Author Topic: .30 cal Disco Double (Read 73352 times))

SeanMP · « **Reply #120 on:** June 03, 2013, 03:51:16 PM »

Then the chamber was cut

Then the barrel was flipped and the choke rolled in

After that the lead lap was cast at the muzzle

And after a thousand strokes we have a tubular mirror with a slight taper

rsterne · « **Reply #121 on:** June 03, 2013, 11:18:10 PM »

Very cool, Sean.... looking forward to getting them.... 1000 strokes?.... WOW !!!

Bob

lloyd-ss · « **Reply #122 on:** June 16, 2013, 01:09:27 PM »

I'm just catching up on the progress here, and am finding it fascinating.
Sean, that is one of the barrels from Mike Sayers, correct? And you are doing a choke plus a taper lap, correct?
Do you have a mechanical set-up to do the lapping, with an ever increasing stroke length or something of the sort? I really like the taper reamer you made for the breech.
Just so that I fully understand, the main reason for all the attention to detail on the barrel is for accuracy, correct? But you also mentioned the possibility of increased fps?
Thanks for any additional insight you might have to offer,
Lloyd-ss

strever · « **Reply #123 on:** June 16, 2013, 11:12:33 PM »

Sean
did you make this reamer ?

Quote from: SeanMP 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.

rsterne · « **Reply #124 on:** June 17, 2013, 12:33:27 PM »

Yes, he did.... He makes custom reamers to do all his airgun chambering jobs....

Bob

rsterne · « **Reply #125 on:** June 18, 2013, 05:42:56 PM »

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

SeanMP · « **Reply #126 on:** June 18, 2013, 11:01:48 PM »

Quote from: lloyd-ss on June 16, 2013, 01:09:27 PM

I'm just catching up on the progress here, and am finding it fascinating.
Sean, that is one of the barrels from Mike Sayers, correct? And you are doing a choke plus a taper lap, correct?
Do you have a mechanical set-up to do the lapping, with an ever increasing stroke length or something of the sort? I really like the taper reamer you made for the breech.
Just so that I fully understand, the main reason for all the attention to detail on the barrel is for accuracy, correct? But you also mentioned the possibility of increased fps?
Thanks for any additional insight you might have to offer,
Lloyd-ss

Lloyd sorry for the delayed response...I have also had my nose on the grindstone for the past month trying to catch up after being away for 11 weeks.

Yes that is one of Mike's barrels. And yes I'm putting a choke in and lapping them. Bearing in mind that the taper is minuscule. It only ensures that the projectile is tight to walls all the way up the bore.
Yes this is done primarily for accuracy but I have found in every case that there is an increase in fps after the bore is properly lapped and polished. Bob has found the same as well. I think the main reason for this is because the pellet is maintaining a seal on a very smooth surface.
I do my lapping by hand. And personally I think that is a job that only be done manually because it is very much a "feel" process. First your feeling for slight drag and release to tell you that there are tight/loose areas or chatter that indicates machining marks and then feeling the equal drag that tells you the bore is parallel. Then your feeling for an increase or decrease in drag to indicate your taper. All the while feeling for when to tighten the lapped based on drag.

SeanMP · « **Reply #127 on:** June 18, 2013, 11:05:56 PM »

Bob....All I can say is WOW!

The shroud and the stripper are going to look amazingly bad.

Sweeeeet!

lloyd-ss · « **Reply #128 on:** June 20, 2013, 08:56:23 AM »

Sean,
Thanks for the additional info on the barrel processing. I understand what you mean about lapping the barrel. The "golden arm" technique with lots of patience where it is more art than science. The increase in fps is good information.

Bob,
Putting the barrel in tension adds another variable to the accuracy tuning process, LOL. Tensioning for a specific pellet and velocity, and my guess is that it just might be tuneable that way. Maybe?

Lloyd

rsterne · « **Reply #129 on:** June 20, 2013, 12:36:13 PM »

I agree, it may very well be possible to tune for a specific pellet and velocity with the barrel tension.... I haven't played with that before, so another variable, which can be good or bad.... The adjustable gap on the air stripper is yet another tuning point, and one I have heard can make quite a difference....

Bob

rsterne · « **Reply #130 on:** June 27, 2013, 12:48:14 AM »

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 · « **Reply #131 on:** June 27, 2013, 06:46:34 PM »

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

grumpy · « **Reply #132 on:** June 27, 2013, 07:07:14 PM »

Most impressive !!!

Bill G · « **Reply #133 on:** June 27, 2013, 07:57:43 PM »

Bob, that is a heck of a gun period. If you must put an application to it, I think it would be best stated as a,"anything under 80lbs gun".

have you looked at what the retained fpe is at 100yrds yet? I don't bet, but if I did, I'd bet that your bullet has more fpe than a .22LR does at 100 yrds. I missed what the .30 jsb weight is but if it is greater than 40gr, There is a good chance I'm right.

yes, MOST impressive.
Bill

rsterne · « **Reply #134 on:** June 27, 2013, 08:59:19 PM »

The BC of the new 46 gr. JSB pellets (they also make a 50 gr. I haven't received yet) is unknown at this time, but I'm guessing it's quite a bit less than a 40 gr. bullet from a .22LR.... Starting subsonic will help, of course, but I don't think it will quite have the FPE of a .22 LR at 100 yards.... Momentum is another thing, they may be close....

Bob

OleTomCat · « **Reply #135 on:** June 27, 2013, 08:59:50 PM »

Quote from: Bill G on June 27, 2013, 07:57:43 PM

Bob, that is a heck of a gun period. If you must put an application to it, I think it would be best stated as a,"anything under 80lbs gun". have you looked at what the retained fpe is at 100yrds yet? I don't bet, but if I did, I'd bet that your bullet has more fpe than a .22LR does at 100 yrds. I missed what the .30 jsb weight is but if it is greater than 40gr, There is a good chance I'm right.

yes, MOST impressive.
Bill

I guessed on the BC of 0.05, everything else is straight from his data....

Your Input Variables
Ballistic Coefficient 0.05
Velocity (ft/s) 995
Weight (grains) 46
Maximum Range (yds) 100

Ballistics Results Range (yards) Velocity (fps) Energy (ft.-lb.) Trajectory (in) Come UP in MOA Come UP in Mils

Muzzle 995 101 -1.5 0 0
25 909 84 3.3 -12.5 -3.6
50 843 73 5.4 -10.3 -3
75 787 63 4.5 -5.7 -1.7
100 738 56 0 0 0

Bill G · « **Reply #136 on:** June 28, 2013, 02:35:32 AM »

56 fpe at 100yrds. 55% retained energy? That is impressive. It is getting to the point with airguns, that the only reason for a powder burner is for ranges that exceed 100yrds and a need for supersonic bullet delivery. It is awfully hard to beat supersonic bullet delivery in regard to effect on target.

Absolutely B--A-- gun
Bill

DG · « **Reply #137 on:** June 28, 2013, 08:26:27 AM »

I shot my .30 build over a chrony at two different distances to calculate BC for the 44gr JSB pellets and came up with @ .042 for the BC. I've not done the 50gr pellets yet.

sperho · « **Reply #138 on:** June 28, 2013, 08:45:17 AM »

That's a good looking powerhouse of a gun Bob. Great work and thanks for bringing us along on the journey. Now for a post in the Hunting Gate!

rsterne · « **Reply #139 on:** June 28, 2013, 12:22:05 PM »

Quote

I shot my .30 build over a chrony at two different distances to calculate BC for the 44gr JSB pellets and came up with @ .042 for the BC

At what velocity (and distances).... that will affect the results.... Seems like a reasonable value, though....

Bob

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.30 cal Disco Double

Author Topic: .30 cal Disco Double (Read 73352 times))