Dual-Power Adjuster for QB 78/9

[rsterne]

Well guys.... I had no idea that converting the QBs to cock on open would lose basically all the pellet loading room.... but I sure found out in a hurry.... Unfortunately, I spent most of the day making my Dual-Power adjuster before I found that out.... Here is the adjuster, shown with the end cap which is drilled out to 3/8" to accept it....



Below is the adjuster set on low power....



Below is the adjuster set on high power....



The nut and bolt on the inside end is to fine tune it.... Yes, it has to be removed to adjust it, but that's only one screw once the gun is out of the stock.... Once you have the adjuster set for the velocity level you want on high power, you simply give the rod a twist and it pops out to a lower preload for low power.... I quickly found out that I had twice the travel necessary, at least on my 1500 psi HPA version.... The 1/4" of adjuster change in the slot dropped the velocity form 900 fps to 150 fps.... I didn't make another adjusting rod, but a 1/8" change of preload dropped the velocity from 900 fps to 630 fps.... which is a 50% reduction in FPE.... I think that's pretty cool with a flick of the wrist.... push in and turn clockwise for high power, and turn counterclockwise (and it pops out) for low power.... 

Now to this cock on open problem.... I found out that now the bolt (when opened for loading) sits against the sear, instead of all the way back.... That reduces the room for the pellet, of course.... To load the pellet, you have to hold the bolt back against the hammer spring, which is inconvenient.... If the adjuster is screwed in all the way, there is even less room (you can't even pull the bolt back to the back of the slot), but that could be changed by simply grinding/turning off the back of the bolt.... I don't see an easy way around the position of the bolt sitting against the sear, however, unless I make a whole new bolt (or maybe hammer).... As I missing something?....

Bob

[Rescue912]

I like the adjuster - quick and easy, no counting turns or anything.

For the cock-on-open, if you put a spacer on the hammer it will give you a little extra room. I used a crimp-on spacer from a farm store made for taking up space on a motor shaft - about 60 cent solution. Could also use a lock washer if you annealed it.

[rsterne]

if you put a spacer on the hammer it will give you a little extra room

Sorry, I don't follow you.... The hammer sits against the sear, held there by the spring (in the cock-on-open option).... and the cocking pin holds the bolt forward covering most of the loading space.... unless you hold the bolt back against the spring while loading.... Where are you putting the spacer?....

I have one QB that needs a hammer.... I think I will make a new one with the hole for the cocking pin further back.... may have to lengthen the cocking slot in the tube as well.... I don't want to go to the trouble of a new bolt....

Bob

[Rescue912]

Here is a picture from the yellow forum, wasn't my idea - I have very little original thought 



I used a crimpable spacer from a farm store instead of the spring coil cutoff.

[rsterne]

That increases the hammer fall distance as the sear will now engage on it instead of the shoulder behind it.... It will definitely not push the bolt back as far forward, though, when cocked.... Not a bad idea if you are going for more power, and I'll probably do that when I build a new hammer instead of moving the cocking pin....

Have you noticed any wear on it from the sear?.... I would think it would wear quickly if it's not hardened....

Bob

[rsterne]

I got this advice on the CAF....

The easiest solution for the cock on open is to machine a groove at the back of the bolt slot to lock the bolt into while you load.

Excellent idea, I've done that.... It works great during normal "cock on close" operation.... or if you don't shim the cocking block to it's normal location (ie where it would stop when the cocking pin is in place).... If, however, you put a shim behind the cocking block to put the same preload on the spring it would normally have, you can't pull the bolt back all the way.... The spring guide pin bottoms in the hammer when the bolt is still open about 1/4" (and hence it can't engage the new locking slot in the breech).... If you shorten the spring guide, then the back of the hammer will hit the front of the cocking block unless you shorten that as well.... If you do both, then you can (I assume, I haven't yet) get the bolt all the way back and down into the new slot to hold it open....  

I agree that drilling the hammer to move the pin (another suggestion from the poster on CAF) is likely a no-go as the hammer is hardened.... but I have some 1045 hot rolled steel here and I can make a new hammer easily enough.... and then harden it once fully machined.... I have made some measurements, and it looks like I can move the point where the sear catches forward about 1/4" on the hammer.... That will result in increasing the hammer fall distance from 5/8" to about 7/8", a 40% increase (assuming I can get all of it).... That gives the potential for a much harder hammer strike.... as not only will the hammer have more travel (and hence more distance to build momentum), but for the same position of the cocking block, 1/4" more preload on the spring.... Of course that might do no good without shortening the steel sleeve that is behind the valve, as that limits the effective valve lift.... If I do that, there is a good chance I might bend the valve stem.... and 'round and 'round we go, where we stop, nobody knows....  

Anyway, my next step is to build a new hammer, and move the point where the sear catches forward as far as I can and have the gun still cock reliably.... While I'm at it, I'm going to make it heavier, and drill the hole for the spring to 3/8" as I have some 0.360" OD springs available, one the same spring rate and length as the original, the other about twice as stiff.... I'll shorten the back so that it doesn't hit the cocking block with the bolt all the way back.... and do some trials at that point....

Bob

[rsterne]

OK, so I spent most of the day in the shop making my new high power QB hammer.... It will work both "cock on close" and "cock on open" with greatly increased hammer momentum due to a 50% increase in hammer travel, increased spring compression, and a 10% increase in weight.... Note that I have milled a new vertical slot in the breech to lock the bolt back in the open position.... guaranteeing normal room for loading pellets when using "cock on open"....  Here is the photo....



The point where the sear catches is moved forward.... which increases the travel and spring force when cocked.... The narrow area is shorter to increase the weight.... The rear portion of the hammer is removed, and the spring guide shortened, to allow the hammer (and therefore the bolt) to move back enough for the bolt handle to engage the new locking slot milled in the breech.... I made the hammer from 1045 hot rolled steel, which is easy to machine and can then be hardened.... The hole for the spring is slightly larger so that I can use either a stock spring or some 0.360" OD x 2.5" long Trakar springs I have.... I have one made from 0.051" wire that duplicates the performance of the stock spring.... and another from 0.059" wire that is nearly twice as stiff....

My new Dual Power Adjuster will work with this hammer when used in the "cock on open" configuration.... As soon as I can get the hammer hardened I'll be able to try it out.... The increased hammer momentum should enable significantly higher HPA pressures to be used.... I'm thinking this might be just the ticket for those 3000 psi QB tubes that AirGunEric sells....  

During the development of this new high power hammer, I also figured out the mods required to enable the stock hammer to be used for "cock on open".... It needs the rear portion (behind the shoulder) ground off, and the spring guide shortened about 1/4" to allow the back of the (shortened) hammer to touch the front of the cocking block.... That will allow the cocking block to be shimmed to the same location it stops at in a "cock on close" setup (giving normal power) and yet allow the bolt to be pulled back fully so that the handle can engage the new locking slot....

Bob

[rsterne]

Yesterday I hardened the hammer, and today I made a new plunger for my Dual Power Adjuster with only 0.10" of travel instead of 0.25".... There is still 0.25" of screw adjustment in addition to that.... It took a lot of fiddling with the dimensions, but I got it so that with the adjusting screw out 5 turns the bolt will just drop into the new locking slot on the breech.... which puts maximum compression on the hammer spring.... At full in on the adjuster and on low power, I only get 350 fps.... so I've got the whole range covered on my 1500 psi regulated setup.... I added a spring loaded plunger inside to insure that the adjuster wouldn't change from low to high power on it's own.... as there is no pressure on it from the hammer spring with the gun uncocked on the lower power settings.... Here are the parts....



The bolt is sitting in the high power notch.... You can see a small hole drilled in the top of the adjuster.... It is an indicator that is covered on high power and visible behind the rear plug on low power.... You assemble the adjuster and install it with the rear plug, and then install the plunger and spring and secure them with the set screw.... Here is a photo of the assembly set on low power....



Since the new hammer has more travel and weight.... and also can put more compression on the hammer spring.... the gun can now be setup for more than 1500 psi.... When I tried the maximum settings on my gun, the velocity basically peaked with over half the travel still remaining on the adjuster on high power.... Here is a graph of the velocities on both high and low power....



Since the adjusting screw is 20 TPI, two turns on the screw is the same as the difference between high and low power.... For example, 1 turn out on high power is the same at three turns out on low power, about 845 fps.... At 1500 psi, the velocity peaks at 2 turns out on high power, and 4 turns out on low power.... In other testing, I have found that adding hammer strike after the velocity peaks only wastes air.... There is no question this was occurring, as at 4-5 turns out on high power, this thing was LOUD.... I wanted the least hammer hit I could get and still be right at or near the plateau.... so I was obviously looking at 2 turns or less.... I tried 1.5 turns and the velocity was down 20 fps to 880.... I ended up using 1.7 turns out and achieved the following results....



The linear trendline shows about a 9 fps loss as the pressure in the tank decreases, which is only 1%.... but the shape of the curve is interesting.... The peak velocity occurs not at 3000 psi tank pressure, but at about 2600.... In addition, the velocity doesn't drop below 880 fps (3% below peak) until the pressure in the tank has dropped to 1200 psi.... which is 300 psi BELOW the regulator setpoint.... This hammer strike is so perfect for this setup that the valve is self-regulating within the tiny amount of regulator creep and below the setpoint.... From past experience with regulated guns I knew this was the best way to not only get the longest shot string, but the best efiiciency as well.... I wasn't disappointed.... I achieved 60 shots averaging 896 fps with 18.1 gr. JSB Exact Heavy pellets.... That's 32.2 FPE x 60 = 1943 FPE total.... This used 1800 / 14.5 = 124 bar of air from the 13 CI tank.... which is 1614 CI.... The efficiency has jumped to 1.20 FPE/CI.... and the shot string on this gun since initial setup has gone from 37 shots to 44, and now to 60 shots at virtually the same power.... 

Now it was time to find out what it did on the low power setting.... I filled the gun to 2000 psi, turned the adjusting knob, and started shooting.... I did two 30 shots strings before the pressure dropped to 1400 psi.... That's 60 shots on 600 psi of air.... 10 psi per shot.... Then I kept shooting as I wanted to see what happened to the velocity below the regulator setpoint, as I expected it to climb.... Here are the results....



Above the regulator setpoint, the velocity averaged 638 fps with the 18.1 gr. JSBs for the first 60 shots.... Once the pressure dropped below the regulator setpoint, the velocity began to climb.... It displayed a classic bell-curve, behaving like an unregulated PCP, peaking at nearly 790 fps at 1000 psi before dropping back below the velocity it was shooting regulated at about 600 psi.... This part of the curve is useless for our purpose, but I wanted to show everyone what happens when you have a very weak hammer hit on a regulated gun.... This gun, from 3000 psi down to 1500, will now produce about 150 shots at 16.3 FPE, which is 2445 FPE of energy from 1345 CI of air.... That works out to an astounding efficiency of 1.82 FPE/CI.... The gun is VERY quiet set up this way, because it's just sipping a tiny amount of 1500 psi air per shot.... The downside is that the SD is quite large at about 12, and the extreme spread is about 40 fps (7%) at 2000 psi and above.... This makes this a good plinking and short range setup.... but you would probably notice some small vertical stringing in the groups beyond 25-30 yards.... I think the reason for this is that any TINY variation in the hammer strike will change the amount of air released by the valve by a relatively large amount in percentage terms.... If you wanted to set up this gun to shoot at 16 FPE all the time.... you could reduce the regulator pressure to about 650-700 psi and then balance the hammer strike to that.... I'm guessing you might lose a bit of efficiency (high pressure tends to be more efficient).... but the extreme velocity spread and SD would be much tighter.... Alternately, if you had a 1000 psi regulator, this gun could be setup for about 800 fps.... and at 1200 psi it could be setup in the high 800s.... However, by using 1500 psi the efficiency is better....

This has turned out to be a very interesting project that not only successfully developed my Dual Power Adjuster.... but it also resulted in a High Power Hammer as well.... To really put that through it's paces will require much higher pressures.... I have a feeling that this could be the perfect setup for DerekVinyard's 3000 psi tubes.... One thing for sure, if the current hammer spring won't cut it.... I have one twice as stiff that I'm sure will....  

Bob

[rsterne]

I did one more mod today.... I replaced the stock valve poppet with one that has a Delrin insert.... There were no other changes to the gun, and surprisingly it lost about 25 fps.... By the time I re-adjusted the screw on the power adjuster to get back to just under 900 fps I had moved it out 0.025" (1/2 turn).... The bad news is that I lost a few shots.... The good news is that I now have a much more consistent gun on the low power setting (although I would imagine I lost some shots there too).... The new setup has the following results:

High Power:
Low 887
High 903
Average 897
SD 1.9
Efficiency 1.11 FPE/CI

Low Power:
Low 664
High 682
Average 676
SD 5.7

The SD and the extreme spread on the low power setting are half what they were before.... The power has increased to 18.4 FPE and I'm guessing the shot count will be down to 120-130 per fill.... but with the increased consistency it's a good compromise.... I'm not sure if the better consistency is due to the harder material on the valve seal.... or to the higher velocity.... or a bit of both.... I rather thought that the harder valve seal would have increased the velocity instead of losing.... but that's the curious thing about PCPs.... there is just soooooooo much to learn and too many variables....

Bob

[lloyd-ss]

Bob,
I can tell that the tourists have left for the year and you are holed up in your shop, LOL.  A lot of info but I will only ask about a little of it.

Seriously nice R&D!  Let me make sure I understand the velocity increase below the regulator set pressure.  in a "normal" unregulated pcp, that peak in the bell curve would be shifted much more to the left, depending on the gun, fill pressure, etc.  But your regulated setup is operating at 1400 psi, but still to the left of the peak, like you were artificially forcing the curve to the right by using a very weak hammer hit.  And you did that to achieve those extremely long shot strings.
Did I get that right?

A very good lesson in this ongoing curriculum!   

Lloyd

[lloyd-ss]

.... This gun, from 3000 psi down to 1500, will now produce about 150 shots at 16.3 FPE, which is 2445 FPE of energy from 1345 CI of air.... That works out to an astounding efficiency of 1.82 FPE/CI.... The gun is VERY quiet set up this way, because it's just sipping a tiny amount of 1500 psi air per shot.... The downside is that the SD is quite large at about 12, and the extreme spread is about 40 fps (7%) at 2000 psi and above.... This makes this a good plinking and short range setup.... but you would probably notice some small vertical stringing in the groups beyond 25-30 yards.... I think the reason for this is that any TINY variation in the hammer strike will change the amount of air released by the valve by a relatively large amount in percentage terms.... If you wanted to set up this gun to shoot at 16 FPE all the time.... you could reduce the regulator pressure to about 650-700 psi and then balance the hammer strike to that.... I'm guessing you might lose a bit of efficiency (high pressure tends to be more efficient).... but the extreme velocity spread and SD would be much tighter.... Alternately, if you had a 1000 psi regulator, this gun could be setup for about 800 fps.... and at 1200 psi it could be setup in the high 800s....

Bob

Bob,
I agree with your assessment of the primary reason for the velocity spread.  With the gun operating on (or very near) the left hand ramp of the velocity curve, the rate of velocity change is greater for minor changes in the other variables (hammer strike inconsistency, regulator creep, pellet, fit, etc) than if it were operating in flatter region of the curve.  You could drop the reg pressure down some, but I also agree that a larger amount of the lower pressure air might be marginally less efficient than the lesser amount of higher pressure air you are currently metering out with each hammer hit.

Again, nice work and nice analysis.

Lloyd

[rsterne]

Correct, the low power setting is operating far to the left on what would be a non-regulated curve when it is above the regulator setpoint.... That's the way you would normally shoot it, I only showed the low pressure part of the curve on the graph to show what was going on.... The gun would be much more consistent running a lower regulator pressure to correspond to the very light hammer hit.... The problem with doing that, of course, is you would have no high power available....

It's all about compromise when you attempt a dual power setup.... The sensitivity from an efficiency point of view to tayloring the hammer hit so that it's on the top of what would normaly be the bellcurve on the high power version is critical, however.... I will never build a regulated PCP without an RVA again.... Giving up just a few fps can save a HUGE amount of air....

Bob