My necking down lesson

[mahlv]

I’ve been messing with a 6x47 for a few weeks now. I necked down some new Lapua 6.5x47 brass with a Redding full length bushing die. I fired the first round of tests, had some promising results but some random pressure indicators (heavy bolt, ejector swipe, etc), which I blew off as just new brass.
I annealed after the first firing, and was expecting much more consistency but found the same random pressure. I am using 115gr dtacs, .050 off the lands, h4350. I found a very accurate node around 3050fps, but every 4-6 shots would have heavy bolt lift and heavy swipe so I backed it down to around 2780 where there was another node it seemed.
I shot this load at a local bench type match and still had an occasional sticky bolt and swipe, wtf right?
Just yesterday I was able to get out and try another work up of brass that I necked down with a standard full length sizer. I was able to work up to and past the faster node from before with no pressure signs. Apparently I put a donut on the other brass.
If you’re still with me on this long winded post, what can I do with the pile of brass that I already likely ruined? I have a 6.5x47, do I blow the brass back out and use it in the 6.5? Really hoping I don’t have to turn necks, although that is the answer I’m seeing in researching.

 

[RTH1800]

FL size and run an inside neck reamer in to clean up. I think I have one of the correct size if you need one. Or send the brass to me and I can do it if I have the correct reamer.

 

[Fig]

I had shitty results with a bushing die, and went to a FL 6X47 Forster, and it does perfectly. Bushing dies are great. I use them and have many, but for whatever reason I've had trouble with them using them to form brass into a wildcat. I find FL dies are way better for those operations. Nothing scientific and I have no evidence or data other than my own experience (which mirrors yours).

 

[mahlv]

FL size and run an inside neck reamer in to clean up. I think I have one of the correct size if you need one. Or send the brass to me and I can do it if I have the correct reamer.

Will that affect final neck size as compared to the other brass that was necked with the FL die? Hate to admit, but I bushing sized 200 pieces (muzzle goes in mouth ha ha). I like to keep 400pcs in rotation for matches and practice.

 

[mahlv]

I had shitty results with a bushing die, and went to a FL 6X47 Forster, and it does perfectly. Bushing dies are great. I use them and have many, but for whatever reason I've had trouble with them using them to form brass into a wildcat. I find FL dies are way better for those operations. Nothing scientific and I have no evidence or data other than my own experience (which mirrors yours).

Exactly what I bought from midway, they had the Forster on sale for $22!

 

[buffybuster]

With a bushing die you have the seam between the body die and bushing that is unsupported. It's looks nonexistent but it's there and that is where the donut forms. A regular FL die, to push the donut inside, and neck reaming it cut it out is the solution. Whenever sizing down use a regular FL die.

 

[RTH1800]

The donut is at the base of the neck. I have seen no difference. I will check for reamer tonight.

 

[Lesco Brandon]

Can’t you just get a Sinclair expanding mandrel die and use the neck turning mandrel? This will ensure the Inner diameter is good to go....

 

[mahlv]

The donut is at the base of the neck. I have seen no difference. I will check for reamer tonight.

If I’m understanding this correctly, I should need a .240” reamer? This is assuming that the brass is FL sized so the ID of the neck should be .240 for around .003 tension.

 

[RTH1800]

My neck tooling it not for 6mm. Sorry.

 

[BLKWLFK9]

I'm wondering if I'm going to have similar experience when I start necking down 6.5cm lapua brass to .25cm using my 6.5cm Redding bushing die. Nobody else has mentioned this problem though. Maybe bc .257 is closer to .264 than .243 is. Not as big of a jump to it wont create donuts??

 

[mahlv]

I necked 7saum to 6.5saum with bushings in 3 steps. Had issues as well, but haven’t been able to confirm the cause. I’m never using bushings to neck down again

 

[Cascade Hemi]

Run a neck sizing mandrel through the neck, it'll push out any inconsistencies such as donuts.

 

[LawnMM]

Neck mandrel after sizing down

 

[Bradu]

I always thought donuts came from necking up not necking down?

 

[smoooth1]

Found a few donut removal methods from a quick google search here:

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K&M Carbide Cutting Pilot 6mm

This pilot is ground from carbide material and also has cutting teeth ground into the end for removal of a case doughnut. FeaturesMade...

www.midwayusa.com

 

[918v]

When you neck down the neck gets thicker. If too thick the neck will cause pressure issues. No doughnut from necking down. Neck not straight, smaller diameter at shoulder junction.

 

[MarinePMI]

When you neck down the neck gets thicker. If too thick the neck will cause pressure issues. No doughnut from necking down. Neck not straight, smaller diameter at shoulder junction.

Respectfully, this is not always the case. It depends on the case (brand) itself, and whether the cases are drawn with a neck thickness different from the case shoulder. If there is a difference between the two, you will see a doughnut when necking down (again, also dependent on where the shoulder/neck unction is being moved). When the case wall is fairly uniform (i.e. thin) you will not. This is why Remington cases (which typically are fairly thin walled near the top of the case) are often desired for case forming (it's easier to form, and there is no doughnut present after necking down). The same goes with necking up (i.e. it depends on the dimensions of the parent case, specific to the case manufacturer not necessarily the parent case itself). The down side to the thin walled cases is that primer pockets don't last long when the cases are run hot.

Anyways, for this reason, you see a lot of debates online about when a doughnut forms; some arguing it happens on necking up, others while necking down. The answer is both groups are right...and wrong, and so the arguments continue (because most base it off their personal experience, not necessarily from using all brands of a parent case, for all types of wildcat cartridges). Again, when wildcatting, there are not hard and set rules...

JMTCW...

 

[918v]

I agree with your position on doughnuts however you do have to admit that neck thickness increases when necking down and decreases when necking up.

Whether a doughnut forms depends on shoulder thickness, that is true. Now, in my experience, Lapua brass is thicker in the shoulder than in the neck, but only half way up the shoulder. So a doughnut will not form when necking down virgin brass.

 

[MarinePMI]

I agree with your position on doughnuts however you do have to admit that neck thickness increases when necking down and decreases when necking up.

Whether a doughnut forms depends on shoulder thickness, that is true. Now, in my experience, Lapua brass is thicker in the shoulder than in the neck, but only half way up the shoulder. So a doughnut will not form when necking down virgin brass.

Yep, I believe we're in agreement on all points.