.357 Big Bore MSP Near Completion!

[Duane38]

Mandrel...

[Rob M]

nice , very curious what the extra length will offer./ that bulldog barrel must be quite heavy ( you mentioned the new gauge , any news on actual pressure ?

[Duane38]

Yeah. Me too.  There is certainly a significant air blast beyond the current barrel muzzle.

The current barrel is 20" at .68". I do have a scale and will check the weights.  Good thought. 

I still need to add the gauge.  I can feel the efficiency in the pump handle.  If one could say that.  When pulling the handle back for the next stroke, the back pressure is almost non existent, more a vacuum when pulling the piston away from the valve. 

[Duane38]

Bulldog barrel: 28.1 oz
Current barrel: 22.4 oz

[Duane38]

Got the Bulldog barrel on!  Shot some strings.  There are gains, but nothing super high. Three shots per string, then averaged. 

Picked up a UTG 3-9x32 AO and illuminated to slap on when ready.  The glass is actually crystal clear. 

10 pumps, average of 458fps
15 pumps, average of 511fps
20 pumps, average of 628fps
25 pumps max, average of 709fps

[subscriber]

Philip,

What projectile did you use?  A pellet or slug?  How tight a fit, if a slug? 

What does the chamber look like?  It may benefit from a more gradual leade.

The whole bore may benefit from being lapped or polished.

Does the barrel have a choke?

Sorry for the inquisition.   The point of the questions is to stimulate your thinking.  Consider the questions rhetorical.

Considering the small air volume of compressed air, adding a few inches to the muzzle won't bring dramatic gains because the air pressure near the muzzle is not very high.  If you made the valve body volume larger you could get more power, but you would always need more pump strokes to get the pressure up.   If you made the body much larger and used this as an air conserving pumper, rather than a dump valve, you could get a lot of efficiency back.

[Duane38]

Philip,

What projectile did you use?  A pellet or slug?  How tight a fit, if a slug? 

What does the chamber look like?  It may benefit from a more gradual leade.

The whole bore may benefit from being lapped or polished.

Does the barrel have a choke?

Sorry for the inquisition.   The point of the questions is to stimulate your thinking.  Consider the questions rhetorical.

Considering the small air volume of compressed air, adding a few inches to the muzzle won't bring dramatic gains because the air pressure near the muzzle is not very high.  If you made the valve body volume larger you could get more power, but you would always need more pump strokes to get the pressure up.   If you made the body much larger and used this as an air conserving pumper, rather than a dump valve, you could get a lot of efficiency back.

82 grain JSB pellet was used.

The chamber I do believe has a very nice leade.  The pellet loads fully into the lands.  The hollow probe is long enough to seat all projectiles far enough. 

The bore appears to be polished.  It has a glassy reflection. 

Choke?  Probably not.  Whatever the Benjamin Bulldog claims to have.

With the valve volume of .65cu.in @ 2500psi, say, the 20 inch barrel has 600+psi at the muzzle. 

This project was intended to be an air conserving design with 1.5cu.in chamber and a foster fill nipple to pre-charge with a pump.  However, the spring needed to pop the valve was silly stiff.  Though, in hindsight, a balanced valve would solve that. 

I may play around with valve ideas for this to make an air conserving pumper.  As it sits now, I'm okay with it being a 90ft/lb pumper. 

Gonna explode some rats with it.  Heck, even with just 10 pumps, it's a monster. 

[subscriber]

Philip,

It sounds like you could make that barrel even longer, if you have 600 PSI at the muzzle now.

Pellets and a shiny bore with a gentle lead sounds like a recipe for good power.

[Rob M]

Awesome results Phil, not too many 91 fpe pumpers out there ! Whats your current porting ( throat , tp)

[JuryRigger]

Not bad at all 
Excellent work!
Jesse

[WyoMan]

Hi Phil,
You may remember me when airgun modders were exploring the limits of msp's on the old green.
I think you've got the record with 91 fpe. Well done.
Your valve volume of .65 vs bore volume of 2.0 suggests that a longer barrel will help (although you're in the sweet spot for the lower pumps), so I think you're on the right track to maximize fpe.
Keep on keeping on... it's nice to discover what is possible -

Wyo

[Duane38]

Hi Phil,
You may remember me when airgun modders were exploring the limits of msp's on the old green.
I think you've got the record with 91 fpe. Well done.
Your valve volume of .65 vs bore volume of 2.0 suggests that a longer barrel will help (although you're in the sweet spot for the lower pumps), so I think you're on the right track to maximize fpe.
Keep on keeping on... it's nice to discover what is possible -

Wyo

Hey, Wyo.  Of course I remember!  Nice to hear from the old crew. 

The original 20 inch barrel is right on 2cu.in.  As of last night, it has been fitted with a Bulldog barrel that's 28 inches long: 2.8cu.in

That would suggest if the valve is at 2500 psi, the muzzle pressure is still 500 psi or so!  Can't imagine going longer!  LOL.  So, one could assume that a smaller valve would suffice in use with a shorter barrel.  I'm thinking a pumper pistol project too....  Have enough pieces parts and stock in the bins...