.30 cal Disco Double

[rsterne]

This gun will have a shroud, but not one that will affect the noise level of the gun, they are prohibited in Canada, unfortunately.... I will be using a 7/8" OD x 3/4" ID Carbon Fibre tube located on two 3/4" bosses, one on the front of the breech, and the other on the back of this modified Hatsan air stripper.... These strippers are available in .177, .22 and .25 cal (shown), having different inserts for the different bores.... The brass insert is adjustable fore-and-aft to adjust the air gap between it and the muzzle, which can have a dramatic effect on accuracy.... I will be making a .30 cal insert for the stripper on this gun....



The rear portion of the stripper was tapered, but I turned a parallel section with a 3/4" diameter up to where the stripper was 7/8" OD (where the shoulder is).... It will thread onto the end of the barrel on standard 1/2"-20 NF threads.... The shroud will mount between the bosses on the breech and stripper, and when the stripper is tightened up, the shouders will put the shroud in compression and the barrel under tension.... which should stiffen the barrel and raise it's resonant frequency.... In theory, this should reduce or eliminate the effect of barrel harmonics.... which can be quite a problem on long, thin barrels.... In addition, the woven finish of the CF tube should look pretty KEWL.... Once in place, all three tubes will be the same diameter, and also the same width as the breech....

Bob

[sholo]

Hehehe...Great minds think alike, Bob! Project I'm doing right now is a sort of hybrid between your grouse gun you just mentioned and this build. Using a shortened Disco tube, 18 - 20" LW bbl and same CF shroud/air stripper/breech combo. Was originally going to get a BNM breech, but now I'm glad I held off on THAT purchase...your breech looks much better and definitely more practical

Eagerly looking forward to your results with the longer barrel and accuracy tests. That is a helluva nice rig you got going on there!


Todd

[SeanMP]

Looks good ,Bob! Can't wait for final everything to be done, and your results and opinions...

Now, some body come up up with a dual tube system for AR/QB :P

Regards,

Doc Sharptail

Absolutely.....Someday

[rsterne]

Sean and I discussed what direction we wanted to go with this project, and decided that we may as well max out the performance and then he will supply a smaller transfer port with the kit so that people can detune the gun easily for more shots.... We also decided to set the gun up for a 3000 psi fill by using 10-32 screws to mount the valve.... With that in mind, I pulled the valve, installed the larger screws, drilled the throat out to 1/4", and enlarged the exhaust port to 7/32", the same size as the transfer and barrel ports.... Here are the results, still using the 21" PB barrel and the .308" upsized pellets.... We expect a bit more with the 25" barrel....



The power at 3000 psi with the preload at coil bind is now 105.7 FPE.... At 2 turns out, the first 3 shots are nearly constant velocity at 101 FPE, and at 4 turns out there is a very good 8 shot string averaging 949 fps (92 FPE) starting from 3000 psi and dropping to 2100, with an efficiency of 0.78 FPE/CI.... Since the magazine will hold 7 shots, this tune will give a full clip at maximum power, a good choice for hunting.... At 6 turns out, the gun is the most efficient, delivering 10 shots averaging 915 fps (86 FPE) at 1.05 FPE/CI, from a 2700 psi fill and refilling at 1900 psi.... At 8 turns out, the power is down to 78 FPE, still at 10 shots, with a pressure range from 2400 down to 1600 psi.... I particularly liked the way the gun shot at 5 turns out (the black line) where it gave 9 shots averaging 937 fpe (90 FPE) from 2800 psi down to 2000 with an efficiency just under 1.0 FPE/CI....

The barrels are now here, and Sean will be chambering my barrels and I hope to have them within a couple of weeks.... Then I just have to find enough time during our coming busy Tourist Season to do the necessary work to install and test them.... I have two .30 cal barrels coming, one of which Sean will be choking, plus a .25 cal for testing the gun with 53 gr. cast bullets, and the 47 gr. hollowpoint version as well.... I'm really looking forward to seeing the results....

Bob

[rsterne]

I couldn't do any more testing until I get the new barrels.... so I decided to see how this barrel would shoot with cast bullets.... I pulled the barrel off and increased the chamber length with the reamer I made so that it would chamber a 118 gr. Lee FN, cranked the RVA to maximum preload, and fired a string across the Chrony.... It was one of those rare times when having the gun maxed out was the perfect solution, I was rewarded with a beautiful 7 shot string with a 4% ES....

667
680
687
693
687
684
670

The peak energy was 126 FPE, the average was 122 FPE, and the efficiency was 0.80 FPE/CI.... which is not bad considering the power level.... This is almost as much power than I got with my 9mm Disco Double, and more than I got with the .308 version, both of which were 24" barrels.... so I was very pleased with the results.... This really has nothing to do with this project, it was just a matter of satisfying my curiousity....

Bob

[rsterne]

I got my new barrels today from Sean, and all I can say is WOW !!!



He machined the chambers, crowned and choked one of them and taper lapped the bore (1000 strokes), and then even polished the outside.... It looks like Chrome inside and out, I can't wait to see how it shoots.... The JSB .30 cal pellets are a PERFECT fit in the chamber and engage the leade beautifully, leaving good rifling marks on the head, but without smearing the area between....

In addition, he shipped me some of the CF Shrouds, and even cut them to length.... I had previously machined a Hatsan air stripper to fit inside the end of the shroud and made a .30 cal insert for it.... and it slid inside perfectly.... The shroud is 7/8" OD, to match the Disco and Disco Double tubes.... It will end up in compression, with the barrel in tension, when the stripper is snugged into place on the threaded muzzle....

Now to find some time to machine in the O-ring groove in the breech and the barrel port and thread the muzzle for the stripper....

Bob

[rsterne]

We had a slow week at the Motel, so I got a chance to get into the shop and machine the O-ring groove and port into the new barrel today.... I shortened the shroud so that when the air stripper is tightened the muzzle is just clear of the front of the threaded section of the stripper and got to take a look at the new gun assembled for the first time.... It still needs some parts blued, but here is the first photo with the new barrel, shroud and stripper in place.... The gun weighs exactly 8 lbs. and I'm extremely pleased with the appearance.....



The first shot over the Chrony was 1045 fps, but my tank need topping up, so after 3 hours on the ShoeBox, after dinner I got to shoot a set of strings.... I filled to 3000 psi and shot until the velocity dropped 4% below the peak in each case.... The last 4 strings required less than a 3000 psi fill, as I was reducing the hammer spring preload for each subsequent string.... Here are the results....



Maxed out, the first shot was the fastest at 1049 fps (112 FPE).... At 4 turns out, I got 10 shots that were within 4% ES, and they averaged 975 fps (97 FPE), peaking at just over 100 FPE.... The efficiency was 0.91 FPE/CI, filling to 2900 and refilling at 1880.... At 7 turns out, I got 12 shots averaging 912 fps (85 FPE), with an efficiency of 1.11 FPE/CI.... The fill pressure was 2400, refilling at 1520.... I think if I installed a slightly smaller transfer port I could stretch the string to 14 shots (2 clips)....

I'm very pleased with these initial results.... With the first serious testing of the new barrels producing MOA acccuracy out to 100 yards, this should be a serious hunter.... I'm looking forward to getting the new 7 shot magazines from Lloyd at AirGunLab.... He has converted .25 cal MRod magazine to .30 cal, and they look gorgeous.... My breech was made to fit them....

Bob

[rsterne]

Since this gun is going to have a 7 shot magazine, I was curious what I could get for 7 shots starting at 3000 psi.... Here is the string....

984
1000
1007
1003
997
993
981

Average fps = 995
Average FPE = 101.1
Total FPE = 708
Press. Used = 750
psi / shot = 107
Total CI Used = 786
FPE/CI = 0.90
% ES = 2.6%

I'm thinking this is a heck of a Coyote gun....

Bob

[sholo]

I'm extremely pleased with the appearance.....

As you should be...that is a gorgeous, well executed build, Bob. Awesome power, too - one of your finest builds yet IMO!

That one-magazine, 7-shot string is beautiful...last shot pretty well mirror's the first, and all 7 shots within 2.6% of peak FPS?......Niiiiiiiiice!


Cheers,
Todd

[bitterman]

Both looks amazing and performs awesome!

Bruce