Benjamin Bulldog: Regulated or Unregulated? Can it be a cheap Bobcat?

Forums PCP Airguns Benjamin Bulldog: Regulated or Unregulated? Can it be a cheap Bobcat?

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    davidsng
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    Here is my final product of my Bulldog.  After 5000 rounds, lots of $, hours spent researching, buying parts; I final have exactly the perfect combination to fit my needs of a big bore.  Here is my informative report.

    This spring I decided to buy my first bigbore. I originally wanted a .30 Bobcat MKI, but could not force myself to drop $1800 and tried to find a cheaper alternative.  When I found the the BD for $537 at grabagun.com, I was determined to make it into a “budget Bobcat clone”.  Which, if done again, I could have done for less than $400 and saved almost a grand! Listen up.

    First problem was the sound. Way too loud! Easy fix- bought a Pittbull Moderator ($100).  Second, was the horrible shot curve.  It went straight down (no curve what so ever).  Just to see how regulation improve this, I bought $45 tank with a paintball 1800 psi regulator with a 4500psi fuse.  I quickly realized that a lot of the reason my groups were wide was because the ammo was all traveling at different speeds, acting different at every shot, and ultimately shifting POI throughout the shot string.  This solved that prob.

    Last problem, and most diffIcult to solve was the accuracy.  When I started, I was getting 5-6″, 5 shot groups at 50 yards! (See below) Horrible, but it was fixed, ultimately down to a consistent inch and a half at 50 yards and a consistent 2.5 at 100.


    First thing to do to get better accuracy was find the correct ammo.  JSB 81.02 stood out from all the others. The problem with the JSB’S was only good at lower power.  One of the Bulldog’s selling points was the 200 ft/lbs.  When the Bulldog fired these at full power, they became inaccurate. 830fPS to 900 fps seem the best speeds.  So then I decided to make two tubes (reservoirs), one regulated (for JSB accuracy), one unregulated (for big game and 125-165grain slugs)and interchange them when needed.

    This was when I fell into a big problems. I bought several different internal regulators, tubes, but they never seemed to work correctly. I always had leaks into the plenum and/or the atmospheric venting hole.  If the gun sat for long periods it would either drain air, or plenum presure would build and shot speed would be different. I even took my Gladius reg (that i knew work correctly) and constructed a way to test it in my BD, but it still did not work.  So, I gave up and fiddled with a unregulated BD. 

    I found machinist who made a large 510cc tube and results were great!  The shot curve was flattened out on the chrono, but back on the range, I ran into a huge problem.  The pressure from the long tube against the Pittbull Long moderator, threw my shot accuracy off. So, I shortened it to the end of the gun (465cc, approx).  That is the graph below.  I filled my BD to 3200-3300psi, loosened hammer a little, and found a nice curve(in blue), about 10 shots with a nice 30 fps spread, with peak at the fourth or fifth short.  The red is my regulated 360cc tank attached, with approx 16-18 shots with a 12fps spread.  I noticed there is NOT any noticable difference in shot POI out to 75 yards. If I ever needed to blast targets past 75 yards, I can quickly attach my external tank. If I ever needed to blast large game, I can quickly detach the bottle, turn the hammer spring, insert a heavy accurate round and go.


    In conclusion, the best priced combination for turning Bulldog from a “Good” gun to a “Great” gun for is to quiet it ($100), exterally regulated it ($45), buy extra support for the barrel ($25), larger reservoir ($150), buy an inverted bipod to absorb the bigbore jump ($100), polish the barrel keep it clean ($3), and expect 85% of a Bobcat for $1000 less.

    Feel free to ask questions.

     

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    Imold
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    Thanks for the info,gives me something to think about with my stock BullDog although I have shot it tetherd up to my 74cf tank with my regulator set up,

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    davidsng
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    You welcome.  Being tethered to a big tank is great for the Bench, but hunting is impossible.  The external tank still sucks to carry, but still is in the realm of being possibe.  It firmly attaches to the gun and feels and looks as if it could be part of it. 

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    davidsng
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    If you want any parts to mod yours, let me know.  I got two regs, tubes, spacers, few supports, custom end caps with male fosters…ect. I won’t be needing them.

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    Kev
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    It’s interesting as to how inconsistent Bulldogs seem to shoot. I was lucky with mine and was shooting sub inch 50 yard groups out of the box.  I was casting .357 revolver bullets from a 1950s Ideal mold out of pure lead that produced a 165g bullet. It shot it like it was on a rail producing 200 fpe. It seems you have taken the Bulldog to a different level,however. 

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    Imold
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    “davidsng”You welcome.  Being tethered to a big tank is great for the Bench, but hunting is impossible.  The external tank still sucks to carry, but still is in the realm of being possibe.  It firmly attaches to the gun and feels and looks as if it could be part of it. 

    
Fortunately Bench is the only thing my BullDog will see well ok maybe the inside of my deer stand Maybe…..But these things are good to know just in case a guy might want to change things up a bit.
    edit reason……….I should add that my BullDog grouped ok at 50 yards but I didn’t get really technical with zeroing it in and I could still hit the 6″ plate,at 75 yard without a problem but never tried 100 yards and I was using JSB 81,02s.

    Thanks again.

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    davidsng
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    Y e a, I had difficulty figuring out how to make it accurate, but it can be fixed.  It seems to me that the plastic stock may have something to do with it.  Make sure all screws are really tight.  It seemed to me that if it had any wobble, groups really spread.

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    c.schulz
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    Dave thanks very much for doing all this work. What a learning curve and good info for us BD owners. Cant wait to start trying some of these mods. 

    Chris

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    tutuan
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    @davidsng, thank you for sharing your experience. Wow that’s a lot of tinkering and swapping parts to fine tune the bulldog. Did you consider the regulated airtube from Crosman Airbow?

     

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    davidsng
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    “tutuan”@davidsng, thank you for sharing your experience. Wow that’s a lot of tinkering and swapping parts to fine tune the bulldog. Did you consider the regulated airtube from Crosman Airbow?

     

    Yes, I attempted to swap an air tube with the Pioneer Airbow, but the part the connects the airbow reservoir to the receiver is different than it is to the Bulldog.  I could not find a part so, then I decided to make a whole new (larger) tube that extended to the end of the rifle.  That messed up my accuracy, so I shortened it back the size of the Pioneer’s.  If I had to do it again, I would have just bought a complete airbow reservoir + regulator, then had a machinist construct an adaptor. It would have been way cheaper.

     

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    tutuan
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    If I had to do it again, I would have just bought a complete airbow reservoir + regulator, then had a machinist construct an adaptor. It would have been way cheaper.

    
 I think  I will take that route.  Thanks.

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    davidsng
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    I’ve had some question were to find this bipod.  This bipod seems to work perfect with the Bulldog, as if it was designed just for it in my opinion.  By having a bipod attached to top of the gun, it reduces the vertical jump of the Bulldog and turns it into horizontal jump back.  This has clearly improve my accuracy. Here is the linkhttps://www.begadi.com/otto-repa-omr-zweibein-helios-verstellbar-schwarz.html?___ 

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    MartMan
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    Hello,

    I Have the bulldog and looking to use it for FL.Whitetail. I have some 2" groups with NSA 126 at 50 yards, So far., going 75 yards next.

    Was wondering what you thought about the Moderator and your experiences hunting.

     

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    legionair
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    davidsng

    Y e a, I had difficulty figuring out how to make it accurate, but it can be fixed.  It seems to me that the plastic stock may have something to do with it.  Make sure all screws are really tight.  It seemed to me that if it had any wobble, groups really spread.

    I agree with you that the plastic stock has something to do with it. 200+fpe vibrating into that flimsy (ABS?) plastic. Perhaps if the plastic was the ballistic type that’s outfitted on the hw 110 st, it might be better for the barrel harmonics. I personally prefer a wood stock and am shocked that with all the tinkering and modifying in the AG community, I have yet to see a custom wood stock for the BD

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    MartMan
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    I just saw that Jefferson State offers a Balanced SS valve for the Bulldog with some impressive specs, Anybody here use this set up, is it worth the $$, and where can I find some installation info,

    Thanks!

    MartMan

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