.30 cal Disco Double

[DG]

starting about 10 feet from the muzzle for the near, and right at a measured 50 yards for the far. Velocity was kept in the 880's with the average being 887fps.

[Bruce]

looking awesome!

Bob, are you having issues getting the 50.15 JSB? If you need a few for testing I could send you a few. I only have 2 tins of JSB 50.15 and 1 tin of Daystate Emperor so I can't spare a full tin. I expect will be shooting cast more than pellets in our barrel but only time will tell.

Bruce

[rsterne]

DG.... In that velocity range, over most of the distance, and from my experience with smaller calibers of JSB Exacts, you should be in the "sweet spot" for the BC.... If you push them faster I would expect the BC to drop....

Bruce.... no joy on the 50 gr. but I think I have a source lined up for a sleeve of 5 tins, thanks.... *fingers crossed, waiting for a PM*....

Bob

[DG]

thanks for the confirmation, Bob... But, I have to tell you a have a wee bit of experience with cobbling something together. It wasn't really an accident that I set up to figure the BC of the .30 pellets the way that I did.



I just finished the last pieces for this one yesterday late afternoon. I will be working on getting it completely finished over the next couple of days once I am happy with the target results.

[rsterne]

Thing of beauty.... Your work looks familiar, but the moniker threw me.... What barrel are you using?....

Bob

[strever]

Dave
i have to agree with Bob
that is a thing of beauty
worth drooling over 

thanks for the confirmation, Bob... But, I have to tell you a have a wee bit of experience with cobbling something together. It wasn't really an accident that I set up to figure the BC of the .30 pellets the way that I did.



I just finished the last pieces for this one yesterday late afternoon. I will be working on getting it completely finished over the next couple of days once I am happy with the target results.

[DG]

don't want to hijack Bob's thread. Worthy build he is working on, and I don't want this to become a distraction from the original content of the thread...

Bob, I work largely with Smooth Twist barrels, but not exclusively. My .30 builds thus far have all been ST's, which I feel work brilliantly with the JSB pellets. For heavier ammo in the same caliber, I am looking to follow the results you guys are getting with the TJ's.

I generally don't produce an action to work with pellets or cast ammo, but rather purpose build for the intended ammo...

[rsterne]

I agree.... For cast bulets, I would stick with the standard 0.308" bore size.... there is a much larger choice of molds / bullets available.... Much like in .25 cal, for pellets stick with 0.250", for bullets, go to 0.257" with a faster twist.... although you can use the 50 gr. .25 ACP bullets in an airgun barrel.... I have a .25 Auto liner from TJ's that I will be putting on this gun and setting it up to shoot up to 53 gr. casts that will fit in an MRod magazine....

Bob

[rsterne]

I finally got back to this project today.... I received some of the converted Marauder magazines from Lloyd at AirGunLab and had a chance to finish them up.... If you are interested in these .30 cal magazines, I suggest you contact Lloyd to enquire about them.... http://www.airgunlab.com/ .... As yet, they are not on the website.... Here is how they look, along with a .25 cal single shot tray I modified by increasing the diameter of the channel to fit the .30 cal pellets....



Lloyd starts with a .25 cal MRod magazine and has a new 7-shot star wheel made by CNC for the larger pellets.... It is engraved with the shot numbers, which I filled in with white paint to make them more visible.... In addition, the clear plastic cover is changed to read .30 cal, and the kidney bean shaped hole is enlarged as well.... On the magazines I received I still had to drill out the hole in the back to feed the larger pellets.... I centered off the original hole, and used a 5/16" end mill for that.... When I reassembled the magazines I added 1/3 turn of tension to the spring to compensate for the larger pellets.... It may have not been necessary for feeding, but they certainly do advance with authourity, and the skirts are so thick on the .30 cal JSBs I can't imagine the slight increase in spring tension causing any damage....

I'm in the process of mounting a scope and hope to do some testing soon....

Bob

[rsterne]

After three months of waiting for Airguns of Arizona to come through with my pellets I cancelled the order and got them from Specialty Shooting Sports.... I originally ordered the 50 gr. JSBs from AoA and they (knowing they were incorrect) shipped the 45 gr.... I told them I'd keep those and to ship the 50 gr. when they came in (in a month), and after 2 months I contacted them and they told me JSB didn't ship them.... After chewing them out (again) for not letting me know, they agreed to substitute the Daystate 50 gr. (same pellet but more expensive) when they arrived in 2 weeks.... A month later I called them yet again and found the Daystates hadn't arrived either (and once again they didn't let me know), so I cancelled the order and got them in 3 days from SSS.... Anyway, that is the reason for the lengthy delay in getting back to this project....

I now have the 7-shot converted mags from Lloyd at AirGunLab, and after a bit of tuning to function with my flat faced bolt, they function flawlessly.... I had four pellets to test now, some #1 Buck from Ballistics Products, 44.8 gr. JSBs, 46.4 gr. FX, and 50.2 gr. Daystates.... I weighed 10 of each and they came out at follows:

#1 Buckshot - 39.6 gr.
JSB - 45.2 gr.
FX - 44.8 gr.
Daystate - 49.4 gr.

The #1 Buck were rather inconsistent in diameter, running from 0.294" - 0.302", with most between 0.296"-0.300".... While they were too loose in a 0.308" PB barrel, or the one on my DAQ, they worked perfectly in our new 0.300" barrel, and chambered easily (without the small ones rolling out the muzzle like they did on my DAQ).... The JSB and FX pellets are from all measurements exactly the same.... The previous tins of FX pellets I had weighed 45.3 gr, so it would appear that 44.8 to 45.3 is normal for both brands.... The Daystate pellets are exactly the same length as the FX, and they are availlable under the JSB label as well, I just haven't been able to get any.... The extra weight comes from a thicker waist, they measure 0.257" instead of 0.214".... All the pellets shot into one (large) ragged hole during my indoor Chrony session, although the roundball group was nearly 1/2" OD whereas the others were more like 3/8".... It's very satisfying to see a big hole appear in the paper and then see the rest of the shots go through it, barely enlarging it, even when shooting at only 20'....

I started out with the hammer spring preload set just shy of coil bind, and tested all four pellets at that setting.... The roundball screamed through the Chrony at 1079 fps and 102 FPE, the JSB & FX 45 gr. weren't far behind at 1050 (110 FPE), and the Daystate 50 gr. hit 1015 fps (113 FPE).... The roundball were really just a curiousity, and I had already extensively tested the 45 gr. FX pellets, so I used the Daystate 50 gr. for the rest of the tests.... I reduced the preload a turn at a time, recording all shots within 4% of the peak velocity in each string, as follows:



At 1 turn out on the preload, I got a 7 shot string (1 full clip) averaging 988 fps (107 FPE) with all shots within a 2.8% ES, and the first 6 shots within 1.8%, with an efficiency of 0.92 FPE/CI, pretty decent for over 100 FPE.... At 2 turns out, the shot count with a 4% ES jumped to 10 at 102 FPE, still starting with a 3000 psi fill (ending at 2200) with an efficiency of 0.99 FPE/CI.... At 3 turns out, the fill pressure was 2800 psi, and I got 11 shots at 97 FPE at 1.05 FPE/CI and at 4 turns out, using a 2700 psi fill, I got 11 shots averaging 94 FPE at 1.09 FPE/CI.... Any of these tunes would be very usuable, and selecting the 7-shot sweet spot at the top of the curve would give minimal POI change, even out to 100 yards.... at peak velocities of 940, 960, 980, or 1000 fps (with the 50 gr. Daystates) depending on choice of preload and hence fill pressure....

Testing at longer ranges is problematic at the moment as pressing family matters and travel is going to detract from my target time.... However, with two weights of pellet to choose from, and the ability to fine tune the velocity, I would expect to find at least one combination that proves stellar....

Bob

[lloyd-ss]

Bob, my good man, you have done it again! Your attention to detail always makes the big difference, IMHO. Even though you haven't thoroughly tested it at long range, I am sure that with Sean's barrel, the end result will be striking.  An honest long range hunting gun.

You mentioned the 7 shot 30 cal mags that I made for this project. Even though I do not yet have them on the AirgunLab website, I will certainly make them available to anyone using one of Sean's barrels. Other responsibilities continue to keep my airgun time at a painfully low level, but there is an end in sight where I will be able to ramp the airgun effort back up. It is still  a few months away, but I'll be back.
Lloyd

[rsterne]

I finally had a chance to get the gun out for some long range shooting today.... It is tuned for one 7-shot clip at 107 FPE with the 50 gr. Daystates (988 fps) or 105 FPE with the 46 gr. FX/JSB pellets (1012 fps).... I first shot a 3-shot group with each pellet at 50 yards, and they were all under a quarter, with this being the best....



That measures 1/2" C-T-C.... I then shot a 5-shot group with each pellet at 100 yards.... Here are the targets....

Daystate 50 gr.



JSB 45 gr. (higher aim point)



FX 46 gr.



There was a slight wind swirling around though the trees.... Four of the five shots in each group are within 1.0" - 1.2", and the average group size was under 2" except for the 1 shot I pulled.... I didn't do any tuning of the air stripper, nor did I check to see if the accuracy is any better at a slightly lower velocity.... To be frank, I wasn't shooting at my best in the cold weather, it was just above freezing today, and I know for a fact I pulled the one FX pellet up and to the left.... Overall, I'm very pleased with the groups for a first time out.... I stapled a pellet tin (2.5" D) to the 100 yards support and nailed it first shot.... All three pellets print at very nearly the same POI at 100 yards....



The development work on the .30 cal version is now complete, and it's time to start work on the .25 cal barrel.... This testing certainly proved that the .30 cal barrel Sean and I designed for the .300" head size JSB pellets does the job....

Bob

[SeanMP]

Hmmm....Awesome!

Excluding the called flier that FX group is actually sub MOA. Excellent!

I think it would be safe to assume that with tuning this would improve.

Thats quite an achievement. Sub MOA with an air rifle shooting pellets is remarkable....something high end bolt actions only achieve after some tweeking.

nothing like setting the bar up a notch

[rsterne]

Before leaving the .30 cal, I had one more thing I wanted to try.... The bolt on this gun is probeless, you push it forward to seat the pellet, turn the handle down, and then retract it clear of the barrel port.... It occurred to me that if I had an adjustable stop in the "J" slot I could set how far back the bolt retracts, and hence use the nose of the bolt to restrict the barrel port.... Here is a photo of it installed in the breech....



I drilled a 3/32" hole in line with the "J" slot from the back of the breech, then drilled in and tapped the back of it for a 1/2" long 6-32 SHCS.... The screw pushes on a 0.8" long brass pin for the bolt stop, which can be adjusted from fully open to stopping the bolt with the nose virtually at the front of the barrel port.... The screw might have a tendency to back out, so I drilled up from the bottom of the breech, near the back, and installed a 1/4" long piece of 0.095" weedeater line pressed against the adjusting screw by a 6-32 setscrew to provide a "brake" by adding friction so it won't self-adjust.... Everything worked great, so I proceeded to testing it....



I ran the adjuster in all the way, filled the gun to 3000 psi, and fired two shots.... turned the screw out a turn and fired two more, and repeated until the stop pin was flush with the end of the shot and therefore having no effect.... The purple stepped line on the graph above shows the results.... 310 fps, 550 fps, 740 fps, 870 fps, 950 fps, 980 fps, and just over 1000 fps.... There was no change in velocity for the last turn, it was the same completely clear of the "J" slot or 1 turn (0.032") in.... I turned the screw in 2 turns from maximum and backed off the hammer spring preload a turn (the measurements on the graph, eg. 0.337", are the preload, which moves 0.042" per turn) and shot a string.... My goal was two 7-shot magazines (ie 14 shots) at the highest possible FPE level within a 4% ES.... I played around with a few settings, and three of the 14 shot combinations are on the graph above.... It took the adjuster screw turned in 2.5 to 3.0 turns to get my 14 shot strings, and I ended up with the following:

86.6 FPE average at 1.08 FPE/CI
84.0 FPE average at 1.14 FPE/CI
82.7 FPE average at 1.18 FPE/CI

With the gun set for a single 7 shot string (1 magazine) at maximum FPE, it shoots 101.2 FPE at 0.90 FPE/CI with all the shots within 17 fps (1.7% ES).... All these strings are with the JSB 45.2 gr. pellets, the FPE levels are slightly higher with the 49.4 gr. Daystate pellets, averaging 107 FPE over 7 shots.... I have no doubt that by turning the velocity adjuster in more I could achieve more shots at less power, but two full magazines at 83-87 FPE is a good compromise.... I'm very pleased with the way the .30 cal version of this gun turned out.... When time permits, I will be getting on with fitting a .25 cal barrel to see what can be achieved when set up as a quarterbore....

Bob

[tkerrigan]

Is the end of the probe flat? If it is, what do you think would happen if the business end of the probe was scalloped out a bit for air flow purposes or does the o-ring position allow for this?  Regards, Tom

[drewciferpike]

I drilled a 3/32" hole in line with the "J" slot from the back of the breech, then drilled in and tapped the back of it for a 1/2" long 6-32 SHCS.... The screw pushes on a 0.8" long brass pin for the bolt stop, which can be adjusted from fully open to stopping the bolt with the nose virtually at the front of the barrel port....

While reading this, I found myself involuntarily yelling "YEEEEEESSSSSSSSSSSSSSSSSSS!!" (My wife thought I'd won the lottery, or something else equally pleasing. She was not happy when I responded to her query with, "Bob made the best stupid-simple power-adjuster, ever!")

Sometimes the simple things are best.

I honestly cannot wait to get a breech like this. I don't even have a PCP--I don't care if it's for my espresso machine. I just like things that do their job well, with a minimum of fuss. I like it Aristotelian, yo.

You just made my weekend.

[PakProtector]

You can incorporate this into a Marauder pretty easily. I am having the pull-back/probeless done for my .224 Marauder. Looking at the spare 2563 breech, there is plenty of meat available to run the adjustable stop into. I don't see a marauder in your sig tho...?
cheers,
Douglas

[drewciferpike]

I don't see a marauder in your sig tho...?

Nope...

I don't even have a PCP--I don't care if it's for my espresso machine. I just like things that do their job well, with a minimum of fuss. I like it Aristotelian, yo.

I just think this is so awesome, I want it to hang on my wall: "This is an example of something that is simple and effective."

[rsterne]

The end of the bolt is flat (there is no probe), scroll back through the thread for details.... It has to be flat to load the pellet squarely in the bore as it pushes on the outside of the skirt.... In "full power" operation it retracts completely, flush with the back of the barrel port.... and presents NO obstruction to the airflow.... One other advantage is that it will load bullets and pellets to the same place in the bore, just the other side of the barrel port.... All the adjuster does is limit how far it can retract....

Bob

[tkerrigan]

Just meant like this, though not quite as deep.  Regards, Tom    http://imageshack.com/scaled/large/802/tt8j.jpg