OAL confusion

[Squeaky Wheel]

I'm confused regarding cartridge lengths. I have Lyman #49 and Lee's Modern Reloading (latest edition). One of the first cartridges that I'm working with is .30 Carbine. The cartridge diagrams in both manuals show 1.680" as the maximum overall length for the cartridge. But, the manuals also show a minimum overall length of 1.680" for 110 grain bullets loaded with H-110 powder. If I understand this correctly, that means that there is no tolerance at all? (cartridge length must be exactly 1.680" for every load)

I still have about a half-box of factory loaded .30 Carbine rounds (Remington) loaded with 110 grain bullets (I don't know which powder was used at the factory). Out of curiosity, I measured the overall length of each of the factory loads and found that the maximum was 1.660" and the minimum was 1.644".

Can someone explain how to properly interpret these manuals regarding cartridge overall length in this case of .30 Carbine with 110 grain bullets and H110 powder? Many thanks!

 

[NeuseRvrRat]

the 1.680" max is to make sure it'll fit the magazine. i've never seen a minimum COAL listed. are you sure that isn't just the COAL tested?

for example, my Speer manual lists 3 different 110 gr bullets for 30 carbine. the COALs tested for each bullet are different. 1.635", 1.675" and 1.680". it lists 1.680" as the max COAL.

 

[Magnum Shooter]

I still have about a half-box of factory loaded .30 Carbine rounds (Remington) loaded with 110 grain bullets (I don't know which powder was used at the factory). Out of curiosity, I measured the overall length of each of the factory loads and found that the maximum was 1.660" and the minimum was 1.644".

This should be a good indication that COL is not as critical a dimension as you have been lead to believe.

 

[mitchz]

Hope this helps you. Max. COL is the factory standard so that it will chamber in all guns. If you look at the recipies from your powder manufacturer you will notice your COL line will vary. The reason is that all bullets are different lengths, so to keep the same air space inside the case the COL changes. If you set an extemely long bullet in at the same COL of a very short bullet you can cause a very high and possibly unsafe pressure in you chamber. When you buy bullets that you can't find recipies for do the math to make that air space right and you will always be safe. I experimented with .357's and found that for every .10 deeper the bullet was set the FPS went up 140. That dosn't sound like much but that was the differance between a starting load and a max load FPS. I don't have a way to measure camber pressure but from the recipe charts my guess is the presure went up 10.000 CUP. So even if you are loading midrange loads if you seat a bullet just .10 to deep it can be dangerous.