variations in COAL in relation to case trim length

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7mmVertigo

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May 2, 2012
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#1
so here's my conundrum, and its prob very obvious, but! My body and i are relatively new reloaders, he's got about a year on me and im reloading 22-250 rem. using once and twice fired brass and rcbs fl sizing and rcbs seating dies im notincing an interesting relationship to case tim length and coal / seating depth. my case trim length is 1.902 and i seat at 2.200 measured at the ogive of the bullet using hornady oal gauge and digital micromoeter and before i load each case i sort my cases by case lenght after they're trimmed deburred and chamfered and im noticing something that my friend and i are confounded by. in my "bastard" cases as i call them, meaning they are either >2.200 by .02 or more or <2.200 by .02 or more im noticing that after seating my bullets (no adjustments made to press or dies) my final product (COAL) is exactly > or < my target COAL by the same lenght the cases miss by. so for example

trimmed case measures 1.888 than my final product (COAL) measures 2.186 +/- .005
OR
trimmed case measures 2.250 than my final product (COAL) measures 2.264 +/- .005

(keep in mind these are examples to help get the point accross my trims arent varying but this great of a spread)

Just FYI i trim my cases with the LEE trim system with the shell holder drill chuck and trimming stems and hand held cutter.

So im finding it believable that my case lenght plays a role in my COAL so when i asked my buddy on the matter he insists it has no variance on COAL. He said the dies are designed to press the bullet in at measurement thats constant from the press plate where the case sits. So Im looking for some input here as to if anyone else has noticed this or is there rhyme or reason to either my findings. or if im using shitty dies or am i doing something wrong. Any input would be appreciated...

and in case anyone asks YES my micrometer is always zeroed, has new batteies and is a quality micrometer. and my measuring techniques are very OCD. I look forward to any input.

in advance i apologize for any misses in nomenclature or spelling i wrote this at work in between seeing pts.

Safe shooting

Scout
 
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#2
Case length has effect on coal. Look at it this way...more neck length you have the longer you seat the bullet out. Less neck length you have less or a bullet you can seat so less coal.
 
#4
Your buddy is right. Case length has nothing to do with COAL as long as you're seating bullets properly and the powder load isn't so compressed it affects seating depth. The seater stem contacts the bullet slightly below the meplat, which is nowhere near the case neck. The seating die stem doesn't "know" where the case neck is located.

One way in which you can encounter this issue is if you're using comparator inserts where the hole diameter is very close to the bearing surface diameter of the bullet you're seating. Although desirable for a lot of reasons, if you're seating bullets fairly deep in the case where the ogive/bearing surface junction is very close to the edge of the neck, or even slightly buried in the case, what you will actually be measuring is the case length itself. Hornady's comparator inserts have a slightly oversized hole and measure a tick further away from the ogive as compared to those from Sinclair, for example.

Based on the measurements you gave, it doesn't sound as if that is your problem, however. You mentioned that you're sorting cases by length after they're trimmed. Why is this necessary? If the trim length of your cases varies by more than .001"-.002", I'd very quickly look into a different method of trimming. I looked at the Lee Quick Trim system, but it's not clear to me how it indexes. Does it index off the case shoulder? It looks from their cutaway picture with the die mounted in a press as though it might. If it indexes off the case shoulder, rather than the true OAL of the case, your trim length will only be as good as your resized case shoulder dimensions. If your case shoulders are differentially pushed back to any significant degree during your resizing operation, I guess it's possible they might fit differently into the seating die. I suspect that something like this is at the root of your issue, although I'm not sure specifically what it is. Ordinarily, changing the case neck length by .020" either direction should not affect seating depth or COAL.
 
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#6
InfScout1/69 said:
Length of neck def has an effect on COAL. Longer the neck further out you can seat he bullet.
Click to expand...

Look at the link below of the photo of Frankford Arsenal Cartridge Overall Length Gage and notice the cartridge is measured from its base to the bullet tip. The case neck length has NOTHING to do with the "Overall Length" of the cartridge.

Frankford Arsenal Cartridge Overall Length Gage

Meaning you can circumcise the case neck all you want but it still doesn't effect your overall length.
doh_zpsa2e8f099.gif



BUT if your Jewish and your Mohel drank too much wine at your Bris Ceremony you may come up short.
facepalm_zpsf5c6ea89.gif



The only possible thing that could be worse is if the Mohel is really drunk, and he is seeing double and forgets he is right handed.

trim_zps7b27921f.jpg


Bottom line, if you still think after reading this that the case trim length effects the overall length then your just being a real dick.
bangHead_zps24aecf27.gif
 
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#7
Edited to add: bigedp51 beat me to it, but we're in agreement on the answer.

That is how far you CAN seat the bullet out, not the seating depth that is actually obtained when the seater die mic is set to a specific depth. As I understand his post, the OP is experiencing significant seating depth variation that is proportional to variation in the neck/case length, even though he did not change the seating depth mic setting on the seating die micrometer. Within reason, meaning where neck/case length variation is not so large as completely disrupt seating die function, this should not happen. Contact between the seating die stem and bullet is far removed from the neck. I could easily seat bullets to exactly the same COAL (within the normal variation of bullet OAL) in cases where the neck length varied 20 or 30 thousandths. I don't do that for obvious reasons, but my seating die would never know that one case neck was .020" or .030" longer than another. Unless the ogive/bearing surface junction at the desired seating depth is closer to the neck than the overall variation in case length, that should not be the cause of his issue. As I mentioned, I suspect it has something to do with the way his trimmer functions and or variation in the case base to shoulder distance.

I suppose it is possible that increased friction from a longer neck might prevent the seating die from seating a bullet to the same depth if the neck tension was pretty high, but that would be another problem in and of itself. I find it surprising that his case trim length is varying significantly. It's hard to tell from his post exactly how much, but sorting trimmed case by length really shouldn't be necessary as cases prepped with a good trimmer ought not to vary by more than a couple thousandths at best. That is why I think the variation in seating depth has something to do with his trimming operation.
 
#8
variations in COAL in relation to case trim length

I just re-read the OPs post... I apologize! You guys are right... I thought he was just asking if the OAL has an effect in general. Lol in my defense the OAL does effect how the the round will shoot 8) but I'm sure you guys already know that! Hahha
 
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#10
The only thing I can think of is that you've got the die body screwed down too far and it's starting to crimp the longer cases. Depending on how tight it was, that MIGHT cause the bullet to stop a little early in the seating process. I'd back the die off a turn and reset the seater to the correct OAL and try it.
 
#11
Oal off the ogive should not vary by more than a couple thou, within the same lot...this holds true for me across 4 different lots of SGKs. I'd guess either your seating stem is having issues and/or you are noticing a correlation where there is none through a statistically insignificant sample. Please let us know when you figure it all out.
 
#12
Great thread here i realy appreciate all the input. its nice to be able to tap into the combined knowledge of the hide when i hit a stump... So so far my buddy did some brainstorming and advised me to check the case head space of my "bastard" cases, so i did, every case all of them measured exact with minor variances of <.005 so we ruled that out. In regards to my trimmer as mentioned by gstaylorg it doesnt really index off the case at all rather that is has a long steel pin measured to SAAMI standards foreach case type the is screwed into the cutter head and passes through the primer pocket of the case onto a steel plate attached to a drill chuck. once the pin touches said plate it stops cutting at the pin lenght which in this case (i measured it) is 1.9024. So i thought about the trimmer issue and pulled a couple bullets from the longer bastard cases and retrimmed them and i got a very small bit of material off the case but didnt make too much of a difference as after reseating the bullets COAl stayed the same. I didnt give the die mounting depth any thought as mentioned by MJY65 so ill be looking into that next. I just find it strange that i have a lot of about 80 reloads that are tits on the mark and these last 15-20 are simply put "bastards" i will reset my dies and update... I dont think it matters that these are being loaded on hornady lnl progressive press do any of you? i may just break down and buy some new dies if i keep getting bastard loads and try that. Ill update the post after resetting the die. Thanks again.

Safe shooting

Scout
 
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#13
The Lee case gauge/trimmer can give long cases if the gauge doesn't go through the flash hole (stays inside the case), and will give slowly decreasing case lengths as the gauge itself wears out from spinning against the mandrel.

But neither of these is your problem . . . and even if they were . . . the COL of a finished cartridge where the bullet is pushed down cannot vary based on case length . . . unless the long cases are somehow getting in the way of operating the die (so the bullet can't be seated as low as it should) or somehow flexing either the shellplate or the toolhead (LnL bushing).

Are you seating with a die that can also crimp? If so, can you back the crimp all the way out so that it's not a factor at all?

Is there significant slop/movement either at the shell plate or the LnL bushing when seating in a "bastard" case? Is flex at either point different when seating in a non-bastard case?
 
#17
Twoboxer said:
The Lee case gauge/trimmer can give long cases if the gauge doesn't go through the flash hole (stays inside the case), and will give slowly decreasing case lengths as the gauge itself wears out from spinning against the mandrel.

But neither of these is your problem . . . and even if they were . . . the COL of a finished cartridge where the bullet is pushed down cannot vary based on case length . . . unless the long cases are somehow getting in the way of operating the die (so the bullet can't be seated as low as it should) or somehow flexing either the shellplate or the toolhead (LnL bushing).

Are you seating with a die that can also crimp? If so, can you back the crimp all the way out so that it's not a factor at all?

Is there significant slop/movement either at the shell plate or the LnL bushing when seating in a "bastard" case? Is flex at either point different when seating in a non-bastard case?
Click to expand...

Twoboxer, i avoid wiggle on the shell plate by use of a lock washer but i will definately take a look at that once i get home. as for the lnl bushing i never gave that a thought. ill make that a priority tonight and report back. So as it stands im gonna check for proper fit of both shell plate and die in the bushing and bushing to the press, im then gonna check the die itself to make sure its not installed too deep as into its bushing, last ill take the die apart and make sure i dont have a lemon die. As for the question regarding the crimp thes dies do NOT apply a crimp to the neck. Its prob gona boil down to either novice error... or something silly like a lemon die set or lose components. i will report back by end of weekend. thanks again to every ones input...

safe shooting
Scout
 
#18
As promised i did my investigating on this and could only come to one conclusion. Lemon dies. i checked everything even took press apart, cleaned, dry lubed and adjusted. checked plate for wiggle, nothing, checked the depth my die sits in the press, perfect no issue there. so after brainstorming my buddy got me some new hornady dies and low and behold, not only do they feel better built and look of better quality than the rcbs i was using but ive loaded about 20 cases (intentially shorting the cases at different measurements) and every single bullet is now seated nicely at 2.120. thank you for all your input here i appreciate the help in brainstorming. safe shooting ya'all.

scout
 
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