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Discussion Starter · #1 · (Edited)
Hello all. I need help from the collective here.
I've been having some issues with my UTR45 build.
11.1v quality batteries
Perun Hybrid V2
Lonex blue piston and POM head
Lonex cylinder head and MAXX cylinder
MAXX 21.25mm nozzle (same length as stock nozzle)
13:1 gears, short stroked 4 teeth
Krytac hop up with ML macaron 60" packing. ( 1st 2 outings krytac orange)
Lambda 6.03 barrel
22k 22tpa ASG Infinity motor.

It's first day on the field everything worked fine. The thing shot lasers. If I recall correctly, I may have been running lesser quality batteries.

The second time I took it out, I would get some random shots that would drop too early.
I suspected compression/seal issues, so I replaced the bucking from Krytac orange to ML macaron 60*

Took it out for it's first day back on the field yesterday and was still having the exact same issues.

This time I tried to pay closer attention to what was going on.
Some shots would drop way too early and sounded weak, like the compression was off.
It was random. During spam and slow fire. No rhyme or reason.

Listening back on the video, I think it could possibly be PME, as some, but not all of the weaker shots I would hear a slight clicking sound.

When I built it, I only removed a few teeth from the piston. Should I remove the remaining unneeded teeth?
What would you do?
Possibly remove the extra teeth from the rack and double check airseal, stretch of the oring a little?

ETA: This is a pic from when I built the gun.



Here is a short video where you could hear it the most. SOme of the shots were hitting so low, they were hitting the barrier I was shooting over.

If I left anything out that is pertinant to the troubleshoot, let me know.

 

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Not seeing the typical signs of PME (chewed up pickup/rack). Did you see the same issue with a lower powered battery (7.4v instead of 11.1v)? What spring are you using?
 

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Discussion Starter · #3 ·
Not seeing the typical signs of PME (chewed up pickup/rack). Did you see the same issue with a lower powered battery (7.4v instead of 11.1v)? What spring are you using?
Sorry, that picture is from when I built it. I haven't taken it apart yet. Was going to try to rip into it tomorrow.
Previous batteries were also 11.1v, just lower quality ones.
Spring is an M105 asg I believe.
 

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M105 seems a bit weak for preventing PME in the 30rps range, SS by 4 makes things a little foggier to diagnose.

EDIT:Also if you SS by 4 on the sector, I don't see why you shouldn't SS by 4 on the piston release side.
 

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M105 with a 4t SS, could see PME being possible. Maybe try using Perun ROF control and seeing if there's any difference as you slow the cycle down? Make sure AB is on, no pre-cocking.
 

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Discussion Starter · #6 ·
Okay. Sounds like a plan.

Since I pretty much exclusively shoot semi-auto, would a potential fix be removing one more tooth from the sector pick up side, and using an m115 or m120 spring?
 

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Potentially, although 5t SS could start messing with your timing - may want to take one off the release side instead. What's the current FPS (before it started acting up)?

Personally, I'd start by using ROF control and/or a 7.4v to ~confirm if it's PME. If it looks like it is, you may be able to get away with just lightening your piston assembly some more - every g you remove gives you more headroom and you might be right on the edge if it cycled ok previously. Get that piston assembly under 20g one way or another lol. If that doesn't do it then I'd try adding a spacer to the spring guide to give it a bit more oomph if you can gain a few fps while remaining legal - if not, stepping the spring and taking another tooth off may be needed. Or be lazy and just use ROF control to keep everything in one piece - definitely done than a few times.
 

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Discussion Starter · #10 ·
M115 or M120 would almost certainly eliminate PME being a possibility. Ona side note, don't maple leaf macaron packings require a bit of modification to work properly?
Yeah, they definitely require a little bit of trimming. I found a pretty good method to take care of that. It drops about 5 or 10 FPS but it feeds 100%. What I do is use a one and a half inch Dremel cutting wheel, and just barely kiss the lips to the face of it. It removes material very evenly and smoothly.
 

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Discussion Starter · #11 ·
Potentially, although 5t SS could start messing with your timing - may want to take one off the release side instead. What's the current FPS (before it started acting up)?

Personally, I'd start by using ROF control and/or a 7.4v to ~confirm if it's PME. If it looks like it is, you may be able to get away with just lightening your piston assembly some more - every g you remove gives you more headroom and you might be right on the edge if it cycled ok previously. Get that piston assembly under 20g one way or another lol. If that doesn't do it then I'd try adding a spacer to the spring guide to give it a bit more oomph if you can gain a few fps while remaining legal - if not, stepping the spring and taking another tooth off may be needed. Or be lazy and just use ROF control to keep everything in one piece - definitely done than a few times.
Sorry, forgot to mention. FPS was 350 with the Krytac orange. After trimming the macaron down for proper feeding, it was around 342, which was ok with me.
I try to keep everything around 350fps. Although, I could go up to 400, but MED changes from 10ft to 20ft, but I could probably live with that.

I will try the suggestions with the battery etc before ripping into it and see if anything changes.

I also should have mentioned. The sector came stock with a delayer chip on it. Not sure how much that would play into helping or hurting if I did end up needing to remove 1 more tooth from the sector.

Since i want to take everything apart to see how the insides are holding up, I think I will definitely lighten the piston, and remove any teeth from it that aren't needed. Pretty sure I still need to take off 1 tooth. That should lighten it up a bit. I'll finish the swiss cheesing I started, as shown in the picture above.
I don't remember if I left the bearing in for the piston head. If I did, I may remove that while I'm in there.
 

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Must be quiet a barrel to squeeze 340 out of a m105 with a 4t SS, if you can get it to cycle smoothly that'll be one heck of an efficient setup.

Removing the bearing from the piston head will decrease spring compression by ~5mm, will lower fps slightly. Just a heads up. I found some hard plastic washers of approx the same size, 0.5g vs ~5g bearings.
 

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Discussion Starter · #13 ·
For sure.
Last time I was at the hardware store, I went prepared with a list of measurements to hunt to nylon spaces for correcting AOE and other various parts. I found some in the exact sizes I would need to replacing the piston bearings. I'll see how those hold up. I believe they are the off white nylon type spacers. They seem pretty stiff and durable.
 

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Take off your upper receiver and fire a few rounds in semi. Make sure that the nozzle ends up in about the right place, or it could potentially be causing feeding issues. Active braking can help with this.

I've seen instances where the nozzle stuck, or even the tappet timing was off where the nozzle would return and extend in the wrong places. The nozzle could even be pushing BBs too far past your hop rubber.

Do you own a chrono? Some chrono results would be really helpful.

Look up the silicone cylinder head buffer mod. I've found it to be extremely easy and useful. You can add more material than you need and correct AOE exactly with a razor blade, it's a soft buffer, piston sound is a lot better, silicone immediately returns to its original shape, so your FPS will be more consistent. I've never had any damage (yet) either.
 

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Discussion Starter · #18 ·
Take off your upper receiver and fire a few rounds in semi. Make sure that the nozzle ends up in about the right place, or it could potentially be causing feeding issues. Active braking can help with this.

I've seen instances where the nozzle stuck, or even the tappet timing was off where the nozzle would return and extend in the wrong places. The nozzle could even be pushing BBs too far past your hop rubber.

Do you own a chrono? Some chrono results would be really helpful.

Look up the silicone cylinder head buffer mod. I've found it to be extremely easy and useful. You can add more material than you need and correct AOE exactly with a razor blade, it's a soft buffer, piston sound is a lot better, silicone immediately returns to its original shape, so your FPS will be more consistent. I've never had any damage (yet) either.
I will get some chrono results before doing anything. My chrono seems spot on with my fields chrono in regards to FPS. It does suck at measuring RPS though.

Sounds good. I'll check in on the nozzle positions before ripping the gearbox open.
I haven't had a feeding issues, at least not to where a BB didn't fire. But I get what you're saying about the nozzle potentially pushing the BB past the hop rubber. That could definitely cause FPS drops I would assume.

I'm not so concerned with the gun being loud, as much as I can hear an occasional clicking sound when the shot seems to have low FPS.
That's why I was thinking mild PME, but being so new, I'm not 100% sure what to be looking/listening for.

My though process was if there was any mild contact with the sector gear while the piston was returning towards the cylinder head, it would produce a weaker shot.
I mean, I think the piston release tooth is ever so slightly contacting the sector pickup tooth on it's way back forward.
That's the only thing I could think that is making that clicking sound when there is a weak shot.

It's really hard to hear in the video. It is very faint, but you can hear some shots sound slightly weaker at the same time there is the clicking noise.

Spots in the video where you can here it
23-24 second mark.
29-30 second mark.
34 seconds
and at the 49 second mark I shoot a slow 3 round burst.
The first shot sounded and shot normal. The 2nd and 3rd shots had the clicking noise and had weak FPS.
 

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Will have to listen to the vid somewhere quieter than here lol

I check for PME with a Chrono or by watching the amps the motor is using - will spike at the end of a cycle if the piston catches.

Buffers, sorbo, etc - prob ok here but can be dangerous in high speed guns. The buffer compresses, that's it's job, but in doing so the AOE becomes inconsistent which causes a lot of stress/wear on pickup/gearset/bearings, FPS creeps/wanders, and if you're unlucky the buffer separates from the CH and gives you some nasty PME by jamming your compression set. Better to have a light spacer behind the piston head for speed - can't compress, can't come loose, stable, etc. Does add weight to the piston assembly, but only half a gram or so if you make it out of POM ABS etc. All imo / based on my experience oc.
 
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