[JoePapa]

I'm trying to understand why does the overall length of the bullet vary so much?

I'm reloading .40 cal and using 165 grain ball ammo with Unique powder and cci primers.

I noticed the OAL between the 135, 155, 165, and so on varies quite a bit. I noticed this with some 30-06 guides too.

So why is this? I thought the overall length was supposed to be a set length to fit the gun chamber.

How does this vary from pistol to rifle and what's the rule of thumb for OAL - just follow the instructions?


Thanks!


ps - sorry for such a noob question - just trying to understand.

 

[Rocky Raab]

If you are measuring OAL from the base of the cartridge to the very front of the bullet, the only important aspect is whether it fits and feeds the magazine. That's because the nose of the bullet never ever touches anything in the bore.

The important place on a bullet is the spot on the curve (the ogive) that is bore diameter. That is NOT groove diameter, but land-to-land diameter, which is always smaller. (It is .300" in a .30-caliber, .350" in a 357/38 caliber, and .450" in a .45, for example.)

Most handgun bullets have a cannelure that serves to mark the proper seating depth, and give a place to crimp. Bullet designers adjust the weight of a bullet by lengthening or shortening the bullet - often in both directions from that cannelure. So some bullets, when seated to that cannelure, will protrude from the case mouth more or less than another bullet. That's normal.

Seat to the cannelure, and unless the loaded round won't feed correctly, just ignore OAL. If the bullet is designed to be used with that round, it'll be fine.

 

[ranger335v]

"I'm trying to understand why does the overall length of the bullet vary so much?"

The OAL of bullets don't vary much but they do some.

The OAL of cartridges vary a lot because the bullets vary some, the chamber throats vary quite a bit, so do magazines. And, for rifles, final cartridge OAL will/should vary a bit if the loader actually takes the time to learn what bullet jump to the lands his rig prefers.

 

[unclenick]

The guys have it covered. Bullets have different shapes. Cartridge OAL usually must not exceed what fits in a magazine, usually must not let the bullet ogive touch the throat of the bore, and it should never be so seated so deeply that the bullet bearing surface is below the case mouth, which would leave a gap there. You normally want the case neck to have a good grip on the bullet, too. There are certain more exotic loading methods that break these rules, but for normal loading you want to steer clear of those situations.

For example, you'll find some light bullets are so short that if you used the SAAMI maximum COL the bullet would not even be inside the case. That's one case when COL needs to be shorter.

By the way, you will see COL, COAL, and OAL, and in older NRA literature Cartridge OAL. They all mean the same thing: finished cartridge length from stem to stern.

 

[CCAguns]

Oal

Say, UncleNick,

Is it common practice to set the bullet 0.01" off the lands for best accuracy, providing a magazine, etc., doesn't prevent it from being that long?

 

[ranger335v]

"Is it common practice to set the bullet 0.01" off the lands for best accuracy,.."

Nick is lucky enough that I ain't him, but the answer to that question is NO. There are common rumors and web fables but there are no common seating practices for "best accuracy".

 

[broom_jm]

However, it IS common practice to determine at what length a given bullet contacts the lands and then to make an educated decision on how far off to seat the bullet. Many barrels absolutely show a preference, in terms of accuracy, in how far off the lands a bullet is seated. The distance a bullet travels from case mouth to lands can effect many things that are determining factors in accuracy, including working pressure, concentricity and standard deviation of velocity.

Perhaps there are no "common seating practices for 'best accuracy'", but to ignore seating depth entirely is to compromise on the potential accuracy of any given firearm.

 

[MikeG]

I start at 0.020" off the lands as a matter of habit (have to start somewhere) and then adjust if necessary. Exception is monolithic solids (ie. Barnes) and those don't start any closer than 0.050 per Barnes' recommendation.

 

[Rocky Raab]

Keeping in mind that this particular question was about .40 S&W. it's probably pointless to talk about "off lands" - or "best accuracy" for that matter.

 

[MikeG]

Good one Rocky. I didn't notice the thread topic before I replied Got my mind wrapped around rifle cartridge OALs. Disregard the above as not being relevant to the current thread.....

 

[Rocky Raab]

Mike, it happens to us all.

And before anybody gets his knickers wadded, I did NOT say the .40 S&W is inaccurate. But it isn't a target gun, either.

 

[JoePapa]

My immediate goal is for .40 cal but I do have some rifles that I'll be reloading for (just not immediately) so I did appreciate the comments geared for rifles as well. Thanks for the help and insight, much appreciated.

--Joe

 

[ironhead7544]

The length suggested by the maker will generally work OK. You may have to vary it a bit to fit your pistol. Most bullets for pistols are designed to hit the feed ramp at a certain spot to make them feed properly. Also a bullet farther down in the case may produce higher pressure than would be safe.