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bulgy74 build + psl gas piston finally done


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finally finished this up. put a PSL gas tube and piston on a bulgy 74, and moved a custom fs/gb up to the fsb journal. relocated gas port hole as well. need to testfire before paint, but i did this in an attempt to acurize the 74. :)

 

DSC_0155.jpg

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That's pretty neat. How does it help with accuracy? You plan on testing it soon?

i plan on testfiring soon, yes.

 

i moved the gas block forward after seeing the slowmo vids of the ak. the barrel in front of the gas block would whip when the ation would begin to cycle, and the fsb all the way at the end adding weight did not seem to help (if the galil is an improved, accurized version of the ak, then i feel that there is a reason they went with the fs/gb combo instead of adding a seperate fsb all the way at the end as in the standary ak47/akm/74)

 

. if the bullet is still in the barrel while it is whipping that would affect accuracy. by putting the gas block more forward, the bullet will have less to travel down the barrel when the action begins to cycle. i plugged and welded the original gas port hole, then pressed and pinned a sleeve over it (made from an old beat up gas block). i am hoping this adds a little bit of reinforcement to the barrel if there is any barrel whip when cycling. i have read up on PSL owners who cut down their barrels to reduce barrel whip, and that also gave me a bit more incentive to go ahead and do this.

Edited by m1lk
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I like the look, but I don't get how adding a heavier/longer gas piston will increase accuracy in the gun. Can you explain that for me?

 

He explained it pretty well - the longer gas piston is a necessary part of moving the gas block so far forward - he wants the barrel whip caused by the action cycling to start as late as possible, as close as he can get to the time the projectile is exiting the barrel.

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Very interesting and very unique, my only concern would be if there will be enough pressure to cycle the weapon with the gas port so close to the end of the barrel.

 

my previous build had a 45 degree galil gas block on an amd65 barrel. the gas port is 1/8 in, and 1/2 inch away from the muzzle, with an extended amd65 brake at the end. cycles fine. so that gave me hope when doing this.

 

i drilled the new gas port hole to be the same size as the original that came on the barrel. but as for cycling and dwell time, that is the reason for using an ak74 brake. i am hoping the brake can provide enough backpressure to cycle the action, just in case. and being that its a brake, it should add performance by reducing recoil

 

also, take a look at the AKSU. it has the port close to the muzzle as well, and yet it cycles fine even without its booster/flashhider

Edited by m1lk
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I think worst case, you would just have to open up the port a little. There was a guy on AR15.com that cut the barrel right up against the FSB. It still cycled the action when fired. I think it should be fine. I can't wait to hear how this thing runs. Hows the weight balance of the rifle?

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He explained it pretty well - the longer gas piston is a necessary part of moving the gas block so far forward - he wants the barrel whip caused by the action cycling to start as late as possible, as close as he can get to the time the projectile is exiting the barrel.

 

The part I don't understand is adding weight should make the reward bolt movement heavier and cause more recoil when it is in motion, whether it be later or not, as he explained with the barrel whip. That should make all follow up shots less accurate, which would reduce the accurizing factors of extending the area between the GB and its original position. I think its a great project, don't get me wrong. I just want to know how well it does in increasing accuracy overall, not just per bullet

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He explained it pretty well - the longer gas piston is a necessary part of moving the gas block so far forward - he wants the barrel whip caused by the action cycling to start as late as possible, as close as he can get to the time the projectile is exiting the barrel.

 

The part I don't understand is adding weight should make the reward bolt movement heavier and cause more recoil when it is in motion, whether it be later or not, as he explained with the barrel whip. That should make all follow up shots less accurate, which would reduce the accurizing factors of extending the area between the GB and its original position. I think its a great project, don't get me wrong. I just want to know how well it does in increasing accuracy overall, not just per bullet

 

i realize that there will most likely be barrel whip. but since the gas block is so moved forward, i theorize that the barrel will have been "reset" back to its original state by the time the next follow up shot exits the barrel. even while the next quick-followup-shot is travelling down the barrel while in the "whipping stage", soon as it passes the gb, the barrel wouldve already have flexed back and when it goes to flex again due to the action cycling, the bullet wouldve already exited the muzzle. again this is in theory.

 

i forgot to mention, i added an rpk pluger recoil assembly and wolff xp spring for extra rigidity. also a pg reinforcement plate. the wolff xp spring should dampen the rearward bolt movement a little

 

ive yet to testfire but i will let you guys know soon, when time allows. i will be testing this alongside a friend's standard config ak74. even so, going by all this, i sometimes wish i had the resources at the time to build this on a 1.5mm receiver with thicker RPK barrel

Edited by m1lk
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It would e cool on a longer barrel? I understand your thinking that the gasblock on the end helps whip though. Also if it doesn't cycle you could bet one of the 4piece muzzle devices that are made to increase back pressure.

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i realize that there will most likely be barrel whip. but since the gas block is so moved forward, i theorize that the barrel will have been "reset" back to its original state by the time the next follow up shot exits the barrel. even while the next quick-followup-shot is travelling down the barrel while in the "whipping stage", soon as it passes the gb, the barrel wouldve already have flexed back and when it goes to flex again due to the action cycling, the bullet wouldve already exited the muzzle. again this is in theory.

 

i forgot to mention, i added an rpk pluger recoil assembly and wolff xp spring for extra rigidity. also a pg reinforcement plate. the wolff xp spring should dampen the rearward bolt movement a little

 

Ok, that's the stuff I was looking to hear. Thanks for the reply and can't wait to hear how it goes in testingbeer.gif

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I've watched the slo-mo videos too, but to me it's always looked more like the barrel whips after the round has left the muzzle and gases begin to escape. I realize though that there's no way to really tell without some serious camera power.

 

http://www.youtube.com/watch?v=o2SL5YQ5h1E

 

Either way the build is cool and unique - looks a lot like an AK-107. I bet you could fool some people.

Edited by mancat
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that is a great idea and i hope it works. looks cool. looking forward to an update. I am getting ready to build a ak 74 mismatched parts kit and was going to try and free float the barrel by shortening the gas tube to where it doesn't touch the gas block and welding the tube to the rear sight block. but after seeing this i may try this out if it works. have you tried it out yet?

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  • 2 weeks later...

took it out last week. it is shortstroking. the carrier moves back, but only 1/2 an inch. i am thinking of drilling the gas port hole bigger, about 1/8.

 

i am actually suprised it is short stroking. my previous build, the amd65 with galil gas block, has the 45 degree port 1/2 inch away from muzzle, and it cycles really well.

 

if this doesnt work, then i guess there is too much of a pressure drop way up front on a 16 inch, and ill just go ahead and turn this into an ak105 clone

Edited by m1lk
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That thing looks awesome!

 

p.s. maybe its shortstroking due to having less powder than the 7.62x39, which you said worked well in your amd.

 

What will you do if widening the gas hole wont work? Shorter/weaker recoil spring? Hotter loads?

Edited by Agent Lemon
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What will you do if widening the gas hole wont work? Shorter/weaker recoil spring? Hotter loads?

I would say the best idea would be the weaker spring, getting hotter loads could end in a bigger disaster than trying springs first and that may just be what it needs. Probably too much weight with the larger bolt carrier and regular strength spring, replacing springs that are weaker for the regular one could offset that issue, but could also inhibit the ability to strip rounds and chamber them. Keep us posted

Edited by VR6Shooter
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That was the first thing I thought, that the extra weight of the PSL piston screws up the gas pulse. He could go about it either way, but cutting a few coils off the spring is easier and more reversible than re-drilling a gas port.

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im going to put this project on hiatus. gonna turn the build into a khyber 105, and eventually put an underfolder on it. after giving it much thought, i think this project would fare better if it was in 7.62, for two reasons: more pressure, and the ease of the 45 degree gas port hole.



That thing looks awesome!

 

p.s. maybe its shortstroking due to having less powder than the 7.62x39, which you said worked well in your amd.

 

What will you do if widening the gas hole wont work? Shorter/weaker recoil spring? Hotter loads?

exactly. the 45 degree port on my amd is a 1/2 inch away from the muzzle. and it goes. even after testing it with a handful of dirt, it shot like an ak should. this is why my next build will be this project but for now the 5.45x39 gets turned into a 105



how did it group?

wasnt able to group. it was pretty much a bolt action

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