Cocker Blowback Help

[Parksy]

My cocker seems to have developed a small fault. When firing I have noticed the stack in my Egg jumps up, basically meaning under rapid fire it chops because the balls are bouncing up over in the stack and half feeding.

I know this is most likely caused by blowback. Have done the tissue over the top of the feedneck thing and it don't move at all, so is it just blowback in the breach I'm getting?

Anyone got any suggestions as to what it could be or how to sort it out?

Any help appreciated.

Dave

P.S. Have removed the o-rings on my delrin bolt a while back, as I was told this would reduce friction. Don't think this is what has caused it though as it has only started doing it @ the PA cup

 

[vantrepes]

First off, do the tissue test with paint in the barrel. The back pressure of the ball being fired can dramatically change the results.
Second, check to see if the paint is jumping up when the gun fires, or when the bolt comes forward. It's possible that the bolt is hitting the bottom of the next ball in the stack, and popping it back up into the feed tube.
Since you said you removed the o-rings on the bolt, your best bet is to replace them. Most delrin bolts are sized small to fit all guns smoothly, and without the o-rings to seal, I have found they are a common cause for blow-back.

 

[Parksy]

Cheers Vantrepes will give that a try after work tomorrow

 

[Parksy]

Okay, have replaced the o-rings on the bolt again and the problem still persists

Have done the tissue test again but with a ball in the breach, tissue jumps about 1/2-1cm up over when fired.

The ball stack when the hopper is attached jumps up about 1cm, it is upon pulling the trigger that the ball stack jumps up, not when the bolt comes back forward again. Have checked the bolt with the trigger held down and its about 1-2mm showing at most, same as all me other cockers have been setup

Anyone else got any ideas please

Dave

 

[Parksy]

Just had someone talking me through trying something to see if my LPR is set too high (Cheers Eric )

Its an evo LPR, and no matter if I turn it all the way in, or back it all the way out the marker still cycles normally, can't remember which way it is (so tried both) but one of the directions should starve the lpr of enough air shouldn't it so the marker won't cock??!! Even more confused now

Dave

 

[pbjosh]

Okay-

Potential blowback is from a bad tip seal on the bolt, which is VERY commom. No matter the hype, you need a good seal there.

I designed this bolt to fix it, but have sold the rights:

http://pbnation.com/showthread.php?threadid=298435

Also look for the timing of the 4-way. Alot of the cheesy imatations LP setups have simply used a light valve spring and a medium hammer setup that lets the valve completely dump. This causes the same thing as Bolt Stick on an Imp. To counter this the companies who use the light valve spring tune the 4-way to switch before the valve has opened, so that there is air in the ram before the LPR dumps with the valve. The bolt is actually moving while the valve is open, but also the backblock is suppose to pull the hammer off of the valve.

So, do the tissue test with paint in the barrel, but also try a better bolt. Ask around and fit a couple here and there, and if when you air up the gun you need to make sure your hammer isn't holding the valve open, then you might need a heavier valve spring

Josh

 

[Parksy]

It isn't a poor bolt, its a belsales evolution delrin, o-rings on it are lubed and brand new

It also isn't a cheap LPR, its an Evolution LPR, in fact the whole marker is top end being an Evo

Have been advised to try the sear lug to see if it is that

Dave

 

[Parksy]

LPR sorted (cheers to Si of Hellfish fame ), but as he thought it didn't reslove the blowback problem. So going to try and adjust the sear.

So when I'm adjusting the sear lug to release later in the pull am I turning it clockwise or anti clockwise, and do you know what size allen key goes in there?

Cheers

Dave

 

[vantrepes]

OK, first, it's a 1/8" hex key to adjust the hammer lug.
Second, you want to check the timing. If the cocking point, and firing point are too close, you get blow back.
You and move the firing point to earlier in the pull, or move the cocking point to later in the pull. Personally, I'd try the three way first, since it will be the easiest to return to the pre-adjustment setting.

 

[pbjosh]

l1f3-

Yes, the cocking lug (smacks self in head)- totally forgot (spent to much time with e-cockers) but do try the 4-way first. The hammer should be dropping right almost instantly when you pull the trigger.

Which gun do you have? It will help to let us know which frame, valve, valve spring- and maybe even ram and 4-way.

And the evo bolt- unless the tip of the bolt fits your breech, where there is no o-ring, you will still get blowback. I have gotten horrible blowback on AKA bolts with 2 o-rings, and they are larger than most. Just getting it annoed again can throw the tolerances off by quite a bit.

Josh