FX Odd Behavior from Dream-Tac

[FLgunner]

I was shooting my FX Dream-Tac yesterday and am experiencing some odd results. It's set up with a 500mm .177 barrel, reg set to 110 BAR. Shooting 15 gr NSA slugs I'm getting intermittent velocities. I'll shoot a couple rounds at 916 FPS and then get one at 370 FPS. One or two more at 916ish and then another at at 340 FPS. The regulator gauge is showing 110 BAR between each shot, so I'm not real sure what could be causing this. When shooting lighter ammo (10.5 gr pellets or 12 gr slugs) I'm not experiencing this... Any thoughts?

 

[Dairyboy]

I think I've seen something like this before if im not mistaken I think the valve is going bad? But I'd also check the hammer area and make sure nothing got in there somehow causing issues.

 

[rcarlisle]

I don't shoot slugs from my .177 Dreamtac, but if I were to hazard a guess, perhaps check the size of those 15gr slugs against the lighter ones. Could be they're a bit over-sized and slowing down in the barrel when they hit a tight spot, or they're a bit under-sized and not getting the push they need due to pressure running past them in the bore.

 

[FLgunner]

I think I've seen something like this before if im not mistaken I think the valve is going bad? But I'd also check the hammer area and make sure nothing got in there somehow causing issues.

Thank you! It might be the hammer, I recently replaced the stock hammer weight with a slightly heavier hammer weight. The replacement is brass, so that might be the issue. If so, it will be much easier to remedy than a bad valve!

 

[FLgunner]

I don't shoot slugs from my .177 Dreamtac, but if I were to hazard a guess, perhaps check the size of those 15gr slugs against the lighter ones. Could be they're a bit over-sized and slowing down in the barrel when they hit a tight spot, or they're a bit under-sized and not getting the push they need due to pressure running past them in the bore.

There is no difference in the feel while feeding them, but I'll check just in case. When shooting at 900+ FPS, they are making nice little clover leafs at 37 yards, so hopefully, it's not the slugs. NSA usually has pretty good consistency in their slugs, so I would be surprised if they are that different.

 

[Joedirt199]

Seems like the dreamline has a weak valve pin design that when people push them hard, have problems with snapping the valve pin. If the hammer weight is sliding smooth and not sticking in the hammer, the valve would be my next step. Thinking of getting a couple valve pins as backups in case mine break. Have to pull it to verify which one as there are a few different versions they made to combat the breakage.

 

[FLgunner]

The valve is good, I pulled it, inspected it and wiped a little lead dust off it, but otherwise it was in good shape. I also pulled the hammer weight and inspected it. There was a little grime in the area where the hammer sits and I cleaned that as well. Put it all together and still have the same issue with the 15 grain NSA Slugs. All others seem to be just fine, shooting the 13 grain, 12 grain and 10 grain slugs all have consistent velocities. 10 grain pellets do also. Maybe when I hit the 15 grain mark, there's just not enough oomph with the reg set at 110 BAR and they just aren't making the trip down the barrel. Next thing I'm going to try is a good barrel cleaning and polishing and see if that helps any... If they were consistently low, I'd increase the reg pressure a little, but with the wide inconsistencies (320 FPS to 830 FPS) I din't think its the regulator pressure since about half the shots are hitting 830 FPS and the others are between 320 and 480 FPS.

 

[Xcaliber]

put the stock hammer back and see if the issue persist, did the action noise sounded different whenever it dipped down to 300fps range?

 

[FLgunner]

put the stock hammer back and see if the issue persist, did the action noise sounded different whenever it dipped down to 300fps range?

Nope, everything cycles smooth and sounds the same, except when I pull the trigger, then I get the normal sound and the sound like it just spit out a low velocity shot! The brass hammer I have in it is only 1 gram heavier than the stock hammer, but will try that also. Thanks...

 

[Xcaliber]

hope you get it sorted out, i have only seen this problem reported by another member from different gun, but it was valve related where he get one full power shot, the next was way down in velocity, the high low high low high low keep repeating the whole way through: https://www.airgunnation.com/threads/uragan-2-and-the-assisted-valve.1303365/

 

[Dairyboy]

I missed the part where you said it's only with the NSA 15gr. I have no idea why that would only happen with them except it's likely something ammo related. One would think maybe some aren't getting pushed past the TP enough. But being a slug it should have a very shallow dish if not flat so shouldn't be the issue either.

 

[FLgunner]

I missed the part where you said it's only with the NSA 15gr. I have no idea why that would only happen with them except it's likely something ammo related. One would think maybe some aren't getting pushed past the TP enough. But being a slug it should have a very shallow dish if not flat so shouldn't be the issue either.

It's got me baffled! After cleaning everything and reassembling, I ran a full magazine of 12 grain NSA slugs, a full magazine of 13 grain JSB slugs and a full magazine of 10 grain JSB pellets and never had an issue. I load up a magazine of the 15 grain NSA's and get the sporadic velocities. I'm wondering if maybe they are sealing enough in the barrel and since they are heavier, maybe air is blowing by the slug as it travels down the barrel, where the others are light enough the air just pushes them right on out?

 

[coastal drifter]

so is the slower shots grouping lower? sometimes a crono can read weird.

 

[FLgunner]

Yes, considerably lower, like about a foot+ lower! It even sounds different with the slower shots, kind of a muffled poof...

 

[KatoKevin454]

you might have gotten an accidental mixture of different size slugs, some smaller diameter than what it suppose to be, I'd break out a Micrometer and test the size of several slugs.....

 

[Trucker3573]

Bigger…longer slug maybe not being seated consistently far enough into the breech ? The low velocity ones are maybe blocking the TP just a little ??

 

[FLgunner]

The probe is a pin probe and it has the dual port end on the barrel. The probe isn't adjustable, so how would you get it to seat the slug further in the chamber?

 

[FLgunner]

you might have gotten an accidental mixture of different size slugs, some smaller diameter than what it suppose to be, I'd break out a Micrometer and test the size of several slugs.....

I have yet to test this, will do that next, thanks...

 

[coastal drifter]

I remember seeing a video of a pin probe that retracted when cocking the gun so as to set the slugs deeper, might have been Matt Dubber? other than that A single load with an adjustable probe.

 

[HogKiller]

Thank you! It might be the hammer, I recently replaced the stock hammer weight with a slightly heavier hammer weight. The replacement is brass, so that might be the issue. If so, it will be much easier to remedy than a bad valve!

A brass spring?????? WTH!!!