When to trim .284 cases

[ecomeat]

Hoping for some professional opinions regarding if and when I should trim new 284 Win cases that I just necked up from 6.5mm.

New Lapua cases are very even at 2.160" . Not the 2.159" that IanP measured. Technique ?
Necked up to .270 (stage 1) they are 2.155" (virtually 100%)
Necked up to 284, i put the calipers on 200 :

2 only are "short" at 2.1505
157 are 2.151
38 are "maybe's" at 2.152
3 only are "long" at 2.153

I trashed 6 dud cases (from an earlier, initial 300) getting my Wilson/Sinclair micrometer trimmer set to trim to 2.151".
I cant help thinking that there is probably at least 1 thou "flex" in any micrometer......even a good one like the Sidchrome that I used to measure these. I am a cattle farmer, not a laboratory technician, and no matter how hard I try, i get different reading from Calipers. (Dont have the same problem miking case necks.....different mechanism)

It surely wouldnt be worth trying to trim everything to 2.1505 .....almost 0.010 short of the published "Trim to" length....and there is only 2 ? Would it ?

Is it basically a waste of time trying to trim everything to 2.151" ?
Or will that 0.001 make enough difference to "consistency" of shot release, that I should try to make 198 (157 + 38 + 3)

Or should I just shoot the bloody things, and maybe trim later if they get apart by........0.005" ? or 0.010"?

Bottom line ..........how do you F Classers define "close enough" with your own cases ? Should I trim at this stage , or if you were me....would you trim ?
Many thanks in anticipation !
Tony

[AlanF]

Tony,

IMHO the main reason by far for trimming is to prevent the end of the neck from being too long for the neck of the chamber, and pinching the projectile as it is chambered - this is not only an accuracy and annoyance issue but a safety one as well.

As far as evenness of length goes I'm not convinced it makes a huge difference to accuracy. If anything, a longer neck will have more neck tension - someone may have done the extensive testing required to measure how much - I suspect that it will be insignificant compared to the other causes of neck tension variability.

FWIW my 284 Shehane cases seem to find their equilibrium at about 2.151. Any that get away from this by more that about 0.002, I may trim or cull. Also any that are obviously out of square will get attention. I have a 7mm K&M expander mandrel that does them in a single stage. I learnt very early that lubricating the mandrel before every case is important. Before I did this, necks were actually forming shorter and staying shorter (by up to 0.005).

Alan

[DaveMc]

+1 with Alan.
Actually your cases are remarkably similar.

Trim them all to the same length if you feel the need. There will be no noticeable difference in neck tension from 2.153 -2.150.

[ecomeat]

Thanks for the input Alan and Dave.
That's what I was hoping to hear ! Hopefully my chamber measuring gear will turn up from Sinclairs in the next few weeks, but for now I am feeling quite relieved after hearing your respected opinions, and will just start fire forming at Club matches.
Thanks again for sharing.
Tony