brass coming out of a new box of brass.

However, I've created donuts in brass, that has never been outside turned, simply by necking up new brass. It happens with 220 Russian necked up to 6mm and in 6BR brass necked up to 30BR. I tend to see it more in the 6 necked up to 30.

 

[fdshuster]

6BRinNZ: My findings on the round count are identical to yours. New Lapua brass out of the box is donut free. Between 5 and 7 loadings the donut is enough of an issue to stop the bullet from dropping all the way into the case. It's only a problem for me when using the 80 gr. Berger flatbase because of the zero freebore and with the 223 if wanting to seat the 80 gr. SMK at .010" or more from the lands. With all others, especially the boatails I'm in front of the donuts. If needing to remove them I use a half round jewelers needle file & in a few seconds the donut is "gone". I believe this is something that should be routinely checked for by doing a simple bullet drop. Only takes a few seconds & from now on is a part of my case prep. To seat a bullet on top of the donut has to have an effect on accuracy/ group size but more importantly, on pressure.

 

[6BRinNZ]

To seat a bullet on top of the donut has to have an effect on accuracy/ group size but more importantly, on pressure.

Yep - I was new to the reloading game (still am..I just know more than I used to ) and thought it was the "me" factor for seating depth issues with the 88s. I carried on and suddenly started blowing primers...long story short, I was forcing the 88s into the donut and as the donut grew it gripped the bullet tighter until eventually the primers blanked...not on every case just some...

The symptoms were - difficult to get accurate seating depth (+- .002"...004" spread) and inconsistent groups (still under .75 moa for the worst groups at 200...3 shots would be ~ .25 - .5 moa)....it was the lack of consistency for the grouping that was key.

 

[mikecr]

No, no.. If you precisely measure new Lapua 6br brass out of the box, you'll see that is 1/2thou thicker 1/4 of the neck from the neck-shoulder junction -vs- 1/4 from the mouths.
Expanded, it also measures 1thou larger in OD 1/4 of the neck from the neck-shoulder junction, as you would expect.
If you dissected a case and measured mid shoulder it would be another 1/2thou thicker, and thicker again at the body, progressing ever thicker to the webs.
Also, brass doesn't move thin toward thick unless compressed (both sides) in a matter that forces it so. It does move thick towards thin though, which is why FL sizing causes donuts.

A bullet drop test wouldn't work with new unformed/unsized portion of necks.
You both partial NS, so it takes a few firings before the thickness variance is hammered inward -from firing. By then your bullet drops catch it.
You both FL size, neither turned necks, AND you both blame partial neck sizing for donuts..
You both reached for a new theory, while IMO, denying basics in reloading.

But to be sure, I just checked your theory on 223, 6br, 6xc, and 6.5wssm and cannot find evidence of thickening brass below my neck size lines.
With every cartridge I turn necks, partial NS with bushings, never FL size(bump only), and after many reloadings(+30 on a couple) my necks measure exactly the same uniformity (full length) as they did with preps finished and fireformed.

If you turn necks up onto shoulders, and size minimally, you can forget about donuts.

 

[fdshuster]

mikecr; Don't want to start an argument: you've gone a long way in pointing out my errors & I appreciate it, but I never blamed partial neck sizing as the cause of the donuts. When I first discovered them in the 223 Lapua brass I had no idea what caused them. Now that you've made it clear that the walls are actually tapered in thickness from the shoulder to the mouth I can understand that. I do have the die adjusted so the bushing is sizing as much of the neck as possible, cannot take it any lower, so I don't think that's partial neck sizing. Since the new Lapua already has a reduced inside neck diameter, ( the case could be loaded as-is), I've never attempted to do the bullet drop test until after the first firing, when the neck I.D. is blown out to accept the bullet's smaller diameter. I'll make it a point to do a light outside neck turn & take it all the way to touch the shoulder with all new brass. I never took into consideration that the brass is thicker at the shoulder than at the mouth, but with my Mitutoyo tubing mic that has the flat, rather than tapered stud I am limited as to how close I can get to the shoulder.

 

[rcw3]

There is a lot of discussion here on the subject of brass and donuts but I do not know it addresses certain issues:

1. Lapua brass and Norma brass both have a characteristic that our domestic brass (Winchester, Remington, etc.) does not typically have, which is that the shoulder metal of the brass is significantly thicker than the neck metal (not just a thickness difference due to a taper in the brass, but a marked difference in the thickness). Try necking up a Lapua 6BR case to 30BR and you will see a noticeable bulge at the base of the neck because part of the shoulder of the 6BR case just became the neck of the 30BR case. No one shoots 30BR brass made from Lapua 6BR brass without neck turning it for just that reason (i.e. two entirely different thicknesses of brass in the neck upon neck up). Lapua brass is good for a neck down without neck turning, but not a neck up.

2. If the shoulder metal stays at the shoulder with Lapua brass, then things could be fine, but with a cartridge with a mild shoulder angle of 23 degrees (like a .223 Rem), the brass migrates forward very quickly (that's why you typically need to trim .223 Rem brass very often) and part of that thick shoulder metal is working its way forward into the neck (instant donut). With a case like the 6BR that has a steeper 30 degree shoulder angle, the brass migrates forward more slowly and a donut may not be apparent for a while. Forward brass migration on a 40 degree shoulder case is typically very slow and that's why they typically need very little in the way of trimming over their life.

3. A chamber reamer can be designed to minimize the potential for a donut when using brass like Lapua or Norma brass by setting up the proper radius at the junction of the neck and shoulder in the chamber reamer, but this will only work well if a sizing die is used that coordinates well with that radius at the junction of the neck and shoulder in the chamber. To put it bluntly, most commercial sizing dies have a sharp corner inside at the junction of the neck and shoulder inside the die and essentially crimp the brass there and make a donut there with brass like Lapua brass if any of the shoulder brass has migrated forward even the slightest bit. I just had a wildcat chamber reamer made up for a .260 Rem Imp. 30 degree shoulder cartridge I designed. The cartridge was designed for using Lapua .260 Rem brass and at the junction of the neck and shoulder I used a .090" radius, but I also ordered a batch of 25 Redding Type S FL bushing dies for it specifying that the through hole under the bushing in the dies to be approximately .034" bigger than the loaded neck of the case so that the sizing die (when used) stays clear of the brass that blows out into the radius in the chamber. With this set up a shooter can look forward to a good bit of shooting with Lapua brass with no donut issues.

4. Having a tight chamber neck clearance at the junction of the neck and shoulder and using brass like Lapua brass is begging to get a donut fast on a no neck turn chamber ( a good bit of "spring back" at the junction of the neck and shoulder in brass there, especially with Lapua brass that's "bomb proof").

Robert

 

[BoydAllen]

Typically, a new case has a generous amount of bolt face to chamber shoulder clearance. On the first firing, the case is knocked forward by the force of the firing pin blow and the primer explosion. At that point the chamber pressure increases so that the case body grips the chamber wall in its forward position, so that the clearance is at the bolt face, leaving the primer protruding by the same amount. Next the pressure increases to the point where the case is stretched, near the back, to the point that it comes in contact with the bolt face, and the primer is brought flush with the head. If this is the first firing, there is enough spring back of the brass that the case still has some clearance in the chamber, from shoulder to head. After this first firing the typical reloader may FL size the case, and in doing so set the die so that the case's shoulder is bumped back (even though at this point it may not need to be (unless it is being fired in a semiautomatic) and some of the thicker brass from the case shoulder is forced up into the case neck in the process, forming what has come to be known as a donut. It has been mentioned that chambers that are designed for unturned brass should have some taper in their necks, IMO this is correct, because if the shank of a bullet fills the neck, the OD will be tapered, larger in the back, so if clearance is to be uniform the chamber needs to be tapered. Now, beyond the "how it happens" there is what is to be done about it. You can expand the necks so that the donut is forced to the outside and set the turner so that it only cuts the neck in that area (if you do not want to increase the clearance of the neck in the chamber) or you can use a reamer that is ordered in the correct diameter to cut out the donut, from the inside. I believe that Forster offers these in custom diameters, for a reasonable amount. Recently, I have thought about custom chambers designed to accomodate the donut, and one piece sizing dies that match. The dies could be used with an expander ball, and as long as the dimensions were set up for the brass being used, only a couple of thousandths of expanding would have to be done, which would not cause any concentricity issues. As far as neck clearance goes, for my .262 neck 6PPC, I am using .003 as a maximum total clearance, and have only gone to .0025, which works fine, and allows the bullet to be slipped into a fired neck, past the shoulder. Of course I form the cases with minimal head to shoulder clearance, and limit shoulder bump on subsequent sizings to .001 or less. There is one more thing that tends to push brass into case necks, FL dies that significantly reduce the diameter of the shoulders of fired cases. This increases case growth, and contributes to the formation of donuts. As it happens, the FL die that I use for my PPc does not modify this dimension by a measurable amount, and there are no problems caused by this. Indeed, when I specify a chamber reamer from fired FL sized cases, I only use a shoulder diameter that is .0005 to .001 larger than the brass measures at the shoulder.

 

[ttfreestyle]

Ok just checked my 5 times fired 6br lapua brass. I never wanted to say this but I HAVE DONUTS! The donut is below the bottom of the bullet seating depth. Is this a problem since the bullet does not come in contact with the donut? Would this have happened if they were neck turned? Thanks from a newbie in the neck turning world.