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Plunk test issues


Blackstone45
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This description of the issue is rather long, so please bear with me. My gun is a CZ 75 SP-01 Shadow.

 

The first rounds I loaded were 124gr copper jacketed round nose 9mm Frontier bullets made, with OAL of around 1.13"; these pass the plunk test perfectly, they drop into the chamber and drop back out without issues. They also spin freely in the chamber. I still have around 60 of these loaded rounds.

 

I then made the decision to change to 125gr polymer coated round nose bullets made by Ares, also with OAL around 1.13". I loaded a few to chrono, they all cycled fine and velocites were good so I made a larger batch.

 

At the same time as when I changed to the polymer coated bullets, I also bought some copper jacketed flat nose/truncated cone bullets as I'm a fan of the neater holes they punch. Today, I decided to load a few to check what the optimal OAL is, and check velocities with the same powder charge. At 1.13", it couldn't pass the plunk test. I kept reducing the OAL all the way down to 1.05" with no luck. While the bullets do make a 'plunk' sound, they won't spin in the chamber, and their cartridge rims don't sit flush with the bit of metal near the feed ramp (if that makes sense). 

 

Therefore, I went back to check those polymer bullets I loaded at 1.13", and they also fail the plunk test. But they've been cycling absolutely fine in my gun. So, what do I do here?

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7 hours ago, AHI said:

3 different bullets. 3 different profiles. 3 different overall lengths.

So what's so hard to understand?

 

I guess my question is, can it be factors outside of the bullet that affect the plunk test. For example, the bulge in the case after seating the bullet?

 

5 hours ago, Dwbsig said:

Are you doing your test with the barrel in same condition clean-dirty?

Yes, I tested all three rounds at the same time on the same barrel

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4 hours ago, Blackstone45 said:

 

I guess my question is, can it be factors outside of the bullet that affect the plunk test. For example, the bulge in the case after seating the bullet?

 

Yes, I tested all three rounds at the same time on the same barrel

Yes.  The crimp and lack of crimp will affect the plunk test.  If you don't remove the flair or over flair the case it will affect the plunk test.

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6 hours ago, Blackstone45 said:

I guess my question is, can it be factors outside of the bullet that affect the plunk test. For example, the bulge in the case after seating the bullet?

Brass can and will have an effect.     Bullets not being seated straight can have an effect. Mark up a failed round with a marker. See were it fails. May not be length.

Note:  I have to adjust crimp from jacked to coated to plated. Each has its on setting. All 3 after will have the same measurement. This has to do with spring back/reaction of brass and projectile. 

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After using a sharpie to mark the cartridge, I've determined that it's the bulge in the case where the base of the bullet is seated that's causing it to fail the plunk test.

My original loads that worked well use 124gr TMJ round nose Frontier bullets with a .355 diameter. The polymer round nose, and TMJ flat nose bullets that don't pass the plunk test have .356 diameter.

Edited by Blackstone45
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    Some bulging can be expected due to differences in bullet diameter and brass thickness. The thing to avoid is lopsided bulging. I use an M-die expander and a Redding competition seater and every round is concentric and gauges. I'm not saying that's what you need but it's been the easiest for me. Others find a Lee FCD works best for them.

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