What am I missing here?

[randyman]

Hoping for some insight and words of wisdom on a question about case overall length for a reloaded cartridge. I shoot mostly with my magazine fed AR in .204 and get some pretty nice groups (would like better) but I'm limited to COL as to what I can get to fit in the magazine. I'm using a Redding die to full length size,then check case length prior to trimming, reaming and chamfering. I trim to 2.840. I've primed and powdered and started to seat bullets which are Nosler 32 grain tipped Varmageddon (factory seconds). I use an RCBS competition seating die and have found that seating bullets for an overall cartridge length of 2.250 works and shoots great. While loading this afternoon I was getting finished COL anywhere from 2.240 to 2.255 and all lengths between. I measured the bullet length and found these were from .621-.608. That's .013 difference in overall length so I put the Hornaday comparator on my calipers so I could measure from the ogive and the distance from the base to ogive was consistent at 1.281 including the comparator. But, when I seat the bullets I'm getting seating depths all over the place. I guess this all comes down to my question-if the seater die is set to seat at a particular depth, why is my COL anywhere from 2.243-2.255? Isn't there a fixed point between the shell holder and the part of the die that contacts the bullet that would give a consistant COL? I realize that due to overall bullet lengths I'm getting inconsistent bullet seating depths into the brass but that's a whole different conversation. What am I missing here that gives me different COL? Randy.

[Bill K]

Just a thought Randy, but do you have your die set to bottom/touch the shell holder ? Make sure you have the same contact each time with the die/shellholder, then your Comp setting should be the same, or at the very least, way closer than what you show for COLm even with slight differences in bullet tolerances, between loaded cartridges. Just a thought. Bill K

[BitterClinger]

Take the die apart and look in the seating stem for debris. You might have something trapped in the cavity of the stem that as it changes positions in there it is contacting the bullet at differing points along it's taper.

[randyman]

This die requires that I use an extended shell holder that goes all the way into the die body with the stroke of the handle. Right now the ram does not contact the die but I'll make that adjustment and see what happens. I'll also check for debris inside the die to eliminate that possibility. Thanks for the suggestions-R!

[BitterClinger]

Have you used a case comparator to check the shoulder datum points on all the cases after sizing? If they are the same and you then trim, your issue lies in the seating die and in that case the die to shell holder distance only would come into play if you are also crimping. If your shoulders are at varying points when measuring, your overall case lengths will also vary as the necks move with the shoulder when bumped. If you size all the cases and find differing shoulder datum points try annealing them so they spring back equally after sizing.

[jo191145]

Situation normal. Almost. Your seater is seating from a different datum point not the tip of the bullet.
It’s also a different point than your Hornady comparator even though you say those measure good.
To be exact at determining seating variations you would need to use your seater plug as a measuring device. Bet those would be all spot on.
No offense but your using seconds. Can’t expect perfection. Cartridge overall length only matters to fit a magazine. What counts is distance to lands and any variation thereof. In the real world that would also be a different datum point than the seater plug or comparator but that’s getting too picky. If the comparator says they’re good call it good.