first shot chuff

[93klauss]

Xvalve
lvlX
ULT

Changed the spring and carrier. Holds air fine. first pull, chuff pball rolls out the end. Fires fine after the first shot and many more with out a chuff or leak. Dont shoot for a while, pull the trigger chufff, ball rolls out the end. then fires fine again. Go to the next carrier up and crazy leak down the barrel. i could at least pick it up and throw it.


Thinking a leak in the on off orings. Correct assumption?

Thx

[Justus]

Sounds like "First-Shot-Drop-Off", and everything I've read on the topic says that it's likely the carrier o-ring that is the problem. I did a search on this last week. Here's the 3 most pertinent threads I found:

http://automags.org/forums/showthread.php?t=201701&highlight=fsdo

http://automags.org/forums/showthread.php?t=251187&highlight=shot+drop

http://automags.org/forums/showthread.php?t=261251&highlight=shot+drop

Hope that helps!

[BigEvil]

Take all of the shims out of the lvl 10 and try it. . Is this a twist lock of cocker threaded gun?

[athomas]

Sounds like you have a tiny bit of bolt stick. Its not enough to cause reset problems, but will cause the bolt to start moving a bit slower than it should after it sits for a while. Once the oring gets broken in, there won't be any problems. It can be a pain until then. You can smooth the inner surface of the oring a bit using really fine sandpaper, like 1500 grit. It will remove any surface imperfections and make the oring not so tight.

What is the minimum velocity that your mag will start to cycle using the current bolt spring? If you use the short bolt spring or clip a longer spring to lower the starting velocity a bit, then the higher pressure differential will reduce the bolt sticking until the oring gets broken in.

[Henchman]

Could be a case where, because you haven't fired awhile, the balls themselves are a bit stuck together, to something like that. It could be a simple case of the Level 10 working, and preventing a ball break. Maybe too much tension from your hopper, causing the ball in the chamber to be a bit flat,Mathis allowing the ball above to just enter the breach.

[Justus]

If he's experiencing what I've experienced recently, it's not due to the tension in the ball stack. If you take a few shots, wait a minute or two, and shoot some more then it doesn't happen. But if you wait 5 or 10 minutes between taking shots, the problem reappears on the first shot.

It can even lead to a super low velocity on the first shot, making it seem like a chuff with the ball barely moving, and the second shot then seems like a double-feed. You can even shoot the first ball right at the end of your barrel with the second shot. It makes a splendid mess when done correctly.

[athomas]

I agree with Justus. It isn't a ball stack issue. Its an issue that occurs when the bolt sits for a bit and any oil that may be on the surface of the oring gets pressed away so that the oring sits directly against the metal of the bolt stem. The oring sticks to the metal if there is any amount of tension on it. This has the effect of increasing the starting friction force which drastically slows or stops the starting movement of the bolt. Once it moves and fires, a new surface tension is developed without any sticking until it sits a bit longer and the process is repeated. Once the oring gets broken in and/or if the tension isn't high enough, then the oring doesn't stick to the stem anyway. This is the desired scenario that usually occurs with most setups. As long as you use a bolt spring that can overcome the sticking force, it won't be an issue anyway. That is why it is sometimes suggested to use the short bolt spring on some setups until the oring gets broken in.