El Ak74una FPS Drop

[FirsthandSnow]

Hi, so I got an E&L AK74u w/ railed handguard, it looks very, very pretty. Out the box it was doing around 333fps with drops down to as low as 112fps. I was a bit pissed about this, but, I'd worked on enough M4's and a G36c umpteen times to feel more than comfortable and confident in taking this apart, assuming it was likely a dodgy seal somewhere in the compression parts. 

 

The only slightly poor compression part was the nozzle seal on the cylinder head; it leaked at full extension.

E&L have used a machined one piece cylinder and cylinder head, which sure provides a good seal given its one piece, but it's ribbed on the inside and when the piston moves down it sounds like someone sawing through something, it sounds horrific. Not sure for who's pleasure it's ribbed for lol

 

I digress; I had a spare cylinder, piston and piston head, I bought a new double seal cylinder head, and replaced the spare piston's o-ring with a 19.5mm one for that extra little bit of seal.

 

Everything together, the compression was great, no leaks, felt absolutely solid and everything moves great inside the gearbox.

 

Shimming in the gearbox was good, I tweaked it ever so slightly with some 0.01mm shims and got the gearset spinning flawlessly.

 

I also cleaned the hop rubber, and chamber. Whacked it all back together with an m110, expecting the fps would be hot, but it's the only spring I had and bam! 320fps with random drops to 269fps. So still got the same issue as out the box, but the drop isnt as significant and inconsistent.

 

So having spoken to AK2M4, I'm going to try a harder bucking at 70⁰.

 

Failing that, it's a new hop unit I suppose, unless any of you guys have had similar experiences and have any suggestions to help a brother out! Lol

 

Thanks guys.

[Speedbird_666]

Did you buy the gun new, or off the forums by any chance?

[Adolf Hamster]

the stock e&l cylinders to seem rough but they tend to still have great compression regardless.

 

the nozzle at full extension is a curious one.

 

tbh though sounds like the culprit is more likely the nozzle-hop seal, either rough/torn feedlips or the nozzle isn't contacting the feedlips well enough.

 

assuming you've checked the above and the new nozzle is the correct length then maybe it's hop unit positioning.

 

if you're using the default screw system for hop mounting then the outer barrel position is important, if the outer is sitting slightly forward and you have the hop bolted to the barrel and not the box then the whole unit is sitting forward just enough to cause a leak.

 

if you do plan on changing hop units then the combat union is the best i've seen for the ak platform.

[FirsthandSnow]

On 10/03/2021 at 16:32, Adolf Hamster said:

the stock e&l cylinders to seem rough but they tend to still have great compression regardless.

 

the nozzle at full extension is a curious one.

 

tbh though sounds like the culprit is more likely the nozzle-hop seal, either rough/torn feedlips or the nozzle isn't contacting the feedlips well enough.

 

assuming you've checked the above and the new nozzle is the correct length then maybe it's hop unit positioning.

 

if you're using the default screw system for hop mounting then the outer barrel position is important, if the outer is sitting slightly forward and you have the hop bolted to the barrel and not the box then the whole unit is sitting forward just enough to cause a leak.

 

if you do plan on changing hop units then the combat union is the best i've seen for the ak platform.

Hi, so I actually fixed the inconsistency by filing away some plastic from the front of the tappet plate, it's now consistent at 295-300fps on .25g, as that's the only BB's I had spare, without any drops. But will try again with an SHS AK tappet and see if that makes any difference

 

Thanks for the detailed reply