The Plunk Test - Setting your OAL

[Hi-Power Jack]

_{Sorry for placing this in 9mm Reloading - applies to all semi-auto}

_{pistols, but I couldn't figure out how to make it more generic.}

Setting the "best" OAL for your gun involves ensuring that the loaded rounds

fit through your magazine and slide easily in and out of your chamber.

Once you've set the "crimp" properly, the only component left is the

OAL. So, first set your crimp properly, and then leave it alone - no reason

to change it once you've removed the belling and the rounds chamber

properly.

Set your OAL for the longest recommended - then try The Plunk Test -

remove the barrel from your gun, and drop the loaded round into the

chamber.

The cartridge should fall all the way in, without any pushing, and spin

freely in the chamber, and drop freely from the chamber if you turn the

barrel upside down.

IF IT WON'T SPIN OR DROP FREELY, YOUR OAL IS TOO LONG

FOR THAT PARTICULAR BULLET IN YOUR GUN.

If your OAL is too long, you have to shorten the OAL, and try it again.

Once you've found your longest possible OAL for your gun, then you

shorten that my .05" and load up 10-20 rounds and try them - make

sure they all will spin freely and drop out of the barrel easily. If you get

any that are too long, try shortening the OAL a little bit more.

FAQ'S

1. "I ran the drop test, and my rounds are still sticking in the chamber"

- shorten the OAL

2. "But the longer rounds feed perfectly in ....... gun".

- Great. But not in YOUR gun - shorten the OAL.

3. "But I load 124 grain MG FMJ's at .... OAL, and these BBI 124 gr

bullets don't pass the Plunk Test".

- Exactly right. Now you have to shorten the OAL of the BBI bullets

until they pass the Plunk Test

4. "But I'm at ...." OAL, and don't want to go shorter".

- Fine. Use another bullet. But if you have 1,000 of these new

bullets, they will probably work if you shorten the OAL until

they PASS the Plunk Test.

5. "But, I ran the Plunk Test, and they still don't feed."

- Exactly right. They will NOT pass the Plunk Test until you

load them short enough to drop freely from YOUR chamber

6. "But, the manual says to load them at ...." OAL. And they

don't spin/drop in my chamber".

- Exactly!! Drop the OAL, shorten the rounds, until they PASS

the Plunk Test.

7. "It is really important to me to run these long cartridges in my gun,

but they won't feed"

- Buy a new gun, have the chamber reamed or shorten the OAL.

8. "I ran the Plunk Test, and they don't feed. I think the bullets are

oversized or I don't have enough "crimp".

- Set your crimp 1st, then measure your bullets - doubt any major

mfgr of bullets is selling incorrect sized bullets, but it's possible.

Shorten your OAL until they feed.

9. "Man, that's a Lot of Work".

- Welcome to the wonderful world of reloading.

10. "My buddy has the same gun I have, and his cartridges won't

feed in my identical gun".

- Sorry, guess they're Not Identical. Shorten your OAL and

try the Plunk Test in Your Gun.

11. "But, if I shorten the OAL, won't that affect pressure / velocity"?

- It might. You must test each change (OAL, etc) for velocity

and watch for pressure signs on the primer.

12. "But, this is a Great load - really accurate at ...." OAL - but it

won't feed. When I shorten the OAL, it's not as accurate."

- Up to you, if you want a very accurate single shot, go with

the longer OAL. If you want a reliable gun, go shorter.

If you want both (accuracy & reliability) try another bullet.

13. "But, I'm going to a major match tomorrow morning, and

my favorite load won't spin/drop".

- Too late, procrastinator. Bring along some already

tested rounds that work in your gun, and when you get

back from the match, work on the proper OAL for your

new bullets.

14. "But, my rounds all pass the gauge test from EGW".

- Unless your gauge has a 5" barrel, I'd test your rounds

in the chamber of the gun you're going to shoot. If

they don't pass the Plunk Test in YOUR chamber,

you have to shorten the OAL.

Sorry for being so long-winded, but every other day we get one

or more of these excuses why members can't feed rounds thru their

guns.

If you have any to add, pls let me know.

Hope this helps - should this be in New Shooter Forum?

Jack

[bowenbuilt]

This should be a sticky......

[ZackJones]

Agree with bowenbuilt. Excellent information here, thanks, Jack!

[zhunter]

Sticky vote +2

[kneelingatlas]

Thanks for posting this Jack!

If there's one which bears repeating it's #11:

11. "But, if I shorten the OAL, won't that affect pressure / velocity"?

- It might. You must test each change (OAL, etc) for velocity

and watch for pressure signs on the primer

I'd say the majority of popular loads for USPSA are pushing the envelope, even 9 minor loads when you mix heavy bullets and fast powders, so it's important to remember that the shorter the OAL, the higher the pressure and most times that correlates with higher velocity, but not always. Powders can behave strangely when pushed past their limits, so if you get a lower velocity than you expect, you may be at the limits pressure wise with that powder.

[houser52]

I just recently ran into this exact OAL problem with a new bullet I wanted to try, a 9mm, 124 gr. coated RN without a lube groove.

I started with the recommended lead bullet OAL from my manual and it failed the plunk test. After shortening several times it still was too long. I'm now at 1.075. Some will still not pass the test but I was unsure to go any shorter. After reading the post above I feel safer now about shortening them enough and adjusting my powder so all will pass the test.

Thanks for the info.

[grouptherapy]

1.050 is the limit last time I cked. Good sticky.

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Edited August 18, 2014 by grouptherapy

[levellinebrad]

I have some lead that I load down to .990 with wsf.

[mississaugagunnut]

Great post. I have a Cz shadow and I have to load some projectiles much shorter than others in order to pass the plunk test.

[Laughingdog]

Just bear in mind that there's no reason to have to randomly try a bunch of different lengths, dropping in one after another for the "plunk test". That's a pointless waste of time. Doing this, you can determine the maximum length load for any particular bullet/barrel combo without having to load a single dummy round.

http://www.brianenos.com/forums/index.php?showtopic=196723&hl=

I just calculated the maximum length for two bullets last night to load in my CZ-75 in a couple of minutes, and that included field stripping the gun. So the first rounds I loaded dropped in and out flawlessly, right off the bat.

[Hi-Power Jack]

Laughingdog, sounds like a great alternative:)

I'll stay with random, but for those so inclined, your technique looks excellent. :bow:

[ToddKS]

I like the idea of using Laughingdog's technique to baseline what should be max and then follow that up with the plunk test on some dummy rounds.

That would save you from the random starting point but still give you the physical verification of the plunk. It is a little extra effort but I spend a lot of time reloading anyway.

[grouptherapy]

Once it's set for that barrel and the crimp is good let it roll.

Sent from my iPhone using Tapatalk

[Laughingdog]

I like the idea of using Laughingdog's technique to baseline what should be max and then follow that up with the plunk test on some dummy rounds.

That would save you from the random starting point but still give you the physical verification of the plunk. It is a little extra effort but I spend a lot of time reloading anyway.

As long as you include a 0.010"-0.020" buffer, you should be fine every time...at least with the rifling.

something to keep in mind is that the case wall gets a little thicker as you move towards the base. So if you're doing a load that is under 1.100", you'll find an increase in the number that don't pass case gauge. When you do, it's a bulge in the middle of the case, not the base of it, that's hosing you.

[1sickPuppy]

Thanks for the write and comments. I'm going to try out these techniques...

[mjmagee67]

You forgot the; if you don't like the short AOL you can have the chamber opened up to accept the longer AOL. I own several 9mm, I got a Kimber Target II and I would have had to shorten the round way more that I want to, so my gunsmith opened up the chamber. Now the gun runs great and doesn't take a different load.

[GARD72977]

You forgot the; if you don't like the short AOL you can have the chamber opened up to accept the longer AOL. I own several 9mm, I got a Kimber Target II and I would have had to shorten the round way more that I want to, so my gunsmith opened up the chamber. Now the gun runs great and doesn't take a different load.

7. "It is really important to me to run these long cartridges in my gun,

but they won't feed"

- Buy a new gun, have the chamber reamed or shorten the OAL.

[basman]

Great! thanks.

[Hi-Power Jack]

Can anybody add to this list?

[Steve RA]

To possibly save some time and effort, if you are buying a custom barrel direct from the mfr, contact them and ask if they will throat the barrel to a dummy round you send them. If they will, this will save time and aggravation.

Just make up a dummy that fits in your magazines with a little room to spare (lengthwise) and send it, then you can load as long as you will be able to, magazine wise. Try to make the dummy with as blunt a round nose bullet as you have/can find so that anything you want to load in the future will fit.

[Youngeyes]

This was great Jake. I must have missed it the first time. It's cold as hell here and the dog just peed on the rug... I know. I'll go shorten the OAL on my loads..

[Hi-Power Jack]

Just because your dog peed they're, doesn't mean you have to

shorten their OAL. There not always in need of shortening.

Sounds like its really coooolllllllddddd they're. Hope it warms

up for you over their.

[1sickPuppy]

Is it better to go with the longest OAL that clears the chamber and mags?

[Steve RA]

Maybe !!!

[Hi-Power Jack]

Is it better to go with the longest OAL that clears the chamber and mags?

As Steve said, MAYBE.

Best to 1. make sure you leave enough clearance that you don't find a round too long - back off "the longest" a bit, and,

2. experiment - might be more accurate at lower OAL's - but be cautious re: reducing your powder charge

a bit to prevent too much pressure - have to be cautious in developing loads.