Allowable Cartridge Length

[longwinters]

Here is another question for you reloaders.  I see in my reloading manuals that there is a "maximum allowable cartridge length" for each caliber.  Yet there is also information talking about different rifles having different "maximum cartridge lengths" depending on that specific rifle.  I see that there are various ways to measure for the best cartridge length . . . what would be your prefered way to measure.  Or do you just make sure that you have the same measurements as the manuals.  I find it kinda strange that my Nosler manual says one specific length, but when I measure a factory Winchester cartridge the length is different.

Finally, how much variation can you have from the published S.A.A.M.I length.  My manual says (for 7mm) 3.290".  How much can I be off from this.  A hundredth, a thousandth or what? :?

[Kragman71]

LW,
Sinclair makes a "chamber length case gauge insert" which fits into the mouth of a shortened cartridge case.
This insert,which looks something like a "wadcutter"bullet,is placed far out into the case mouth.
When carefully placed into the chamber,the insert will be forced back into the case mouth.
The overall length of this assembly is the maximun overall length of a case in your particular rifle.
You will probably find(recheck your finding several times)that the length is greater then any cartridge length published.
Prepare your case by depriming and full length resizing. Then drill and tap the primer pocket,and install a bolt to push the insert out of the case. Remember to remove the bolt when you make the measurement.
Frank

[KN]

The main reason that the max overall lenghth is in the manuals is for use in rifles with a magazine. It's the longest that will fit in a factory rifles magazine.  KN

[savageT]

Here is another question for you reloaders.  I see in my reloading manuals that there is a "maximum allowable cartridge length" for each caliber.  Yet there is also information talking about different rifles having different "maximum cartridge lengths" depending on that specific rifle.  I see that there are various ways to measure for the best cartridge length . . . what would be your prefered way to measure.  Or do you just make sure that you have the same measurements as the manuals.  I find it kinda strange that my Nosler manual says one specific length, but when I measure a factory Winchester cartridge the length is different.

Finally, how much variation can you have from the published S.A.A.M.I length.  My manual says (for 7mm) 3.290".  How much can I be off from this.  A hundredth, a thousandth or what? :?

longwinters,
I have prepared test-length cartridges with de-primed and full-length sized cases by barely inserting a bullet into the case (no crimping).  I then take a Marks-a-Lot permenant marker and cover the bullet, then insert it into the chamber until I can close the bolt.  You may have to keep re-seating the bullet, in small increments, till the bullet will chamber and the bolt will close.  At that point, you have the full-length cartridge length for that bullet.  There should be marks on the o-give of the bullet where the rifling has made an impression in the black Marks-a-Lot.  Measure the over all length and set up your seating die to seat about -.030"(LESS) than this so your pressures are not too high.  You should be in business.

Finally, check to make certain that the finished/loaded cartridge will eject, as it is possible that you will have to shorten the length more to unload a live round.  That's the routine.  Label your test round and save it for future set-ups.

Jim

[Flint]

A reason for differing lengths (assembled overall length, not just the case) is the differing ogive, or curve of the bullet.  A long gentle curve will not reach the rifling as soon, a blunter curve will, and needs to be set back into the case further.  You do not want to jam a bullet into the rifling when you chamber the round.  Many say it should just gently touch, or be a hair short of touching.  One way is to seat a test cartridge (empty) with the bullet long, smoke the bullet with a candle or magic marker and attempt to chamber it.  If the rifling marks it before it's chambered fully, reseat it deeper until it will chamber and just touch or just short of that.  If this length will fit your magazine, it should be a good length (with that brand/weight/style of bullet).