Punctured Primers on New AR 9 Build

calicojack · May 13, 2020

Based on m1carbine's post, my measurements may not be meaningful. I concluded that the NO GO gauge protrudes to the point where the BCG sticks out past the upper receiver; still syas nothing about the GO measurement. 556 is MUCH easier; either the bolt closes or it doesn't.

clandestine · May 13, 2020

The firing pin tip should not be rough.

Cassette Triggers are problems in regular AR's. They are even worse in blowback AR's. I would put in a factory FCG and retest

I'll have to look at my notes on 9mm protrusion. I believe it begins at the high end of 5.56 measurements.

Short and excessive F.P. protrusion can lead to punctured primers as can short or excessive headspace.

No go Headspace gauge means nothing in my opinion. You should be checking with a GO and FIELD Gauge. I disagree with the idea of skipping the use of Headspace gauges.

A short throat/lead can allow problems as can the weapon being underbuffered. That buffer is kinda light in my opinion. 9-10 ounce is what I like to see.

Are you checking to see if you have projectile setback after feeding.

calicojack · May 13, 2020

Doco Overboard said:
When you do that, the fp protrusion subtracted from the head gap + the depth of the primer intrusion -.025 primer cup average or maybe .017 for pistol primers or as close as you can get it may give some clues.

Does this explains then why 9mm FP protrusion measurements are longer than for 5.56?

Let me get this straight; 9mm bolts may not be flush against the barrel since it does not lock, and the GO and NO GO differ by 0.021", while 223 Rem GO/NO GO differs by 0.003", or a factor of 7. Hmmm.

calicojack · May 13, 2020

Ok - thanks. I have an ALG trigger I can try.

I am unable to find a FIELD gauge for 9mm; but I see what you mean, there is a big difference between NO GO and FIELD. I will try to find one. I'll be honest with you, I don't know how to use the gauges in a meaningful way on a blowback system. Do I use a feeler gauge to check the bolt gap between the bolt face and barrel? How much of a gap is acceptable?

I have not checked to see if you have projectile setback after feeding; but I would like to. What am I looking for?

clandestine said:
The firing pin tip should not be rough.

Cassette Triggers are problems in regular AR's. They are even worse in blowback AR's. I would put in a factory FCG and retest

I'll have to look at my notes on 9mm protrusion. I believe it begins at the high end of 5.56 measurements.

Short and excessive F.P. protrusion can lead to punctured primers as can short or excessive headspace.

No go Headspace gauge means nothing in my opinion. You should be checking with a GO and FIELD Gauge. I disagree with the idea of skipping the use of Headspace gauges.

A short throat/lead can allow problems as can the weapon being underbuffered. That buffer is kinda light in my opinion. 9-10 ounce is what I like to see.

Are you checking to see if you have projectile setback after feeding.

clandestine · May 13, 2020

calicojack said:
Does this explains then why 9mm FP protrusion measurements are longer than for 5.56?

Let me get this straight; 9mm bolts may not be flush against the barrel since it does not lock, and the GO and NO GO differ by 0.021", while 223 Rem GO/NO GO differs by 0.003", or a factor of 7. Hmmm.

Can't compare a pistol caliber to a rifle caliber when it comes to protrusion and headspace.

clandestine · May 13, 2020

calicojack said:
Ok - thanks. I have an ALG trigger I can try.

I am unable to find a FIELD gauge for 9mm; but I see what you mean, there is a big difference between NO GO and FIELD. I will try to find one. I'll be honest with you, I don't know how to use the gauges in a meaningful way on a blowback system. Do I use a feeler gauge to check the bolt gap between the bolt face and barrel? How much of a gap is acceptable?

I have not checked to see if you have projectile setback after feeding; but I would like to. What am I looking for?

Measure the OAL of a loaded projectile before feeding it. Then feed it from the magazine and remeasure.

As far as a 9mm Blowback AR goes, I want to see no gap between the bolt face and barrel face when it closes on a GO. If there is a gap with the NO GO or FIELD, then it's good.

PTG makes a GO, NO GO, and FIELD Set.

Some companies NO GO can be equal to a FIELD. This is a very long subject.

m1carbine · May 13, 2020

calicojack,

please take a closer look at your primers and clean one or two to check if they are even actually punctured/ruptured or just dirty. If not, then you don't have a problem as long as the gun is functioning correctly.

m1carbine · May 13, 2020

calicojack said:
Does this explains then why 9mm FP protrusion measurements are longer than for 5.56?

Let me get this straight; 9mm bolts may not be flush against the barrel since it does not lock, and the GO and NO GO differ by 0.021", while 223 Rem GO/NO GO differs by 0.003", or a factor of 7. Hmmm.

The SAAMI specifications for a 9mm case is a length of .754 with a minus tolerance of .010. The chamber length is .754 minimum and .776 maximum length. With blow back designs the spring pressure is all that hold the bolt forward and the cartridge into the chamber. Subsequently there is a fare amount of flex in the system in comparison to the locked breech designs. Longer firing protrusion can be used in these designs to help compensate for the flex.

calicojack · May 13, 2020

I tried the headspace gauges again looking very carefully to see if the bolt face touches the barrel with both the GO and NO GO gauges. It is very, very obvious that the bolt face does not touch the barrel with the NO GO. I can say that with 100% confidence. The GO gauge is harder to see because you have to find at what points the bolt face contacts the barrel. It looks to me like it is contacting against the barrel, so I think it swallows the GO gauge. A 5.56 is so much easier; the bolt either closes or it doesn't.

Now we'll see what happens with the firing pin; I ever so gently smoothed the rough spot (didn't take much). When a new firing pin arrives I plan on using that and discarding the original.

calicojack · May 13, 2020

m1carbine said:
calicojack,

please take a closer look at your primers and clean one or two to check if they are even actually punctured/ruptured or just dirty. If not, then you don't have a problem as long as the gun is functioning correctly.

Looks like there is a small hole there, using a magnifying glass.

calicojack · May 14, 2020

clandestine said:
Measure the OAL of a loaded projectile before feeding it. Then feed it from the magazine and remeasure.

As far as a 9mm Blowback AR goes, I want to see no gap between the bolt face and barrel face when it closes on a GO. If there is a gap with the NO GO or FIELD, then it's good.

PTG makes a GO, NO GO, and FIELD Set.

Some companies NO GO can be equal to a FIELD. This is a very long subject.

Page 125 of this SAAMI document. I feel better if I can see it in print. That's just me.

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

[EDIT] Yeah - and have not even covered what constitutes "FIELD", I'll take your word for it as being another long and drawn out subject.

m1carbine · May 14, 2020

Calicojack,

Here is what I was looking at with your first picture of the primers. I have circled in blue the artifact from the pit on the tip of the firing pin.

calicojack · May 14, 2020

m1carbine said:
Calicojack,

Here is what I was looking at with your first picture of the primers. I have circled in blue the artifact from the pit on the tip of the firing pin.

There definitely is a pit there; that does not seem normal. There is also is what appears to me to be a gouge above the shoulder. I have a replacement firing pin coming from Foxtrot Mike, and I ordered a titanium FP as well.

I was wondering if the firing came this way or was normal and then became damaged (didn't inspect it ahead of time). I don't know - at any rate checking the headspace is (as clandestine suggested) a good idea esp. for a firearm that was assembled. Also the other suggested checks (e.g. displacement of round).

alucard0822 · May 14, 2020

AR9s hit the pin really hard compared to a pistol, and even though they are inertial, they tend to be pretty heavy, so any little rough spot can easily cause a spot to crack or punch through, leaking gas, eroding the tip, and making the problem worse. Some brands have softer or harder primers, probably why he wanted you to try steel cased ammo(usually really hard berdan primers). I was an early customer of FM's, got an early side charging upper after a PCC match to try a few years ago when he was first starting out. The chamber was really oversized, and has issues with any crimped case(handloads and most defensive ammo) getting pushed too deep into the oversized chamber to the point the extractor wouldn't grab it, and just hammered it in deeper. His version 2.0 barrels were better, he sent me one, and it has been fine, but for some reason he really likes steel cased ammo, and wants his stuff to run it, so IIRC he went to a chamber between the two. Firing pins in AR9s are problematic, they often break, crack chip etc, and partially peirced primers are a frequent occurence. I think the design is just rough on them, and being everyone makes a 9mm upper now QC, especially heat treating leases a lot to be desired.

calicojack · May 18, 2020

Shot the Foxtrot Mike AR9 with the new firing pin. Ran perfectly. No punctured primers. I am really starting to like this rig

Pics show some old reloaded Geco ammo and Tula steel cased ammo.

John from MD · May 18, 2020

You're good to go!

Enjoy,

outrider58 · May 19, 2020

Don't ya just love happy ending?

asdaven · May 19, 2020

I have the same problem. Happens more when I shoot +P or even the NATO ammo. No apperent signs of bad headspacing or bulged brass. Im running a pretty heavy buffer and spring combo. But my firing pin is like that, has a divot in the point. So I at least need a new firing pin.

But it appears my firing pin hole out of round and is causing somewhat angled and inconsistant strikes on the primers. I see on your some of your strikes are like mine and not always in the center either. A lighter (standard) hammer spring (I was using an XP hammer spring at first) helped. But still the problem remains. So something to check out with this problem is the firing pin hole itself in the bolt. A new firing pin mightve temporarily fixed it. But I think the loose firing pin hole in my bolt caused the firing pin to get messed up because the divot in mine was not a manufacturing defect, it occured after some (not a lot) of use.

asdaven · May 19, 2020

Double Post.

Punctured Primers on New AR 9 Build

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