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rsterne · Moderator

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

rsterne · Moderator

I found this photo of a QB hammer with a spacer fitted to give more room when cocked in a gun that has been converted to "cock on open"....

It seems to me that the sear would now catch on the spacer?.... If that's that case, yes you would have more room for loading, but the hammer fall distance is increased, isn't it?.... that might be great if you were looking for more power, of course (providing you could still close the bolt, which would limit how far you can go with this mod).... Wouldn't it need to be hardened so that it wouldn't wear?....

EDIT: Although the photo of the above hammer modification was sent to me by person or persons unknown, it was brought to my attention yesterday (Aug. 20, 2016) by Steve in NC that this photo was first published by him on July 20, 2010....

http://www.network54.com/Forum/79537/thread/1279673517/Followup+to+Sunday%27s+post+of+the+world%27s+cheapest+QB79+cock-on-open+mod.

I apologize to Steve for not knowing he originally did this mod, and giving him credit, and thank him for bringing that to my attention....

Bob

SMP · Silver Status Member

I agree the sear would then be hooking on the spacer. And it certainly does look like it's been heat treated.

The other issue is how does it go on? There must be a notch on the backside that can't be seen.

rsterne · Moderator

Some sort of a "motor shaft spacer" that crimped on, apparently.... so it couldn't be hardened, in fact must be anealed.... Shocked

Bob

SMP · Silver Status Member

Really!

I agree that's not so hot. It wouldn't take long for the edge to gall and erode away.

rsterne · Moderator

I got this advice on the CAF....

Alstone · Moderator & Site Supporter

A lot of people have had a go at a cock on open but each idea shows up a problem, and so far I haven't seen one that works properly, that’s why I designed an adjustable cock on close, everything stays the same and you have fully adjustable power.

But I do like the two power level setting idea, it's just holding the bolt back to load and locking it down when closed. As for the ring on the hammer do you think it is fixed to the hammer or lose?

Al

rsterne · Moderator

I don't know if the ring on the hammer is loose or not.... but I figure on my new hammer I can move the sear catch point forward nearly 1/4"....

Bob

AirGunEric · Site Admin

I had spoken with Steve Woodward on this modification in the past (where that picture of the hammer with the ring on it came from) and it did eliminate the pellet loading issue. He also found as you did that the RVA had a very small range to adjust things radically- unfortunately, I don't recall any mention of the sear catch moving. Of course this may not be because it didn't occur, but perhaps because it was never inspected throughly. Either way- he would not produce them as his main QB 'customer' who have him a QB to develop such parts decided he did not want to purchase them. If you can "perfect" a design and want your name on some custom parts- I would pay a shop to have them produced and sold as the "Sterne QB Power Adjuster" Wink

rsterne · Moderator

Nice offer, Eric.... I'll try and keep it simple as if the parts count gets out of hand it's a no-go.... At the moment it looks like a new hammer is necessary in addition to the adjusting bar and drilling out the rear plug.... I'm not sure if that's all or not....

Bob

SMP · Silver Status Member

Way to go Bob....Your going to be Famoos (note: spelling is for the aboot crowd) Smile

The Sterne Adjuster...I like it Thumb Up!

It could also be mistaken for supportive knickers Mr. Green

(Sorry couldn't resist the sailor jokes)

radar · Silver Status Member

This looks like a fascinating project to a tinkerer like me. I just wish I weren't such a n00b and knew exactly what was going on here.

rsterne · Moderator

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.... Mr. Green

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 · Moderator

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.... Shocked

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.... :wink:

Bob

radar · Silver Status Member

Wow! You rock!
I love it!