Recently acquired the Bulllshark in .177. Actually shoots quite well for it's price. It currently shoots around 1100 FPS w/ crossman premier HP too hot for my needs. I'd love to be able to get this thing down to under 800 FPS. Is that possible and how? I can't seem to find any tuning instructions on this specific rifle. I'm assuming this can be adjusted via hammer spring tension and or regulator adjustments, but have no idea where to start. Any help appreciated.
Stoeger Stoeger XM1 Bullpup How Tune Down?
- Thread starter roaoro
- Start date
Reduce the hammer spring tension. It is done by turning the screw counterclockwise. It’s the large Allen screw below the cheek rest. Mine is .25 but the setup is the same. 
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I haven’t tried lighter pellets, but have shot most pellets above 10gr. My bullshark shoots FX 13gr the best, and 10.3 grain well. But the crosman and Benjamin single die not so well. It all depends on what type of accuracy you’re looking for though.
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I totally agree that you should start with the hammer spring. It may get you to where you want to be and if it does, it's much easier than adjusting the regulator. One thing to check if you think you got there is first shot velocity after the gun has set overnight. If you try to decrease velocity a lot with the hammer spring I sometimes find the first shot velocity will be 20-40 fps lower than subsequent shots. I do not like that so I turn it back up a little (like try 1/4 turn). If the hammer spring alone does not get you where you want to be you should change the regulator.
Always, always, drain the air before opening the air tube. There is a screw for draining the air on the rear end ot the air tube on the side. Turn it counter clockwise and the air will rush out. Don't take it all the way out or it could go flying and be hard to find. Just turn it a little and it will be obvious air is escaping. Next you want to use a tool that should have come with your gun which looks like a tube. It is actually a socket to fit over the pressure guage and allow you to remove a big nut on the front end of the air tube. It takes a lot of turns to remove it. They are fine threads and the threaded length is long. When you get it unthreaded it will not fall out, there are O-rings that have to be pulled past the threads. Once it is out, you can see the lock nut and straight screwdriver head of the regulator. The nut is 12mm if I remember right. You will need a long extension to get there. Once the lock nut is loose you use a long screwdriver to rotate the regulator stem. Clockwise will decrease the regulator setting (probably what you want) and counter clockwise will increase it. I would only turn it 1/2 turn or less. Then tighten the lock nut and put the big nut back in the air tube. Cock the gun and fill it.
If the regulator has been recently removed or if the lock nut is really tight you can have to go in through the back of the air tube. That requires removing the air tube from the gun. It is not hard, there are two screws with 3 mm allen heads that clamp the barrel to the air tube. Loosen them and you can untread it from the block where the valve is. Once the air tube is off, you remove the nut on the back end of the airtube. It takes a 19mm wrench. The degassing screw is in this nut. If you are lucky when you remove the back end nut the regulator might come with it. But probably you will have to push it out with a piece of pvc tuning or something else long and not so hard you risk damaging the regulator. The most challenging thing about going in this way is getting the yokes with the 3mm headed screws in the right position where the gun will cock and the safety will work. It is not really hard but it doesn't happen automatically you should check to see that it's working right before putting the stock back on.
Once you do this you will discover none of this is really that challenging. It is easier to adjust regulators with an external screw like my Avenger but it is really not that hard to do internal ones like the Bullshark/P35. I can normally change my regulator setting in 15 minutes or a bit less. I did it on my 25 caliber several times yesterday and had to go through the back end because I had just rebuilt the regulator. You can probably reuse the O-rings but spares come with the gun. But I always put a little more silicone grease on them before reassembly.
Always, always, drain the air before opening the air tube. There is a screw for draining the air on the rear end ot the air tube on the side. Turn it counter clockwise and the air will rush out. Don't take it all the way out or it could go flying and be hard to find. Just turn it a little and it will be obvious air is escaping. Next you want to use a tool that should have come with your gun which looks like a tube. It is actually a socket to fit over the pressure guage and allow you to remove a big nut on the front end of the air tube. It takes a lot of turns to remove it. They are fine threads and the threaded length is long. When you get it unthreaded it will not fall out, there are O-rings that have to be pulled past the threads. Once it is out, you can see the lock nut and straight screwdriver head of the regulator. The nut is 12mm if I remember right. You will need a long extension to get there. Once the lock nut is loose you use a long screwdriver to rotate the regulator stem. Clockwise will decrease the regulator setting (probably what you want) and counter clockwise will increase it. I would only turn it 1/2 turn or less. Then tighten the lock nut and put the big nut back in the air tube. Cock the gun and fill it.
If the regulator has been recently removed or if the lock nut is really tight you can have to go in through the back of the air tube. That requires removing the air tube from the gun. It is not hard, there are two screws with 3 mm allen heads that clamp the barrel to the air tube. Loosen them and you can untread it from the block where the valve is. Once the air tube is off, you remove the nut on the back end of the airtube. It takes a 19mm wrench. The degassing screw is in this nut. If you are lucky when you remove the back end nut the regulator might come with it. But probably you will have to push it out with a piece of pvc tuning or something else long and not so hard you risk damaging the regulator. The most challenging thing about going in this way is getting the yokes with the 3mm headed screws in the right position where the gun will cock and the safety will work. It is not really hard but it doesn't happen automatically you should check to see that it's working right before putting the stock back on.
Once you do this you will discover none of this is really that challenging. It is easier to adjust regulators with an external screw like my Avenger but it is really not that hard to do internal ones like the Bullshark/P35. I can normally change my regulator setting in 15 minutes or a bit less. I did it on my 25 caliber several times yesterday and had to go through the back end because I had just rebuilt the regulator. You can probably reuse the O-rings but spares come with the gun. But I always put a little more silicone grease on them before reassembly.
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Thank you fellow members for all of the help and suggestions. I'm really looking forward to tackling this as soon as I get a chance in the next day or two.
JimD, thank you for the very detailed post. That will take a lot of the guesswork out of fiddling with an unfamiliar gun.
JimD, thank you for the very detailed post. That will take a lot of the guesswork out of fiddling with an unfamiliar gun.
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I finally had a chance to tinker with this. Surprised how easy it was to get the results that I wanted so quickly. 3 full turns out on the hammer spring adjuster put me right at 800 fps. I ended up tuning to 850 fps with exactly 2.5 turns out. Thanks again for all of the helpful comments.
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I'm glad you were able to get a reasonable speed with only the hammer spring adjustment. If you went all the way from 1100 to 850, however the velocity of your first shot after the gun sits overnight will probably be quite a bit low. If that is OK with you that's fine. But if you want to get it up, you may have to shoot heavier pellets so you don't have to turn it down so low. H&N Baracuda Match pellets, 21 grain, shoot great in my P35 and I tested another members bullshark with a bunch of pellets and they were the best in his too. But if you want to shoot light ones you still might want to reduce the regulator setting. 5% below the peak velocity is the normal recommended tune. You are like 30% below.
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I'll be following suit as I just ordered a Bullshark in .177 with the thought of tuning to 12fpe. Seems very simple!
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My P35-177 is shooting H&N Baracuda FTs at about 880 fps. I think that's about 18 fpe. I clipped a coil on the hammer spring to get it turned down like I wanted but I could have just lengthened the recess behind the adjustment screw and accomplished the same thing (in my custom wood stock). I get about 100 shots per fill with it tuned this way. It is also quiet. I wish the pellets did not drift so bad in the wind. It's OK for backyard pesting but hitting that 10 ring on the 30 yard challenge is quite tough if there is any wind at all. Definitely a fun gun. Some have had success with knockout slugs but mine throws they out crazily.
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This has been one of my more accurate guns under 30 yards. I'm quite happy with it. I ended up adjusting the regulator down as @JimD suggested. Just an FYI for anyone attempting this. "a long screwdriver" was an understatement lol. You need to get down roughly 16" of tube to get to the adjusters. I didn't realize how deep it was until I took it all apart. Had to order some special tools to finish the job. I ordered a 24" flat screwdriver and an 18" 3/8 socket extension to get the job done. Got her all back together today. Can't wait to test it out. I ended up going about a 1/2 a turn in on the adjuster. Hoping that will get me where I wanted more efficiently. Thanks again to JimD for his detailed instructions.
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Well, I tested it, and seems that it had the opposite effect (went higher FPS). I thought for sure that I followed @JimD 's instructions and went 1/2 turn clockwise to lower the FPS, but maybe I fubbed and went CCW... Just to confirm, CW is the correct way to go on the regulator adjustment screw to lower the FPS?
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I’d suggest removing the regulator from the cylinder to make the adjustments, it’s the only method I’ve ever used. The P35/Bullshark uses the same regulator as the Notos just for additional information. I learned along the way to measure the exposed screw with calipers to know where I’m at. I think I saw Sub12 doing that. Take some shots and let it settle. If the reg is original I highly suggest careful disassembly of the regulator and everything in the cylinder being cleaned and lubricated with quality silicon grease.
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Yes Clockwise to lower.
Got a .25 Bullshark, and got my regulator out of whack attempting from front of tube. Reg adjustment screw kept moving when tightening back down lock nut. Ended having no clue where it was set. And since I didn't remove it and measure in the beginning, as was just mentioned above, I had no idea of where to set it back to. And o-rings didn't hold up to repeatedly removing and trying to guess it back right. Hopefully not scaring you with all that.
I just went ahead and got the Huma power tune regulator w/extra large plenum, and the regulator tester. Would have gotten the tester adapter for the Stoeger regulator because I believe it can be set higher than the Huma, but those are out of stock.
I'm still learning so not nearly as knowable like JD. Hopefully he can guide you in what to do next.
Think it sounds like you're hammer spring is now over powering the reg setting. But I'm not one that can explain it.
Hopefully haven't scared you.
The Huma Regulator has a taped on setting guide and an indicator line on the side of the set screw. I used an engraving tool to transfer those marks to upper surfaces of regulator then dabbed a little orange paint into those lines. Now I can look down the air tube at my lines if I need to adjust without pulling it. Plus have the initial measurements and reg tester if needed.
Sorry such a long reply.
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I'm struggling to find any info on how to remove it from the back. Would you happen to have any more info on this?
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I have done regulator adjustments from both ends but lately I've just been doing it from the back like Florida_Man. Doing it from the fill port end of the airtube doesn't work if the regulator has been out recently or if the lock nut is pretty tight. You are depending on the O-rings to be stuck enough for you to get the lock nut loose. That would not appear to be what happened to roaoro but is it possible you did not get the lock nut loose so you just rotated the regulator with the screwdriver (I've done it)? In any event doing it from the rear on a Bullshark is not clearly a lot more work, depends on how good you are with a 18 inch screwdriver. After degassing the gun, I just loosen the two 3mm allen head screws on the clamping mechanism and unscrew the airtube from the action. Then take off the back nut on the airtube and if you are lucky the regulator comes with it. If not, you have to take off the nut on the other end of the airtube and use your 18 inch extension to push the regulator out. Taking the airtube off does make it necessary to get the clamping mechanism reclamped in the same spot but leaving the action in the stock (with the stock nuts loosened a bit) can help them not shift. Another helpful step for getting the clamping mechanism right is to have the safety on. That limits how far the mechanism can slide. I find having there be a little clearance between the safety button and the trigger guard is about right. I check to be sure it will cock, release the sear, and not release the sear with the safety on. There are positions where any of these will not be true.
Half a turn on the adjustment screw is a lot. I've done it but I've gotten my regulator messed up doing it too. I would try 1/4 turn. If you google up a picture of the Huma you can see the marks on the paper tape are a fraction of a turn apart. The SPA regulator is not identical but it's similar. It doesn't take much of a turn to make a meaningful change.
An advantage of taking the regulator out is you can more carefully control your adjustments. I've started measuring the total length of the regulator with my digital calipers. Lengths around 50.5mm seem to work. I measured the regulator of my P35-22 at 50.57 inches and then shot it down. I think it came off reg about 140 bar but it is a little unclear because the velocity started to modestly climb, not go down. I think the hammer spring might be a tad light for the regulator. It is not a terrible way to have it, however, since I was still getting very usable shots at 130 bar but it was going down at that point. The velocity peaked about 15fps faster than it had been. A full turn of the regulator screw will change it's length by 0.5mm.
Half a turn on the adjustment screw is a lot. I've done it but I've gotten my regulator messed up doing it too. I would try 1/4 turn. If you google up a picture of the Huma you can see the marks on the paper tape are a fraction of a turn apart. The SPA regulator is not identical but it's similar. It doesn't take much of a turn to make a meaningful change.
An advantage of taking the regulator out is you can more carefully control your adjustments. I've started measuring the total length of the regulator with my digital calipers. Lengths around 50.5mm seem to work. I measured the regulator of my P35-22 at 50.57 inches and then shot it down. I think it came off reg about 140 bar but it is a little unclear because the velocity started to modestly climb, not go down. I think the hammer spring might be a tad light for the regulator. It is not a terrible way to have it, however, since I was still getting very usable shots at 130 bar but it was going down at that point. The velocity peaked about 15fps faster than it had been. A full turn of the regulator screw will change it's length by 0.5mm.
Here's a link to some Stoeger's YT videos on the Bullshark disassemble and reassembly. This is actually my play list.
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