Benjamin Bulldog Tuning Help

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I just did a bit of work on my Bulldog and here is the 10 shot sting using 81.02 JSB .35 cal. Chronograph was measuring at the muzzel. I opened up the transfer port and valve to .281. I tightened the Hammer Spring 2.5 turns from stock. Everything else is stock. I've never shot big bores and I'm curious as to what a decent shot string looks like. This string would be unacceptable in my .22-.25 guns, but this gun may be different. Can anyone with more experience with big bores give me advice on how to better this tune? Groups are acceptable at .75" at 50 yards.

1. 968 (3000 psi)

2. 950

3. 1030 (2800 psi)

4. 1042

5. 1033

6. 1024

7. 1012

8. 984

9. 939

10. 938 (2000 psi)

Average: 992

Min: 938

Max: 1042

ES: 104
 
Adam 

I've found in my bulldog a 2900psi fill does better as you can see your fps was better at 2800 your porting at .281 is right in the ball park by everything I've read I have my hammer adjusted to 1 turn ccw from max but I'm shooting 128, 130 and 148 grain HP's, I'm sure some other fellas who have more experience than I will chime, triggertreat and tkerrigan where are you :)
 
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View attachment 1593885183_12727453035f00c1ff59bba0.62878323.PDF

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View attachment 1593885206_1699743715f00c2166681d4.15531011.PDF

The valve spring is item 15 on the second page. As you can see, it blocks a lot of air. Just don't shoot it down too far or you will have to disassemble to put the poppet back in as it will get blown into the air tube I think. Regards, Tom
 
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 with the oem poppet you can remove the valve spring without worry, other than the obvious challenges associated with filling from empty. The poppet will not fall into the tube as it is held captive by the tube adapter. If you want a pellet shooter, I see no value in removing the valve spring to improve airflow--the BD has more than enough airflow for a pellet shooter. If your goal is a pellet shooter and you want to make the valve easier to open, leave the valve spring. Reduce the OD of the OEM poppet. It is grossly oversized, thus far more difficult to open than it needs to be. Reducing the poppet OD is an often overlooked variable in tuning the Bulldog.

You really have to decide what your intention is with your Bulldog. If you want to shoot short, light projectiles such as JSB pellets, you will want to shoot them much slower than you are right now with your .281 porting. Your .281 porting is good for 250fpe slug shooting with 3 or so shots on a fill, not so good for a light, short bullet shooter and the BD's relatively fast rate of twist.. If you want a good 10-15 shots of 81gr pellets, you will find better results when strangling the transfer down at .200 or even smaller.

As you likely learned with your .22 and .25's, especially when unregulated, the same tune isn't going to work well across a broad range of projectile weights. simply dialing HST in or out will be a compromise in performance at one end or both ends of your projectile weight range.....

Good luck with your Bulldog, IMO it is one of the best designs ever produced by Crosman. Too bad they didn't make a rifle out of the BD action......
 
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