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How do your like your QB 78/9 to cock?
1. I like it to cock when I close the bolt (stock) 11%  11%  [ 5 ]
OR: I would like it to cock when I open the bolt 38%  38%  [ 18 ]
2. If it meant having an RVA, cock on open would be OK 36%  36%  [ 17 ]
OR: Even with an RVA, I would like it to cock on closed 15%  15%  [ 7 ]
Total votes : 47
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 Post subject: Re: Poll - QB Cocking
PostPosted: Sat Dec 10, 2011 12:36 pm 
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Location: SW Ontario:Canada
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. I also seen a mod where they relocated the pin, but that hammer steel is hard. Probably need a carbide bit to drill it. Could use a torch to take the hardness out and re-harden after too.


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 Post subject: Re: Poll - QB Cocking
PostPosted: Sat Dec 10, 2011 6:07 pm 
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Posts: 8977
Location: Coalmont BC
Quote:
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.... :roll:

I agree that drilling the hammer is likely a no-go.... 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.... :lol:

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

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: High Power QB Hammer
PostPosted: Sun Dec 11, 2011 11:12 pm 
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Location: Coalmont BC
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....

Image

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.... :mrgreen:

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: Poll - QB Cocking
PostPosted: Wed Dec 14, 2011 12:22 am 
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Location: Coalmont BC
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....

Image

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....

Image

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....

Image

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....

Image

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.... :shock:

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....

Image

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Dec 14, 2011 1:30 am 
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Joined: Fri Nov 10, 2006 12:02 am
Posts: 1076
Bob with one of Derek's HPA tubes you will have a killer QB. That is some real fine R&D on your part for sure. You done a super job with that QB.



George.


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PostPosted: Wed Dec 14, 2011 10:47 am 
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Location: Coalmont BC
Thanks, George.... as one of the resident "QB Guru's" that means a lot.... The new hammer is the key to a whole new world of QB power and the ability to dump increased pressure.... whether the cocking direction is changed, and a velocity adjuster used, or not.... Pretty cool that it's a drop in with any QB.... :mrgreen:

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Dec 15, 2011 11:00 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
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Location: Coalmont BC
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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Aug 21, 2016 10:24 am 
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Joined: Sat Nov 03, 2007 4:19 pm
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Location: Coalmont BC
EDIT: Although the photo of the above hammer modification on the previous page (with the ring installed on it) 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/th ... n-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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Aug 21, 2016 9:43 pm 
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Location: Coalmont BC
Note, it was not my intention to start this poll again, only to credit Steve for the photo I used without even know it was his work at the time I posted it.... My apologies for bringing this thread back to the top.... :oops:

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Aug 31, 2016 10:40 pm 
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Joined: Sat Dec 27, 2014 12:27 am
Posts: 10
I like the cock on close, bolt springs back load pellet close bolt fire. I have done most of the mods I think that needs to be done on this rifle, Took the valve apart remove the screen and filter opened up the path for the gas to get to the pellet, crowned the barrel, polished the tube and the breach and it's attack driver now with a good scope and bipod. The only thing this rifle needs is a HDD and the power adjuster would great but I don't think much else. I use this rifle to get ride of some critters and target shooting with some friends. I looked at cock on open but don't see any advantages to it.


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