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.
