After reading all that has been suggested here I put them to work ................but ! not until I measured a larger sample of cases . Glad I did that as the 100 case sampling changed the percentages a bit , ok , a lot . A great case in point for large sample numbers as the math whizzes insist upon .
The cases that are .005 longer than min sammi spec are in the minority ( 10% ? ) . The largest number of cases ( haven't put a calculator to this to get exact percentage , but roughly is 80% ) measure .006 to .0065 longer with the last group going .007 to .00725 ( 10% ?)( these numbers past the thou mark are approximations of the figures indicated by my dial caliper which is only gradated to the thou. Thinking about this a bit cause me to realize that those percentages are probably a close approximation of the ladder test loads by charge weight . That is to say 10% at he low pressure end , 80 % in the middle normal working pressure loads and 10% at the high pressure end .
After the long winded session of measuring several points on the cases I have this info to share .
new lapua cases......... belt .529 all
forward of belt......... .508 to .509
Extractor groove ....... .451 to .452
shoulder body junction.. .488
4 fired cases .005 longer than min.
belt...................... .532 to .533
forward of belt ....... .513 to .514
extractor groove ....... .453 to .455
shoulder body junction . .490 , all
4 fired cases .006 longer
belt .................... .532 to .533
forward of belt ....... .513 to .514
extractor groove ....... .453 to .456 ( one case at .456)
shoulder body junction. .490
4 fired cases .007 longer
belt .................... .533 to .534
forward of belt ....... .514 to .515
extractor groove ....... .455 to .457
shoulder body junction. .490 all
Moving on to the " close the bolt on a fired case " test results were as following:
.005 longer...... almost no difference from the closing without a case in the chamber .
.006 longer...... noticeable difference from the .005 cases but not any big diff, just enough to notice .
.007 longer...... big diff even from .006 cases , very big increase in effort , also uneven spots in closure , kinda draggy rough .
At this point I am thinking that .oo6 longer is very close to chamber actual . Thinking that actual may be right at .0065.
I suppose a Cerrosafe cast would answer this more definitively , but I am a bit apprehensive about a procedure that use molten metal in my LSR hammer . Just occurred to me to do a trial on one of my takeoff bbls .That would be fun and no tension involved .
You have a penchant for putting your finger in the middle of the pie .
Probably so you can eat the rest of it ! [img]/ubbthreads/images/graemlins/blush.gif[/img]
you reckon bolt thrust can account for 5 ten thousandths ?
p.s. Chris Matthews , please chime in on this ...............we are dumb and need the light ! [img]/ubbthreads/images/graemlins/crazy.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]
[ QUOTE ]
Or more simply put, the area in shear for all lugs is multiplied times the shear modulus, and this number is divided into the thrust. Often the resulting number will be in the .001"-.002" range. This explains why it becomes necessary to bump the shoulders of brass cases back after a few reloadings. New brass is elastic enough that it will return to its original shape, but with progressive loadings the brass becomes more plastic until it does not return to its original form at all. Cases become sticky, bolt lift more difficult and eventually the cases have to be replaced. With very high pressure loads this can happen on the first firing.
Some good advice has been given. I would only add this:
Some brass in the same lot can have different grain structures and slightly different alloys or percentages. Add to that the fact that not all ammo has the same pressures associated with it by factors such as temperature, load development, case capacities and such means that the brass gets abused worse sometimes-even with the same load. This is the reason why some go in easy, and some need to be FL sized already. I would take the ones that just barely let your bolt close easily without galling your lugs and make all the others as close to the same size as those possible. To to this, the Redding indicator works great but so does the Stoney point tools. They make the headspace gauges and bullet comparators on seperate tools that are affixed to your caliper which frees up your press for other things.
For instance, when I have to "bump back" my brass that I normally just Neck size, I can set up my Stoney POint tool on my caliper and set up my FL die on my press. Then it is size, then measure. IF the die needs to be threaded further down to get more bump, then I can do it quickly without having to thread an indicator on then off then on again. Make sense?
Anyhow, I think you're on the right track here.
Thanks for the info,factoring in the brass differences is something I had not done .
I like the Redding tool but you pointed out a problem with using it that I don't like ...it ties up the press ! You just about have to have separate press to use it easily .....now where did I put that Midway catalog [img]/ubbthreads/images/graemlins/laugh.gif[/img]
BB thanks for the bolt thrust info , that is a lot of push!