Case length tolerance

[jasonbterry]

in the last little bit i've been getting really picky about my hand loading. i shoot a Winchester M70 Super Shadow chambered in 270WSM. i'm shooting a 150gn Nosler BT over 68ish grains of Hodgdon Retumbo (haven't tuned it in just yet). SAAMI puts the brass at 2.1" in length, but i've surmised that my particular chamber allows 2.12" for case length. i know i don't want to fill all of that space as there needs to be room for the elastic expansion of the brass, but what is a good amount of clearance? odds are i'm being to persnickety about this as i'm not likely to shoot so consistent that it matters, i'm just trying to remove all the inconsistency i can. i figure if i improve a bunch of little things it may add up to matter one day. i'm preparing to shoot distances up to 500 yards at deer and will only be satisfied when i can hit an 8" circle in full confidence. thanks for all of your help guys.

 

[Slamfire]

On my target rifles, I push the shoulder back an average of .003", I small base size, I trim the maximum amount of trim, which is about 0.015", because I don't want the case ever jamming in the throat, and I seat the bullets so I have lots of magazine clearance and absolutely no chance of jamming in the throat.

I am more interested in safe reliable functioning than slavishly following bench rest reloading techniques. I am not shooting a bench rest rifle, nor am I shooting off a 400 pound bench with 40 pounds of sandbags. I shoot hand held rifles. My ammunition will shoot inside my hold even when I am prone with a sling. So it is good enough for me.

My ammo will shoot sub MOA at 100 yards, will keep within the X ring at 600 yards, if only the darn wind would cooperate.

 

[bgr2014]

Neck Length

What you want to do, is have all the necks trimmed to the same length. Stay away from the free bore it can get you into trouble, and even destroy your rifle or you. The load you mentioned is reaching max. capacity for that case, I'm loading Retumbo in a 270WSM case necked down to 257cal. using 65.5gr and the 110gr. Accu-Bond goes down into the powder, not compressed, but that far in. The WSM chambers are long throated to compensate for the higher pressures they generate, Don't get your bullets seated out too far. Have you uniformed the primer pockets?

 

[jasonbterry]

slamfire... so are you indicating that you trim the cases to allow .015" of clearance? i'm seating all of my bullets .01" off the lands so i'm right at or dang close to factory spec. plenty of room in my magazine.

bgr... i trim all of my cases to within .001" of each other. consistency there is no problem. 68 gr of retumbo is middle of the road for my rifle so i've got room to make adjustments to things elsewhere in the cartridge so long as its nothing major. haven't uniformed primer pockets, but i do clean them well. i've been looking at uniforming tools and have been impressed (depressed) at their expense for such a small tool. i'll probably break down and get one, though.
i haven't been able to find any resources to indicate the average elastic expansion, lengthwise, of a rifle cartridge. you guys know of anything?

 

[bgr2014]

Case Length

I guess I've done everything to cases that can be done, reamed inside neck, turned outside neck, de-burred flash holes, annealed necks, full length, neck sized and the only thing that really showed any improvement was the primer pocket being uniformed. The primer has a good seat and gets better ignition I guess, that's the only thing I can figure out.

 

[Slamfire]

slamfire... so are you indicating that you trim the cases to allow .015" of clearance? i'm seating all of my bullets .01" off the lands so i'm right at or dang close to factory spec. plenty of room in my magazine.

Max case length for a 308 is 2.015" http://en.wikipedia.org/wiki/.308_Winchester

I trim to 2.00"

I use a Giraud and Gracey trimmer. Trim length is not off the base but off the shoulder. So case trim length varies if measured from the base. Might be as much as .002" or .003 if measured from base. I think the shoulder measurement is more important as cases headspace on the shoulder.

The only bullets I seat close to the lands are the 600/1000 yard ammunition. Even then I am worried that a bullet might stick in the throat. I have had, and have seen, plenty of occasions where a competitor opens the bolt, and the bullet stays in the throat. Darn mess to clean up.

I want function reliability so I stay away from the throat standing, rapid fire sequences.

Since I shoot HM scores in the RF, (used to shoot HM standing, but then the older I get, the better I was ) a little bullet jump with 308 and 223 does not effect groups. Unless you are using Berger bullets which are jump sensitive.