Trimming: Indexed Off the Shoulder vs COAL

[pacificnw]

I think/thought the fastest way to reach a fixed COAL, from which you could set proper ogive/seating depth, was using a COAL neck trimmer. I've since read that many COAL trimmers don't have a precision shell retention mechanism, and produces differences in measured COAL from case to case. Usually to the tune of .001 or .002. Has anyone experienced this, or found it to be a problem?

I know there are many trimmers on the market that index off the shoulder that people are using. When using these trimmers, do you: (a) bump your shoulders back until all of the case bodies are the same length from base to shoulder datum, and then (b) set the cutter head to trim COAL when indexed from the shoulder?

 

[427Cobra]

Re: Trimming: Indexed Off the Shoulder vs COAL

Just buy a hand crank trimmer and start reloading, you seem to be all bent out of shape on trimmed brass length.

 

[Bloody_Tailgate]

Re: Trimming: Indexed Off the Shoulder vs COAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body">Just buy a hand crank trimmer and start reloading, you seem to be all bent out of shape on trimmed brass length. </div></div>

I don't care who you are...that's funny right there!

But back to the question my RCBS crank style trimmer nails it to .0005 unless I do something wrong.

 

[pjparker]

Re: Trimming: Indexed Off the Shoulder vs COAL

The primary reason for trimming the length of your cartrige cases is to keep them shorter than the portion of the chamber that is made for the neck of the case. Too long and the mouth of the case will be pinched down between the smaller portion of the chamber forward of the case and the bullet. With no room for the case neck to expand and release the bullet upon firing, dangerous overpressures will occur.

I challenge anyone to prove that a varation in case length of only .001 to .002 will really make a visible diference on paper unless you are shooting a true benchrest rifle that will consistently shoot in the 2's or less ( 5 shot group at 100 yds .200" or less).

If you have trimmed back to the "trim - to" dimension for your cartrige case overall length and they're all the same, then they are all the same.

All trimming should be done <span style="text-decoration: underline">after</span> full length sizing.

Shoulder datum dimension will then be the same for all those cartrige cases so it won't make any difference which type trimmer is used. You will still measure the overall case lenght from base to neck with your dial calipers to insure compliance with published data for your chosen cartrige cases.

Paul

 

[former naval person]

Re: Trimming: Indexed Off the Shoulder vs COAL

1+ for pjparker. If some done before sizing, and some after, then lengths will vary. If using a trimmer that indexes off the datum line...then BIG variences. JMHO

 

[USMARINE1108]

Re: Trimming: Indexed Off the Shoulder vs COAL

If your brass is all the same headstamp, lot, x fired, same load and (most importantly) sized the same you will have no problem either way.

I find the OAL way to be less accurate on my Forster hand trimmer because as you tighten the collet that holds the head of the case the case itself will get "sucked" into the collet. The way it ends up is, the tighter you tighten the collet the less brass will be trimmed and you will have a longer length case.

I like the type of trimmer that sets the depth off of the shoulder. It works great if your sizing is correct. If you size 10 cases (same head stamp and all that) and all are within .001 on your shoulder bump gauge, you are golden for this type of trimmer.

Make sense?