OACL Question

[Researcher]

So I have a Browning Hells Canyon in 300 win mag. I have been reloading for about a year and have not played around with very many of the variables yet as I learn how it all works.

I have a OACL question. I normally just go by the SAAMI OACL when I load my ammo however today I wanted to try the method described in my Nosler reloading book. They have you mark a bullet, set it in a spent cartridge, and chamber it to see how much of the mark is removed. This is supposed to tell you where the bullet is contacting the lands. They then say to seat the bullet .015 to .030 more into the case.

So I did this five times and came out with an average of 3.539 OACL which is a lot more than the SAAMI OACL of 3.340. It does fit into my magazine just fine but the difference has me concerned. I have not loaded any ammo with these measurements as I am uncomfortable with the difference. Am I missing something?

 

[Gunnersdad49]

I couldn’t get my .270 to group for anything until I went much longer than spec

 

[cornfedkiller]

Am I missing something?

Nope, not missing anything. I'm no expert so someone pleasecorrect me if I'm wrong, but because bullets are different lengths/tapers, some have a very long OAL and some are shorter. For instance, a bullet with a tip is going to be much longer than one that is not tipped.

If you look in the hornady book for a 6.5 CM, it shows an OAL of 2.69 for the 140gr SST, and 2.80" for the ELD-X.

The method you used doesn't lie unless the bullet is sticking into the lands a little and actually pulling it back out when you ejected it - but you should be able to see if that's the case.

 

[deerkiller]

use a fired case, squeeze it lightly so it's slightly out of round, put your bullet in the case and gently chamber it (if it sticks in the lands you squeezed too "out of round") gently pull it out and that is Max OACL for THAT bullet in YOUR gun - There is also a tool that's not very $$ for this

 

[ericwh]

Maybe this is obvious to everyone else but, when increasing COAL, I believe you also need to make sure you have "enough" (many people suggest a bullet diameter) of the projectiles bearing surface engaging the neck of the case. Depending on the shape of the projectile this may limit your COAL rather than the throat or the magazine (this is my situation). Supposedly this can affect concentricity and projectile stability after loading etc...

I am still relatively new so this is just based on my research and limited experience with a certain projectile and the long throat in my Tikka.

 

[Piscatory_4]

Maybe this is obvious to everyone else but, when increasing COAL, I believe you also need to make sure you have "enough" (many people suggest a bullet diameter) of the projectiles bearing surface engaging the neck of the case. Depending on the shape of the projectile this may limit your COAL rather than the throat or the magazine (this is my situation). Supposedly this can affect concentricity and projectile stability after loading etc...

I am still relatively new so this is just based on my research and limited experience with a certain projectile and the long throat in my Tikka.

True, generally only an issue I believe in really long throated rifles and/or light for caliber bullets when trying to seat close to lands.

 

[CT Barrett]

Hornady makes an overall length gauge one for bolt rifles and one that is curved for autos etc. They use a special threaded cartridge case that is loose fit for bullet. I used to do it the way you mentioned and the tools allow you to do it more precisely. I also use the hornady head space gauges to measure at the ogive of the bullet rather than the tip. This is because when measuring bullets at the tip it is not always consistent as bullet tips can vary especially poly tips. Just a suggestion if you want to be more precise than your described method which works ok.

As mentioned I have also ran into problems with seating depth with light for caliber bullets on my 243.

 

[mtswampfox]

have the old stoney point which is still around with different manufacture. Every bullet design will require different seating depth,,that said every time you shoot a round a small bit of metal is eroded from the throat. Over time depending on the chambering your seating depth is going to change Like the 17-223 is notorious for erosion or a 220 swift ..jus sayin

 

[wind gypsy]

Considering factory Berger 215 ammo is over 3.6”, you’re fine. Enjoy your newly found case capacity.

 

[Mable300]

Do yourself a favor and do it the right way...go get yourself the Hornady lock in load gauge with the correct cartridge, and measure your chamber, that will be the most accurate..

 

[HiMtnHntr]

The posts above that mention the overall length gauge is the way to go. Also, measuring to the ogive will give much more precise length measurements. I'm assuming that you are seeking greater accuracy and this is a common method of achieving that. If you have a powder a charge that works with the spec length, back that off to near minimum and test various seating depths. Depending on the bullet you use, manufacturers or the internet pros may have advice on where to start.

 

[LaHunter]

The Cartridge Over All Length (COAL) measurement is really not useful other than for magazine length. The measurement that you need to work with is the Cartridge Base To Ogive (CBTO). You will need to order some tools for this. Hornady makes a good set for this, which is mentioned above. The CBTO is what you base your seating depth on.

 

[recurveman]

Oh the can of worms you have opened. This is the reason to reload. Changing the seating depth of the bullets is part of the fine tuning your loads so that you can drive tacks. Though some bullets like to be on the lands and others like to be way off the lands. Just depends and you will figure that out with time.

 

[cooperjd]

So I have a Browning Hells Canyon in 300 win mag. I have been reloading for about a year and have not played around with very many of the variables yet as I learn how it all works.

I have a OACL question. I normally just go by the SAAMI OACL when I load my ammo however today I wanted to try the method described in my Nosler reloading book. They have you mark a bullet, set it in a spent cartridge, and chamber it to see how much of the mark is removed. This is supposed to tell you where the bullet is contacting the lands. They then say to seat the bullet .015 to .030 more into the case.

So I did this five times and came out with an average of 3.539 OACL which is a lot more than the SAAMI OACL of 3.340. It does fit into my magazine just fine but the difference has me concerned. I have not loaded any ammo with these measurements as I am uncomfortable with the difference. Am I missing something?

You are creating the perfect ammo for your rifle/chamber/throat/bullet. if it is longer or shorter than SAAMI spec, so be it. My 7RM, which is what i load most for, loves a 20thou jump to the lands, and with 160gr ab's, is quite a bit longer than spec as well. It fits in the magazine and shoots great, so carry on!

 

[shtrbc]

After you choose a method to measure and compare a few things you will also find that the OAL that shoots best often times DOESNT fit in the magazine. Meaning, too long. You could certainly shoot that specific load in that specific rifle single shot for optimum accuracy but that isn't why you have a rifle with a magazine. My point is that often time its all a compromise between what shoots best and what cycles/functions best in the rifle. Don't get discouraged just keep learning.

 

[Researcher]

Thanks all for the help. Definitely enough for me to go on. Thanks again.