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Efficiency in terms of shots/bar

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In a roundabout way I would think most tuning is about getting the most power for the least amount of air. 

Unfortunately there is no way to do an apples to apples comparison unless it is between two of the exact same airguns. With different valve, regulators, plenum spaces, air storage space there are too many variables to make a valid comparison. 
 
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Yes, it’s very common to run the efficiency numbers. For me, it’s just a way to recognize if things are working about like I expected but I don’t get too fixated on it. That is to say, chasing ever higher efficiency can lead to poor outcomes in other areas so I’m generally more interested in good efficiency than amazing efficiency.

Regarding a lightweight hammer, the improvement in efficiency or shot count will usually be somewhat modest unless there was previously a lot of air-wasting hammer bounce that it happens to remedy. 

All things being equal, it will require more hammer spring tension to make up for the loss of mass, in order to develop the necessary valve lift and dwell. So a lightweight hammer works best when paired with a poppet made from a material like PEEK that is easy to knock free from the valve seat. Many times that will offset the increase in hammer spring tension that would have otherwise been required. For the same reason, I like to also alter the hammer’s dimensions to give more stroke when possible.

Altogether it brings a number of benefits:

1. Faster hammer acceleration which improves lock time.
2. A more pleasant shot cycle, not just in a subjective sense but in terms of less recoil and easier follow through.
3. Shorter valve dwell for improved air usage and softer report.

For a gun with which you are well acquainted, this type of conversion can completely transform its character in a positive way.
 
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As usual, n-n-nervoustrig does an excellent job of explaining in succinct detail. Good show, nt.

A couple times I have had good results reducing hammer-bounce with the 'B Staley tune' trick of installing o-rings in the tube between the hammer and valve, in order to cushion and absorb hammer energy as it rebounds from the initial hammer-strike. That trick usually costs a bit of velocity, but returns exponential gains in efficiency/shot-count. Example-

1701 New.1622141801.JPG


Crosman 1701P, 10.3 Exact, 2800 PSI, .075” transfer port, 15 shot bell-curve powerband- Low= 684, Hi= 709, ES= 25, SD= 8, Average= 699 FPS/11.2 Foot Pounds

After doing a B-Staley tune*-

Crosman 1701P, 10.3 Exact, 2600 PSI, .075” transfer port, 22 shot bell-curve powerband- Low= 641, Hi= 670,ES= 29, SD= 2.5, Average= 657 FPS/9.9 Foot Pounds

*The B Staley tune improved shot-count by 47% at the expense of 12% muzzle energy, and reduced velocity Standard Deviation to 31% of pre-tune SD (from 8 FPS SD to 2.5).

The wonderful Crosman 1701P is surely the most easily souped-up airgun to return the most dramatic power increases ever. It took me about 15 minutes to remove, drill out, and reinstall the transfer port. That simple modification increased muzzle energy over the stock transfer-port by a WHOPPING 300% (from 3.7 foot-pounds to 11.2 FP)! And whether in box-stock, mild-mannered target gun form or souped-up into a equally mild-mannered magnum, the 1701P shoots rings around anything anywhere near its price-range.

1/5/2020- Three consecutive five-shot groups at 25 yards with 10.3 grain JSBs averaged .33” center-to-center; six consecutive groups averaged .40” c-t-c.

  




 
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Nicely done! My 1720T will most likely benefit from a similar tune too.

Nervoustrig, I set my dreamline for HFT by changing caliber to .177 (from .22) and tuning dowm to 19fpe. I believe the hammer weight used in old .22 dreamline is heavier from the current .177 ver. At my tune the hammer spring adjuster nut is all the way back out. With a lighter hammer weight, I will be able to increase the spring tension yet still use less air and improve pellet stability (not too bad with present setup but 1 in 15 shots seems to get affected by too much air from valve). Should recieve the lighter weight in a week or so to test out theory.
 
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Soloshot, I just wanted to clarify that as I have been speaking of a lightweight hammer, my mind has been on changing from a steel hammer to a plastic one, either MDS nylon or PEEK. A weight reduction of perhaps as much as 80%. Granted I haven’t done this conversion on a Dreamline so it may be that the parts are not conducive to it, but generally speaking I expect it to be feasible with almost any small caliber pellet shooter up to at least 40-50fpe. All the better on a 20fpe rig. If you have the means to try it, I highly recommend it. Honestly I was unable to appreciate it until I tried it and now I’m spoiled.
 
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Update: Recieved the .177 hammer weight from FX and it is significantly lighter than the .22 hammer weight I was running. So long story short, after running the tuning/accuracy gamut, 100bar reg with finely tuned hammer spring yielding consistent 925fps using 10.3g FX pellets at 60+ shots per fill. The groups are TIGHT and flyers are history. I am DONE tinkering with this rifle :)
 
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Update: Recieved the .177 hammer weight from FX and it is significantly lighter than the .22 hammer weight I was running. So long story short, after running the tuning/accuracy gamut, 100bar reg with finely tuned hammer spring yielding consistent 925fps using 10.3g FX pellets at 60+ shots per fill. The groups are TIGHT and flyers are history. I am DONE tinkering with this rifle :)
Click to expand...


How many shots per fill were you getting prior? 

Or to be brief, what was the gain in efficiency, either thermally or volumetrically?
 
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Update: Recieved the .177 hammer weight from FX and it is significantly lighter than the .22 hammer weight I was running. So long story short, after running the tuning/accuracy gamut, 100bar reg with finely tuned hammer spring yielding consistent 925fps using 10.3g FX pellets at 60+ shots per fill. The groups are TIGHT and flyers are history. I am DONE tinkering with this rifle :)
Click to expand...


How many shots per fill were you getting prior? 

Or to be brief, what was the gain in efficiency, either thermally or volumetrically?
Click to expand...

Based on his original post he should have been getting 70 shots at 915. He indicated he was using 2 bar per shot. 230 bar fill and 90 bar reg leaves 140 bar. 140/2=70

If he (after tune) got 64 shots (at 925 as opposed to 915) he broke even. If he got 63 or less his efficiency is lower, if he got 65 or more his efficiency slightly went up.

Based on the 210cc of air, 230bar fill, 90bar reg, 10.3 g at 915 for 915fps = .75 fpe/cuin

If he is now using a 100bar reg and shooting at 925fps for 64 shots then his efficiency is still .75 fpe/cuin

If 60plus=69 then is efficiency is now .81 fpe/cuin. If 60 plus = 61 shots then it is just .72 fpe/cuin

While it looks like his efficiency has basically stayed the same, a decrease in group size is a win.
 
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Shots per fill or shots per bar are only relevant when comparing two identical guns. However, if you calculate FPE/cuin you can compare your efficiency between any guns. The easiest way is to use the online calculator.

http://www.calc.sikes.us/1/

Many variables affect efficiency as noted by NT above. When I tuned my .30 Vulcan2 by adding a plenum and various other mods I got the efficiency to go from stock at about 0.95 to about 1.50. Granted, the stock tune was horrible, but the 1.5 number is about what a well tuned .30 Impact with PP will do. 
 
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Update: Recieved the .177 hammer weight from FX and it is significantly lighter than the .22 hammer weight I was running. So long story short, after running the tuning/accuracy gamut, 100bar reg with finely tuned hammer spring yielding consistent 925fps using 10.3g FX pellets at 60+ shots per fill. The groups are TIGHT and flyers are history. I am DONE tinkering with this rifle :)
Click to expand...


How many shots per fill were you getting prior? 

Or to be brief, what was the gain in efficiency, either thermally or volumetrically?
Click to expand...

Based on his original post he should have been getting 70 shots at 915. He indicated he was using 2 bar per shot. 230 bar fill and 90 bar reg leaves 140 bar. 140/2=70

If he (after tune) got 64 shots (at 925 as opposed to 915) he broke even. If he got 63 or less his efficiency is lower, if he got 65 or more his efficiency slightly went up.

Based on the 210cc of air, 230bar fill, 90bar reg, 10.3 g at 915 for 915fps = .75 fpe/cuin

If he is now using a 100bar reg and shooting at 925fps for 64 shots then his efficiency is still .75 fpe/cuin

If 60plus=69 then is efficiency is now .81 fpe/cuin. If 60 plus = 61 shots then it is just .72 fpe/cuin

While it looks like his efficiency has basically stayed the same, a decrease in group size is a win.
Click to expand...



Thanks for doing the math, although that is also assuming 2 bar per shot which seem fairly rounded off, which is why I didn't heed that path.



Seems to me dwell is in excess and could use refinement if the efficiency is in fact between .72 and .81 fpe/ci, but if the shooter is happy and so are the groups, let 'em rip!
 
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