.223 Inconsistent Trim Length - I'm stumped.

[Webster]

Gents,

Need some ideas/help. I'm using a Giraud trimmer to trim all my .223 brass, and I've used it successfully for quite some time. That said, I've changed a few things in my reloading process, and as of late my trim consistency has gone down hill; I would normally attribute this to a shoulder bump consistency problem, but I can't seem to detect a problem with headspace comparator.

Brass Details:
Lapua .223 Brass
~4-7x fired with heavy charges of Varget behind a 90gr VLD.

(Relevant) Reloading Process:
Deprime
Wet Tumble
AMP anneal
Resize w/ Redding Type S bushing die & Redding comp shell holders (setup for .003 bump w/ a 'camover' fit).
Mandrel expand back up .001.
Dry tumble lube off
Giraud trim

Here's the screwy thing, I'm getting consistent shoulder bump indications on my brass using a Hornady comparator. They're all within .001 of each other on the setback (showing 1.458 - 1.459), however when I run them through the Giraud, I'm getting wildly inconsistent trim lengths. The trim lengths are varying ~.010.

Typically with a trimmer that indexes off the shoulder this would indicate a shoulder bump problem, however they're all showing very closely on the comparator.

Any ideas? I've re-setup the trimmer/dies/shell holders repeatedly, and can't seem to figure it out.

Are you lubricating the neck before sizing? Some people don't to make clean up easier. Pulling any expander or mandrel thru the neck seems like a bad thing to me. Why would you expand then size back down with a bushing? That's really cold working the necks a lot.

 

[MikeMcCasland]

Are you lubricating the neck before sizing? Some people don't to make clean up easier. Pulling any expander or mandrel thru the neck seems like a bad thing to me. Why would you expand then size back down with a bushing? That's really cold working the necks a lot.

Yes. I was lubing, and using a carbide mandrel. I've also run tests without the mandrel; just sizing the neck to the diameter I want, and it does the same thing.

The theory behind doing it is on unturned brass, to push the imperfections to the outside. You end up sizing it down .001 over what you want, then expanding back up.

Ned Ludd/Greg talks about it in depth on the 1st page of this thread.

 

[Webster]

Yes. I was lubing, and using a carbide mandrel. I've also run tests without the mandrel; just sizing the neck to the diameter I want, and it does the same thing.

The theory behind doing it is on unturned brass, to push the imperfections to the outside. You end up sizing it down .001 over what you want, then expanding back up.

Ned Ludd/Greg talks about it in depth on the 1st page of this thread.

It's impossible to push imperfections to the outside. The neck tension is related to both combined sizing it up then sizing smaller, both cold work the brass. Something like if you size it up 5 thou then down 4 thou then up 2 thou by seaing the bullets you have what some people would call 11 thou tension or cold working. The grip/hold is not just the change from seating the bullet.

 

[dstoenner]

The title of this thread caught my eye so I read through the whole thread. My first reaction was that if this high dollar equipment isn't getting it right what is mine doing. I had just this morning trimmed 82 223 Norma cases from last nights shooting so I measured 15 of the cases. Using a pair of calipers (yes I read the post about these having +/- .0005 tolerance) I found that they varied from 1.749 to 1.751. Not bad for a $15 tool.

To me I am more concerned about the squareness of the case mouth to the case head than I am to overall length tolerance. That has to do with getting rid of at least 1 factor for loading induced runout. I set my sizer up to just kiss the shell holder on the cam over point. That way I have a constrained sizing volume. I do try to maintain the same rhythm on the upstroke and return so each shell gets the same amount of time. But I know that the biggest variable is the shoulder set back. So indexing off the shoulder can be an issue. So I choose a setup that indexes off the case head for trimming.

I prefer the Lee case length set up. I create a complete setup for each case I load for. I spread the screw at the top for a tight fit and then red locktite it into the cutter assembly. Then I put the cutter in my drill press and set for lowest RPM and insert a case in the shell holder and hold it in my hand raising the case to contact the cutter blades. When you feel it run free I loosen the shell holder and put the trimmed case in the finished and pick up the next case and put in the shell holder. I typically get 6 cases per minute of smaller cases and maybe 4 per minute of military 30-06. At maybe 2K trimmed cases I just build a replacement assembly and keep trimming. Because the index pin goes through the flash hole, the cutter blades are very perpendicular to the case axis. Perturbations in the shoulder to not influence the length or the squareness of the mouth.

I use only Redding competition seaters which hold the neck in tight relationship with the case axis. Net is I typically run >50% 1 mil runout in a 100 case run. Highest I have hit was 70% 1's.

Thought I would share FWIW

David

 

[MikeMcCasland]

Hey David,

I appreciate the comment. I have an RCBS trimmer that I could dust off; I'm sure I could get accurate trims that way.

Although I would really like accurate trims, the problem I'm most worried about isn't trimming related; it's a problem with resizing that's just manifesting as inconsistent trim length. The same problem would show up on a case gauge for sure.

Just to make sure I hadn't suddenly forgotten the basics of Giraud/Die setup, I took some .260 Rem brass that I'd just fired from a newly headspaced barrel, and setup my dies/trimmer the exact same way I did it 10x the day before with the .223. Fortunately I proved to myself I wasn't crazy; they were all trimmed to within .0015"

I'm strongly of the opinion that it's something going on with the brass that the two Redding dies aren't touching with sizing; this is probably exacerbated by the fact that I run this brass hot. I halfway suspect if I ran these through a small base die, and then the bushing die, that would get the consistency back....but I don't know.

In general though, this brass has had it. It's a batch of ~200 pieces where I've culled ~1/2 of them for incipient case head separation.

 

[mac86951]

Runout of the motor shaft? Maybe a thrust bearing is gone?

-Mac