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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