Calculating TP Size

[FuzzyGrub]

I'm working on detuning my bulldog for pellet use only.   I'm getting 150FPE at the peak of the curve, and want to detune to 135FPE at peak.   That is 90% of peak or a 10% reduction.  Is it valid to reduce the area of the ID of the TP the equivalent percentage?   As an example, assuming the ID of oem is 0.250" I get 0.237".   

[Dairyboy]

I would think so but then again I'm no expert. But I've tried a bunch of different TPs in .25 and .22 Mrods and think your assumptions sound right

[oldpro]

I'm working on detuning my bulldog for pellet use only.   I'm getting 150FPE at the peak of the curve, and want to detune to 135FPE at peak.   That is 90% of peak or a 10% reduction.  Is it valid to reduce the area of the ID of the TP the equivalent percentage?   As an example, assuming the ID of oem is 0.250" I get 0.237".   

I would leave the TP alone and use a shorter spring thats stiff and add some free flight into the mix. This will reduce dwell and lower your FPE output. You should see a gain in FPE/Ci per shot and thus more shots fuzzy. Maybe SHORTY could make you up a twin wound spring for this. This would be a perfect place for one of SHORTYS springs as the side lever will remove almost all the cocking effort and you can benefit from the SSS. JMHO

[ackuric]

-Reduce TP (I observed around 10-15 fps gains in my .25 marauder for every .1 in porting, obviously yours will be different)
-Reduce Hammer Spring by 1-3 lbs per inch?
-Reduce Hammer travel

The downside to going to a short stiff spring is you're trying to lose fps, not gain, so idk how that will benefit the fps reduction as that is more along the lines for efficiency IMO, but still a great suggestion IF you rate your spring lower than your current spring.

The TP sizing may be a challenge to get right, probably should use a combination of tp reduction + hammer spring adjustment...

I think your guesstimation on the tp port reduction is probably spot on for your bulldog, I bet that would do the trick as tp reduction itself reduces dwell.

[FuzzyGrub]

I'm working on detuning my bulldog for pellet use only.   I'm getting 150FPE at the peak of the curve, and want to detune to 135FPE at peak.   That is 90% of peak or a 10% reduction.  Is it valid to reduce the area of the ID of the TP the equivalent percentage?   As an example, assuming the ID of oem is 0.250" I get 0.237".   

I would leave the TP alone and use a shorter spring thats stiff and add some free flight into the mix. This will reduce dwell and lower your FPE output. You should see a gain in FPE/Ci per shot and thus more shots fuzzy. Maybe SHORTY could make you up a twin wound spring for this. This would be a perfect place for one of SHORTYS springs as the side lever will remove almost all the cocking effort and you can benefit from the SSS. JMHO

Travis,  that is exactly what I'm trying first!     The extra springs came from crosman today (that I can shorten), and others from MC will be here tomorrow.  So, I'm playing with more a TSS than a SSS, but trying to accomplish same.

I posted the question, in case the overall peak wasn't lowered enough.

FWIW: the ID of the bulldog TP sleeve is 0.195"   OD is 0.300" and 0.5" long.

[Dairyboy]

If the TP is only .195 ID on a .357 I wouldn't mess with it and would do as Travis said. I say get Rocker1 to make an MDS hammer for it with the dual spring and you got a winner!! sorry not trying to make you busier than you are David 

[ackuric]

Yea that TP is small, going by your assumed #'s it would of been a decent idea to reduce TP but with a .195"...I would go to Ace hardware with your spring and look for a slightly shorter stronger one in similar dimension if possible for a buck, or do as others have mentioned.

[FuzzyGrub]

The oem is a pretty hefty spring, and at my baseline tune of 6.5T out, still has about 1/2" of preload.  Stock is 4.5T out, which gives max power for the first 5 shots.   I used a 12 and 14lb rate springs in parallel (26lb), with zero preload and only got 450 fps.  Cocking distance is 0.9" from poppet stem contact to sear engaged.  The heaviest two springs I have to test is the oem with an inner one from MC that is 15.7lb rate.  If that doesn't do it, will need to go to three springs. 

I haven't had the hammer out yet, but it is smaller OD than a Mrod one, and suspect it weighs less. 

[oldpro]

The oem is a pretty hefty spring, and at my baseline tune of 6.5T out, still has about 1/2" of preload.  Stock is 4.5T out, which gives max power for the first 5 shots.   I used a 12 and 14lb rate springs in parallel (26lb), with zero preload and only got 450 fps.  Cocking distance is 0.9" from poppet stem contact to sear engaged.  The heaviest two springs I have to test is the oem with an inner one from MC that is 15.7lb rate.  If that doesn't do it, will need to go to three springs. 

I haven't had the hammer out yet, but it is smaller OD than a Mrod one, and suspect it weighs less.

The hammer is super light and doesnt need any lightning or modding.  Serioiusly Id OPEN the TP up to .250 and TSS or SSS it and run a short dwell. This should be a good baseline for others Fuzzy and Im glad your doing it. This should also increase accuracy from recoil and extend shot count by a good margin. Anything  I can do just call ok.

[ackuric]

Travis has some good input, likely better than what I'd give! But I'd tread lightly going that high of a port unregulated...


a .357 with a 28" barrel...hmm. The numbers I run say....you're running very near your *Ideal* max FPS if shooting 145 grain @ 150 FPE @ .195" ports, where absolute max would be closer to 200 fpe.

You want 125 FPE? Reduce the tp to .165"-.17" would be a huge help, that itself will reduce dwell and limit air flow all in one go!

That barrel length could make use of a snappy short dwell with huge ports but that would really require LOTS of work on your part which I do not oppose, just be mindful of the work involved, as it would be a cool project but would likely require valve throat/exit port / barrel work ect, and at that point it would benefit immensely from being regulated...

a .25" port is good for 155-160 FPE @ 2k psi with a 28" barrel and .357 cal/145 grain! D:

unregulated a .25 port would be good for 200-250 fpe max with the 145 grain D:

Travis's thoughts on really big ports + short dwell did not work on my setup/marauder as I went to .205" ports even when shooting at 20-30 fpe my FPE/CI was atrocious, no amount of spring adjustment corrected FPE until I reduced my TP. I would go in depth into my thoughts why but they've been covered elsewhere. GL though!

[FuzzyGrub]

The oem is a pretty hefty spring, and at my baseline tune of 6.5T out, still has about 1/2" of preload.  Stock is 4.5T out, which gives max power for the first 5 shots.   I used a 12 and 14lb rate springs in parallel (26lb), with zero preload and only got 450 fps.  Cocking distance is 0.9" from poppet stem contact to sear engaged.  The heaviest two springs I have to test is the oem with an inner one from MC that is 15.7lb rate.  If that doesn't do it, will need to go to three springs. 

I haven't had the hammer out yet, but it is smaller OD than a Mrod one, and suspect it weighs less.

The hammer is super light and doesnt need any lightning or modding.  Serioiusly Id OPEN the TP up to .250 and TSS or SSS it and run a short dwell. This should be a good baseline for others Fuzzy and Im glad your doing it. This should also increase accuracy from recoil and extend shot count by a good margin. Anything  I can do just call ok.

Thx Travis.  As I get into the internals, indeed may need some guidance/help.  I know you worked extensively on one when they first came out.    Thx.

[FuzzyGrub]

This was kind of a sidebar discussion, and the main thread is here: http://www.gatewaytoairguns.org/GTA/index.php?topic=126825.0 
I welcome all to add/contribute there.