9mm Plunk Test Failure

[Sharper2112]

So I’ve been reloading 9mm for several years now ever since I got into IDPA/USPSA. I shoot a P320 X5 Legion and use Blue Bullets .356 125gr Truncated Cone. I seat to about 1.115 COAL. I consistently have a high percentage of plunk test failures; usually about 10%. I typically will shoot that 10% in a practice session and rarely will one of those rounds not cycle. What I have noticed is on the rounds that will not plunk the measurement at the case mouth is .380-.383, while the 90% of rounds that do plunk measure .377-.379 at case mouth. My question is what could be causing this apparent bulge at the case mouth on 10% of my loaded rounds? I’m kind of at a loss

 

[Hartkopf]

Do you sort your brass? Some brands of brass are very thick. FC, Speer and Blazer are all thin and work great for plated or lead bullets.

 

[Sharper2112]

Do you sort your brass? Some brands of brass are very thick.

Oh definitely not, all mixed brass. And because of that this just may be something I accept and live with. It’s not a huge deal, I was just more curious as to why this was happening than anything else. You make a good point

 

[Hartkopf]

It’s easy to sort out thick brass during case prep if you are using a single stage press. (I use a manual turret). Resizing is usually hard to tell but when expanding the necks, I can feel the extra resistance of the thick cases. It’s at this point that I sort out the thick cases and they get used with jacketed bullets.

 

[Tilos]

Another variation to consider.
Some of the bullets you bought in bulk may be bigger than the others...
I push all the bullets I buy thru a lee sizing die when I receive them, knowing that they come from many different molds and the coating thickness can vary.
Pushing them thru a sizing die to qualify them takes less time than measuring them and judging by the different lever effort it takes to resize them tells me they are different sizes.
RE-sizing them is quick and easy and eliminates a variable for me.
jmo,

 

[AJC1]

If your not sorting at all during case prep your crimp function may not be closing the neck on shorter brass.

 

[FROGO207]

I have some brass that I consider thick wall in several caliber brass and sort them out on initial inspection and use them with plated or jacketed bullets. This has solved your problem at my bench. I have to make sure they are 9X19 brass anyway so sorting is a minimal addition to my time. I have to sort out 9X18 and 380 then anyway.

 

[Sharper2112]

If your not sorting at all during case prep your crimp function may not be closing the neck on shorter brass.

Interesting. I wouldn’t have thought of that

 

[wlkjr]

I would load some dummy rounds, no powder or primer, and shorten the OAL to 1.110 or so and if that doesn't work, tighten up the crimp a tad. That worked for me. My original OAL was a little long.

 

[AJC1]

Interesting. I wouldn’t have thought of that

Lower the crimp on those that fail to plunk, easy test cost you 0

 

[nettlle]

I don't sort brass. Either 9mm or 45acp. If there is a bulge at the case mouth it may be the bullet that is causing this. If your sizing die is not properly set it can cause issues.

 

[AJC1]

It could be exactly the opposite as well. The longest cases are over crimped and bulged.

 

[tightgroup tiger]

I have loaded Blue Bullets also. They are made close to here. The coating is very easy to damage. Are you seating and crimping at the same time?
If you are look at the top of the mouth of the case of a loaded round and see if there is some lead on top of the mouth that was pushed forward when you seated and crimped.
That lead piles up on the mouth and adds length to the case. This will make them stick in your plunk test.
I seat and crimp lead bullets in separate steps because I don't chamfer 9mm cases.
Just something to check.

 

[lordpaxman]

I shoot a P320 X5 Legion and use Blue Bullets .356 125gr Truncated Cone. I seat to about 1.115 COAL.

Very close to what I shoot! I use their .356 147gr RN at 1.120”. I have loads for the lighter bullets but haven’t yet tried them to see if it makes any difference in my HF. Their standard sizing is .355 and I’ve heard it’s so they don’t get called when reloads fail to chamber. I see you discovered their special profiles.
What press and do you seat/crimp in the same step? I’m currently reloading on an RL1100 with Dillon dies and have a small percentage of mixed brass failing the Shockbottle gauge, but they’re only 1/8” high from seating. They do chamber as the 320’s chamber is generous, and I use them for live fire practice. The high ones are typically CBC brass, but there are some others like “.FC.”. It’s good brass but I didn’t want to crank down the crimp anymore than I have to. You may need to try just a bit more crimp on mixed brass to account for all the wall thickness variation.
I don’t sort by case length, good grief I’d never shoot if I had to measure everything. Shorter cases shouldn’t be belled as much and therefore shouldn’t need to be crimped as much. Good luck.

 

[wild willy]

Do you check to see if its always the same brand of brass?

 

[Sharper2112]

I have loaded Blue Bullets also. They are made close to here. The coating is very easy to damage. Are you seating and crimping at the same time?
If you are look at the top of the mouth of the case of a loaded round and see if there is some lead on top of the mouth that was pushed forward when you seated and crimped.
That lead piles up on the mouth and adds length to the case. This will make them stick in your plunk test.
I seat and crimp lead bullets in separate steps because I don't chamfer 9mm cases.
Just something to check.

Yes I load on Square Deal B so seating and crimping are two separate stages.

 

[Sharper2112]

Very close to what I shoot! I use their .356 147gr RN at 1.120”. I have loads for the lighter bullets but haven’t yet tried them to see if it makes any difference in my HF. Their standard sizing is .355 and I’ve heard it’s so they don’t get called when reloads fail to chamber. I see you discovered their special profiles.
What press and do you seat/crimp in the same step? I’m currently reloading on an RL1100 with Dillon dies and have a small percentage of mixed brass failing the Shockbottle gauge, but they’re only 1/8” high from seating. They do chamber as the 320’s chamber is generous, and I use them for live fire practice. The high ones are typically CBC brass, but there are some others like “.FC.”. It’s good brass but I didn’t want to crank down the crimp anymore than I have to. You may need to try just a bit more crimp on mixed brass to account for all the wall thickness variation.
I don’t sort by case length, good grief I’d never shoot if I had to measure everything. Shorter cases shouldn’t be belled as much and therefore shouldn’t need to be crimped as much. Good luck.

Yes I shoot the .356 because I have heard that Sigs prefer them over .355 but I honestly don’t know if that is true. I’m thinking of just going back to plated bullets because I didn’t have this problem when I loaded those.

 

[Rule3]

You have a 10% "plunk failure" That is a lot
10 out of every 100??
You plunk test every round you load? Is that in your barrel or a case gauge??

SAAMI is .3800 so you are living on the edge

Yet you then shoot them for practice and they work?

Why bother then?

When a gun cycles, it slams the round into the chamber with more force than just plunking.

https://saami.org/wp-content/upload...FP-and-R-Approved-2015-12-14-Posting-Copy.pdf

 

[Sharper2112]

You have a 10% "plunk failure" That is a lot
10 out of every 100??
You plunk test every round you load? Is that in your barrel or a case gauge??

Yet you then shoot them for practice and they work?

Why bother then?

When a gun cycles, it slams the round into the chamber with more force than just plunking.

Yes approximately 10 of every 100 fail. I plunk each loaded round into my barrel. And yes 9 out of 10 bad rounds will still cycle but the one that doesn’t causes a jam that takes a few seconds to clear. Wouldn’t want that to happen in a match.

 

[243winxb]

Trim length difference effects crimp. Set the taper crimp up on the shortest case of the range Brass.

Find the brass with the thickest case walls. Set crimp on it.

Basic, turn taper crimp die down more.

 

[koz4guns]

I agree with some of the statements above, you should take the rounds that fail the plunk test and increase the amount of crimp and check them again.

Your Dillon crimp die will be a taper crimp and I don’t think it will cause a bulge if the crimp is increased.

 

[webrx]

Compare some that won’t plunk with some that do and find the common denominator. Are they a hair longer, thicker, bulge, same manufacturer, etc.

Maybe the angle of the cone in the bullet itself is the issue. Then take the ones that won’t plunk and shorten them a hair. 1.1 instead of 1.115 see f you still have an issue.

I have a kimber with a tight chamber and with truncated cone bullets I find I have to run them shorter to get them to plunk. Every other 9mm I have is fine at 1.12. The kimber needs 1.10 or it won’t plunk. With rn bullets no issue but with TC I have to adjust.

You can also run a batch of uncrimped no powder dummy rounds and see if 10% end up a little shorter than the others once chambered.

my guess is it is variance in the cone angle or thickness of the plating on the cone section if all are the same length when measured.

d

 

[rfwobbly]

So I’ve been reloading 9mm for several years now ever since I got into IDPA/USPSA. I shoot a P320 X5 Legion and use Blue Bullets .356 125gr Truncated Cone. I seat to about 1.115 COAL. I consistently have a high percentage of plunk test failures; usually about 10%. I typically will shoot that 10% in a practice session and rarely will one of those rounds not cycle. What I have noticed is on the rounds that will not plunk the measurement at the case mouth is .380-.383, while the 90% of rounds that do plunk measure .377-.379 at case mouth. My question is what could be causing this apparent bulge at the case mouth on 10% of my loaded rounds? I’m kind of at a loss

► 0.380" is in the cartridge drawing in your load manual, which is telling you that's the normal maximum dia at the case mouth for finished 9x18 Luger ammo.
► A 0.356 to 0.358" bullet should not be exceeding the 0.380" finished case mouth dimension with normal case wall thicknesses. Therefore, it almost has to be your Taper Crimp Die setting or function.

Hope this helps.

 

[tightgroup tiger]

which is telling you that's the normal maximum dia at the case mouth for finished 9x18 Luger ammo

9x19 Luger.
I agree with those who have said to turn the taper crimp die down more. Sounds like a classic case of setting up the crimp die on a long 9x19 case instead of a short one.

 

[Sharper2112]

Thanks for all the comments and helpful suggestions. I really appreciate it