Any reason for different cartridge specs?

[briannmilewis]

I have noticed while I trolled thru Steve's website's cartridge drawings, that from time to time the dimensions in his database are different to my Lee Modern Reloading manual. I suspect with all the different reloading manuals out there, there may be more than one instance of dimensions not matching. Most are minor differences of one or two thou, but there are some (can't give an example right now) that would stop me from rechambering a H&R because one spec indicates OK and the other indicates NO by more than just a few thou here and there.

Just wondering...Brian

[Steve P]

Depends on where the drawing came from.  The original drawing may differ from the "factory" drawing.  The SAAMI spec may be a little different from original drawings or Factory drawings.  A good thing to know is the specification is not tight tolerance.  For example, brass length could be different because one person drew the brass at "trim" length where another person drew the brass on "production" length.  You also have the third dimension (sounds kinda eerie doesn't it....) of the "max" length.  You don't want to have your brass exceed the "max" length as it could bulge in your chamber when closing the action.  (if the action will even close.) So length of brass between several drawings could be in the +/-.10" range or more.  There are also drawings out there based upon chamber dimensions vs ammo dimensions.  If ammo was exactly the same size as the chamber, you would have no margin for error or growth.  This is ideal for accurate ammo, but unrealistic in the ammo market.  The ammo manufacturers make their ammo to fit within the spec which includes the entire range.  I do not know what the SAAMI spec is, but here in my industry it is +/-.030".   Maybe someone will chime in with actual SAAMI tolerance spec.

Steve

[roper]

Lee's Modern Reloading really goes into details even give headspace on their drawning.     What happens alot of times the #'s  get rounded off  if you look at the 264 case in Nolser #6 vs Barnes # 4 vs Lee's  from rim to start of neck on the case is 2.246 Barnes has it at 2.2459.   Ahead of the belt Lee has .513 Barnes has .5127 but doesn't give how give how far up the case that measurement was taken.  Lee measure different places same with the width of the case at the shoulders he just takes his measurement further back on the shoulders so it can shows a .001 difference.

I only look at case dimension in the reloading manual and it interesting comparing them just have to make sure where the measurements are taken IMHO.

[Autorim]

IME Sierra has consistently published the most complete and accurate drawings of cartridge dimension. As an architect, I am very particular about good, accurate drawings and some manuals do not pay attention or hire poor draftsmen to produce their drawings. Some drawings are not to scale or proper proportions and may indicate a long neck on a cartridge when in fact it has a short neck. Thumb through the various manuals compared to Sierra and judge for yourself.

Ken

[jedman]

 Hello Brian,  The diameters given on cartridge drawings are suppose to be the maximum diameters of a loaded round.  If you measure actual casings you will see all are undersize of what is usually shown in the drawings. Sometimes I notice where a sholder dia. is given right at the point where the angle forming the bottle neck starts and others may show the dia. of the same cartridge at a point measured from the base to somewhere along the body near the shoulder but a good ways back from the shoulder. That type of measurment tells me nothing really.
In my years of playing with all types of reloadable ammo the brand that seems to vary the most are the Weatherby magnums ?       Regards,   Jed