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Discussion Starter #1
A funny thought occurred to me this morning.

I have an SLR-106UR, it's a .223/5.56 AKS-74UN with a spring loaded steel firing pin.

I also have two ACRs in the same house, one with the steel firing pin and one with the newer upgraded tit. firing pin.

To my understanding early ACRs were doubling thanks to the firing pin with certain commercial ammunition. Trashmaster came out with a statement that said to the effect of that the firing pin was too heavy and the spring called for in the design was too light hence causing the guns to double.

For those who remember, FS2000s were also doubling, and doing the same thing early in their commercial release after FN removed the safety sear from the action. I believe they remedied it by adding a stronger spring, that ended up being so strong that people were cutting two loops off so that they could run military ammo.

The spring in my AK's bolt is a monster, it almost takes two people to compress it during reassembly. It looks to be made out of a thick music wire, like the type and thickness you see inside a grand piano.

The spring on the second ACR is almost toy like, and takes very little force to compress it.

With reports of the newer "upgraded" firing pins breaking floating around I'd be interested to see what a heavier spring set would accomplish.

Would anyone be interested in a report of sorts if I started toying with new spring weights?
 

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The steel firing pins are a contributing factor, along with the weak firing pin spring, massive (heavy) bolt carrier and soft commercial primers.

Mine never went full auto, but I did get some doubling and one triple pop. For liability reasons they did some over kill for the fix. My firing pin has held up so far, (3000 rounds on it) but I still wish I could get another one.

As far as maybe a heavier spring being enough to fix the problem, it wouldn't hurt. I never had an issue with hard (military) primers. The slam fire issue only occurred with 1 specific ammo and it was consistant. (in my expierence)

Just remember you safety rules and all is good if you have an issue while testing. ;)
 

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Discussion Starter #4 (Edited)
Interesting, I've never seen one with a firing pin safety.

You would of thought that they would have left that feature in.

Taking the "recall" rifle out today with the stock spring in it, will report back.

ETA: Stock spring produced no doubles with Wolf, PMC, and Remington ammo.
 

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With that logic, a stronger spring would make sense. If it would allow all the same ammo and allow users to keep the heavier firing pin, that'd be tits.
 

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Here's the trick. When adding springs or changing the mass of components within a mechanical system that relies on harmonic motion to cycle, all the variables can be hard to account for. The variables are different types of ammo, gas settings, mass of componentry in play, springs acting on said componentry, suppressor or no suppressor, altitude/atmospheric pressure, recoil of the shooter on the rifle and they all come in to play on the cycle of a weapon system operated by gas and springs. I am not saying it is impossible but I think the fix is good and I wish they had kept the firing pin block in the design to avoid this mess in the first place. I think aftermarket guys will go after different things especially when you take into account how the BATF will look at a small company that makes parts that could allow a weapons platform to go full auto. I think they would be more likely to do a different handguard or something along those lines first. Just my opinion and it's worth what you paid for it.
 
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