Another OAL question

PepNYC

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Wondering what you guys go by when calculating your min/max OAL Do you go by the manuals or SAMMI spec? Let's say you have a Hornady 9mm 115gr FMJ RN projectile using Titegroup. SAMMI spec is 1.000 min. 1.169 max. The Lee reloading manual has 1.125 min. 1.169 max. The Hornady manual just says 1.100. I'll assume that's min. The Lyman manual only has 115 JHP. No RN so I'm not even sure what to do there.
 
Different profile bullets will necessarily need to be seated to different lengths. Learn the “plunk test”.

The bullet manufacturer’s load data will have an OAL listed that should chamber in all guns with a chamber cut to SAAMI min specs, which may not be optimal for YOUR gun. Most guns are reamed slightly looser than SAAMI. For bullet manufacturers that don’t create their own load data, their bullets may not match up to other bullets from published loads, and you are on your own to determine proper seating depth.

Basically this is what I do (for pistol bullets). Perform the plunk test to determine how long the bullet can be seated before it touches the lands. (On edit: always back off at least 0.020" from the lands). You may have to seat shorter to fit the magazine, and even shorter still to get it to properly feed/cycle. Then look for load data that lists an OAL for that is closest, but not less. Keep in mind that different bullets will be different lengths, and it is the base of the bullet that determines case volume.

If you have more than one gun in a given caliber, you need to do the plunk test on all of them. You may soon learn that one of them has a tighter chamber than the others, so go by that one.

Err on the side of caution, start low and work up.
 
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You really have to read the fine print to understand what the manuals are telling you when they give OAL measurements. It could be max/min for that chambering, max/min for that specific bullet, or OAL as tested. Toprudder gave good advice. Too long may not feed or fit in the magazine. Too short may not feed and may increase pressures due to reduced case volume. Find a length that works in your pistols for that specific bullet and then work up a load to the desired performance within published data.
 
AGAIN- COAL is NOT a hard and fast rule. It IS a guideline for ammo to reliably cycle in a given action type and magazine (if your gun has one). It also can affect internal pressure depending on burn rate and case capacity. I'll repeat- It is NOT a hard and fast rule.

COAL can vary widely depending on throat erosion, freebore, bullet ogive, etc and on and on. If you saw how we seat boolits in black powder cartridges, you'd be shocked. Often there's only about .125 seating depth with a paper patched 550gr boolit in a case like 45/90 etc and that's based on chamber profile, boolit profile, etc. I can guarantee, it's waaaaay over the nominal COAL listed for that round.

If an ammo you're reloaded is too long for your magazine and won't cycle in your gun but still meets COAL, then COAL for your gun/ammo combination is different. Keep in mind, it's a guideline for ammo to be able mechanically to properly cycle in a given action type.
 
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