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AR9 vs hard primers? (Updated: Incorrect headspace?)


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I just got a new completely stock Foxtrot Mike FM9B.

And I'm having some problems with light primer strikes.

The ammo I'm using is known to have hard primers (Swedish military ammo), but they work very reliably in my Glocks, and other duty-type handguns.

 

I'm pretty new to AR9s though. 

So I was thinking maybe they are picky about primers due to their firing pin spring...?

 

I have tried bending the hammer spring as much as I could, to increase the power of the strike, but it wasn't enough.

 

The firing pin looks good and runs freely in it's bore

 

Any thoughts?

 

20210131_150520_copy_604x805.jpg

20210131_150912_copy_604x805.jpg

Edited by grottulf
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both mine have standard AR15 hammer springs in them and no issues with CCI SP or SPM primers.

 

When I got my M&P 15 5.45X39 it came with an extra power hammer spring for the hard primers in the surplus ammo.  So, someone out there makes extra power hammer springs in case you find you need one of those.

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What did you do to your hammer spring? It looks like it has collapsed - if that is how you bent it, you went in the wrong direction. You know its supposed to sit on top of the trigger pin, right?

 

55AFF97.jpg?x99531&f=1&nofb=1

 

ALG-ACT.jpg&f=1&nofb=1

Edited by StealthyBlagga
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2 hours ago, StealthyBlagga said:

What did you do to your hammer spring? It looks like it has collapsed - if that is how you bent it, you went in the wrong direction. You know its supposed to sit on top of the trigger pin, right?

 

55AFF97.jpg?x99531&f=1&nofb=1

 

ALG-ACT.jpg&f=1&nofb=1

Yes, as I said, I bent it to stiffen it up.

Not to soften the pull, as most people do 🙂

It sits on top of the trigger pin.

But it was tricky to get it there, when it was bent so much.

20210202_065345_copy_604x805.jpg

Edited by grottulf
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Could it be a headspace issue?

I don't have a feeler gauge that is narrow enough to get in there, but I'm thinking about narrowing one down so it fits...

Or is there a better way to measure that?

 

20210202_065844_copy_1209x1612.jpg

Edited by grottulf
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11 minutes ago, Bdh821 said:

If the trigger is the issue, I recommend the Hiperfire Eclipse as those are known for extra hard smashing of primers!  I set off all primers with this setup.

Thanks, they are a little over my budget though.

I'll try to make do with a polished stock trigger, at least to begin with.

 

 

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I've done some more research, and I'm pretty sure it's a headspace issue.

I estimate that there is roughly 0.5mm (.02") of play between the bolt and the bottom of the casing as it is now, and that can't be good.

I will measure both the chamber and bolt recess (and casings) tonight to see which one is out of spec...

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  • grottulf changed the title to AR9 vs hard primers? (Updated: Incorrect headspace?)

Now I've removed the barrel to get a correct measurement.

I wasn't so far off in my estimation...

The headspace seems to be 0.46mm (.01811") too long...

 

Here are the numbers:

 

Length of my 9mm ammo casing: 19.03mm (.7492")

 

Bolt recess: 3.34 mm (.1315")

Chamber depth: 16.15mm (.6358")
Total headspace: 3.34+16.15= 19.49mm (.7673")

 

Difference in length between ammo and headspace: 0.46mm (.01811")

 

Protrusion firing pin: 0.75mm (.02953")

 

In other words the firing pin does only poke 0.29mm (.01142") into the primer...

 

Can anyone tell me what part or parts are out of spec?

Thanks!


 

 

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  • 3 weeks later...

FM didn't have the required export permits, so Brownells will ship the bolt.

But unfortunately, at the moment they can't export any gunparts that requires a permit over here, due to corona...

So it might take a while until I get it... :(

 

But I'm curious about how deep the pockets depth is in the revised FM-bolt.

I asked them, but didn't get any answer.

Does anyone here have one?

If so, could you please measure the depth for me?

Edited by grottulf
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