Semi auto, to auto inconsistancy?

[Janz99]

Just curious as to what could be causeing some inconsistancy between semi auto and full auto. If i put the gun on semi auto for the first few single shots, the BB doesnt have any sort of range to it, and has very little force behind it.

Now, if i switch it to auto, and shoot a few rounds (which fires perfectly) and then switch it back to semi auto, it shoots as it should?

Thanks
Ryan

[m102404]

If you shoot a burst of full auto first...then immediately switch to semi and shoot 1 or 2 shots...do the semi-auto shots go as far?

Tys

[Styrak]

Most likely the hopup rubber?

[Janz99]

Originally Posted by m102404

If you shoot a burst of full auto first...then immediately switch to semi and shoot 1 or 2 shots...do the semi-auto shots go as far?

Tys

Pretty much. Its not AS far, but its pretty damn close. I normaly have to shoot off about 5-10 fully auto shots, then switch to semi.

Here's the kicker. If i single shot on fully auto, they come out perfect.

What exactly do you mean by it could be the hop up rubber. Its not seated properly, or the type of material its made of? Or something completely different.

Ryan

[m102404]

My internet guess is that your piston o-ring seal needs a bit of work. The burst of full auto is probably getting it warmed up and stretched out to create a nice seal...which will then last for the next couple of semi shots. From a "cold" state...the o-ring will shrink back and not provide an optimum air seal.

If that's the case, either swap the o-ring or reshape it (heat form it). If it's lost it's "rubbery-ness" ditch it and get a new one (good time for other general maintenance as well).

Just a guess obviously, but that's what came to mind from your description.

Best of luck,

Tys

[Janz99]

Originally Posted by m102404

My internet guess is that your piston o-ring seal needs a bit of work. The burst of full auto is probably getting it warmed up and stretched out to create a nice seal...which will then last for the next couple of semi shots. From a "cold" state...the o-ring will shrink back and not provide an optimum air seal.

If that's the case, either swap the o-ring or reshape it (heat form it). If it's lost it's "rubbery-ness" ditch it and get a new one (good time for other general maintenance as well).

Just a guess obviously, but that's what came to mind from your description.

Best of luck,

Tys

I was actually thinking of that, but here is the problem with our theory. When i assembeled the gear box with a new modify bearing piston head, i noticed that the o-ring that came with the piston was actually to small, and wasnt sealing properly. So i got an o-ring that sealed properly. When i did a compression test, the piston would make it just past the port, and stop dead. The o-ring is brand new and i made sure it sealed properly.

I think im going to open up the gear box again and have a look at the o-ring, and cylinder itself. Maybe the cylinder got bumped from being handled and isnt perfectly round now, and when its in full auto, the ports in the piston push the o-ring out enough to make a good seal. Once in semi auto it looses the seal?? Just my wild guess lol.

Ryan

[m102404]

Heheheh...got to love guessing via the Internet...

The piston isn't going any faster or slower when the rifle is in full auto or semi.

Friction will heat up the cylinder/o-ring...but I'm not sure how appreciable that will be. Heat will also "liquify" the grease a bit relative to its cold state. But all these effects should be minimal.

If the compression system is solid...shoot a couple of hundred rounds through it to blow out any grease that may be in the nozzle/rubber. Let things settle and then do some semi auto tests. Swap the hopup rubber for a clean one after if you want to ensure that it's clean.

Other than that...swap the nozzle.

Dunno

[Janz99]

What will swapping the nozzle out do?

[m102404]

Honestly...don't know in your setup.

Some makes/models of nozzles seal better with either (or both) the cylinder head nozzle and hopup unit/rubber lips.

If you look closely at a bunch of different M4 series nozzles, you'll note some are angular, come are virtually squared off, others are rounded. Some have an o-ring inside to seal with the cylinder head...some don't...some have 2. Some are plastic, some are metal. Then there's the whole debate as to cross cross-section or plain round cross section.

Regardless of the one you go with...you want it to seal well (or perfectly) with the cylinder head nozzle, but still move freely/easily...and you want it to fit the hopup unit as tightly as possible, but still move freely...and you want the tip of it to seal perfectly with the hopup rubber rim.

So if the compression in the mechbox is great...that's all you can readily test. There are some tests that you can do to see if the nozzle is sealing well with the hopup rubber...but I've not found them very easy/sure to do myself (I'm probably doing it wrong).

Best of luck,

Tys

[Janz99]

I see what your getting at. Yes, i have a modify nozzle with a single o-ring. I tested the whole cylinder/nozzle together and it had very good compression after i changed out the o-ring.

I didnt test the nozzle itself, because i wasnt exactly sure how i could do this without some how pressurizing the cylinder with the piston out, and cover the port and end of the nozzle.

Im going to take the barrel/hopup out, and clean everything as best i can, and see if that helps at all. Are you guys using any sort of lubrication on your hop up rubbers, or do you generaly use them dry?

Thanks
Ryan

[m102404]

Mine are typically dry.

There's a general sense that putting a couple of drops on a mag of bbs and running them through once in a while isn't a bad thing to do.

I definitely notice the first mag or so is a little wonky after working on a mechbox...excess grease is getting blown out of the cylinder and nozzle...straight onto the bb and rubber. Takes several shots to clean it out. But once it's stabilized...it should be consistent.

Best of luck,

Tys

[Janz99]

Thanks for all the help! I"ll update this thread if i track down a definitive answer.

Ryan

[Janz99]

Just thought i would update this thread. I ended up putting in an upgraded motor, and i tried a friends 9.6v sub C sized battery, and the single shot issue seemed to disappear.

Im not sure if its just a coiencident, or if some other issue just so happened to work itself out.

Ryan

[m102404]

Motor and battery have zero effect on the FPS. But...loosening/tightening things on your rifle does.

Dunno...just hit the field and have fun now.

Tys