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nounnoun
August 26, 2017, 18:36
So, replacing an original 5 slot fh with the new png one, it tightens at 9 o'clock. Looks like whoever rethreaded my barrel timed the threads to fit the original FH without a washer or timing spacer or whatever this part is called -- there's not one with the original FH and it times right to 6 and bottoms out on the threads.

What size washer/spacer to I need to back it up 1/4 turn?
Where might I find said item?

For the time being, it seems pretty solid with some loctite blue, and the key fits and locks, as one side is flattened. Think that should be good enough to try out this "20% reduction in recoil" talk after this hurricane passes, and before I start making any more cuts into this barrel.

I'm 5'5'' and looking to start going to local shooting competitions, hopefully it delivers as promised. This rifle's already such a great shooter, I'd love to see it 1/5 gentler.

OLDMANPBK
August 26, 2017, 20:30
OK. The barrel is threaded 9/16 24. 24= threads per inch. 1inch divided by 24= .0417. This means that for every revolution of the flash hider it will move .0417. Another number that comes in handy here is the amount of movement that you will get per degree (.0417 divided by 360 =.000116) so for every degree you turn the flash hider it will move .000116. You also have to allow for a crush factor when you torque the flash hider down. The crush factor for a regular size FH positioning washer is 15-30 degrees. Flash hider positioning washers come in a range of sizes from .1505 to .189 so you will need one that is at least .1505 thick. So in your case we back off 4 turns (.0417x4=.1668). Now to get it backed off another 90 deg. we need to add 90x.000116=.0104 to .1668 (.1772) and allow a 15 deg. crush factor 15x .000116= .00174. Add the crush factor .1772+.00174= .1789. so you need a .1789 or so positioning washer which are available here. http://www.arizonaresponsesystems.com/store/store-l1a1-barrel/store-l1a1-barrel.html
Now I've had a couple :beer: so check my math and remember, if you buy a thicker one you can always sand it down to fit.

gunplumber
August 27, 2017, 08:15
Looks like whoever rethreaded my barrel timed the threads to fit the original FH without a washer
What size washer/spacer to I need to back it up 1/4 turn?
Where might I find said item?

They didn't
There isn't
you won't

Use a #1 and see what happens. go from there.

been working on a script to kick out an answer but where it times without a washer doesn't tell you whether you are bottoming out on the face or the shoulder. It's supposed to time off the face. Pull the washer out and you can run out of threads before contacting the face.

As said above, except I carry it out a few more decimal places for the calcs, so the rounding is different.

http://www.falfiles.com/forums/showthread.php?t=416270

nounnoun
August 27, 2017, 17:08
Thanks much for the help.

Took another look at the original FH a little while ago after remembering that parts of the gas system were essentially soldered together with soot and lead -- and that I was getting advice from someone who probably put this rifle together, so I should probably check my work -- turns out there was a washer in there.

Took some scrubbing and some light hammering, but was able to free it without tearing everything up. Put it together with the new FH and torqued it down, timed perfectly.

gunplumber
August 27, 2017, 19:07
Awesome! I turned a rod with one end for Canada and the other for everyone else, and often I need to pound on that sucker to get the timing washer out.