Why different oal

[brick196]

While looking at different load books like lee and Lyman I notice that within the same caliber that different weight bullets have different oal why?why load a 155g bullet for 40s&w at 1.125 and then load 180g at 1.115. Why not make them all the same as long as it don't go over max or under min coal. Can some one explain

[brick196]

What I'm trying to ask is:
as im looking at Lyman's third edition pistol and revolver handbook under 40s&w they are loading 180 ft jacketed hps at 1.115 oal and 165gr tmjs at 1.120. What I want to know is why do they do that. Why wouldn't they use max at 1.135. It just makes it more difficult for me to try to grasp this pressure thing. I mean if you load a 180g bullet at max length isn't under less pressure than loaded at 1.115. I'm just trying to understand why wouldn't they use the same oal for all bullets in the same caliber. Does it make a difference.

[Rodvan]

I load my .40 the same oal for 165 and 180 grain rnfp and jacketed bullets. But, I worked up the loads until I found what was safe/accurate for my gun. May not work in yours, they don't in my buddy's gun. All bullets are not created equal, they are different length, different size ( lead or jacketed) and different profiles. I wouldn't worry too much about the pressure as long as you follow a load in one of the manuals. You do have to be careful with oal and powder charge, but what you should do is measure your barrel and bullet for the oal that your gun likes and work up a powder charge -starting at minimum- until you find the sweet spot. You will probably get a lot of responses about how dangerous and critical oal is in 40 S&W. It is important, but don't let that deter you. Check out my post about 9mm and .40 oal at the xdtalk forum. http://www.xdtalk.com/threads/i-dont-believe-it.353713/#post-6086409
have fun:-)

[44man]

Depends on the ogive of the boolit. have to do the "drop test. Yes seating depth can increase pressures so it is still up to you to work every different boolit.

[runfiverun]

nose shape/case volume.
it's a minimum oal they give.

[Wayne Smith]

Specific answer to your question, boolit length varies, thus OAL varies. As mentioned, more specifically, ogive varies even within boolit weight, thus where it contacts the rifling varies. Pressures are determined by the space under the boolit in the case, not OAL.

[buckshotshoey]

I refer you to the Speer 13 reloading manual. The front of book gives many insights to the internal and external ballistics of ammunition.

[reddog81]

Different shape noses require different seating depths. If you had different weight bullets with all the exact same nose profile then the seating depth would be the same. You cannot seat a truncated nose to the same OAL as a round nose bullet because too much of the bullet body would be sticking out of the case.

When I start using a new bullet I figure out the longest OAL that will work in my guns and magazines and load some at that long OAL. If that OAL works at the range I put a note in my reloading manual for future reference. I also create a dummy round I can use to make setup of the seating die easy when changing from bullet to bullet. I always try to find the longest OAL that will work for each bullet I use. I have a reloading block full of dummy of rounds in everything from 32's to 45's and it is one of the most useful tools I own.

If you only have 1 or 2 guns in a caliber it's fairly easy to do. Once you get up to 6 or more guns in 9mm it can be a pain to figure out an OAL that works in all guns...