Replacing Dominator 200 spring with gas piston?



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Offline rdtricks

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #20 on: November 10, 2018, 07:34:45 PM »
Mossonarock,  Great write-up of your testing and progress on the Dominator.  I will be most interested to read more as you continue testing new springs and other options.  My .25 cal Dominator has felt a bit less than, and after reading your posts I have a direction to improve the beast.  Thanks!
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #21 on: November 11, 2018, 01:16:49 PM »
Nice. I'm glad my experiences could help. I'm pretty sure that the 0.128 spring is ideal for this rifle for power and accuracy. However, whether the spring ought to be 35 coils or 40, I'm not sure about. That would be the next step to explore. If a person was more concerned about accuracy and didn't care about power, the 0.125 spring may be best but I didn't bother with installing my 0.125 spring. I think I'm going to leave the 0.128 spring in for awhile- a tin of pellets or so like I did with the 0.135 spring.

I got out and did some proper target shooting yesterday. I have to admit that I'm not able to be any more accurate with my HW97 than with my Dominator. That says more about me as a shooter than the rifles. I don't feel that I can speak on accuracy. The groups I get with both rifles are about the same and I won't be winning any competitions with my shooting skills. Laugh if you will, its ok.
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Offline rdtricks

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #22 on: November 11, 2018, 05:07:09 PM »
I ordered replacement parts for my Dominator last night; Vortek spring 0.128 with 38 coils, Hatsan breech seals and piston seals.  Wanted to try the Vortek molly piston seals but not currently available.  We shall see if Vortek sends out a 38 coil spring or the standard 40 that I might need to cut down.  Thanks again for making your testing and progress available to the rest of us.

Anyway, trigger time and concentration on your shooting style should help improve the groupings - if that's what you are after.  There are a couple of YouTube sites I follow picking up tricks and tips for my shooting every episode.  I especially like VarmitHuntersTV because of how well the guys can shoot: be aware it is a hunting site.
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #23 on: November 13, 2018, 06:46:04 PM »
My main challenge is its almost always raining when I get home from work and now with the time change I basically have no daylight either when I get home to do any target shooting. If you are able to chrony test your rifle with the new spring, I'd like to see the results. 38 coils is interesting.
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Offline mentolio

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #24 on: November 15, 2018, 07:21:57 PM »
Firstly: nice work! A lot of guys end up cutting-down their Hatsan springs to make the gun shoot smoother/have less of a harsh shot-cycle, and obviously give up some power to do it. That you have found a spring that shoots smoothly AND makes acceptable power is no small feat.

Aftermarket seals: just my experience, but every aftermarket seal I've tried has disappointed. Many need to be sized, and missing that mystical, magical mark by 1/2 millimeter makes your expensive seal...well...junk. All the seals I have tested aside from one needed sizing to deliver optimum velocity, and none of them delivered the velocity I get from just slapping a new factory seal in the gun. Admittedly I may just be missing the "magic," but I'd rather spend 5 bucks on a seal I know works without the hassle than to spend 10 or more dollars on an aftermarket seal, knowing I will likely ruin at least one or two getting that seal anywhere near its peak. Are aftermarket seals "nicer" than what Hatsan sends? Heck yeah! They're all softer, thicker, make for a quieter and smoother shot cycle, and are turned on a lathe vs. pushed out of a mold (meaning: round, not square like at least 1 out of 3 stock units). They just don't make great velocity.

Pellets: I know it seems counter intuitive, but try a few heavier pellets. My Mod 95 in .25 shoots most pellets well enough, but LOVES JSB King 25.39s. Last time I tested it (with a good stock seal, hone, lube tune, and after buttoning the piston) it averaged 608 fps with these JSBs (at almost 21 ft lbs!), and will shoot them more accurately than I am capable of.

Gas piston: I like a gas piston, even prefer them as I like to airgun hunt, and can leave them cocked while hunting without triggering my OCD. That said, if you look around I think you will find that if you want the most power, you get it from a steel spring. Gas pistons are quieter and feel smoother (to me, anyway), but they typically give-up a little velocity to do it. That said, with no spring tar necessary, they may not lose the velocity a spring powered gun can in cold weather (I've never noticed a difference myself, but I don't live where it gets much below 20 degrees F, and if it does I'm not out in it).

Keep up the good work, I'll be following this post.
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #25 on: November 16, 2018, 10:52:27 PM »
Thank you for sharing your experience. I couldn't find any after market piston seals that I was certain I could use on my Dominator. HatsanUSA reduced the price on their Vortex Dominators and I have to admit that I bought one of those too. It'll be interesting to compare that to the 200S that I have.

I still haven't been able to do any rigorous target shooting but I was able to do some plinking out to 75+ yards today. My accuracy is about the same as with shooting my HW97kt- not great but enough to have fun. Also, the recoil feels about the same. Both rifles buck and kick just about the same. However, I realize that's a very subjective observation. Overall though, I do feel like this 0.128" 35 coil spring is satisfactory. Sometime, I really ought to try the 0.125 spring since I bought it and all.

I didn't dive into this being a complete newb. I had some experience with making my own springs for some antique camp stoves that I have and restored. Some of the European members here may know the stoves I'm talking about- Radius, Primus, Optimus. So, I had some understanding of wire diameter, coil count, spring OD and how all that works together. However, making a spring for an airgun is totally out of my league. That's why I didn't choose to cut down the OEM spring. Besides, I prefer leaving original stuff as original as possible. Swapping out parts is ok but I don't like permanent alterations.
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #26 on: November 29, 2018, 09:43:27 AM »
HatsanUSA put up the Vortex Dominators for close-out sale. I couldn't resist and bought one. Now I can really compare spring vs gas.
I haven't had time to do much chrony testing for the vortex dominator. I took it apart and cleaned it up. Initial fps for Barracuda Greens 19.91gr after cleaning seems to have settled around 700fps. That's almost 90 fps faster than the 0.128 spring. I'm curious to see what speeds I'll get with the other pellets.

I found significant differences in build quality between the two rifles with the spring dominator  having better fitted components. The components on the vortex dominator just don't seem to fit together quite as well. I had a really hard time pulling the trigger out and putting it back in. So, its interesting that I'm a getting faster speed with the vortex dominator. I haven't figured it out.

Back to my original question for this thread: can a gas piston be put into the spring dominator? I believe the answer is yes. However, the end plugs for the two rifles is very different. I'll try to put up pictures sometime. So, if someone would want to swap powerplants, they'd also have to swap end plugs. Otherwise, without taking careful measurements which I did not do, a casual observation indicates everything else looks the same.

Well, the clients are pouring in here at work. So, that'll be all for now. This evening I need to split firewood. Not sure when I'll get to that chrony testing.
« Last Edit: November 29, 2018, 10:06:46 AM by Mossonarock »
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #27 on: December 02, 2018, 04:16:11 PM »
Chrony testing with the vortex dominator:

Predator GTO avg fps: 786
Barracuda Green avg fps: 697
Coppa spitzkugel avg fps: 601
AA Diabolo Field avg fps: 561
Barracuda avg fps: 524

Summary: anywhere from 50 to 100 fps faster than the .0128 spring.

I wonder it there's differences in how the rifles are built and engineered. Or if its merely a powerplant difference. I'll have to swap powerplants to see, meaning take the spring out of the Dominator 200S and put it in the Vortex Dominator and vice-versa. Mysteries.

One thing I found interesting is that the extreme spread and standard deviation for the pellets was similar with both rifles even though the avg fps was very different. I'm going to attribute it to the pellets. Meaning some had more irregular shapes and some were more uniform and all that stuff. The Barracuda Greens and Coppa Spitzkugels tended to have wider standard deviations while the Predator GTOs had the tightest standard deviation and extreme spread.
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Offline rdtricks

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #28 on: December 02, 2018, 04:31:06 PM »
'Airgunners Edge' on youtube converted a Hatsan 200s from spring to gas ram.  I believe he was able to obtain the necessary parts for the conversion directly from Hatsan, but not sure. 
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #29 on: December 28, 2018, 05:08:38 PM »
I finally got a round tuit and tried swaping powerplants between the two dominators. The end caps for the two rifles are different and each endcap had to go with its respective power plant. The spring went right into the vortex dominator and worked right away. However, when I put the vortex piston and its end cap went into the spring dominator, the seer wouldn't engage. Later on, when I put the spring back into the spring dominator, the seer still wouldn't engage. After taking the rifle apart and putting back together several times, the seer finally would engage again. By that time, I was sick of it and didn't want to bother putting the vortex piston in it. I did some chrony testing with the 0.128 spring in the vortex dominator and here are the results:

Predator GTO 16.54gr avg fps: 777
Barracuda Green 19.91gr avg fps: 693
H&N Field Target Trophy 20.06gr avg fps: 658
JSB Exact King Diabolo 25.39gr avg fps: 595
Barracuda 30.86gr avg fps: 511

Since I ran out of some of the pellets I had been using, here's a baseline chrony test with the vortex piston in the vortex dominator:

Predator GTO avg fps: 779
Barracuda Green avg fps: 702
H&N Field Target Trophy avg fps: 639
JSB Exact King Diabolo avg fps: 586
Barracuda: 496

Looks like the 0.128 spring delivers very close to the same power as the stock vortex piston in the dominator. I found that very interesting. As I mentioned awhile ago, I had also gotten a 0.125 spring and hadn't yet tried it in the spring dominator. I finally did after I got that seer to engage. (not sure what I did to get it working again) Here's chrony results with the 0.125 spring:

Predator GTO avg fps: 698
Barracuda Green avg fps: 626
H&N Field Target Trophy avg fps: 589
JSB Exact King Diabolo avg fps: 526
Barracuda avg fps: 479

I'm still trying to make sense of these results. At first glance, it appearsthe 0.125 spring is able to deliver similar power to the heavier pellets. There could be some issues of difference since the top hat wouldn't fit the 0.125 spring. So, I couldn't use it. The spring may not have been lubed enough. And who knows what else? Also, I shot some of those JSB pellets at a rat-on-the-run field target using the 0.125 spring and collected some of the splattered pellets for a photo. It looks like the 0.125 spring is able to deliver enough power to a pellet to fully flatten it upon impact at 30 yards. Below that is a pic of the two actions of the dominators side by side.
« Last Edit: December 28, 2018, 05:14:52 PM by Mossonarock »
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Offline mikeyb

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #30 on: January 08, 2019, 11:08:25 PM »
If you don't already have a Hatsan fill probe and a HPA hand pump, I suggest you consider buying both now. You can use them immediately to vary the pressure on Vortex pistons to simulate MANY different power levels. You will also want to have the pump on hand later for your first PCP acquisition. If your future PCP stores less than 400cc the hand pump should be all you need.

Links below are the ones I ordered off ebay. Both are working well to fill my Bullboss and Vortex air springs. Not endorsing these sellers, just using the listings as examples.
Note: Overseas shipping time was not bad for my order, but sometimes it can be really SLOW!.

https://www.ebay.com/itm/PCP-Airgun-Hand-Pump-High-Pressure-Hand-Pump-for-Benjamin-Hatsan-HPA-4500psi/401314270659

https://www.ebay.com/itm/FX-Fxgun-Webley-Hatsan-RWS-Prestige-Evanix-PCP-charging-filling-Probe/123143967568

From your photo it looks like the main tube has the holes drilled in it to access the Vortex bleed screw and the fill port while still in the action. That makes "tuning" go a lot faster since you don't have to pull out the spring for each adjustment. I don't know what your Vortex pressure should be for that rifle, but I'd check the max spec written on the Vortex spring so you don't exceed that value.

Similar to your coil spring testing, I'd change the air spring pressure and test many different pellets for velocity, consistency, and accuracy. Unless you can find some factory recommendations, I suggest starting at 100 bar and going up in 5 or 10 bar increments, but never exceeding the ratings on your air spring.  I think you will be able to find a "sweet spot" pressure that will give you a nice smooth shot cycle with good accuracy near the velocity/energy you want.

I had a weak Vortex (~60 bar?) in a used Mod95 that I pumped back up to 150 bar. My Vortex said "160 bar max" on the side label so I thought 150 bar was good pressure. The rifle returned to shooting at factory velocity, but the shot cycle was a HUGE WHUMP! and I almost needed 2 hands to cock the darn thing! I later read that the suggested pressure for the Mod95 Vortex was 120bar to 130bar. I popped the stock, opened/closed the bleed screw, and re-pumped the Vortex back to 125 bar. Rifle STILL shoots at factory velocity but is  easier to cock and now has a "short thump" shot cycle. That was a nice "proof" to me that beyond an optimum value excess spring energy does NOT transfer to the pellet. That extra energy just goes into thrashing the gun (and the shooter) a lot harder than is necessary.

Good Luck!
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #31 on: January 09, 2019, 10:21:47 AM »
Mikeyb,
I appreciate your enthusiasm. Please share chrony data with your rifle. I'm pretty much done with any testing now. I'm still waiting for a day with good weather when I have time to shoot to work on my marksmanship. I really liked the results I got from the 0.128 spring but I still have the 0.125 spring in it. Also, as I said, I think pellet weights between 20 and 25 gr are ideal for this rifle in .25 cal. I'd love to hear other's opinion and experiences with this subject.

If I made any adjustments to the vortex piston, I'd reduce the gas pressure. I wouldn't increase the pressure. I have a hard time shooting that rifle accurately. I think the OEM stock pressure is more than enough for this rifle.

This is totally outside of anything I'm will to do but I wonder about tweaking the dimensions of the transfer port- such as rounding out the edges maybe making it a wee bit wider. But I won't be attempting anything like that.
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Offline mikeyb

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #32 on: January 12, 2019, 12:04:54 PM »
Mikeyb,
I appreciate your enthusiasm. Please share chrony data with your rifle. I'm pretty much done with any testing now. I'm still waiting for a day with good weather when I have time to shoot to work on my marksmanship. I really liked the results I got from the 0.128 spring but I still have the 0.125 spring in it. Also, as I said, I think pellet weights between 20 and 25 gr are ideal for this rifle in .25 cal. I'd love to hear other's opinion and experiences with this subject.

If I made any adjustments to the vortex piston, I'd reduce the gas pressure. I wouldn't increase the pressure. I have a hard time shooting that rifle accurately. I think the OEM stock pressure is more than enough for this rifle.

This is totally outside of anything I'm will to do but I wonder about tweaking the dimensions of the transfer port- such as rounding out the edges maybe making it a wee bit wider. But I won't be attempting anything like that.

I've read  a lot about modifying transfer port size. IMO there are RARE instances for very specific rifles where this advanced mod can improve rifle performance. Most air rifles we are likely to acquire already have optimum transfer port sizing and any mods in this area will probably cause a performance drop. Just advising caution.

I think there may be a place for a Dominator in my collection. Really like the look of that series and I don't have any  sliding compression tube style under-lever models yet.  I initially though the sliding barrel mechanics of the Torpedo series was "crazy". After getting a cheap Torpedo refurb, I am now a big FAN of that series. Awesome power and accuracy, but HEAVY!

The images below contain my chrony data for the Mod95VQE22 which I  repaired/adjusted. We are in complete agreement that factory Vortex pressure is near optimum for each specific rifle. Tuning pressure up is a usually a bad idea,  but tuning pressure down "may" give you a smoother more accurate rifle.
« Last Edit: January 12, 2019, 12:14:37 PM by mikeyb »
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Offline 72NOVA

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #33 on: January 13, 2019, 01:00:19 AM »
Unfortunately  what I have found along with others is the dominator  has an  Engineering flaw with the breach seal compartment,  does not seem to be every gun but a lot , I have done almost everything  possible except machine the tubing for a seal to sit on the nut of the barrel for a better seal... think I made a out 8 YouTube videos  of this gun...  My problem is I love looks and accuracy of this gun when it is functioning properly...
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #34 on: January 14, 2019, 09:51:48 AM »
Richard, I've seen a lot of your videos. At first, I thought my dominator might be one with a breach seal issue. After messing around with it, I don't think that is the case. However, its obvious Hatsan did several manufacturing runs of these rifles and some engineering specs were changed with each run. Although, I think the variability is only true with the coil spring models. I think they got production standardized without the bugs for the vortex models. And my research seems to support that since there's a lot of difference in fps between the spring and vortex models with using the 0.128 spring. I wish I could have gotten the spring dominator to work with the vortex piston in it. If anyone has any other interpretations of the data I've presented here, I'd like to hear it.
« Last Edit: January 14, 2019, 10:21:20 AM by Mossonarock »
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Offline mikeyb

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #35 on: January 14, 2019, 09:43:35 PM »
A possible explanation... maybe?

Gas springs have a very limited dimensional operating range. Not enough preload and a gas spring will tear itself apart. Too much preload and it will bottom out before piston latch. Coil springs will eventually bottom out or become "coil bound" if compressed too far, but they will usually function over a much larger range of manufacturing tolerances and user adjustment.

I did a little experiment last year replacing an Edge spring with a Crosman Nitro piston. I'd researched similar conversions and after taking careful measurements found I needed a custom bushing to center and space the NP body correctly in the edge. Turned a piece of scrap nylon in my "wood" lathe to get a perfect fit for the base (cylinder) end of the NP.

The other (shaft) end of the NP needed to be centered in a shallow dimple at the back of the piston head. This dimple is either cut into the piston metal itself or can be a separate metal disk with a centered depression for the NP shaft. I had tuned an older Edge and the back of that piston head did NOT have the centering dimple. To my surprise the one I decided to experiment on DID have the dimple already cut into the piston! I think Hatsan made a design change so coil or Vortex springs could use the same piston with no extra centering disk needed.

The point to this long story is that both the rear bushing dimensions AND the piston dimensions need to be precisely correct for a coil spring rifle to function properly with a gas spring installed. You swapped (coil spring + guide + tophat) and (Vortex + spacer) which is correct. But if there is ANY difference in the piston dimensions, you may have needed to swap pistons also.

If your spring version piston has no dimple, then the Vortex spring MAY have had too much preload and bottomed out BEFORE the trigger could latch the piston.

The coil spring + guide+ tophat should work fine in either rifle since a dimpled piston would not affect the springs operational length.

If you ever take apart the rifles again, look for a centering dimple at the back of the piston heads. I think your Vortex rifle piston has one and the spring rifle piston does not.
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Offline Mossonarock

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Re: Replacing Dominator 200 spring with gas piston?
« Reply #36 on: January 17, 2019, 11:40:13 AM »
I was also wondering about the gas piston possibly bottoming out and thereby keeping the seer from engaging. But then I had the same problem with the seer not engaging when I put the spring back in. Then the problem went away on its own or so it seems. So I dunno.

The two cylinders do differ in the that the vortex has that dimple you mentioned and the coil springer doesn't have one. I would suspect that's the reason for the seer not engaging but it didn't want to engage for a few times with the spring in it either. ??? :-\
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