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PostPosted: Mon Jul 22, 2013 9:58 am 
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Location: Coalmont BC
HUGE!.... Stage 1 was a lot louder than Stock as well.... However, the gun is noticeably quieter with the reduced hammer strike as you would expect in extending the string by 50%.... it's blowing less wasted air out the barrel....

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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PostPosted: Thu Aug 01, 2013 9:49 pm 
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Location: Coalmont BC
Sometimes leaks can be a good thing.... I've had a slow leak in this gun virtually since new.... It lost about 600 psi the first day, then 3-400, then a trickle.... I tested everything with soapy water and couldn't find anything, which pretty much meant it was the valve.... I pulled the breech, and found a very small leak coming out the exhaust port, so it was the poppet that wasn't sealing on the seat.... I pulled the gun all apart, and on inspecting the seat with a loupe I saw a very small nick on the sealing surface, and a corresponding mark on the soft seal insert on the poppet.... The brass seat was easy to polish, but rather than take a chance on the seal in the poppet I decided to replace the poppet head with a Delrin one which is more suitable for HPA use.... I drove the stem out of the old poppet and reused the stem, and made a new poppet head from a piece of 3/8" Delrin.... Since I didn't have to worry about the OD of the brass poppet, I was able to turn the entire head down to 0.32", which is the diameter of the valve spring, and 0.050" smaller than the original.... I lapped the new poppet against the repaired seat, and reassembled the gun....

The first test shots, with the RVA set at 4 turns out as before, were a bit of a shocker.... Instead of getting 847 fps (22.8 FPE), the velocity was in the high 880s with the occasional 890+ (25.0 FPE).... Obviously the new Delrin poppet was a big improvement.... Since the throat and seat is still the same size, I figure the increase must be from the decrease in head diameter and the corresponding easing of the flow around it.... There was another big change, and this one I expected.... I was able to reduce the hammer spring preload another 2 turns to get back to the "knee" of the velocity curve.... This is because the harder seal material compresses less, and that reduces the amount of hammer energy required to "unstick" the valve from the seat.... It sure is nice to see theory backed up by results....

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: Sat Aug 03, 2013 12:48 pm 
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Location: Coalmont BC
Here is the results of preliminary pellet testing indoors at 20 feet....

Image

I shot 5 shot groups from the bench, and then sorted the results by using two washers of 3/8" and 1/2" diameter.... If the 3/8" washer completely covered the group, it is coded green above.... If the 1/2" washer would NOT cover the group, it is coded red.... All others (3/8" to 1/2") are left unmarked.... The best group was the 15.9 gr. JSB Exact Jumbo, which was just a ragged hole, closely followed by the other JSB Exact Series pellets....

The Ballistics Coefficients listed are taken from testing over 25 yards with another gun that shot about 1 FPE more muzzle energy, so they will be very close in this gun.... Pellets shown in blue will be tested at longer range....

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 04, 2013 12:19 am 
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Location: Coalmont BC
Today I added a Hatsan Air Stripper to the barrel and did a few tests with the JSB Exact 15.9 gr. pellets which produced the best groups yesterday.... I had never tested a stripper before, so I set the gap between the stripper cone and the barrel at maximum (about 2 calibers gap from the muzzle) and then moved it in about 1/2 cal. for each group.... I shot 5 shot groups through the Chrony with the target still at 20 feet, not knowing what to expect....

Without the stripper, the velocity was 849 fps, and with the gap at maximum it seemed to be a couple of fps less.... Each time I moved the stripper closer to the muzzle it picked up a couple of fps, and by the time the gap was down to just over 1/16", the velocity was 855 fps.... I figure that when the gap is small, the stripper is focusing some of the muzzle blast behind the pellet and effectively lengthening the barrel a fraction, although not very efficiently.... The group size did, in fact, seem to vary as I adjusted the gap, although at this short range realistically the changes were very small.... I expect it would be easier to see results at longer ranges.... Since the smallest group seemed to be with a gap of just under 1/4", I decided to adjust the gap to exactly the same size as the head of the pellet (just because) so I clamped a pellet in some forceps and them used the head like a feeler gauge and adjusted the stripper cone so that the pellet just touched it and the muzzle.... Here is the 5-shot group I shot at that setting....

Image

That is a .22 cal JSB Exact sitting in the hole.... The target won't meet the Feinwerkbau test where a pellet will hang in the hole with the target vertical, but it won't fall through either.... I figure the group is 0.03 - 0.04" C-T-C, or about 0.25"-0.26" OD.... In any case, I'm pretty pleased with it, and indeed the stripper seems to help....

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: Mon Aug 05, 2013 12:30 am 
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Location: Coalmont BC
I tested the efficiency at various hammer spring preloads today, using the 15.9 gr. JSB Exact Jumbo pellets which are very accurate in this gun.... The new slimmer Delrin valve has picked up about 2 FPE, so it shoots the 15.9 gr. pellets at nearly the same velocity as it did the 14.3 gr.... I had to back the preload out several turns relative to the stock poppet because the harder Delrin is much easier to knock open than the soft seal on the stock valve.... Here are the results....

Image

The efficiency seems slightly higher than before, and the plateau starts at 6 turns out instead of 3.5 turns.... Based on the results, I tried a short string at 6.5 turns out, and the velocity was only about 10 fps below the plateau and the efficiency was about 1.10 FPE/CI.... I think that's pretty good for a QB79 shooting at 25 FPE, and it's likely where I will end up tuning it.... That should give me over 70 shots per fill....

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: Mon Aug 05, 2013 5:17 pm 
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Location: Coalmont BC
I finished and installed the stock today....

Image

It's a Richard's Microfit Wildcat Thumbhome in Select Grade Black Walnut with Ebony Grip Cap.... beautiful figuring in the grain....

Image

I had to shorten the forearm and inlet it for the tank block and regulator.... The finish is 7 coats of Watco Danish Oil, each coat wet sanded, ending with a white Scothbrite pad of 1200 grit equivalent and then a coat of Dark Minwax.... The scope is a Leapers 3-9 x 32 AO with Sunshade.... The gun weighs 8 lb. 7 oz. as shown.... The Air Stripper is from a Hatsan PCP, I threaded the barrel 1/2"-20 NF to accept it....

It's no longer a $200 PCP, however....

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: Mon Aug 05, 2013 6:03 pm 
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Joined: Sun Jul 15, 2012 10:49 am
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Location: Victoria, BC and Clarkston, WA
Beautiful Bob! Now you need to go have a proper field test on gophers!

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3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
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PostPosted: Mon Aug 05, 2013 10:53 pm 
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Wow that looks so nice and well balanced Bob. 8)
Congrats on a fine job all around. :wink:

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PostPosted: Tue Aug 06, 2013 1:18 am 
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I made one more slight change today before the final testing.... The off center RVA screw was canting the cocking block slightly, and I noticed a slight scuff mark on the spring spacer.... I made a longer, one piece cocking block, with an integral spring guide and spring spacer.... The new cocking block is 1.25" long, of which 0.25" is a spring spacer that is 0.34" diameter, the other inch being full diameter to eliminate it canting in the tube.... That allowed me to shorten the RVA screw and just tidy things up a bit.... It shouldn't have changed the performance at all, but in fact I picked up about 10 fps, and gained a bit of efficiency as well.... The Preload numbers have changed, as I can't put quite as much preload on the spring at maximum with the shorter spacer.... Here is a new graph of Velocity and Efficiency vs. Preload using the JSB 15.9 gr. Exact Jumbos pellets....

Image

As per my usual practice, I selected a preload on the knee of the curve, just below the plateau, in this case 4.5 turns out.... I refilled the tank to 3000 psi and shot a string with the following results....

Image

I got 80 shots between 844 and 856 fps, an ES of just 12 fps (1.4%).... and was able to shoot down to 1100 psi before the velocity dropped below 840.... The average was 849 fps (25.5 FPE) at an efficiency of 1.21 FPE/CI.... During shooting the string, I shot 5 shot groups and sighted in the scope in my 20ft. indoor range.... By the time I was done, it was punching group after group in the same place on the target that were only 1/4" across, barely bigger than the pellet.... I can't wait to try this rifle out at longer ranges.... This is just about the perfect velocity to shoot the 15.9 gr. Exact at, putting it right in the middle of it's sweet spot for the Ballistics Coefficient....

This has been an exciting project, and I'm extremely pleased with the final outcome....

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: Tue Aug 06, 2013 11:55 am 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 5998
Location: P.G. B.C.
Well done and presented, Bob. Your stock work is very nice. The Richards Microfit Thumbhole is a solid topped stock - no inlet? It looks very good indeed. V-nice grain structured Claro.

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PostPosted: Tue Aug 06, 2013 2:44 pm 
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Location: Coalmont BC
I purcashed it inletted for a QB78, the only Air Rifle they do, and it fit well.... Man are they rough on the outside, though....

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: Tue Aug 06, 2013 2:52 pm 
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Joined: Sat Jan 12, 2013 6:08 pm
Posts: 117
rsterne wrote:
I purcashed it inletted for a QB78, the only Air Rifle they do, and it fit well.... Man are they rough on the outside, though....

Bob


Do you mind me asking what They charge for the stock inletted for the QB?


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PostPosted: Tue Aug 06, 2013 2:54 pm 
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Location: Coalmont BC
I can't honestly remember, I bought two stocks a long time ago, both for QBs, from their "Specials" page.... stocks that were ordered and never then returned or never picked up....

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: Tue Aug 06, 2013 3:07 pm 
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Joined: Wed Jan 05, 2011 12:35 pm
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Location: P.G. B.C.
Thanks again, Bob. Some of the boys on Saubier's small bore forum have noted the 'roughness' of the Micro-fit stocks, both inside and out, compared to Boyd's.

Most of Boyd-Boy's pre-carved stocks are around $120.00 I think, in the various laminates (Ruger & maybe Remington uses them I believe). Their solid walnut might be cheaper. It's been many years since I purchased one, but wouldn't hurt to check them out at well.

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Daryl


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PostPosted: Fri Aug 23, 2013 8:31 pm 
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Location: Coalmont BC
I finally had a chance to do some testing outdoors today, so I tested all the pellets scoring "green" in the last tests indoors that I expected to have a decent BC at 25 yards.... I measured the average velocity at the muzzle and at 25 yards, for 5 shots with each pellet, and then used ChairGun3 to calculate the Ballistics Coefficient.... Here are the results....

Image

The groups were sorted as usual, with any group you could cover with a Dime scoring green, any group you couldn't cover with a Quarter scoring red, and in between no colour code.... I was surprised that all the JSBs were the only pellets that produced sub-dime sized groups.... and the best of those was the 15.9 gr. Exact Jumbo.... When you look at the JSB Exacts, the heavier the pellet the better the BC, as expected, and this results in a lot more FPE at 25 yards.... However, with the combinaton of good velocity and high BC, plus superb accuracy, I chose the 15.9 gr. as the pellet to use.... After sighting the rifle in 1/4" high at 25 yards, here is a typical 5-shot group....

Image

The small squares are 0.1", and the black squares are 0.4", so the C-T-C size of that group is less than 0.25".... I can get 70 shots per fill at 25 FPE, and basically it just keeps dumping them in a ragged hole at 25 yards.... I think we can call this project an unqualified success, and this rifle has earned a place on my "wall of keepers"....

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!


Top
 Profile  
 
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