How important is case length?

75

Well-Known Member
I've got a batch of norma brass which has been fire formed in my rifle but is all shorter than the standard Lee resizing tool (the small, handheld basic one), so no brass is being trimmed. Problem is that case length varies quite a bit (0.005 to 0.010") and they are all shorter than the Lee trimmer which means that when I compare finished lengths using a comparator the bullets will all be seated fractionally different amounts (in order to get the same overall length).

How much is acceptable in difference in case length and should I buy a proper resizing kit and take all the cases back to a consistent, but shorter length?
 
1: as long as the cases are not longer than the book figures or your lee trimmer, then its ok from a safety PoV. I have exactly the same thing with my 7-08 and nosler brass.

Regarding consistency, well depends what you want.. It will have an affect, whether its noticable or not is another thing. I have 20 cases which i prepped to be as tight tolerances as possible. all are the same length +/- 0.002'' and all weigh the same. They all have the same neck wall thickness by neck turning and to be honest i dont notice a difference between those any my standard cases.. although my standard cases are similar tolerances to what you mention on length but are neck turned and weight batched.

If it pleases you to be as accurate as you can, do it.. then you can rule out that variable when shooting. If it doesnt really bother you, forget about it!
 
Thanks FF!
Being slightly anal, I will probably do it to rule it out :D If the case lengths differ by 5 to 10 thou then that means my bullets will be seated different lengths by a similar amount, which kinda makes it pointless trying to get overall lengths to within +/- 0.002" (which is what I aim for!).
 
well if your using the comparator, then your measuring from the head of the case to the ogive, and that will be consistent, so distance to the lands will be the same..

the only thing is that there will be more or less bullet in contact with the neck walls which will alter pressures maybe?

im with you, do it and rule it out.. i also check my ogive length to +/- 0.002 which takes time but is worth it in my eyes. The biggest increase in accuracy and ES etc came from using bushing dies and altering neck tensions though.
 
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I would say that my Lee Case trimmer has only actually trimmed about 5-10 cases out of over 200 on my norma 270 brass, so over 95% are under the max length.
 
I ran some figures through QL and as a rough guide for each 1.0mm difference in case length there is a 15fps gain or drop.
Whilst this is not a replacement for testing over a chrony it could be a help in working out what to expect performance wise.
 
Yeah, that's my thinking, +/- 10 thou less or extra bullet in contact with the neck walls is likely to make a difference (or at least it will in my head :lol: )

All the Norma brass I have (including once, twice and 3x fired and original Norma factory loads, unfired) averages around the 2.027" mark, which is right at the bottom end of the .243" case length range I've got in the relaoding manual of 2.025" to 2.045". Guess I'll be cutting it all back to 2.025" and working from there!
 
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Is it not strange that the major ammunition companies cannot seem to make cases that are actually to the design specs?

Surely tis not that hard a thing to do.
 
Case length variation has a big effect on es and sd for the long range shooter
But at short range is will be fine as long as it's not to long for the chamber
 
I ran some figures through QL and as a rough guide for each 1.0mm difference in case length there is a 15fps gain or drop.
Whilst this is not a replacement for testing over a chrony it could be a help in working out what to expect performance wise.

This is a blatant generality. (Quick Loads, not yours!) Like Flyingfisherman says. What of neck tension? And if this is the case, why do people struggle to set their bullets out to the lands all the time?? Would not every mm of added length in effect, lessen the amount of neck gripping the bullet?:stir:~Muir
 
This is a blatant generality. (Quick Loads, not yours!) Like Flyingfisherman says. What of neck tension? And if this is the case, why do people struggle to set their bullets out to the lands all the time?? Would not every mm of added length in effect, lessen the amount of neck gripping the bullet?:stir:~Muir

It's true that the amount of bullet seated in the case will to a large part determine the amount of initial resistance, and therefore determine the starting pressure, in a similar way to how sticking the bullet into the lands does.
It's something I pondered a lot before I bought QL. I always imagined that there were vast differences for each mm of seated bullet length, but it's not the case.

If you enter the correct case length then QL will tell you the amount of bullet actually gripped in the case, and, using all the calculations and information that it contains, it is able to give a fairly accurate estimation of pressures, and the resulting fps. But as I said you really need a chrony to see what you actually have.

I suppose the only way to get a constant, if there truly is one, is to always use neck turned cases and bushing dies, and to anneal the cases before each loading. :)
 
I take it you only neck sized the cases.
You could try full length sizing them and this may increase the length enough to allow them to be trimmed.
I've got a batch of norma brass which has been fire formed in my rifle but is all shorter than the standard Lee resizing tool (the small, handheld basic one), so no brass is being trimmed. Problem is that case length varies quite a bit (0.005 to 0.010") and they are all shorter than the Lee trimmer which means that when I compare finished lengths using a comparator the bullets will all be seated fractionally different amounts (in order to get the same overall length).

How much is acceptable in difference in case length and should I buy a proper resizing kit and take all the cases back to a consistent, but shorter length?
 
It's true that the amount of bullet seated in the case will to a large part determine the amount of initial resistance, and therefore determine the starting pressure, in a similar way to how sticking the bullet into the lands does.
It's something I pondered a lot before I bought QL. I always imagined that there were vast differences for each mm of seated bullet length, but it's not the case.

If you enter the correct case length then QL will tell you the amount of bullet actually gripped in the case, and, using all the calculations and information that it contains, it is able to give a fairly accurate estimation of pressures, and the resulting fps. But as I said you really need a chrony to see what you actually have.

I suppose the only way to get a constant, if there truly is one, is to always use neck turned cases and bushing dies, and to anneal the cases before each loading. :)

I agree with the above. The other way of getting a constistent ( or improved consistency) load is to apply a consistent crimp. Factory ammo does it all the time. I have used a crimp to great success, especially when the brass quality is suspect. Velocities and SD's leveled out nicely and accuracy improved. In the Hornet, the results were dramatic.~Muir
 
just fill 'em and fire 'em and get on with it!

FL resizing fireformed cases in order to trim them to length strikes me a bit like squeezing one end of a balloon to make the other end look bigger!
 
yeah im with bewsher, i wouldnt bother f/l resizing to increase the neck length, after all the trimmer cuts them back to the max length? I would go with what you suggested before, cut them all back to match the shortest one.. or the average length. Even if theyre not all identical but +/- 0.005 opposed to +/- 0.010 then you will have better consistency.

Im interested to hear what grant said about reducing ES. Ive not actually run any of my 20 identical cases over the chrono, but look forward to seeing if my ES has reduced..
 
flyfisherman
if you want a es of 5 or 7 and a sd of 2 you have to do everything possible to get their thats just 1 thing that gets you thier ,this isnt for a hunting rifle though only my target rifles
 
Cheers Grant, Im not shooting a stock hunting rifle but a custom build. ok its not a dedicated F class rig but ive got the ES down to the 20s, and that was with weight sorted cases, neck turned and run through a bushing die with a couple of thou neck tension. I will be interested to see if these 20 cases ive prepped give me a reduced ES/SD.

Heres a question.. which has a bigger effect on ES/SD, amount of neck tension or consistent neck tension? ie annealing after each firing and through a decent die?

Im assuming with increased neck tension, your pressure increases and therefore velocity increases?

Its not shooting badly at all, its on an average day 0.5 MOA but regularly shows better performances. I had a 5 shot group at 510yds of 0.57MOA the other day.

Do you think powder type has a lot to do with ES/SD? Im using H4895 and think im running out of options to get it below 20..
 
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