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plunk test / OAL


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I'm a newbie to reloading and this puzzles me. My dad gave me a barrel of Red Dot (#12) that he has had for a long time. My load is from the 2005 Alliant manual. 115gn bullet, max powder 4.5 with and OAL 1.120. I started out low and 4.0 seems to cycle and shoot just fine. If i shoot factory ammo and the OAL is 1.150 then why is my load by Alliant 1.120 different? why if it were .125 or .130 or even .014. any help would be helpful. by the way I like shooting steel and just plinking. And oh yes I know how luck I am to have that much powder even if it is not the best for handgun use.

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The loads you see in the manuals with the OAL listed is what they work up and deem to be safe for that particular set of components. Most pistols I've shot require or really like a long OAL so most of us that reload, take it out longer than what most manuals list. Also, the OAL length will depend on the type of bullet you have. Some will be shorter due to their design. For example, when I load up my Montana Gold (MG) 95 grain JHP bullets, my OAL is 1.070. When I load up my MG 124 JHP, I go about 1.150-1.160. When I load up my MG 124 CMJ, I go out to 1.170-1.180. Remember a shorter OAL also increases pressure as you increase powder and this tends to spike differently in shorter vs longer OALs.

The other big factor is the longest OAL that will fit in your chamber AND your mags. These have to be tested by using the "plunk" test for the chamber (search "plunk", you'll get lots of hits) and then load up your mags and make sure they are not rubbing the front.

Then you just have to make sure they are chambering/loading reliably and you are on your way.

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I just "found" a pound of Red Dot that I've had kicking

around since the early 60's (1960's) ...

Just loaded up some soft plinking rounds for my 9mm

(around PF 100), and had a Ball with my FREE gun

powder in my KelTec P11. Very soft.

Don't discount it - it's not a bad powder for 9mm if

you don't care too much re: PF.

BTW, if you're not interested in PF, you can probably go

quite a bit lower than 4 grs, esp with the lead bullets. :cheers:

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Every bullet has slightly different ogive and meplat geometry and differing bore-riding surface length. This should have been covered in the two or three reloading manuals on your book shelf. Every gun has different chamber dimensions. COL in a manual is simply what they used for their testing in their gun and means nothing to you (other than being careful if you have to load to a shorter COL).

Per Ramshot:


It is important to note that the SAAMI “COL” values are for the firearms and ammunition manufacturers industry and must be seen as a guideline only.

The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.

This parameter is determined by various dimensions such as

1) magazine length [ed: also where in the loading cycle the magazine lips release the round to be chambered],

2) freebore-lead [ed: lede/rifling] dimensions of

the barrel,

3) ogive or profile of the projectile


4) position of cannelure or crimp groove.

• Always begin loading at the minimum "Start Load".

• Increase in 2% increments towards the Maximum Load.

• Watch for signs of excessive pressure.

• Never exceed the Maximum Load."

Your COL (OAL) is determined by your barrel (chamber and throat dimensions) and your gun (feed ramp) and your magazine (COL that fits magazine and when the magazine lips release the round for feeding) and the PARTICULAR bullet you are using. What worked in a pressure barrel or the lab's gun or in my gun has very little to do with what will work best in your gun.

Take the barrel out of the gun. Create two inert dummy rounds (no powder or primer) at max COL and remove enough case mouth flare for rounds to chamber (you can determine this by using an empty sized case, expand and flare, and remove the flare just until the case "plunks" in the barrel).

Drop the inert rounds in and decrease the COL until they chamber completely. This will be your "max" effective COL.

You can also do this for any chambering problems you have. Remove the barrel and drop rounds in until you find one that won't chamber. Take that round and "paint" the bullet and case black with Magic Marker or other marker. Drop round in barrel (or gage) and rotate it back-and-forth.

Remove and inspect the round:

1) scratches on bullet--COL is too long

2) scratches on edge of the case mouth--insufficient crimp

3) scratches just below the case mouth--too much crimp, you're crushing the case

4) scratches on case at base of bullet--bullet seated crooked due to insufficient case expansion (not case mouth flare) or improper seating stem fit

5) scratches on case just above extractor groove--case bulge not removed during sizing. May need a bulge buster.

Edited by noylj
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