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Forum Index > Rifles general discussion > Donut problem .., maybe...?

Donut problem .., maybe...?

22 May 2018
@ 09:59 pm (GMT)

Anders Österberg

Hello
Reasently I did a fautigetest on a single GGG 308 win case to see how many relodings it would persist...?

The load was my precisionOCWload of 44gr N140 and Lapua 155gr Scena , 71.15mm .

First shot on top aimsquare hit six o'clock , than 7 shots in the middle of the square 😎

Shot 8 and 9 moved to 7 o'clock..... without knowing....

Change target to low right ....😝 , disaster....

Thinking that the neck had been workhardernd .., so I annealed the case and shot at the target low left .... , not much better....

Cleaned the rifle and tryed it on another target , no better....



I shot a total of 23 shot with the case without any cracking or loosen primerpocket ,the only thing was it lengthened about a total of 2mm , trimmed 3 times along the test .

Notised when I got a closer look at the neck ( with glases on...) I noticed that the lengtheningof the cass had pushed the sholdermaterial forward out on the neck and thicken it....

The question is if the thickening of the neck at the sholder/neck-junction is the reason that the precision went bad ...?

My thinking was that with a conventional resizingdie (hornady new dimension) the donut would be at the outside and not effect the bullet ...?


Replies

23 May 2018
@ 09:04 am (GMT)

Nathan Foster

Re: Donut problem .., maybe...?
Hmm, very hard to say Anders. Low left can indicate a couple of things, either a settling in of technique (human factor) or a reduction in power (cartridge factor).

If you look at the top target, its actually a double group. There are some shots in the center, some low left apart from one centre low. So there is a possibility that you were finding your natural POI, then when you moved to the lower right target the groups steadily opened up, whether by brass fatigue or shooter fatigue. Understand that it is possible to find your groove yet also begin to feel tired as you work the groove. But this greatly depends on how much we are shooting. The more you shoot, the longer your bell curve will be. Looking at the groups, I am willing to guess (that's all I can do from here) that it was a cartridge issue more than a human issue.

If the case has shed about 2mm, it may be that it has lost a wee bit of velocity. This can cause low left shots. You would have to check velocities to be sure.

The donut can only appear on the case inner, though if you seat through it, the seating will cause an unseen bump on the outer. In any case, from memory, 71.15mm is not the ideal location for this pill, it may like 69.5mm. You should not be seating in such a way that there is any possibility of a donut forming unless the rifle only shoots well with the projectile seated out into the case neck.

As for annealing, this is certainly a factor. It is very difficult to be accurate with traditional annealing techniques. The results are not greatly predictable, we can only 'do our best'. To obtain truly repeatable results, you would need to use the Kiwi made AMP (Annealing Made Perfect) machine. Without this, you may find that after annealing, the case need to be fireformed, after which the group may regain consistency.

Do be aware that both copper and carbon fouling can also be issues. If this is a Tikka rifle, copper may not be an issue, but if the rifle is suppressed, excessive carbon fouling and chamber caking may be an issue. Having said this, caking normally puts shots high.

This was a great test Anders. Although there are many variables, it does show how many rounds we can get from a case. Sure, the rifle may not have been tack driving at the end of it, but the group was still fairly good for 18-23 reloads.
24 May 2018
@ 06:42 am (GMT)

Anders Österberg

Re: Donut problem .., maybe...?
Thanks for your answer.

Sure it may be a shootererror ... but when I cleaned the barrel and tryed again on the right cross it still shot bad ,
Than I shot 7 shots with the same load , but with Norma cases , on the left side ..😉 , the flyer was me fore sure .



I annealing with the molten salt bath metod .
https://www.google.se/search?q=salt+bath+annealing+brass&oq=salt&aqs=chrome.4.69i57j69i61l2j69i60j69i59j0.15500j0j7&client=ms-android-samsung&sourceid=chrome-mobile&ie=UTF-8



24 May 2018
@ 08:05 am (GMT)

Nathan Foster

Re: Donut problem .., maybe...?
Hi Anders, yes although I mentioned the possibility of shooter error, I felt the same as you in that it was more likely a cartridge issue. The second photo certainly confirms this.

One aspect of the bath instructions that may be misleading is the cooling phase. In the video, they place the case into cool water immediately after pulling it from the bath. A key when annealing is to allow the part to naturally air cool. Alternatively, you might be able to get away with dropping the case into very hot water for the cleaning phase. But it really is best to just leave things be, then move on to cleaning in a separate step.

Yet another possible variable is the neck tension produced by the die. If for example the brass is hard and the die does not reduce the neck a great deal, the neck may spring back and give less tension than when the brass was soft. With a tight neck die, it may show less of a difference in velocities and ES between annealed and hardened brass.

Also keep in mind that there will be some difference between the behavior of neck sized versus full length sized brass with regards to how much energy is expended when expanding the case to the chamber walls. With neck sized brass, once the case is formed, you will not see a great difference in velocities from shot to shot. But if you are FL sizing each time, the temper of the case may effect velocities (and therefore harmonics) depending on how much movement the case is allowed, both forwards and outwards. The stretching of the body (a die issue) before the shoulder is set back (shoulder goes forwards, then back) can work harden the brass quickly.

But as far as the donut goes, again, try to seat projectiles in a manner so as to avoid the donut. The .308 is very forgiving of jump so there is no need to seat the bullet boat tail / body junction out into the case neck.

Also keep in mind that 44gr of N140 can be mild in action, resulting in low velocities from a 20 to 22" barrel. A stout load of N135 may overcome minor differences in case temper and yield higher velocities. But the rifle must be up to handling such loads. Factors such as these will not eliminate case temper issues but can help minimize effects, depending on how much energy is being expended within the chamber. It is now very common to run the medium burn rates in the .308 such as Varget (2208) and N140 etc, but these powders are better suited to very long barrels. In regular sporters, the hand loader may completely miss upper nodes, most especially with 150 to 168gr projectiles.

Certainly a complex subject, more so if trying to guess cause and effect due to a wide range of variables.
24 May 2018
@ 04:04 pm (GMT)

Paul Leverman

Re: Donut problem .., maybe...?
Following Anders' link led to http://68forums.com/forums/showthread.php?54267-75-DIY-Automatic-Case-Annealer-Project-Complete!-Plans-and-parts-list-included . Pretty nifty.
24 May 2018
@ 04:14 pm (GMT)

Paul Leverman

Re: Donut problem .., maybe...?
Went even further, there are dozens that are worth looking at. Cheap is the key word. These guys know how to build stuff that works with very little cash outlay.
24 May 2018
@ 05:36 pm (GMT)

Anders Österberg

Re: Donut problem .., maybe...?
[/quote=."nathan"]But as far as the donut goes, again, try to seat projectiles in a manner so as to avoid the donut. The .308 is very forgiving of jump so there is no need to seat the bullet boat tail / body junction out into the case neck. [quote]

So you mean that by seating the bullet past the neckline I will avoid the donut to be able to form..?

What I'v red.... , it's the thicker sholdermaterial that moving forward during fireing and sizing ... and could only be avoided by carefully sizing to tight headspace... and thereafter, neckturning and/or reaming .


The reason that the case grow so much in the test was that the GGGcase was softer than the Normacase that I normally use , so the case/headspace was around 0.12mm instead at my normal 0.05mm .

I stupidly used the sizingdie setup to Normacases for maybe the first 10 sizings before I discovered the issue...and ended up with unnecessary case/headspace ...and growth of the neck...


I heard on another forum that you ( Nathan) had used only 40 cases of 308win to shoot out a barrel ....
If so... ? What is your caseprepping ? Sizing , rurning necks , loads/pressures...?
 

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