Author Topic: .30 cal Disco Double (Read 73329 times))

rsterne · « **Reply #100 on:** May 23, 2013, 12:36:41 PM »

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

lloyd-ss · « **Reply #101 on:** May 23, 2013, 12:37:11 PM »

Quote from: rsterne on May 20, 2013, 10:41:17 PM

HI Lloyd, thanks for chiming in.... much appreciated.... I used 1010 mild steel with a 44K yield in my calculations, and with three screws all taking equal load, I get a 0.150" contact width per screw required at yield at 3000 psi.... in other words, if the yield strength is 44K, with 3 screws, they in theory should "settle in" and stop moving after that.... Using a 0.312" hole and a 0.270" head, that means the screw has to move 0.004" aft.... for a total of 0.025".... This is assuming, of course, that all the holes in the valve and the tube are drilled in EXACTLY the same plane, which is VERY unlikely.... I didn't duplicate the calculations using 70K for the compressive strength of the tube because I don't know what material it is.... but CrMoly is only 63K yield IIRC?....

Anyway, I overestimated how far the valve is likely to move back, but since I've seen a fractional settling in even with a 5/16" head size on the 10-32 screws at 3000 psi (I thought you had as well?).... I think we can assume that the valve might, on average, end up about 0.025" further back than it should.... but we can also assume that once it has settled into it's new position it should be perfectly safe.... wouldn't you agree?.... Sorry if I first erred on the side of caution....

Bob

Bob,
Sounds like we are pretty much in agreement on this, and I agree that the full dia 5/16" heads are by far the best choice. The 72ksi compressive yield figure for the tube that I used is for A513 Ty 5 DOM steel tube which is basically strain hardened 1020. I could be wrong, but that is a good guess for many air tubes (A513 Ty 5 DOM 72ksi Y, 87ksi UT; 4130 Normalized tube 63ksi Y, 97ksi UT) . Plus it is much cheaper and threads more nicely IMO.
Lloyd

rsterne · « **Reply #102 on:** May 29, 2013, 07:56:41 PM »

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

Bruce · « **Reply #103 on:** May 29, 2013, 08:11:56 PM »

Awesome progress and great numbers!!!!!!! the longer barrel should up the numbers even more if you want!

Congratulations!

Bruce

rsterne · « **Reply #104 on:** May 30, 2013, 07:46:35 PM »

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

PakProtector · « **Reply #105 on:** May 31, 2013, 07:01:15 AM »

Thanks for publishing the fine work Bob. I am getting a serious case of the shakes over making the next set of Marauder valve mods; bigger holes are definately called for...

and what you have gotten leaves me confident in its ability to deliver near 100 FPE energy with 50-53 gr castings. getting peller-cheap boolits is quite another story...LOL and an order for my Very First Mold should be completed today.
cheers,
Douglas

PakProtector · « **Reply #106 on:** May 31, 2013, 07:01:43 AM »

ooops...gonna have to delete this one

rsterne · « **Reply #107 on:** May 31, 2013, 08:18:58 PM »

It will be tougher to get 100 FPE with 50-53 gr. in .25 cal than in .30 cal of course.... Not impossible, but the larger area gives more force for acceleration in the bigger bore.... Having said that, the much higher SD of the cast bullet in .25 cal will allow you to keep the valve open longer without loosing too much efficiency.... or so goes the theory.... I'll be doing the same thing, once the new .30 cal barrel is installed and tested I will be putting a .25 Auto liner on the gun and seeing what I can get with cast 47 gr. HP and 53 gr. Solid .25 ACP bullets from an RCBS mold.... I'm thinking I may even try a .357 liner chambered for the new 78 gr. JSB pellets after that....

Bob

PakProtector · « **Reply #108 on:** May 31, 2013, 09:18:45 PM »

Quote from: rsterne on May 31, 2013, 08:18:58 PM

It will be tougher to get 100 FPE with 50-53 gr. in .25 cal than in .30 cal of course.... Not impossible, but the larger area gives more force for acceleration in the bigger bore.... Having said that, the much higher SD of the cast bullet in .25 cal will allow you to keep the valve open longer without loosing too much efficiency.... or so goes the theory.... I'll be doing the same thing, once the new .30 cal barrel is installed and tested I will be putting a .25 Auto liner on the gun and seeing what I can get with cast 47 gr. HP and 53 gr. Solid .25 ACP bullets from an RCBS mold.... I'm thinking I may even try a .357 liner chambered for the new 78 gr. JSB pellets after that....

Bob

I got one from Veral, and found a 252435 on the auction site. You have any idea what the marking FW after the model number means? The 100 FPE is jus' a number...I don't think I will be able to live with its efficiency at that power level. Upper 800's will be fine...

cheers,
Douglas

rsterne · « **Reply #109 on:** May 31, 2013, 09:42:10 PM »

Don't know what the "FW" means....

Bob

SeanMP · « **Reply #110 on:** June 01, 2013, 10:29:05 PM »

Bob

I really like that #3 and #4 string. I'd like them even more if they were shifted up about 5%.

And I think its possible with a really good barrel. With that in mind I think a full length taper lap with ultra smooth finish is a must on the barrel that's getting the choke. It only seems fair to see just how much of a powerhouse you've got there.

OleTomCat · « **Reply #111 on:** June 02, 2013, 02:03:33 AM »

Just took an hour and read all six pages, all I can say is WOW.....

Can't wait to see the finished project....

rsterne · « **Reply #112 on:** June 02, 2013, 02:19:35 PM »

HEY Sean.... Welcome back to the land of the living.... *grin*.... If you want to do that fancy lap job, be my guest.... *LOL*....

I can't wait to see the new barrels.... We'll lose a bit of efficiency with the 0.008" smaller bore, but should gain way more with the 4" increase in barrel length.... It was nice to hear that the pellet fit in the new barrel was spot on.... full rifling engagement on the head without shaving it from the groove diameter.... It was also good news that the first order is nearly sold out and you will have to get some more already.... (gentle nudge for anyone still interested to send a PM to SeanMP to get in on the second order)....

Bob

grumpy · « **Reply #113 on:** June 02, 2013, 03:44:19 PM »

I need to get off my butt and put that 29" barrel to use..

SeanMP · « **Reply #114 on:** June 02, 2013, 04:21:14 PM »

Quote from: grumpy on June 02, 2013, 03:44:19 PM

I need to get off my butt and put that 29" barrel to use..

Hey, I'm gonna take a wild guess and say you got it okay then?

SeanMP · « **Reply #115 on:** June 02, 2013, 05:33:59 PM »

Okay Bob here is the finished chambering ream

The leade is subtle at 1.1* This is what the angle worked out to that will hold the head and the skirt equally.

grumpy · « **Reply #116 on:** June 02, 2013, 06:57:07 PM »

I did and thank you. Just curious how the unchocked barrel will do with the 50 gr pellets.

Quote from: SeanMP on June 02, 2013, 04:21:14 PM

Quote from: grumpy on June 02, 2013, 03:44:19 PM
I need to get off my butt and put that 29" barrel to use..

Hey, I'm gonna take a wild guess and say you got it okay then?

rsterne · « **Reply #117 on:** June 02, 2013, 07:27:15 PM »

All the blanks are unchoked.... I'm having Sean roll a choke into one of the two I'm getting so that hopefully I can answer that question....

Yeah, that's a shallow leade, Sean.... I'm trying to figure out your reamer, is the portion between the front of the pilot and the smallest part of the leade undercut so that it doesn't touch the rifling?....

Bob

SeanMP · « **Reply #118 on:** June 02, 2013, 11:32:21 PM »

Ya that's it exactly Bob. It gives a bit of distance between the pilot which has minimal clearance and the business part where the swarf is.

You can see the same idea going on here in the cartridge reamer pic

SeanMP · « **Reply #119 on:** June 03, 2013, 03:37:28 PM »

Okay Bob your barrels are ready to go

First they were dialed true to the axis. Concentric and axial to 0.0001"

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.30 cal Disco Double

Author Topic: .30 cal Disco Double (Read 73329 times))