Donuts vs. no donuts... Pressure Trace data

kombayotch

kombayotch

Gunny Sergeant
Full Member
Minuteman
Sep 20, 2007
1,907
106
#1
This is interesting, so I thought I'd share it.

I've been getting unexplained (formerly unexplained) flyers with my 190 SMK load (308 Win.). This load was awesome when I first developed it. 5 shot groups in the .3's and .4's at 100 yards consistently and many 300 yard 10 shot groups under 1 3/4".

The brass was 7x fired Lapua, annealed after the 6th firing. It was FL sized, setting the shoulder back only 0.001-0.002" each time. I thought my brass all had uniform neck thickness and runout. But, I missed the donuts because the pilot on my case inspector runs in the part of the neck beyond the donut.

Here are the traces I was getting with brass that had been sorted by neck thickness and runout. This was supposed to be the "golden" brass, the best of the lot.

donuts.jpg

"Golden" brass with donuts.

donuts_2.jpg

"Golden" brass with donuts.

donuts_3.jpg

"Golden" brass with donuts.


I was still getting SD numbers in the singles, but the traces were all over the place. Many of the traces had lags in them, so I knew something was wrong. I tried cleaning the bore thoroughly and playing with seating depth. I ended up buying a box of FGMM and it shot fine. So, I knew the problem was in the brass.

I sized some cases, but didn't run them over the 0.336" mandrel. I took the 0.335" mandrel and tried to insert it. Sure enough, it only slid down 3/4 the length of the neck and then it was a tight fit. So, I took a 0.336" reamer, chucked it in the drill and stuck it in the neck. It too only got 3/4 of the way down. A touch of the drill trigger and it went through.

Now, here is the interesting thing: I did this to my reject brass first to see if that was the problem. This is the brass with lots of neck thickness variation and necks that are dinged or scratched on the inside. I use this stuff for foulers and rough sighters... It gave me traces like this:

No_donuts.jpg

"Reject" brass with donuts removed.

No_donuts_3.jpg

"Reject" brass with donuts removed.

No_donuts_2.jpg

"Reject" brass with donuts removed.

Groups shrunk to ragged holes again. The largest group from the "rejects" was smaller than the smallest group from the "golden" brass, over all seating depths.

So, even if you don't want to turn necks, one of those pilots with the donut cutter (K&M???) may be a worthwhile investment. I was just using a regular chucking reamer.
 
#2
Re: Donuts vs. no donuts... Pressure Trace data

For your interest, this is what the FGMM traces look like:

FGMM1.jpg

First shots down a bore that has been polised to the bare metal. First two groups had flyers.

FGMM2.jpg

Next 5 shot group formed one ragged hole...

 
#3
Re: Donuts vs. no donuts... Pressure Trace data

Kris,

Excellent information!

I'm a little surprised that you had donuts in a plain-jane .308 Win fired a half-dozen times. Now I'm eye-balling a big pile of .308 Win brass that I have, wondering that might be why it just 'stopped shooting good'.

I have a K&M donut reamer pilot on my 6.5 neckturner mandrel because I used to shoot 6.5-08 (which was notorious for donuts, depending on how you formed the brass). Given the cost of their carbide cutter mandrel compared to the regular ones, I've never sprung for them in any other size.

I've read in Zediker about using inside neck reamers from Wilson; found out someone I know locally does it on some of their stuff, but I've never done it. Something else to worry about, I guess
wink.gif
 
#4
Re: Donuts vs. no donuts... Pressure Trace data

Monte,

You have no idea how surprised I was to find them...

I've started to check other brass that's been fired only a few times and there is definitely some constriction in a lot of it. Its made me look at neck turning in a whole new light (I don't do it, btw). The fact that brass with up to 0.004" variation in neck thickness (around the circumference) shot better than brass with 0.0015" variation or less, is telling. That constriction plays a bigger role and it would also be removed during the neck turning.

I'm now putting more emphasis in what the pressure curves look like than on velocity SD numbers. It seems to be a better indicator of accuracy.
 
#5
Re: Donuts vs. no donuts... Pressure Trace data

FWIW, I've seen where one person (benchrest type who is prone to fiddling and experimenting with things of this sort) claimed a large portion of the problem is the use of factory dies vs. dies cut to fit your chamber. Starting to wonder if maybe he was onto something there...
wink.gif


Seeing as I shoot mostly 155gr bullets w/ shorter bearing surfaces, I don't know if I'm getting down into the donut region or not. I'll have to take a look.
 
#6
Re: Donuts vs. no donuts... Pressure Trace data

That would be one advantage of the 155 Bergers and Sierras...

I also bought one of those Forster Bushing Bump dies that only sizes 2/3 of the neck. I think that would have solved the problem too. But, I have yet to try it out.
 
#8
Re: Donuts vs. no donuts... Pressure Trace data

Some very interesting stuff. Thanks for the post.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I'm now putting more emphasis in what the pressure curves look like than on velocity SD numbers. It seems to be a better indicator of accuracy.</div></div>

at 100 and 200 yards, but what about beyond 400?
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">

I also bought one of those Forster Bushing Bump dies that only sizes 2/3 of the neck. I think that would have solved the problem too. But, I have yet to try it out.</div></div>

There's something to be said about only sizing a portion of the neck. Many say that the unsized portion helps align the cartridge when chambered.
 
#9
Re: Donuts vs. no donuts... Pressure Trace data

I anneal after 4 or 5 reloads and then as SOP I will run a reamer in the neck and then run a bore brush wrapped with 0000 steel wool chucked in the drill press, in the neck. In Glen Zediker's book "Precision Shooting" he talked about doing a "drop test". You should be able to take a fired case, before resizing, and drop a new bullet right in.
myerfire
 
#11
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: myerfire</div><div class="ubbcode-body"> In Glen Zediker's book "Precision Shooting" he talked about doing a "drop test". You should be able to take a fired case, before resizing, and drop a new bullet right in.
myerfire </div></div>

Isn't this always the case (no pun intended) especially with factory chambers?

I can see it might show up donuts in turned necks which are a .001" type fit, but I can pretty much always drop a bullet into a fired case, before resizing.

I've got a Wilson 7mm inside neck reamer that I've looked at and fiddled with, but since I don't turn, they suggest I don't use it. However, with the proper bushing, I guess it would remove the donut.

Chris
 
#12
Re: Donuts vs. no donuts... Pressure Trace data

I was thinking along similar lines as Chris... by the time that a donut gets severe enough that it interferes w/ a bullet dropping into a fired case mouth on a .308 Win fired in even a 'match' chamber (.340-343 neck, depending on the chamber reamer)... that'd have to be one heck of a ring! Different story on a 6mm BR or similar w/ a .272" no-turn neck- fired cases measure (for me) ~.2715, loaded rounds measure .2700-.2705, so a donut could very easily interfere with things there.
 
#14
Re: Donuts vs. no donuts... Pressure Trace data

Unless you take steps to remove the donuts they will occur with any die brand.

To remove mine I use a bullet size chucking reamer (.308") in fired but unsized brass. With the case spinning in the drill I insert the reamer and it usually passes through fairly easily.

(I use a DeWalt 1/2" keyless chuck cordless drill in back gear (Slow speed). It needs no adapter. The brass chucks directly into the chuck with hand pressure and it turns true.)
 
#16
Re: Donuts vs. no donuts... Pressure Trace data

I use the reamer because when I do the bullet drop test, it doesn't drop on all the cases, so I just ream the entire lot. I figured it was simply the natural flow of brass.
myerfire
 
#18
Re: Donuts vs. no donuts... Pressure Trace data

Victor Sir, would'nt neck sizing only part of the neck with a Wilson or Forster bump die eliminate the donut from forming after repeated firings?
 
#19
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body">

There's something to be said about only sizing a portion of the neck. Many say that the unsized portion helps align the cartridge when chambered. </div></div>

I may have try that!
 
#22
Re: Donuts vs. no donuts... Pressure Trace data

I have bought several reamers from MSC Industrial Supply. 1-800-645-7270 L. E. Wilson also makes one for 2 or 3 times the money, as does Forster I believe.
 
#23
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body">Victor Sir, would'nt neck sizing only part of the neck with a Wilson or Forster bump die eliminate the donut from forming after repeated firings? </div></div>

If the case has a powder charge and a bullet, the brass will flow toward the case neck. No matter how you size or in what kind of die. It happens. The hotter the load the more it flows. Isn't science a pain in the butt?
 
#24
Re: Donuts vs. no donuts... Pressure Trace data

So... if one was shopping for one of these 'chucking reamers', do we need one that is .308" in size, or one that is closer to the actual ID of the fired cases (dependent on chamber diameter, neck thickness, etc.)?

 
#26
Re: Donuts vs. no donuts... Pressure Trace data

I was told to shape my cutting mandrel to turn onto the shoulder a bit. When the brass flowed foward it would stop at the new junction on the shoulder instead of at the neck, thus causing the donut to form there. Never got a donut at the neck shoulder junction again.
 
#27
Re: Donuts vs. no donuts... Pressure Trace data

I use a bullet size reamer for whatever caliber I'm reaming. If there is a slight difference left in the case neck, it's usually only a couple of thousandths. Versus the .020"+ of a donut.

If you want to try something different, try something different. I was just saying how I've been doing it.
 
#28
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body">at 100 and 200 yards, but what about beyond 400?
</div></div>

Well, with this load, the SD numbers got better when the traces tightened up. But yes, SD also need to be addressed for long range. If the traces are tight and the SD is still high, its probably time to change something like the primer or the powder. But, until the traces tighten up, you may be discounting a really good load because something is wrong like a fouled bore or in this case, a problem with the brass. They don't always get super tight on the downward (right) side of the curves, what you want to get rid of is those lags at the beginning (left side), where the pressure is building.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchAlsup</div><div class="ubbcode-body">Question: Does the 41.8 chargeweight go crunch as you seat the 190 bullet? </div></div>

Nope, but it isn't loose either. I think the fill ratio is in the high 90's.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bzinbv</div><div class="ubbcode-body">MSC or McMaster Carr has HSS chucking reamers by the half thousand, here is a link to MSC, enter the diameter to narrow down the search:

http://www1.mscdirect.com/Chucking/Reamers/Cutting-Tools/s676.HTML </div></div>

That is exactly what I used. However, I only used it because I had it on hand. It left the inside of the necks a little rough where the donut was. A a bit of Flitz on a bore mop cleaned that up. The brass in the traces above didn't not get polished though.

After pondering this for a bit, if I were to do it again, I'd just expand the inside of the neck with a mandrel and turn the outside of the necks. It would have been less work overall and I would now have brass with all uniform necks. I think its better to leave the smooth finish on the inside of the necks alone also.
 
#29
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Originally Posted By: Weda'
at 100 and 200 yards, but what about beyond 400?


Well, with this load, the SD numbers got better when the traces tightened up. But yes, SD also need to be addressed for long range. If the traces are tight and the SD is still high, its probably time to change something like the primer or the powder. But, until the traces tighten up, you may be discounting a really good load because something is wrong like a fouled bore or in this case, a problem with the brass. They don't always get super tight on the downward (right) side of the curves, what you want to get rid of is those lags at the beginning (left side), where the pressure is building.</div></div>


Got it... very intriguing stuff. Wish I had time to hook my sticks up to this program.
 
#30
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body">

There's something to be said about only sizing a portion of the neck. Many say that the unsized portion helps align the cartridge when chambered. </div></div>

I may have try that! </div></div>

This is a BR trick. I used it to shoot a 3.9" group at 1K.

Shot a 4" then 2, 6.2" groups after that. It worked really well for me.

I sized about 1/2 the neck or just under a 1/2
 
#31
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body">

There's something to be said about only sizing a portion of the neck. Many say that the unsized portion helps align the cartridge when chambered. </div></div>

I may have try that! </div></div>

This is a BR trick. I used it to shoot a 3.9" group at 1K.

Shot a 4" then 2, 6.2" groups after that. It worked really well for me.

I sized about 1/2 the neck or just under a 1/2 </div></div>

Holy Crap... I need to try that. Like using a small neck chamber.
 
#34
Re: Donuts vs. no donuts... Pressure Trace data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Citysmasher</div><div class="ubbcode-body">Incredibly cool data BTW. </div></div>
Just what I was thinking.
 
#35
Re: Donuts vs. no donuts... Pressure Trace data

link to pic of tool I made for donut chopping
I made for the tool for chopping out donuts, from tool steel, and then hardened, and then honed.


link to pic of tool I made in use, chopping out donut
The tool is held in a collet bullet puller die and the ram is raised and then the case rotated and then the ram is raised again.


One way around donuts might be to neck size with a Lee Collet Die and a washer [spacer] around the case. The base of the neck is then not sized and makes the case get centered next time in the chamber. And it also leaves the donut inside diameter larger than the bullet, so the bullet does not run into the donut when seated.
 
#36
Re: Donuts vs. no donuts... Pressure Trace data

I was that the Lee die would probably have some benefits in preventing this...

I also wonder if neck turning would have helped in preventing this.
 
#37
Re: Donuts vs. no donuts... Pressure Trace data

Has anyone theorized why the donut causes these changes in pressure curve?

Is this caused by the varying neck tension or can some or all of it be caused by the turbulence in the flow of the gases as they go around the donut, or both?
 
#38
Re: Donuts vs. no donuts... Pressure Trace data

It is probably a reasonable assumption that there is a lag in pressure buildup initially as the bullet gets clear of the donut. I don't know that turbulence played a role, I don't think the donuts were more than a couple thou higher than the other neck material. Maybe.


Also, if anyone is wondering, all of those loads were dispensed on a Chargemaster (with reducer and s/w tuning).
 
#40
Re: Donuts vs. no donuts... Pressure Trace data

I've examined more of my brass and I've found similar things even in once fired brass. It seems most brass has a slight taper in the necks. It gets thicker at the bottom of the neck. Makes sense, a slight taper is a requirement for high speed stamping.

I've been using bushing dies and a Dillon trim die that I modified by opening up the neck. With these dies, there is no taper in the neck area. I believe standard sizing dies do have a bit of taper in the neck area. Using a mandrel, or a Lee Collet die will also push the thicker material to the outside. Or at least, it should. However, if the neck area in the chamber is tighter, accuracy may still be affected by the thicker material (which will only get thicker as material flows from repeated firings).

So, this leads me to conclude that I would benefit from turning the necks. And by policing the donuts in some way, perhaps as an operation to do each time I anneal.

Seems this guy had similar findings:
http://home.comcast.net/~jesse99/doughnuts.html
 
#41
Re: Donuts vs. no donuts... Pressure Trace data

Wouldn't turning the necks and then using a Lee collett die avoid most of these issues - at least until such time as enough brass flows into the neck from repeated firings to cause a problem.
 
#42
Re: Donuts vs. no donuts... Pressure Trace data

I think so... that's one of the things I'm contemplating. However, I'm going to give that Forster Bushing Bump die a try for a while since I already have it. I'm definitely going to neck turn my brass because I see the thicker material at the bottom of the neck as a problem.
 
#43
Re: Donuts vs. no donuts... Pressure Trace data

Picked up a K&M system with the donut cutter pilot. This thing does a very nice job when you run it fast on a drill. I turned some once fired Hornady Match brass that had been resized with the bushing bump die. This dies doesn't size the bottom 1/5 of the neck. I set the cutting depth on the neck turner to only clean up the outside of the neck. Well, both the reamer and the cutter took off a bunch of material at the base of the neck on both the inside and the outside. That 0000 steel wool on a brush stick polishes the insides of the necks up very nicely.

I also wanted to find something I could use to be able to quickly check for donuts periodically. Gage pins work nicely! You can order then individually in 0.0005" increments for only $2.50 each:
http://www.meyergage.com/products/individual_class_z_pins.htm

They work pretty nicely for verifying neck tension too...
 
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