FX Dream Tac, .25 and .30, not enough power for these calibers...???

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That's pretty darn good. If the gun is losing power on higher pressure I can only conclude the hammer needs more weight added to it. Seems your gun has plenty of power on tap after all. But may need a bit of massaging (like mine)

Have you ported it any or cut the probe for more airflow?
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It does seem to have enough power, it's curious that the power slips downward with a pressure increase and no other changes applied... A half a turn out on the regulator and the FPS drops from 900 to 860 or so... I'm wondering if a bad gauge on the Dream Tac is behind the discrepancy of enough power at 115 BAR and a complete drop in speed at 150 BAR (reading on the gauge)...???

I'm going to go get my bottles filled today, I will continue tweaking a little to see what kind of performance I can get before doing any grinding or filing on my Dream Tac, if I can get it to a consistent 900-910 FPS I would rather avoid any major modifications... I really like my Dream Tac, I would like it to be my multi-caliber platform and use it in competition if it's capable of delivering the performance I'm looking for...

I did get out to my permission for a couple hours Sunday to do a little shooting and practice my basics, trigger squeeze, follow through etc... It was a beautiful day...

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Ken


 
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Those brass barrel ends are replaceable as are the probes. They don't even cost much. My 22 picked up 75 fps shooting 30gr before modifying the hammer and operating pressure. So I'm not sure if the gain was actually higher. That was just porting. Gains on 25 woukd be a bit less, however.



Either way, that looks like the perfect day!
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It was a beautiful day Sunday (far cry from today), I had my 22 barrel in my Dream Tac and was playing with different pellets, some NSA slugs and some top secret slugs that I got from Ted B, they shoot really well with only a slight change in POI at 50 yards... I may order up the brass breech section and a second pellet probe to do a little experimenting with some minor porting, smooth the surfaces...

Ken


 
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That's pretty darn good. If the gun is losing power on higher pressure I can only conclude the hammer needs more weight added to it. Seems your gun has plenty of power on tap after all. But may need a bit of massaging (like mine)

Have you ported it any or cut the probe for more airflow?
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I am learning... I do have a question, what are the effects of adding weight to the hammer...??? Does adding weight allow me to back off the hammer spring tension...??? I'd like to minimize vibrations in the system as well as increase efficiency at my desired speeds... I'd rather tune this rifle myself than send it to an air gunsmith to do for me, all the information and help I get here is appreciated... I would like to make it to an EBR event with my Dream Tac...

Ken
 
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First of all I'd like to note that I got more power with rough port surface rather than smooth. Air actually flows faster over an uneven surface than it does smooth. 

In my 22 I basically created a bellmouth to the diameter of the 30 cal port on the TP wheel. It's like a velocity stack that crams more air, smooths the flow, and accelerates the air charge. The middle of the port is still the original factory diameter. The other side has been rounded at the sharp 90 degree turn into the probe/barrel. Turning that down elongates the port on the inside. So, the probe is cut to match. And all edges in direct path of airflow reduced or knife-edged. My probe has material removed from the bottom, but it's very likely that it may be more effective to remove material from the top instead, as that's where airflow is directing as it rounds the turn from the port into the barrel. 

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The hammer on my crown was really only good for 135 bar in my experience. So, if you can get the power/speed you want just from porting, I wouldn't worry about it. Heavier hammer is undesirable as it creates more inertial shift. And a heavier trigger break. The weight is essentially going to allow you to run more reg pressure. You want it to be matched to the needs of the valve (ie, how much force it needs to crack it at X pressure) I use a 7gm one and it peaks in power right around 155 bar. I run the same hammer tension on my 131 bar (unweighted) pellet tune and the 155 bar slug tune. 16-65fpe and some very serious accuracy. Punched out this 12ga primer at 100yrds with a 36gr slug

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Still testing and tuning. There is more power on the table, just havnt seen the need. A lot of the slugs I'm testing actually only shoot well at ~55 fpe 
 
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@Long_Gun_Dallas...

Thanks so much for the explanation, I am definitely learning... I will be tweaking on my Dream Tac later today to see what kind of speed I can get out of it without any modifications...

I understand when you say "velocity stack" and remember reading about porting and "polishing" Harley cylinder heads, that polishing didn't help but removing sharp corners to create radii and smoothing the transitions did... Helps to know why... Thanks...

That's a shot shell next to the pop can eh...??? Was the primer live...??? That would be a "reactive" target if ever there was... Hehe

Ken
 
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@ Long_Gun_Dallas; Now I have more questions about the physics of these air guns, regarding the venturi effect, like your "velocity stack" provides...

Are we defeating any benefits of the venturi effect with porting and opening up passages...???

Logic tells me there must be an optimum passage length and diameter (volume) after the plenum and valve based on caliber and barrel length, exceeding that volume would in my opinion result in diminishing returns on performance and efficiency...

See my photo in the post above, if we remove material in one place would it be beneficial to add it in another to maintain the volume of the transfer port passages...???

i'm learning... Ken




 
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I'm curious to know if anyone has experimented with filling the space in the pellet probe behind the "breech port" with material and smoothing the transition through the 90 degree bend... Maybe JB Weld, epoxy or even lead solder could be used as a filler material...

A photo may help...

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Ken
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Its funny you ask i did both probes in the Boss .22 and .25 with jb weld filled that void and did a kind of sloped transition.

Not sure if it helped anything but didnt hurt it.
 
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@ Clem.Chally...

I was thinking about doing a quick chrono my rifle, do the "JB Weld" mod, then immediately chrono it again to see if there was any change at all... These are interesting topics for sure...

Ken
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That's what I should have done, i did rough up the inside with a burr to give the jb something to bite on. Let us know.
 
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I think the key is to not open the passages, because they are already the optimal size. (bore size) Like I said the middle of the port on my barrel is still original diameter. I basically just made smoother transitions. I woukd have kept my gun on the 22 wheel setting, but I noticed the 30 cal setting upped my power, that's when I did the bellmouth port job. As far as port length or volume, there's not much to be done about it. So I havnt given it much though, but I'm curious to look into it a bit more. 

Your valve seat is likely not bore size. And I'm not familiar with what type of seat or valve stem your gun uses. I have a 6.5mm one for my gun that performs very poorly with the 22 cal barrels. (it's for 30 caliber). And I have a 5.8mm one that is sized more appropriately. I may try switching back to the original 5.56 and seeing if it changes anything. 

Engines are essentially just air pumps, so a lot of the same concepts cross over.

Either way, I'm curious about the probe. I think it did cross my mind, but I think I figured I'd make a mess of it. It would be awkward to shape the surface of the epoxy how I'd like. Maybe there's a better way I'm not thinking of. 
 
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I was reading in another thread about "power kits" and looking at current "hammer weights" parts numbers, seems there's some overlap of parts numbers between the different models from FX, I will need to look into it further but there might be a way to put together a "power kit" for the Dream Tac from already available parts... Others probably know a lot more about the differences in part number from stock to the "HP" upgraded parts...

I'd be interested in hearing more about genuine FX parts that provide an increased range of regulator pressure and performance... I'd have to read the other post again to be accurate... It listed part numbers for various FX models...

Titanium valve seat,,,??? Hammer weight and ported brass breech I think were some of the parts... Perhaps a different spring was mentioned too...

Questions...

Ken


 
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UAG demonstrates a Dreamline in .30 on a hunt. Have a look and see if it has enough power? Uses lots of air (I believe 2 magazines per fill), but it seems to have the power
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I seriously doubt that's a box stock Dreamline and I've no doubt the Dreamline rifles have enough power, having some basic settings for the different calibers for it would be great, I have a chart from FX for my Crown... Need same for the Dreamline... 

Ken
 
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