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Old August 09, 2018, 20:37   #1
FriendBesto
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Piston tuning

I'm also a fan of the M1A and read an article about accuracy mods from a military armorer. It might have been Art here on the board but if not it was another former military match rifle builder during the reign of the M14.
He said they would take a handfull of pistons and swap them out in a gun to see which one shoots best and there would usually be a piston that stands out from the rest.
I wonder if anybody has tried this with FAL pistons?
Could be a fun experiment?
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Old August 09, 2018, 21:31   #2
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There was a thread or two some years ago about dwell time but not much follow-up. I think the difference in the rotating bolt of the M14 and the tilting bolt of the FAL has more to do with consistency and accuracy than the dwell (just a guess on my part).
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Old August 10, 2018, 07:25   #3
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Dwell is absolutely critical to the accuracy of an autoloader... I searched for a slo mo video of a FAL firing cycle & the best one i found was at 600 frames per second... In that video it definitely appears that things are happening (ie movement) well before the projectile leaves the barrel.

If that’s the case then theirs definitely room for improvement
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Old August 10, 2018, 15:31   #4
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Originally Posted by IRONWORKER View Post
Dwell is absolutely critical to the accuracy of an autoloader... I searched for a slo mo video of a FAL firing cycle & the best one i found was at 600 frames per second... In that video it definitely appears that things are happening (ie movement) well before the projectile leaves the barrel.

If that’s the case then theirs definitely room for improvement
I'm skeptical, but nonetheless interested in your results !
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Old August 10, 2018, 15:59   #5
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time to drill those pistons and compare results? Only thing I can say is those pistons are made 'out of' or 'into' unmachinableinium.
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Old August 10, 2018, 17:35   #6
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The piston head can be machined out to form a chamber. Just have the piston head electroless nickell plated after machining, it is also a way of adjusting the head diameter to suit the I.D of the gas block.


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time to drill those pistons and compare results? Only thing I can say is those pistons are made 'out of' or 'into' unmachinableinium.
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Old August 10, 2018, 18:31   #7
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Rather than trying to shorten the head of the piston ?
How about the tail ?
Should be same effect and a Heck of a lot easier to do.

I would use surplus, hopefully inexpensive, Imbel or some Euro stuff.
Worry about U.S. made stuff when the experimentation is done.
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Old August 10, 2018, 18:47   #8
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time to drill those pistons and compare results? Only thing I can say is those pistons are made 'out of' or 'into' unmachinableinium.
This - needing straight locating rods, and having hundreds of pistons, I thought it would be a good choice for scrap metal. Nope. That shit is hard. But it is selectively hard, because when Bill and I were working on a piston for the 7" FAL, we bent pistons after around 20 rds.

The heat treat does not appear to be uniform.
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Old August 10, 2018, 18:47   #9
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Rather than trying to shorten the head of the piston ?
How about the tail ?
Should be same effect and a Heck of a lot easier to do.
One could take an Stg piston, shorten it slightly in the rear, and then screw in something in the rear end and test changes in accuracy with adjustments in piston length. Measurements would have to be very precise, and the adjuster(s) screwed into the piston(s) would have to be hard as hell and impervious to peening.

I'd love to know the results of such a test and I hope someone takes the project on.

My guess is that nothing statistically significant will be obtained from a test of different dwell readings, and even less would be learned that could be extrapolated to various iterations of FALs/L1A1s. But I could be wrong, and I'd love to know if there is something I am not doing that could make my favorite FALs more accurate!
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Old August 10, 2018, 18:50   #10
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Hmm. Another thought. When Frank at POF was prototyping his gas system from my parts, I got to see a number of experimental designs. The two piece one was curious By reversing it, he chould change the gas bleed and make it suppressor capable. So maybe instead of messing with gas plug, the piston head could be modified to some form of 2-piece tappet system.

Just a random thought
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Old August 10, 2018, 18:54   #11
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Rather than trying to shorten the head of the piston ?
And make it lighter? But, I think you are into something: what if the bolt is made *heavier*? But then the question is how heavy it will need to be to slow it enough and what is the unintended consequence.

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How about the tail ?
Should be same effect and a Heck of a lot easier to do.
Now you have a rod accelerating before smacking into the carrier. And against a spring which now compressed it more than it would require to push the carrier and the bolt off the locked position. I know in the G43 this is a great way to break bolt carriers.

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I would use surplus, hopefully inexpensive, Imbel or some Euro stuff.
Worry about U.S. made stuff when the experimentation is done.
Destroy the IMBEL to save the Century Arms ones!
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Old August 10, 2018, 21:37   #12
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Originally Posted by IRONWORKER View Post
Dwell is absolutely critical to the accuracy of an autoloader... I searched for a slo mo video of a FAL firing cycle & the best one i found was at 600 frames per second... In that video it definitely appears that things are happening (ie movement) well before the projectile leaves the barrel.

If that’s the case then theirs definitely room for improvement
1200 fps: http://www.falfiles.com/forums/showthread.php?t=358745

I made a hollow-headed piston years ago to increase the dwell time (had a 24" heavy barrel), but I could never get it to function reliably. I and I saw no measurable change in accuracy.
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Old August 12, 2018, 06:34   #13
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I would think the first step in scientifically approaching this would be to switch the gas plug to Grenade function, then see if it improves the group at all firing single shot. No piston movement, no bolt unlocking, etc.

If no major improvement in accuracy, well then no fiddling with the gas system dwell time issue would be worth chasing in my opinion.
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