Author Topic: Regulated Disco Double  (Read 14645 times)

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #60 on: December 24, 2016, 02:20:13 PM »
Time to get down to business tuning this gun the way I wanted it in the first place.... The SSG using the QB spring did not have quite enough power, so I replaced it with a conventional RVA using the same spring but with preload.... In addition, I added a lightweight sliding spring guide as a valve lift indicator, so that I could make direct measurements of the valve lift at various preload settings.... Here is the SSG (lower) and the Lift Measuring Rod for comparison....



The same spring (from a QB) is used in both, so you can see how much preload I have in the SSG.... Conversely, you can see that with the preloaded setup, the spring will still be pushing the valve open throughout the entire shot cycle.... The Lift Measuring Rod is just a piece of 3/16" K&S aluminum tubing with a short flathead 8-32 screw in the end.... the head of the screw ends up captured between the spring and the hammer, so the tubing slides with the hammer.... There is a #008 O-ring on the end, which you push up against the RVA adjusting screw, then cock and fire the gun.... Since the tube travels with the hammer, the O-ring slides back along the tube the same distance the valve opens.... so the distance between the RVA screw and the O-ring is the same as the valve lift....

The regulator pressure was still sitting at 2000 psi, within as close as I could measure it, so the regulator seems to have settled down nicely and is now showing no signs of creep overnight.... When it was brand new, it was gaining about 100 psi overnight, and it is not unusual to see a short "break-in" period like this.... I filled the lower reservoir to 3000 psi, cranked the preload to maximum (coil bind), loaded the magazine with the new 34 gr. JSB Beasts, and fired 3 shots across the Chrony.... The velocities were 1006, 997, and 997 fps, and it used 1000 psi for the three 75 FPE shots.... Incidently, 75 FPE is exactly what my Spreadsheet predicted for my "lofty goal" with a 24" barrel at 2000 psi.... The barrel on this gun (although I ordered a 25") is 28" long, so that is 100% consistent with my expectations.... to fall short of the spreadsheet prediction by a small amount.... I measured the valve lift, and the O-ring gap was 0.200", which is all the travel the valve stem has before being driven flush with the back of the valve, so I had all the hammer strike I can possibly use (and more than I need).... I turned the RVA out 1 turn, shot another 3 shots, recorded the velocity, pressure drop for 3 shots, and valve lift, and continued doing that until the velocity dropped below 600 fps.... Here are the results....





There is a LOT of useful information in those two charts.... First of all, the velocity plateau, which is at 997 fps, starts when the preload is backed out 6 turns (1/4") from coil bind, and in fact there is no real drop in velocity for the next couple of turns.... At 6 turns out, the pressure dropped 580 psi for 3 shots averaging 994 fps.... but at 8 turns out, the pressure dropped only 400 psi for 3 shots averaging 983 fps.... At 9 turns out, the pressure only dropped 320 psi for 3 shots averaging 963 fps.... In that 3 turns of adjustment, I lost 3% in velocity and used 45% less air.... and the efficiency increased from 0.74 FPE/CI to 1.25 FPE/CI.... Compared to maximum preload, when the hammer was hitting the back of the valve, it is only using 1/3rd of the air.... So 9 turns out is clearly the "knee" of the curve, with the downslope starting at 10 turns out.... You will also notice that until the preload was backed off 2 turns from coil bound, the lift stayed constant at 0.20" because that was the maximum the valve could physically open.... At 6 turns out, where the velocity just starts to drop, the lift is down to 0.14", and at 9 turns out, at the knee of the curve, it is just 0.10".... It is that decrease in lift, and its associated decrease in dwell, that decreases the amount of air released by the valve.... Since the throat of the valve is 0.266", driving the valve more than half that distance open gains nothing in power, it just wastes air.... I have seen this many times before, and now believe it to be a good rule of thumb for how much you need to allow the valve to open.... If it can physically open more than half the throat diameter, that's all you need to allow for.... That means that shortening the valve stem can allow for more useful hammer stroke, which can then reduce the cocking effort.... I may in fact drill a recess in the front of my hammer to allow another 0.050" of hammer stroke.... That should have NO impact on the maximum power, I should still be able to reach the plateau, even with the 34 gr. pellets....

I haven't yet shot a full string with the 34 gr., but based on these tests I should be able to get one 10-shot magazine at 960 fps (70 FPE) by the time the pressure drops to the 2000 psi setpoint.... and that was my goal.... In fact, when I started, I planned on using a PRod magazine, and they are only 8 shots.... but at that time I was unsure if I could get enough power at 2000 psi, and thought I might have to use 2200 for my setpoint.... I did fire a few shots with my 30 gr. BBT, and at 9 turns out the velocity was 1023 fps, dropping to right around 1000 fps at 10 turns out, so logically I should be able to get more than 1 full mag. with the BBTs.... One other thing I should mention, there is a BIG decrease in the report when you hit the knee of the curve, which is to be expected....

Bob
« Last Edit: December 24, 2016, 02:26:03 PM by rsterne »
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #61 on: December 24, 2016, 05:18:32 PM »
I milled a 3/16" diameter recess in the front of the hammer that is 0.050" deep to increase the hammer travel to 0.75".... Without changing the preload I gained about 20 fps at the 10T out position.... This is because the cocked force is the same but the uncocked force is less, dropping the average spring force slightly while increasing the travel distance.... This slightly increases the hammer strike without any increase in cocking force.... I shot a 10 shot string at that setting, and it had not dropped below the setpoint, proving the gun is capable of doing that with the 34 gr. JSB Beasts in the mid 900s on a 3000 psi fill....

I then shot a few shots with my 29.6 gr. BBT FN bullets at each preload from 10 to 12 turns out.... It was nearly 1000 fps at 10 turns, and just under 900 fps at 12 turns.... so that determined that 11 to 11.5 turns will be the likely setting for the FN bullets in the mid 900s.... It was about 50 fps faster with the 27.4 gr. HPs, so 12 turns out will be quite close for those.... I also shot some short strings with bullets sized at different diameters at 11 1/6 turns out, and got the following average velocities....

0.216" FN .... 972 fps
0.217" FN .... 963 fps
0.218" FN .... 956 fps
0.219" FN .... 956 fps
0.217" HP .... 1007 fps

I was curious what the relationship would be between diameter and velocity, and as expected the smaller bullets shot faster, because of less resistance inside the barrel.... I wondered about why the "as cast" bullets (they are the 0.219") weren't slower, and then I remembered that the chamber is 0.218", and the bullets were noticeably harder to load than the others.... so it was resizing them to 0.218" before they were shot, hence the reason the velocity stayed the same.... The total pressure drop for 10 shots was around 950 psi, so the pressure stayed above the setpoint for all 10 shots, in fact I would expect the 11th shot to not lose any velocity.... not that it matters, because it is a 10 shot magazine....

Bob
« Last Edit: December 26, 2016, 05:52:14 PM by rsterne »
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #62 on: December 26, 2016, 02:26:19 PM »
I installed the shroud today, and a scope and bipod.... It weighs 8 lbs. 10 oz. complete, or 8 lbs. even without the Bipod.... Without the scope and rings it is about 6 lbs. 12 oz....



I played around with the preload to find a setting that could work for both weights of BBTs and the 34 gr. JSB Beasts.... The RVA ended up at 11.25 turns out from coil bind.... and the gun is quite easy to cock like that.... I then shot some 10-shot strings, refilling to 3000 psi each time.... At the end of the strings it was pretty much right on the 2000 psi setpoint.... so I can shoot one magazine on a fill.... Here is what they look like....



The 34 gr. JSB Beasts averaged 874 fps (57.9 FPE) at an efficiency of 1.35 FPE/CI.... The 29.6 gr. BBT solids averaged 944 fps (58.6 FPE) at 1.24 FPE/CI.... and the 27.4 gr. BBT HPs averaged 988 fps (59.4 FPE) at 1.21 FPE/CI.... This was using BBTs sized to 0.217".... The ES on the Beasts was just 6 fps (0.7%), and with the BBTs is was just under 2%.... That should prove close enough for shooting out to 100 yards....

I then took the opportunity to see what adjusting the barrel tension does to the group size.... Without the shroud, the 28" barrel was pretty whippy.... It shot OK inside my shop, but the distance is only 20 ft.... Still, I can usually tell if the gun is a shooter or hopeless just during my Chrony sessions at that distance, if I pay attention to aiming.... The JSB pellets were pretty much all 5 touching, but the BBTs ranged from that to a loose 5-shot group you could just cover with a dime.... I installed the shroud, but with no tension on the Bellevilles, just enough to keep the tension adjusting nut from falling off the muzzle.... This did, however, drastically raise the POI, because I had indexed the barrel to the bottom, and it had a noticeable curve to it.... Once I rezeroed the scope, and using the 34 gr. JSB Beasts, I shot a series of 5-shot groups, tightening the nut on the Bellevilles 1/4 turn at a time.... I am using a stack of 5 Bellevilles, and they have a rate of 750 lbs. per 0.010" (singly), so that means each 1/4 turn increased the barrel tension by about 200 lbs.... I stopped at 1.5 turns, which would be about 1200 lbs. of tension in the barrel.... In theory I can go another 1/4 turn without driving the Bellevilles flat, but I don't like to do that, you can ruin them by causing them to take a "set".... I disassembled the stack after tensioning to 1200 lbs., and they had only collapsed less than 0.001" each, so I will use that 1.5 turns as my limit.... Here are the group sizes as I increased the tension with the 34 gr. Beasts....

0 lbs. tension = 0.30"
200 lbs. = 0.44"
400 lbs. = 0.22"
600 lbs. = 0.36"
800 lbs. = 0.19"
1000 lbs. = 0.17"
1200 lbs. = 0.28"

I then repeated the process with the 29.6 gr. BBT FN, sized to 0.217"....

400 lbs. tension = 0.38"
600 lbs. = 0.53"
800 lbs. = 0.48"
1000 lbs. = 0.59"
1200 lbs. = 0.15"

I then tried the 27.4 gr. BBT HP's, also sized to 0.217"....

800 lbs. = 0.45"
1000 lbs. = 0.21"
1200 lbs. = 0.34"

and then at that 1000 lbs. setting I tried other diameters of the HPs....

0.216" = 0.32"
0.217" = 0.21"
0.218" = 0.24"
0219" = 0.25"

I then reduced the tension to 1 turn (800 lbs.) and tried the HPs again....

0.216" = 0.22"
0.217" = 0.45'
0.218" = 0.15"

What I had been told was that once you reached a certain barrel tension, tightening past that point would not decrease the group size.... What I found was that low tensions did not work well, and that I do indeed need about a turn on the Bellevilles (about 800 lbs. of tension) as a minimum.... However, past that minimum, each bullet appears to have it's own optimum tension setting (sweet spot).... and that can change when you change the bullet diameter.... It likely also changes with the velocity.... In fact, anything that changes the dynamic vibrations of the barrel will likely move the sweet spot a bit.... The good news is, that the group size is dramatically reduced by using the tensioned barrel.... I would say that is a 100% success....

Incidently, when I started testing the tension adjustment I found that the POI on the target was walking around in a 6" circle, even at just 20 ft., as I changed the tension.... Since I had drilled only a 1/4" hole in the barrel extension that holds the Bellevilles, I suspected that the pellets were clipping the inside of it.... I removed it and couldn't see any marks inside, but I drilled it out to 9/32" (to provide 1/32" clearance for the pellet) and this went away completely.... There was a slight POI change with tension, as you would expect, but we're talking 1/2" instead of over 10 times that much.... The report is less, with the muzzle blast venting into the shroud, it sounds like a gun where you just backed off the preload a couple of turns.... You can start to hear the ping, but it is certainly not "backyard friendly".... In other words, it made a noticeable, and welcome difference, certainly worth doing if you live where they don't frown on having a quieter airgun.... It seems silly to me that adjusting the power to drop the noise is OK, but venting the air into the shroud and getting the same effect isn't.... It certainly is nothing like what you can achieve with baffles, or a separate LDC.... but it will protect your hearing somewhat, and well worth the 3" increase in length of the shroud....

Bob
« Last Edit: December 26, 2016, 02:27:57 PM by rsterne »
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #63 on: December 27, 2016, 06:50:02 PM »
I made a few small changes to the gun today.... I removed the top portion of the rear triple band because it interfered with the scope position.... It now only clamps the two reservoirs together.... The forward band remains the same, with an O-ring supporting the shroud, so that it can move independently of the reservoirs for expansion, but is located to prevent damage if you drop the gun or fall on it.... I call this arrangement "semi-floated".... I added an internal support, just a simple collar that is setscrewed to the barrel, with an O-ring in a groove that is in firm contact with the inside of the shroud, flush with the front of the band that supports the shroud.... That places it 3/7ths of the distance from the receiver to the muzzle, to dampen any harmonics between the tensioned barrel and the shroud.... I also machined twelve marks on the tension adjusting nut, to make a Vernier so that it is easy to ascertain the position of it during tuning the tension.... Every 3rd mark is slightly longer (3, 6, and 9 o'clock), and the 12 o'clock mark is the longest, and marked with black.... There is a corresponding mark on the top of the flange on the CF shroud that doesn't rotate as a reference mark....



It is the one that was vertical when the nut just touched the Belleville washers, and when tightened one turn puts nearly 800 lbs. of tension in the barrel.... I can tighten at least another half turn from there, and I can record the position as "3 o'clock", or "4:30", or "5:20".... which will make it easy to return to the setting which worked the best.... Each "hour" of rotation is about 65 lbs. of barrel tension.... I haven't yet tested the gun with the intermediate barrel support, and the Motel is booked until after New Years, so it may be a few days before I get the chance.... and even then it will only be at close range inside my shop.... I am hoping the intermediate support will even out the differences between pellets, and allow one tension setting to work for all.... I guess we'll see what happens....

Bob
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #64 on: December 29, 2016, 02:31:25 PM »
I burned through another tin of 34.1 gr. JSB Beast pellets today (actually more than a tin), playing with the tension adjustment on the barrel.... I found out that a "1 hour" change (about 65 lbs.) to the tension makes a significant difference to the group size.... but that virtually all the groups are better than previously, since I installed the intermediate support on the barrel.... Having a support between the barrel and shroud at 3/7ths of the distance from receiver to muzzle really settled down the variation in group size as you change the tension, bullet, or velocity....

I increased the velocity with the Beasts to 960 fps (70 FPE), and found that there was a sweet spot just past 1 turn of tension.... Using a 24 hr. clock, starting from zero tension, 1400 hrs. (2 hrs. past 1 turn) gave me the best groups.... Here is an example.... Yes, that is a 34 gr. JSB Beast .22 cal pellet sitting in the hole from a 5-shot group....



About half the 5-shot groups at that setting met the "Feinwerkbau Test".... Although I only have 20 ft. available, not the 10M that FWB uses.... I find that when a gun shoots like this inside, if there is a problem at long range, is tends to be the pellet/bullet, not the gun.... At this velocity, I am running right on the knee of the curve at the 2000 psi setpoint with the Beast, it uses 1200 psi for 10 shots, which works out to 1.13 FPE/CI.... I think that is pretty good for a .22 cal at 70 FPE.... With a 3000 psi fill, the last shot (taken below the setpoint) loses about 100 fps, but by filling to 3200 (the gun is safe to at least 3500 psi) the gun is sitting right at the 2000 psi setpoint at the last shot, and the ES is hovering right at 1% (8-10 fps) over the 10 shots....

This is pretty much the kind of tune I was looking for, so I think I'm done with the development of this gun until I can get outside in the Spring to test at longer ranges.... I can chalk this up to another very successful project.... with many thanks to Lloyd Sikes for supplying his new Regulated Disco Double Kit so that I could put it through its paces.... I would highly recommend it for anyone modding a Discovery.... It is capable of a ton of shots at lower pressures, and lots of power when you crank the pressure up.... The external adjustment is easy to use, and covers a wider range than I needed (I used 900-2200 psi during this project).... It can be used with a stock Disco, or one that is highly modified like this one.... I don't see how you can go wrong with it.... Congratulations, Lloyd, on another fine product from the AirGunLab....

Bob
  • Coalmont, BC

Monkeydad1969

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2027
Re: Regulated Disco Double
« Reply #65 on: December 29, 2016, 04:18:07 PM »
Congrats, Bob.  A job well done.  Very nice results.  I too can't wait till you can stretch it's legs out in the spring.

Joe
  • Aurora, Colorado
Joe the P-Dawg Slayer!!!!!

grumpy

  • Hero Member
  • *****
  • Posts: 524
Re: Regulated Disco Double
« Reply #66 on: December 30, 2016, 05:11:28 AM »
Can't wait to see you stretch her legs out some  ;)
  • Michigan

Dairyboy

  • Hero Member
  • *****
  • Posts: 887
Re: Regulated Disco Double
« Reply #67 on: December 30, 2016, 05:33:43 AM »
Agreed can't imagine a 70fpe .22 that would sure be a fun gun
  • Outlook, WA
John 3:16

.22 SPA M10
.22 JSAR Raptor Mini (on order)
.22 AAA EVOL Tac (on order)

Monkeydad1969

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2027
Re: Regulated Disco Double
« Reply #68 on: December 30, 2016, 06:29:55 PM »
Man, can't wait to unleash my soon to be beast.  You curious now, guys?

Again, very nice Bob.

Joe
  • Aurora, Colorado
Joe the P-Dawg Slayer!!!!!

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #69 on: January 04, 2017, 02:59:07 PM »
I wanted to find out what affect the Velocity Adjusting Screw on the back of the receiver had, and document it, so I did some testing today.... I tried three different weights at each of the 10 settings (1 turn apart) on the 8-32 adjusting screw by shooting a few shots, taking the average velocity, and plotting the results.... Here is that data....



The nose of the bolt doesn't quite block the barrel port completely, because the front end of the port is rounded to streamline the flow into the barrel.... and when you first start obstructing the port, the velocity doesn't start to drop until you turn the screw in a couple of turns, even though you can see the nose of the bolt through the back of the barrel and transfer port.... I presume this is because there is a bit of wasted volume in the back corner of the chamber, causing a bit of pressure loss when the bolt is fully retracted, which counterbalances the obstruction of the hole when you first start moving the bolt forward.... The black line represents my best estimate of the percentage of barrel port available at each turn of the adjusting screw....

Note that at 2000 psi, the 18 gr. JSB Heavies are Supersonic, hitting nearly 1200 fps.... in fact they don't drop below Mach 1 until the port is about 50% obscured.... I was interested in finding a setting in the mid 900s with each weight, so that I could run a string with each pellet/bullet.... It turns out that with the 18 gr. JSB Heavies I only needed the adjuster open 2 turns, and with the BBTs 4 turns, compared to wide open for the 34 gr. JSB Beasts.... I then used those settings and shot a string starting at 3000 psi, until the velocity dropped off.... Those strings are shown below....



You will note that with the 34 gr. Beasts I get 10 shots, averaging 67 FPE, before the velocity starts to drop off.... With the 30 gr. BBTs, I get 11 at 57 FPE.... and with the  18 gr. JSB Heavies I get 15 shots at 36 FPE.... The efficiency is slightly lower with the BBTs, 1.13 FPE/CI compared to 1.18 with the Beasts.... and even lower with the 18 gr. heavies, down to 1.00 FPE/CI.... This is in sharp contrast to what happens to the efficiency if you back off on the hammer spring preload to reduce the power, instead of choking up the ports.... It makes perfect sense, because choking the port has little effect on how much air the valve releases (other than a bit of increased backpressure), because you aren't really changing the dwell, you are just forcing the air to flow through a smaller port, which is less efficient.... This means that for a quick adjustment in velocity to go with an ammunition change, the Velocity Adjusting Screw is great.... but if you are after increased shot count there are better methods.... Reducing the hammer strike will give you great efficiency, but the velocity will bump up below the setpoint.... A better way is to reduce the regulator setpoint AND the hammer strike, as I showed with the 18 gr. JSBs much earlier in this thread.... I have found previously, however, that a combination of all 3 methods produces the best shot strings with lighter pellets.... In my .25 cal Disco Double, with the basic tune set to shoot 50 gr. bullets at 100 FPE.... the best strings with JSB Kings were achieved with a lower setpoint, less hammer strike, and a slightly restricted barrel port.... It's nice to have the option of that added tuning element when you want to go plinking....

Bob
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #70 on: January 04, 2017, 03:38:03 PM »
The second half of today's testing was penetration and expansion testing of the different pellets and my new Bob's Boattails, both the 29.6 gr. FN and the 27.4 gr. HP.... I used the same settings of the velocity adjuster as for the strings above, 2T out for the 18 gr. JSB Heavies, 4T out for the BBTs, and 9T out (wide open) for the 34 gr JSB Beasts.... The test medium is my standard "Melt-and-Pour" soap, cast into blocks big enough to stop the bullet.... Here is a photo of the block with the four rounds inside it....



The BBT Hollowpoint is entering from the left (at 57 FPE).... From the right, top to bottom, are the 18 gr. JSB Heavy (at 36 FPE), the 34 gr. JSB Beast (at 67 FPE) and the 30 gr. BBT FN Solid (at 57 FPE).... Those FPE levels are the result of wanting all the bullets to be in the mid 900s fps range when they hit the block of soap.... The 34 gr. Beast had by far the greatest penetration, at 6.5".... The 30 gr. BBT and the 18 gr. Heavy were nearly identical, at 4.2" and 4.1" respectively.... while the 27 gr. BBT HP exploded violently and dumped its energy by creating a large cavity before stopping only 2.4" into the soap.... The volume of the wound channel in the block is roughly proportional to the FPE.... I then cut the block apart to photograph the wound cavities with the bullets still in place.... Here is the photo of the 18 gr. JSB and the 30 gr. BBT FN....



Now you can see why the BBT stopped in about the same distance as the 18 gr. JSB.... even though it had way more FPE.... The pellet hardly changed at all, which the large Meplat of the BBT expanded to well over bore-size, while leaving a much larger diameter wound channel than the pellet.... kind of the difference between an ice-pick and a sledge-hammer.... Next is the photo of the 34 gr. Beast and the BBT HP....



The block cracked behind the JSB Beast, so I didn't get to photograph it, but the wound channel was long and thin.... and you can see the pellet was hardly changed at all by the 67 FPE impact.... Not so the 27 gr. BBT Hollowpoint.... It literally blew apart after entering only about 3/4" into the soap, leaving three large fragments of the nose (and 1 small one) behind as the base (and 1 more fragment) continued penetrating.... Below is a photo of the bullets and pellets after recovery.... BBTs on the left, pellets on the right....



As you can see, round nosed JSB Pellets punch through and penetrate with very little change in shape.... Both pellets showed a very slight flattening in the center of the nose, and you can see how the skirts have obturated (blown out) from the pressure inside the skirt.... The Meplat on the BBT FN solid nearly doubled in diameter, showing how effective the large (70%) Meplat is in providing energy transfer to the target while limiting penetration.... The Hollowpoint BBT, however, is in another class entirely.... The nose section blew apart, creating a wound cavity in the soap nearly 3 calibers wide, while the rear portion of the bullet mushroomed completely and continued to penetrate, although less than 60% of the distance penetrated by the solid.... I would suspect that bullet to be devastating on Varmints.... and look forward to trying it out in the Spring....

Bob
« Last Edit: January 04, 2017, 03:55:59 PM by rsterne »
  • Coalmont, BC

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #71 on: January 05, 2017, 05:17:15 PM »
I made one additional test today, I reinstalled the SSG.... I had not tried it since I increased the hammer travel to 0.75" and adjusted the setpoint to 2000 psi.... There was no problem getting either weight of BBT into the mid 900s with a decent gap, and I could just barely push the 34 gr. Beasts at 950 fps (68 FPE) with the gap adjusted to zero (but no preload).... There is still room to increase the hammer travel slightly, which would give me room to create a gap and still shoot the Beasts at 70 FPE.... but with the stunning performance of the BBT Hollowpoints in my expansion tests, and assuming I can get them to shoot accurately, I think I will set the gun up for those.... With the gap increased to 0.10" (2.5 turns out), the velocity with the 27.4 gr. HPs was 960 fps, and I shot a 10 shots string with an ES of just 10 fps (1%) using just 740 psi of air.... and a LOT quieter.... That works out to 1.45 FPE/CI, a 28% increase in efficiency compared to the same spring with preload at the same FPE.... The gun is a bit harder to cock, which could be fixed easily by using a longer, softer spring, but I don't have one on hand at the moment.... It sure shows the benefit to an SSG over a conventional setup, though.... With the ability of this gun to be filled safely to 3500 psi, I should now be able to get two 10-shot mags on a single fill, which at 56 FPE is pretty impressive....

Bob
  • Coalmont, BC

oldpro

  • Guest
Re: Regulated Disco Double
« Reply #72 on: January 06, 2017, 10:30:31 AM »
 Bob I need to make a lot of money and hire you full time Your work is astounding!!!!!

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2149
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: Regulated Disco Double
« Reply #73 on: January 06, 2017, 05:42:09 PM »
Thanks, Travis.... High praise indeed....  8)

Bob
  • Coalmont, BC

Christopher

  • Sr. Member
  • ****
  • Posts: 405
Re: Regulated Disco Double
« Reply #74 on: February 18, 2017, 03:56:42 AM »
Bob,
What is your conclusion on the performance of your VBT that you incorporated on this build?

Thanks,
Chris
  • dead end road KY