Here's one I've been wondering about for a while now. Obviously, having every case trimmed to the same length and each mouth square is ideal. Which condition below is worse for accuracy/consistency:

- each case mouth is known to be square, but the case length varies slightly from case to case. No case is over the std trim length; they are all below it by some different slight amount, like if your case trimmer didn't hold exactly the same length every time but still cut it true.
- each case is trimmed to the std length, but not all/any of the case mouth is touched. The mouth is not square, like you decided on a trim length and then that length only hit some of the cases and even then not the whole mouth on those.

Let's also assume that these cartridges are crimped with a Lee factory crimp die as the last step, so that OAL is the same and crimp location is not dependent on bullet position or case length.

I feel that having a square case mouth, even if the case length varies a bit, will give you better bullet release (accuracy) than a case that is trimmed to the 'proper' length whose mouth is not square. Sound reasonable? I'm trying to track down those weird fliers in my 338-06 AI and am thinking that little differences in case mouth condition can be causing some of this trouble.

I'd say that a square case mouth (and then be sure to keep the inside chamfer "square" to the case mouth) would be a GOOD IDEA. But, how much of a flyer are we talking about here?? It would be my opinion (shooting from the hip) that unless you had a grossly bad job with the case mouth it probably wouldn't make more than .5 moa difference. If you are seeing flyers over an inch outside your groups I'd look at other ideas.

Hey capitan

What type of trimmer are you using? I use the Lee case length gauge

http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=556041

on a ball grip with cutter

http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=136199

along with a Lee Zip Trim

http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=515804

and the cases are always trimmed to exactly the same length and square.

Don't know if this is the reason, but my fliers went away when I started using the Lee Collet Neck Sizers and Lee Factory crimp dies so I did not have to lube the inside of the neck. Also wind some steel wool around a 22 caliber brass brush and work the inside of the neck over. It will get rid of any burrs and smooth the inside of the neck for a consistent release. Seemed to do more good than chasing concentricity for me.