Hammer springs- 2 different approaches. Got Power?

[Bill G]

Good call on the case hard hammer.  I hadn't thought of that due to the stroke adjuster being the point of contact. Either way case hardening would make all of those parts more survivable for the job.  If I can get on the sinker I have no problems. In fact, I cando all the holes at once.  If not, carbide will have to do it.  I can use the cnc lathes with really light cuts.  I figure I will turn and ream the hole of the inlet end first, then press it on to the stem.  Then contour the profile with very light, high speed cuts, to get the bullet nose for the plenum end.   

[Bill G]

Those results, plainly said, are awesome! 

[rsterne]

as the power in the string increased, generally, so did the efficiency.

That's pretty much the norm, in fact I don't ever remember the efficiency increasing as the pressure dropped in a string.... When you compare the SETS of 51.7 gr. bullets, however, the efficiency is higher for the lower powered sets, again as expected.... The 82.7 gr. (double bullet) set is more efficient, again as you would expect....

Those are excellent results.... My choice for the 51.7 gr. bullet would be about 1 turn from coil bind with the 60 gr. hammer (ie just backed off slightly from set #31).... or the equivalent hammer strike using the 100 gr. hammer (ie about 2 turns out).... Alternately, you could use set #30 and fill to ~2600 psi and get 6 good shots (within 4%) averaging ~83 FPE, refilling at ~1800.... You certainly have breathed some fire into that .25 cal, Lloyd.... Congratulations....

Bob

[melloroadman]

I agree with you Bob.  950fps is a solid max velocity target.  If one needs or wants more energy, increase mass and maintain velocity.  When it comes to taking game, if you are going subsonic, heavy and slow will out penetrate light and fast.  Hunting with an airgun is about shot placement and punching holes in vitals.  Supersonic is cool for the sake of study but impractical when applied to airguns. 

Lloyd,  thinking back on the subject of your poppet angles and engagement with the inlet.  what do you think the success of sealing would be with a radius into a tapper.  I'm going to make a new poppet for my Marauder and can't easily or accurately measure the lead in angle of the inlet.  I intend on giving it a bullet point leading end.  I have been thinking about the the benefit of a radius transitioning into a shallow tapper, similar to a boat tail bullet, visually.  I will be reassembling the Marauder in the morning testing it to see what kind of performance I'll get. With the increased port diameter along with the removed valve spring and much more open plenum, I expect to get maybe 100fps increase.  That's what I am estimating with my sheet.  If the results are as priedicted I think I will also drill some small holes longitudinally in the hammer.  Two points of reason here.
1.  Reduce compression between the hammer and valve.  I'm thinking this will allow full use of the hammer momentum.  It would seem to me that some of the momentum is absorbed by this possible compression.
2.  lighten the hammer to reduce the momentum thus allowing quicker reaction of the valve.  I'm thinking that the dwell or duration can be better modulates by controlling force input. 


Interested in your opinions
Bill   

It seems that sealing the inlet from inside as opposed to overlapping the inlet would make big differences and I think you have given solid evidence to that.  If I recall correctly, you indicated that it required less force to pop the valve and gave quicker reaction of the valve.   

Bill I want you to know that my comment about 950 fps has nothing to do with penetration . It has to do with accuracy at the distance you are shooting  a bullet . Bullets even at sub sonic go in and out of stability and accuracy . This is were a lot of pepole make there mistakes when picking their ammo . Marvin

[rsterne]

I guess I should have stated that my 900-950 fps figure is the maximum I strive for, not just a narrow range.... Some pellets/bullets might even stand 1000-1050 fps without accuracy problems (after all, a .22LR spends a lot of time transonic with great accuracy).... other might lose accuracy after 800 fps.... However, with our very limited pressures compared to a PB, I just don't think it makes any sense to spend a significant amount of air trying to go supersonic when the pellet/bullet falls back under the speed of sound so quickly after leaving the barrel....

We talk about efficiencies at the muzzle in terms of FPE/CI.... Can you imagine how poor the numbers would be if we used the velocity at 25 yards with diablo pellets that we are trying to drive out of the muzzle at ~1200 fps?.... I've seen pellets lose 100 fps and 17% of their energy in the first FIVE yards when shot at ~1150 fps.... It just makes no sense to me to waste the air required to get to Mach 1.... and then have the high drag in the transonic region take that extra velocity and energy all back in the first few yards....

Sorry to "drag" us off subject....

Bob

[Bill G]

Marvin
I understand.  the commentary on penetration was off topic.  I should have been more clear.  I was simply trying to convey the importance of accuracy over speed and that adding speed for the sake of more energy, isn't the best approach.  I was also attempting to reiterate the principals that one should keep in mind when considering airguns for hunting.   

[melloroadman]

I guess I should have stated that my 900-950 fps figure is the maximum I strive for, not just a narrow range.... Some pellets/bullets might even stand 1000-1050 fps without accuracy problems (after all, a .22LR spends a lot of time transonic with great accuracy).... other might lose accuracy after 800 fps.... However, with our very limited pressures compared to a PB, I just don't think it makes any sense to spend a significant amount of air trying to go supersonic when the pellet/bullet falls back under the speed of sound so quickly after leaving the barrel....

We talk about efficiencies at the muzzle in terms of FPE/CI.... Can you imagine how poor the numbers would be if we used the velocity at 25 yards with diablo pellets that we are trying to drive out of the muzzle at ~1200 fps?.... I've seen pellets lose 100 fps and 17% of their energy in the first FIVE yards when shot at ~1150 fps.... It just makes no sense to me to waste the air required to get to Mach 1.... and then have the high drag in the transonic region take that extra velocity and energy all back in the first few yards....

Sorry to "drag" us off subject....

Bob

Bob I agree with most of what you are saying . And that is one reason why I stay with bullets not pellets . As much as I shoot air conservation is a must . Even in my BB  . But I have found that this way of thinking is not even hear of as a matter of fact it is  laughed at by most BB hunters . And even most 25 caliber hunters . And with the pressures that we use . I believe that when super sonic is used it should be used to get to the intended target faster [in most cases] . Not to go farther . I have looked at a lot of reloading charts to come to this conclusion . Marvin

[Bill G]

OK
Got everything back together and filled.  It filled and held air just fine without a valve spring.  The enlarged port and transfer passage did increase velocity but I can't be sure I have given the test a fair shake.  My tanks are down to 2400psi but that's no big deal because I have a pump, right?  WRONG!  Pump went south.  I got it wouldn't increase psi at all.  In fact, It had nearly no resistance.  Looked closely at it and the tubing is pitted badly an I wonder if it will be salvageable.  Got to put an order in to Sun Optics i guess.

so with 2400psi as a starting pressure, I shot 3 strings of seven.  The first shot for each string got faster than the last and I found this a bit odd so I started over once the high velocity looked like it settled in.  From there I shot 3 strings of seven that proved to be very close to each other from shot to shot.  The shot to shot avg was as follows
fps      psi      strk    vol used      Vol possible
936   2400   .172      .355ci           .425
923   2334   .177      .366ci           .419
906   2269   .182      .363ci           .413  *This is the max stroke available due to current settings. .250" is max poss setting
897   2205   .182      .363ci           .407
889   2144   .182      .380ci           .401
878   2081   .182      .387ci           .396
860   2020   .182      .387ci           .390
end   1960                                    .384
The psi is calculated with exception of first shot and it is +/- 2%.  The end psi according to the fill gauge is 1900psi and calculated is 1960psi
Previously at 2400psi the velocity was 895fps using .320ci of air.  The stroke was .171" and the possible volume at that psi was .343.  This tells me I have too little stroke available and/or too much spring tension.  Of course this isn't a fair assessment since I can't achieve the same 3200psi fill that I had been getting.  It looks like It is going to be awhile before I can get there again.  My tanks are 3000psi scuba tanks and I used the pump to finish off or if I went to the field for a day.  The promising thing is, It looks like I'll be able to achieve the same performance and shot count from a lower fill psi.  This will allow many more shots per tank with out pumping.  If I want a single mag worth of shots, I think I can reasonably expect to get 60+fpe with a 3200psi fill.  I still have to do a quadratic regression to see where the higher psi shots may be.  I fear the sample isn't large enough since the stroke was limited. 

I was looking over my spreadsheet and noticed that I may be miscalculating my valve duration time.  I may need to bounce that off Bob and Lloyd latter.  Bob caught my bad math on the pellet to bore engagement time awhile back so it is certainly possible. 

That's all for now
Bill   

[lloyd-ss]

Bill,
The math in such a model does keep evolving and never seems to be quite finished.  I sent you a PM.
Lloyd-ss