Author Topic: 9mm Seating Depth  (Read 4064 times)

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Offline Kletust

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9mm Seating Depth
« on: April 05, 2016, 10:41:22 AM »
I have a quick question on Seating Depth for 9mm.  I fully understand the process of both Push Testing and Plunk/Spin Testing a load to match it to my barrel.  My issue is... how deep is too deep?

I have both a CZ-75 and a PPQ that seem to have tight throats.  I recently decided to move up to 147 gr Flat Point bullets and really like them, but I'm running into what I consider to be OAL issues.

147 Gr. Blue Bullet - All bullets will plunk test at 1.125 OAL (meaning they give that nice plunk sound and will fall right out if you turn the barrel over), but will not consistently freely spin until I reach about 1.115".   I loaded about 500 at 1.125 and had one miss feed out of the batch and they shot very accurately.  At this length I have about .310" of bullet seated into the case and you can see just a very slight hourglass shape in a loaded round.  At this length, I get maybe 2 or 3 out of 100 that don't pass case gauge.  If I shorten down to 1.115 then I start to notice more hourglass shape and I start to get 4 or 5 out of 10 that don't pass case gauge.

I have some 147 grain Black bullets that I have to seat to 1.065" to get them to Plunk test.  At that length I have a whopping .355" of bullet into the case.. so I didn't even try loading them.


This forum seems to have a lot of experience with loading to shorter OAL.  I guess my question is... how much base in the case is too much from your experience?  I may end up dropping back to 135 Gr or trying out some RN profiles... but I really like the feel 147 grain bullets and the pretty hole that the FP makes in the target.

Offline Smitty79

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Re: 9mm Seating Depth
« Reply #1 on: April 05, 2016, 10:56:49 AM »
I load 147gn Blue Bullets for a Shadow and a CZ85.    Both push test to about 1.135.   So I load to 1.12.    That gives them a set depth of .295".    They run flawlessly.    I can't remember a a mis-feed that wasn't a mag failure from Idaho dust.

At that insertion depth, there are about 5 headstamps I can't use because they are to fat for the barrel or case gauge.   The most common of those is CBC.   With your barrel, you might not be able to make it work at all.   You may need to get your barrels throated to shoot 147 flat points.

If you really like 147s and don't want to throat, you can try Xtreme or Berry's plated.    Those push near 1.2.   What will fit in a magazine is limiting.
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Offline Kletust

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Re: 9mm Seating Depth
« Reply #2 on: April 05, 2016, 11:27:28 AM »
CBC is the headstamp I'm using.... 

 My local indoor range uses magtech, so there is a ton of CBC brass in my stash!  And when I say a ton I mean it.... I just bought 5 Five Gallon Buckets of 9mm from them at a really nice price and I seriously doubt I'm going to have the time to sort completely by headstamp.   I'll more likely be culling out specific unwanted headstamps and .380 but so far the CBC is probably 1/3 of the brass.

It may be time to find another bullet, because once I find one that works well... I plan to do a bulk order to get the price as low as possible.


Offline benq

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Re: 9mm Seating Depth
« Reply #3 on: April 05, 2016, 12:27:44 PM »

Please note Xtreme's 9mm bullets are sized for 0.355" whereas Berry's and others are 0.356". I've shot a combination of CBC brass and Xtreme 147gr FPs and have had to seat the bullet pretty deep for reliable feeding.  Let us know how it turns out.

Offline Wobbly

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Re: 9mm Seating Depth
« Reply #4 on: April 05, 2016, 07:56:05 PM »
Kletust -
Welcome aboard !!


The answer is that it's a function of BOTH the brass and bullet. They are both unique individuals. So you really have to take your brass and your bullets and answer your own question. No need to listen to anyone else who doesn't have the exact same bullet and case, because it just doesn't matter.

We like to see at lease 0.200" of bullet insertion for 9mm Luger, but, from the bullet's point of view, there is no limit on what's too much. Concerning the base of the bullet, the case is the determining factor because the case gets thicker as it it deeper. The bullet, when inserted too far, will simply bulge the brass on the exterior so that it no longer fits into the chamber. You can't see it, so you have to check for this by using your naked barrel as a measuring tool.

Concerning the nose of the bullet, the interface between bullet and chamber is the limiting factor. That's what the "push test" is all about. Max OAL and the bullet length will give you the necessary case insertion depth.


147 Gr. Blue Bullet - All bullets will plunk test at 1.125 OAL (meaning they give that nice plunk sound and will fall right out if you turn the barrel over), but will not consistently freely spin until I reach about 1.115".   I loaded about 500 at 1.125 and had one miss feed out of the batch and they shot very accurately.  At this length I have about .310" of bullet seated into the case and you can see just a very slight hourglass shape in a loaded round.  At this length, I get maybe 2 or 3 out of 100 that don't pass case gauge. If I shorten down to 1.115 then I start to notice more hourglass shape and I start to get 4 or 5 out of 10 that don't pass case gauge.


1) Forget the case gauge. Use your barrel.

2) The "plunk test" will give you "yes or no" answers, but it will not tell you what OAL you should be using to cover 100% of your rounds. That's because the plunk test doesn't take into account the variations in finished OALs that are bound to occur. And that's why you get 2 or 3 per hundred that don't pass.

At this stage you need NUMBERS to work with. So you must use the hard data that comes from the "push test". It's the difference between going to a job interview and the company says, "Oh, don't worry. We'll pay you a lot." Versus "You'll be paid $xxxx per month."

In some things it's just nice to be exact.

 ;)
« Last Edit: April 05, 2016, 08:16:49 PM by Wobbly »
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Offline Smitty79

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Re: 9mm Seating Depth
« Reply #5 on: April 05, 2016, 11:48:48 PM »
I use all of my CBC on 124/5s.
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Offline 1SOW

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Re: 9mm Seating Depth
« Reply #6 on: April 06, 2016, 12:22:52 AM »
What wobbly said./

Measure the case wall thickness about 1/4" (.250")deep down into the case.  Then go down another .025" and measure,  and then again another.
At some point you'll find the case starts to get dramatically thicker as you measure deeper.  "This" causes case pressure to increase faster for every .001" you add past the point where the case thickens faster.

At a .300" seating depth you're getting closer the that point on many headstamps.  Some cases may not be safe at that depth,  others may be okay.

Just something to consider.