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Old January 17, 2013, 09:25 AM   #5
Rimfire5
Senior Member
 
Join Date: January 2, 2009
Location: Northern Virginia
Posts: 467
The OAL you use and should use depends entirely on the chamber in your rifle. It also depends upon the ogive of the bullet - the spot where the bullet first will touch the rifling.

There is a great article in the new Berger reloading manual by Bryan Litz on page 148 that explains the subject and recommends that you adapt COAL of a load to your chamber for each bullet type (target bullets and hunting bullets are often very different).

Every bullet type has different dimensions and the ogive will be in a slightly different place (the shape of the bullet tip has a lot to do with it).
150 grain Sierra Match King bullets #2190 for example has a recommended OAL according to the Sierra Manual (5th edition) of 2.775.
However if your chamber is deep, you could easily seat your 150 SMK out to 2.810 and still not be close to the rifling.
Then again if your chamber is exactly to spec (pretty rare) you might find that at 2.810, the bullet is into the rifling and you can't close the bolt.

Sierra 150 grain soft Boat Tail bullets #2125 have a recommended COAL of 2.750. Both the #2125 and the #2190 are boat tail shapes but the #2125 has the ogive out further because the soft lead point requires a fatter tip.
At recommended COAL, both would have the ogive approximately the same distance from the rifling so the "jump" distance to reach the rifling would be the same.

From a practical standpoint, you won't know what your chamber depth is until you measure it. Most agree that you should leave 0.020 between the bullet ogive and the rifling if you don't want to increase the pressure.
BUT --- every bullet shape has a different ogive position so you really need to measure the chamber with each bullet type you use.

For example, I have a Savage 10 FP in .308 that has a deep chamber.
I can seat a 168 SMK out to 2.890 and be 0.020 off the rifling.
However, because the bullet shape is different, I can seat a Nosler Custom Competition 168 grain bullet out to 2.958 to get to 0.020 off the rifling.

My buddy's new Savage 10 FCP-K in .308 has a chamber that is much shorter and the 168 SMK bullet will be into the rifling if it is seated at 2.800 COAL. He has to load at 2.760 with the SMKs to get 0.020 to the rifling.

Both rifle shoot very accurately with their favorite loads and once we both knew the rifle's specs, we were each able to get the best out of our hand loads. We just had to load to totally diffenent COALs with each bullet type.
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