Minimum 9mm case mouth post crimp - 0.378"?

[rdtompki]

Background - SA 9mm 1911, 19 lb mainspring, Ti FP, 1X FPS. Most folks change the Ti to steel, but gun had functioned fine for 25K rounds albeit without a really pronounced FP strike. My wife is now seeing very light primer strikes and 1/20 or so fail to ignite.

The suspect rounds also induced a light strike in my wife's backup gun. I've come around to believing that the issue relates to my switching from a two-die seat/crimp setup (RCBS microseater/Lee FCD) to a combo die. Ideal case mouth is .380 - .381. I've measured some rounds at .377. Is this enough to cause the round to seat just a tiny bit deeper in the chamber? It wouldn't take much given our many thousands of rounds of good primer strikes would be classified as light?

I'm going to load some dummy rounds in the am with case gauge, barrel and micrometer in hand. I'll also load some with the two-die setup.

 

[LeftyTSGC]

The max case rim size should be .380. All of my reloads measure around .376-.377. I fire them in all my 9mm handguns with no problems. You can do a plunk test to see where your rounds are sitting.

You may want to look at your firing pin and mainspring to make sure it is correct.

Remember that 9mm headspaces on the case mouth, so it may not be a case rim issue but a case length issue. A lot of variables that could cause this, just need to work them out one by one.

LeftyTSGC

 

[rcmodel]

Ideal case mouth is not .380".

That measurement is SAAMI Max diameter for a loaded round.

I call ideal .376" as that is what every factory 9mm round I have checked measures.

I have no idea what is causing your problem, but it's not that!

1. Pull the FP and check for spring stacking up, or broken, or a dirty firing pin channel.

2. Insure you are fully seating the primers to the bottom of the primer pocket.

3. In your 1911 at least, a round can't seat in the chamber too deep to fire.
The extractor will capture it close enough to fire.
And the inertia firing pin will protrude as far as it needs to to hit the primer.

4. The Ti firing pin is an unknown to me as I have never used one in a 1911.
But if it worked for 25K rounds and now you have problems suddenly?
It's your reloads doing it somehow.

rc

 

[LiveLife]

gun had functioned fine for 25K rounds albeit without a really pronounced FP strike. My wife is now seeing very light primer strikes and 1/20 or so fail to ignite.

I agree with rcmodel that your light primer strikes are not caused by not enough taper crimp at .377". As rcmodel suggested, I would inspect and clean the firing pin/channel and check if light primer problem continues. Perhaps light FP strike was due to not enough firing pin travel that got worse?

BTW, did you change primer?

Remember that 9mm headspaces on the case mouth, so it may not be a case rim issue but a case length issue.

If the cases are too short, they will headspace off extractor instead of case mouth.

You can prime long/short cases (no powder/no bullet) then manually chamber to fire and see if you get light primer strike (just primer going off will be loud so wear hearing protection).

I've measured some rounds at .377. Is this enough to cause the round to seat just a tiny bit deeper in the chamber

No.

What bullet are you using? Jacketed/plated/coated lead?

I use a lot of plated bullets and prefer to add .022" (.011" being average case wall thickness) to the diameter of the bullet to determine my taper crimp amount so as to not cut through copper plating.

So for 355" diameter bullet:

.355" + .011" + .011" = .377" taper crimp measured at case mouth.

 

[Rule3]

As mentioned above, you are looking at the wrong end of the cartridge

Either primers not seated correctly, worn FP or spring. Worn hammer spring??
But if it is happening in different guns then I would look at primer and primer seating.

What primers are you using?

 

[rdtompki]

Using CCI primers (50K rounds worth) which are noted to be somewhat hard.

I did swap FP at the range and ran and check the FP channel. It's strange that my wife's backup gun also experienced the same problem which does point to primer seating.

I do recall when I first got the press maybe 18 months ago mention of primers not being seated deep enough. Now my primers have always been essentially flush, but it may be just a combination of factors. I've plunked, measured and case gauged a bunch of rounds this am and they should all be just fine so I'm going to tweak my primer setup and see if I can get primers to seat just a bit deeper.

The only thing I can see on the press is wear on the powder coat where the primer "ram" contacts the base of the press. I don't know the thickness of powder coat, but it an't be much more than .001" - ".002, maybe that's enough to make a difference. I have a new primer seater and primed some cases with the old and new units - could see no difference. The CCI primers appear to seat dead even with the base of the case; I don't every recall seeing a primer below this level.

I'm going to buy some JB Weld this am and see if I can fill the very tiny divot where the powder coat has been rubbed off. Being in California I'm pretty dependent on online sales for most gun-related items so the steel FP will need to wait for USPS.

Thanks for all the great advice!

I'll also replace the Ti FPs in our guns with stainless. This is frequently done with SA 9mm 1911s when folks replace the ILS MSH and change the mainspring. I've seen some say that they have problems with the Ti; others have no problem. I suspect the setup is right on the edge and depends on primer brand, for example.

 

[LiveLife]

The suspect rounds also induced a light strike in my wife's backup gun.

Insure you are fully seating the primers to the bottom of the primer pocket.

But if it is happening in different guns then I would look at primer and primer seating.

I missed the "also induced a light strike in my wife's backup gun" which indicates it may be the primer seating.

Do you have a hand priming tool? I can readily seat CCI primers to .004" below flush and even .008" crush depth with my hand priming tools to see if you can seat the primers deeper.

thing I can see on the press is wear on the powder coat where the primer "ram" contacts the base of the press.

You could try placing something under the primer ram to seat the primers deeper but could you check to make sure the shell plate carrier is properly seated/tensioned on the ram?

 

[rdtompki]

We found a gunsmith who had .069" SS FP in stock at a not so local indoor range. Put one each in my wife's guns and we are now good to go. FP strikes are more distinct than ever before. I'm going with a small piece of hard debris on the press, but having been through this fire drill I can't imagine why anyone would leave in the Ti FP in a competition gun. I realize that the combination of 2X spring, Ti FP and heavy mainspring is designed to drop-proof the gun, but it's got to go "bang" and few competitions with either a minor PF or no PF (steel challenge) lend themselves to factory ammo and stock springing.

My wife is a happy camper. I don't have the SS FP, but temporarily I'm going with a 20 lb. mainspring.
Rick