Flash,

First, don't be offended because I can be very direct (blunt). I tend to make corrections because I grew up with a teacher and was corrected continually. Words, their use and context are important. The word you wanted is site, a location, not sight, something which is seen. They are not variant spellings but entirely different words.

For this the short answer is NO. Seating depth used to be a specification in reloading manuals, but this practice ended sometime around 1950 and OAL became the standard. Unfortunately they are not interchangeable. The difference is the biggest reason why bullet manufacturer data differs so much for bullets of the same weight. The premise raised in one of the earliest posts, that bullets of the same weight seated to the same depth will give approximately the same pressure is correct.

One problem with published data is that the manual publishers are showing a result in OAL, not a specification. Contrary to Nevada Ed's remarks, the result has nothing to do with "standard length" for the cartridge. Standard length is published by the Sporting Arms and Ammunition Manufacturers Association, abbreviated SAAMI. In reality very little ammunition OAL data is anywhere near the SAAMI maximum OAL. Take the 9mm Parabellum as an example. SAAMI Max. OAL is 1.169". This was determined by the longest cartridge that would fit in the shortest (narrowest) magazine of guns chambered for the cartridge. It gives gun manufacturers a standard for the minimum width to design magazines for new guns, so they will accept SAAMI standard ammunition. This is with round nose bullets. Changing the bullet shape can affect the maximum OAL cartridge that will function in standard magazines. Bullet length can also be a factor. Lighter bullets are usually shorter. In the 9mm a 90 grain bullet may be so short that if you tried to load it to the 1.169" length it wouldn't even enter the case!

Now, direct answer. How do you determine "seating depth"? Simple. Add bullet length and case length, subtract loaded cartridge length, and the result is the depth the bullet enters the case, hence "seating depth". To translate this to how long the OAL needs to be to achieve a specific seating depth do the same thing. Case length, plus bullet length minus seating depth = OAL. Just that simple. This way you can determine what length to load any nose shape to the same seating depth for bullets of the same weight. A semi-pointed, blunt round nose, flat point, truncated cone or hollow point 124 gr. bullet, all loaded to the same "seating depth" will all produce approximately (close enough) the same pressure and velocity. They will all be safe, which is the biggest concern! The OAL will vary by quite a bit though.

How can you feel comfortable reloading? Study! Read everything you can find (printed) and study it until you are sure you understand it. DO NOT rely to what you read on the internet, much of it will be absolute BS!!!

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Gunsmithing since 1961