ULT = sear not catching

[OPBN]

I've often wondered about this. Let's take a little tangent while we wait for the OP to reply.

First, I agree the gap has to be there, or the marker may not complete a full cycle. However, since the chamber is pressurized (pushing on the top of the pin), and the bottom of the pin is at ambient pressure, wouldn't the pin continue to push down until it hit a positive stop (back of sear) regardless of on/off type? If so, I would argue that trigger rod adjustment is more to accommodate the body/rail/trigger frame stack up than a different on/off type.

My understanding is if the sear rod hits the back of the trigger it is essentially keeping the front of the sear from catching the bolt. Once the front of the sear catches/hits the bolt, than the sear rod stops moving forward. If it's too far back, the trigger cannot push it far enough back/up for the sear to fully engage the on/off pin. The on/off pin stops when the sear stops, which stops when it hits the bolt.

With a ULT, as you add shims it pushes the bottom of the on/off down, pushing the back of the sear down and the trigger rod forward. So as you add shims, you have to turn the sear rod in/away from the trigger to maintain the gap.

Correct me if I'm wrong.

[Mic0157]

Okay. Wow that's alot of information. Let's address the sear rod, there is at least a CC gap back there. As for the ULT, there are no o-rigs loose above the on/off assembly; just the recessed o-ring that came with the on/off. The on/off is assembled as directed with no shims and I'm keeping it oiled.

Now one new development, the comment regarding the regulator pin assembly, I did open that up and change a few o-ring that looked hard so ill get back into that tonight and see if anything is amiss.

Regarding the sear, I cannot tell if that is the problem. Looks good to me, but what do I know.

I will say that if the sear is not catching, then the on/off may not be pushing far enough on the back of the sear. so my next line of thinking would be to add shims giving the on/off pin greater distance to travel and thus striking the back of the sear with greater force pushing the front of he sear up. Does that make sense?

Oh and thanks everybody for helping me with this.

[nak81783]

2. Is the rail bushing in place? This is a brass cylinder that press fits into the back of the rail that the field strip screw goes through.

3. Does it go full auto when you hold the trigger back FIRMLY? Does this happen with the RT on/off and the ULT on/off?

FYI, on the reg pin assembly, there are two 006 urethane orings separated by a single turn split Teflon washer. That washer should have the split (many think it's a crack), and it should be hard (harder than the orings anyway).

Where are you located?


-Nathan

[Mic0157]

2. Yes it's there
3. It goes fires twice with a light tap and full auto when holding trigger down ( it does not take alot of pressures to make it go full auto).

I am now suspecting the reg pin is not reassembled correctly. I want to look at it closely this evening and see if it is assembled as listed above.

West chicago area.

[OPBN]

I will say that if the sear is not catching, then the on/off may not be pushing far enough on the back of the sear. so my next line of thinking would be to add shims giving the on/off pin greater distance to travel and thus striking the back of the sear with greater force pushing the front of he sear up. Does that make sense?

No. Regardless of the length of the pin, the pressure behind it should cause it to hit the sear with the same force regardless. With an Xvalve, there is direct full tank pressure behind it. Shimming will not affect the force with which the pin hits the sear.

[Mic0157]

No. Regardless of the length of the pin, the pressure behind it should cause it to hit the sear with the same force regardless. With an Xvalve, there is direct full tank pressure behind it. Shimming will not affect the force with which the pin hits the sear.

That takes me back to tank pressure. I'll see if I can pickup a gauge for the asa tomorrow.

[athomas]

The ULT shims affect the "timing" of the mag and shouldn't affect the trigger rod length. The shims in the ULT push to on-off top and therefore the top oring farther away from the rest of the assembly. This means the pin doesn't have to travel as far to open and release air into the front chamber. It is critical to make sure the sear is rotated far enough forward to catch the bolt before the on-off pin clears the sealing edge of the top oring in the on-off assembly. Thus, it is essential that you don't install too many shims in the ULT or the on-off will open too soon and cause air entering the chamber to halt the reset action of the bolt. It can also cause the bolt to shoot forward again causing a full auto action if enough air gets in fast enough.

The sear in its fully reset forward position is not affected by the location of the top section and is only fully reset when it rests against the bolt spring or a stopper in the rail. You adjust the length of the trigger rod to allow the trigger to move the sear within this range. When the sear is fully rotated forward, hold the trigger against the safety and adjust the trigger rod so that is almost hits the back of the trigger. This will ensure that the sear can always rotate forward to allow a proper unimpeded reset. Yes, the sear will allow the on-off to open before that, but you don't want to limit the forward movement or you will limit the life expectancy of your sear and bolt.

[OPBN]

I stand corrected. I swear when I was shimming my ULT that it seemed like I was having to adjust the sear rod when I was putting in/taking out shims. The more I think about though, it doesn't make sense to have to.

[Mic0157]

Okay I tore it all apart and I reassembled it correctly. Exactly like the blown up diagram. I cannot see why the sear isn't catching. So, I'll be going to the store tomorrow to see about a HP reg or simply having the, fix it. It's killing me right now.

It worked fine, I replaced old seals and dropped in a ULT which after further review, I may have already had in it. So now were looking into tanks and output. Grumble.

Unless there are any other ideas?

[nak81783]

Oh, sure. Listen to athomas but not me. He did put it a little more eloquently though, didn't he?

Enough of my hijack. Let's get the OP's Mag working!

How's that reg pin assembly looking?


-Nathan

[Mic0157]

Looked exactly like the diagram. Split ring and all. Nothing was changed on it and its clean. Hmm... Air restriction up stream??? Checking on the now

[Mic0157]

Reg pin

http://i1289.photobucket.com/albums/b504/mic0157/Automag/image_zps90db7e0b.jpg

Anything in the lvl 10 that could cause this?

[Mic0157]

Is there supposed to be any movement in the pin that holds the sear in place? Not based up, I can see some movement in the pin; up and down. Movement in that could throw off the geometry of the sear to on/off relationship, no?

[nak81783]

If it's happening when you're holding the trigger back, the problem is behind the Level 10.

1. Regardless of what it looks like, try replacing the small oring on the aft side of the reg seat holder.

2. Regardless of what they look like, replace the small oring that sits in the counterbore of the ULT and the oring that snaps around the top brass piece of the ULT (piece with the aforementioned counterbore.

3. Replace the sear as need4reebs suggested. Although I don't think the latch is the issue, if the on/off pin engagement hump on the back of the sear is worn or was ground down by the previous owner, that could cause this issue.

The movement you describe in the sear pin is normal to a point. Can you quantify the movement you're seeing. Remember, it will be constrained by the body when assembled.


-Nathan

[Mic0157]

Well go figure. I followed step 1 and air up before step 2 and were a single shot again. No more automatic.

No that we fixed it, can you explain what that little seal does so I can give it a stern talking to later?

Wow thanks Nak, and the rest.