Question about COAL and bullet seating depth?

[Jasper1573]

A few days ago I decided to get some Hornady Amax 178 grain projectiles in .308 Win. I loaded them up according to the Lyman manual and noted that the COAL according to Lyman is 2.780. I noticed this to be true also of the all the bullets greater than 175 grains, except the Sierra 180...it called for the standard 2.800 COAL.

So why do the longer bullets require a shorter COAL? I am sure I could load them at the standard of 2.800, but they grouped pretty well as is.

 

[USSR]

So why do the longer bullets require a shorter COAL?

They don't. The COAL listed in reloading manuals are simply the COAL they used during load development. Why they used such a short length is beyond me. I load the 178gr Amax bullets to a COAL of 2.84", which is as long as I can load them and have them magazine feed.

Don

 

[Jasper1573]

I thought the 2.780 COAL might have something to do with the polymer tip, but no idea what. By seating the bullet that deeply into the case, it almost turns into a compressed load, but not quite.

 

[amlevin]

Often times the COAL shown in loading data is a Minimum length. As for .308, most load to the max length 2.800 spec'd or 2.840 if your magazine will accept it. Some even load far longer than that in order to reduce the jump and then just feed one round at a time.

 

[gamestalker]

Listed OAL is a refrence point only, a one size fits all standard structured around working pressures for that cartridge and bullet. Typically the ideal seating depth for high powered rifle is to seat at the longest OAL the chamber will accept short of touching the lands, and will still fit the magazine and feed properly. SAMMI listed OAL is the minimum OAL for any given cartrige. Pressures will rise the deeper the bullet is seated, this can limit the degree of load work up range. Most that measure their chambers or load according to their chamber dimensions, do so to increase accuracy by reducing the distance the bullet has to travel before contacting the lands. The further the bullet has to travel to the lands, the greater amount of harmonic distortion.

 

[evan price]

They used 2.78 in their loads. Without a cannelure, you can seat it whre you want; I would go as long as you can but still chamber reliably and feed from the magazine. 2.82 is about as long as I've seen in factory guns. My Rem700 like 2.80"

 

[amlevin]

Even WITH a cannelure I seat the bullet wherever I want to get the length I want. Why would it matter if the cannelure was either way out of, or inside, the case neck.