（转）QB 79 from CO2 to HPA: Efficient Power Tuning + New HPA Cylinders - ...

happydad

QB 79 from CO2 to HPA: Efficient Power Tuning + New HPA Cylinders - longJune 12 2010 at 4:31 PM

I'd like to start right off the bat by thanking Mr. Archer for great service and parts availability. If it werent for the support, you provide for these guns, I would have never taken on this project.

For me, the gun started out as a prototyping mule that evolved into one of my favorite hunting guns. I'll skim over the details of R&D that brought me here and present y'all with the results of my past 9 months. Ive owned PCPs for a few years now, but I wanted to get to understand them as well as I know springers. I always wanted a super efficient, regulated PCP, but there just were not many options for less than my house payment. Then there's CO2. The thing is, CO2 is so much carefree fun in the summer! However, living in Colorado, I just have no use for a CO2 gun during any of the hunting months of the year. As excited as I was about the Discovery, I quickly realized that it was not a true dual-fuel airgun. You could not just switch from CO2 to PCP without purging, and power and zero adjusting. More accurately, it is a one-fuel-at-a-time gun.

There is no need for another post exalting the value per dollar spent on a QB7XX rifle platform, which is why I picked it as my work mule. Then, all that was left was to do my pressure tube research, develop a high efficiency valve, and research my regulators. No sweat, right? ? Well, after examining 4 different PCPs, cutting up a couple CO2 tanks and HPA bottles, and matching my stress and safety factor calculations with available tubing I found a couple tubing manufacturers to choose from, and settled on 6061 T6 tubes in 2 diameters, depending on desired fill volume. Because Im a VERY small (though well liked ) tuner I chose not to invest in my own regulator design and picked two very efficient, moderately priced regs. of the 4 brands I tested. Then, I figured out what was necessary to improve the accuracy of the QB 79, but the most surprising part was the valve. LOL, I never thought the results would impress me so. Well, I've babbled enough. Here is the business end.



First, the Cylinders:
My HPA cylinders do not require pulling the barrel or any other complicated procedure to swap between HPA and CO2 or higher and lower pressure HPA cylinders on a factory gun. Just unscrew them and insert whatever accessory you want. I will be putting all my prototype cylinders for sale on the classifieds for cost of regs. + shipping. If you would like to get more shots out of these, I suggest you replace the Myth regs. with Ninja regs. and/or send me your rifle to tune for power, or efficiency, or both, after you read this post. I can take on a couple to half dozen guns in August and September. My production cylinders will be fitted with Ninja regs. at 650 to 900 psi to produce 12 ft-lbs to 14 ft-lbs with my valve tune, or JDS Airman regs. at 1000 to 1250 psi for 15 ft-lbs.



The salient features of my rifle:

If you are wondering about the finish, it is NP3 from www.Robarguns.com. You can do a search on the main forum for my post about better-than-blued gun finishes.

I reinforced the tank screw-in block, because the little 4 mm screws were making me nervous, when I calculated the force exerted on them by the CO2, and what it would take to shear them off. Not that they would not hold clearly they do, but the relatively low safety factor was not to my liking. Because this modification precludes one of the two O-rings from sealing the tube, I upgraded the remaining O-ring to 95 Durometer Urethane.



The riser you see on my gun was designed to reinforce the breech and free-float the barrel, to improve accuracy without funny looking muzzle weights or other attachments that dont belong on a hunting gun. The barrel band in front of the breech ties the barrel, riser, and breech together to create a very strong assembly. I also performed a general accuracy prep. on the barrel before plating it.




The results show what a true little gem this rifle is. Below is the Archer test of the .22 gun before it shipped to me: 10 shots at 10 yards. The group measures just over 1/2" edge to edge. After my accuracy overhaul, I could not get a credible looking 10 shot group at 10 yards, so I went to 20 yards, which is the farthest I can shoot in my house, to eliminate wind. The 20-yard group measured just under 3/8" edge to edge. This rifle has a distinct preference for CPs and Beeman FTS's and an uncompromising dislike of JSBs. Given the rifle's accuracy, I can only assume the difference comes from rifling twist rate.



Now, onto the valve. He he he
The best comparison with a factory gun I could think of (naturally, I only thought of it after I already finished my design and experiments on HPA) was to compare my gun on 2 CO2 carts against a factory QB rifle on 12 gm carts. The Archer Airguns website shows a test of a .22 QB 78. For copyright reasons, I cannot repost his chart in my post, but here is the link.

http://www.archerairguns.com/Articles.asp?ID=134

So, I tested my rifle with a 2 12 gram cartridge adaptor with the following results. The ambient temperature was around 70 degrees. You can see that the higher temperature alone is not responsible for a similar shot count at 200 fps and 7 ft-lbs more (twice the power) than the factory gun.




I learned through my valve design that a regulator helps with consistency, but it is still no substitute for an efficient valve. Here is a comparison of my valve and factory valve using the same HPA cylinder.



Now, lets move on to HPA. After, as usual, spending 8 times as much on tooling and materials as the gun, LOL, I picked the Ninja reg. and the JDS Airman reg. as my top choices. The JDS reg. is the most efficient, but the Ninja reg. is user adjustable for pressure and costs about $10 less. The adjustability of the Ninja reg. will allow you to exactly match the velocity of your gun on CO2 and HPA, to eliminate POI shift when switching between power sources, and have a true dual fuel rifle. The tube measures 0.965 ID by 10.75 long for 7.86 cu. in. of volume. Here are the tests with the Ninja reg. and JDS reg.




So, whats next?
Now that I have a better grasp of valve systems. Im going to test some Crosman true dual fuel hunting pistol prototypes with adjustable power output from around 6 ft lbs and up to 12 ft-lbs. Then, I plan to build a 1400 psi regulated QB-79 based PCP in .177, for long range plinking. At the same time, Im working on regulating and increasing the efficiency of my AA S400 and T12 for prairie dogs, and Cyclone for rabbits. So, stay tuned on the main forum. For now, Im back to being AWOL, but you can always get in touch by e-mail.
Thanks guys, and good shooting to all.
Dmitry
Dair Designs

happydad

看到大家这么有兴趣这个枪，转篇文来，希望有用。