Posts Tagged ‘Disco Double’
by Tom Gaylord, a.k.a. B.B. Pelletier
Air Arms Shamal is an attractive PCP. It was Air Arms’ first precharged rifle.
This report covers:
• Trigger adjustments.
• Discovering the maximum fill pressure.
• Shot count.
• Velocity with various pellets.
• Discharge noise.
In this report, we’ll discover the Shamal’s pressure curve, which will be instructional for all who are new to precharged airguns. As I mentioned in the first report, this rifle didn’t come with a manual; so when I got it, I had to discover the pressure curve on my own. I did, and it turned out the rifle wanted an initial fill pressure of 2,600 psi. That was on the gauge that was on the fill device that came with the rifle — the device that I no longer have. I need to find out where on the gauge of my carbon fiber tank the needle wants to be when the rifle is full. These small pressure gauges are not that precise, so the number could be off by several hundred psi. Also, the gauge on my carbon fiber tank isn’t marked in hundreds of psi. There will need to be some interpolation involved.
More than a decade has passed since this rifle was mine. I’m not sure where it’s performing today. So in all respects, this is a brand new air rifle to me. That will benefit you if you want to look over my shoulder while I do what needs to be done.
Before I get into that, however, I first want to address the adjustable trigger. Shamals haven’t been around for a long time and there isn’t that much written about them. I want this report to serve as an owner’s manual for all who get one in the future.
The Shamal came with two different triggers — a standard one that my rifle has and an Olympic trigger that sounds more adjustable, but which I know nothing about. My trigger has 4 adjustment screws. From the back to the front (holding the rifle on your shoulder) they are:
1. The sear engagement (clockwise to reduce).
2. The first-stage travel (clockwise to reduce).
3. The first-stage weight (clockwise to increase).
and in front of the trigger:
4. The second-stage weight (clockwise to increase).
Trigger-adjustment screws: (1) Sear engagement, (2) first-stage travel, (3) first-stage weight and (4) second-stage weight.
When I tested the trigger with my electronic gauge, the firs-stage weighs just under 6 oz., and the let-off was between 12 and 14 oz. The first stage is long, which I like, and the release is as light as I like a trigger to be, so I’m satisfied with this trigger as it stands.
Discovering the max fill pressure
This is something that has to be done whenever a new gauge is used. I had data from previous tests that told me the fill pressure should be 2600 psi, so I filled from my carbon fiber tank to 2750 psi. That gave me the following velocities with the same 14.3-grain Crosman Premiers I used over a decade ago.
The fill pressure at the end of this string was 1500 psi. This string tells me almost everything I want to know about this rifle. First, the fill pressure I used was way too high. I’ll fill the gun again to a much lower pressure and see where that gets me.
Next, there are just under 20 good shots on a fill — down from what I thought so many years ago. I like the velocity that runs from 780 to 806 — a spread of 26 f.p.s. Looking at the curve for Premiers, I should start with shot 18, although the shot before that didn’t record, so I can’t be certain whether it was any good or not.
If I end the string at shot 34, I’ll get 17 full-power shots close to my desired range. What should the starting air pressure be? That’s solved easily.
I’ll guess that 2350 psi is the start point. I filled the rifle to that pressure and got the following results.
Okay, as the pressure inside the gun has decreased with each shot, the velocity has increased. The last shot was 781 fps, which is as low as I want the velocity to go on the power curve I’m willing to accept. The gun’s reservoir pressure has now dropped to the maximum pressure that will give me a velocity on my desired power curve (781 fps).
The velocity of 781 is at the bottom of the power curve that I have identified for this rifle. Since my last shot was 781, the rifle is now on the power curve. The pressure in the reservoir is now at the highest it can be and still give me the velocity I want. From this point on, as the rifle’s reservoir pressure drops, the velocity will either increase or remain stable. As long as it’s at 780 fps or higher, the rifle is on the power curve I’m looking for.
Now I can find the ideal starting fill pressure for my desired velocity range. All I have to do is start to fill the airgun, again. When the needle stops moving fast, indicating the fill hose is full and the gun’s intake valve has just opened, I stop the fill by closing the tank’s valve and look at the needle. The needle is pointing at the air pressure that is in the gun’s reservoir. I can see on the gauge that this rifle likes a starting fill pressure of 2250 psi!
To confirm that I’m right, I fired one more shot with Premiers. It went 781 f.p.s. Bingo! I’m right at the start of the power curve, with at least 16 more good shots in the reservoir.
I also discovered that the rifle performs very much the same as it did long ago. I’m using a different chronograph, yet the velocities from the late 1990s and today are within a few f.p.s. of one another.
The power curve I’ve accepted gives me an average velocity of 792 f.p.s., which is good for 19.92 foot-pounds of muzzle energy.
I will now test the velocity of other pellets, but I’m not going to shoot long strings and get the averages. I will shoot 2 of each pellet and take the lowest velocity of each pellet as the average for that pellet. While that’s not exact, it’s far faster than shooting whole strings and averaging. I know I’m on the power band for the next 16 shots; and if I use even fewer than 16 shots (4 pellets x 2 shots each = 8 shots), I can be sure that all of them are on the power band. The power band is the place where the velocity of any pellet will vary the least.
Eun Jin domes
This 28.4-grain Eun Jin dome pellet gave me velocities of 592 and 586 f.p.s. Taking the lower number as the average, I get a muzzle energy of 21.66 foot-pounds.
The Beeman Kodiak pellet weighs 21.14 grains and gave me velocities of 683 and 680 f.p.s. That’s very close to the “magic” velocity of 671, where the weight of the pellet in grains equals the energy in foot-pounds. Using the low figure of 680 f.p.s., this pellet gave an energy of 21.71 foot pounds at the muzzle.
JSB Exact Jumbo Monsters
Next, I tried JSB Exact Jumbo Monsters — a 25.4-grain pellet. They gave me velocities of 584 and 611 f.p.s. Using the lower number, that’s a muzzle energy of 19.24 foot-pounds.
The bottom line is that this Shamal is a 20 foot-pound air rifle as it’s operating now. That’s what it was when I owned it in the 1990s. So, the rifle hasn’t changed, but the gauges have changed and so has my perception of the total number of shots that are available. So, this update was important to the operation.
I don’t know what I was thinking when I reported the Shamal as a quiet air rifle before, but it isn’t. It sounds exactly as loud as a .22-caliber Benjamin Discovery running at the same power.
Someone asked about the loading room at the breech, and on this rifle there’s a generous amount. There’s no loading trough, so it’s easier to get your fingers behind the breech with a pellet. And all pellets load easily because there’s no rifling at the breech. Rifling doesn’t start until after the air transfer port, which is deep inside the breech. The bolt nose has a long probe that pushes the pellet past the air transfer port and into the rear of the rifling.
That’s a 28-grain Eun Jin standing on the receiver. It’s one of the longest .22-caliber pellets around. As you can see, there’s plenty of room at the breech.
That’s it for this look. Next time I’ll scope the rifle and head to the range.
by Tom Gaylord, a.k.a. B.B. Pelletier
Air Arms Shamal is an attractive PCP. It was Air Arms’ first precharged rifle.
This report covers:
• The story of my Shamal.
• Description of the rifle.
• Old versus new.
“Sadly, my Shamal went away. I know the man who owns it and he still treasures it to this day. If I still had it, I probably would not allow it to get away from me a second time. It was proof that you don’t always need a new air rifle to have a good one.”
Those were the last words I wrote about my Air Arms Shamal in the April 8, 2009, report I wrote on the old blog. I wrote that report for blog reader Kevin, who is still a reader and one of the most knowledgeable contributors to this blog. He asked what was the quietest .22 PCP I ever heard, and this rifle was my answer.
I did get rid of the Shamal many years ago, along with many other airguns and firearms that I enjoyed. I never thought I would ever see any of them again, but my Beeman R1 and Whiscombe JW 75 came back years ago — and this year the Shamal has returned. The gentleman who sold it back to me charged just what he had paid for it over a decade ago, so it was a good deal on top of a welcome homecoming.
The Shamal wasn’t the first PCP I ever owned — I think it was probably the second. I remember receiving it and discovering to my utter surprise that the rifle shot very slow with a fresh 3,000 psi fill. So, I recorded the velocity of each of the first 66 shots and learned that the rifle didn’t really come up to its power band until somewhere between shots 29 and 38, depending on how tight I wanted the power curve to be.
That exercise was the first time I used a chronograph as a diagnostic tool. I’d used one to gather data for my book about the Beeman R1, but this time I was evaluating the health and performance of a rifle whose background was entirely unknown to me. Without the chrono, I would have been lost.
The optimum fill pressure of this rifle was 2,600 psi — not the 3,000 psi I’d thought. Years later, I would use that experience when talking with customers who complained that their AirForce Condors were somehow defective because they didn’t get their top-rated velocities at 3,000 psi. “What does it matter,” I would say, “if your Condor starts out with a 2,700 psi fill? All that matters is that it gets the top power and 20 good shots on a fill?” — which they were getting in every case.
“Yes,” they countered, “but I bought a rifle that is supposed to take a 3,000 psi fill. I want to get my money’s worth!”
They were getting the best velocity that Condors ever got, and they were getting the advertised number of shots per fill; but because the number on the pressure gauge wasn’t what they expected it to be, they were dissatisfied. I wonder what they would say if they knew their car’s gas gauge was off…even though they’re getting the promised mpg and advertised speed?
That Shamal experience prepared me for a number of future experiences with PCPs. It was a good start for me. More than that, it was a real beauty that I can now share with you.
The Shamal was Air Arms’ first attempt at a precharged pneumatic air rifle. It’s a sporting design, and the one we are examining today is in .22 caliber. Back in those days, manufacturers used to write the standard working pressure (SWP) on the side of the receiver so you would know what it was even without a manual. Manuals back then were single sheets of paper written on one side, only. This rifle oddly does not have the working pressure marked on it anywhere; so without a chronograph, you’re lost.
The aluminum receiver has a high polish and a deep black finish. Nowhere on the rifle is the standard working pressure noted, though that was typical for UK PCPs of this era.
The rifle cocks by turning a knurled bolt knob and pulling it back to cock the hammer spring. The bolt will open a considerable distance before the spring starts to compress, so you have to pull the bolt back quite far to cock the action.
The rifle weighs 8 lbs., 4 oz. without a scope. The stock is thick at every point, so the resulting feeling is that the gun is big and heavy. It measures 40-3/4 inches overall, which is short for a rifle, but the barrel is a full 23 inches, so nothing is lost as far as velocity goes. The airgun falls into the nebulous category of being long for a carbine but short for a rifle.
No doubt you’ve noticed that the stock is figured walnut. It features an oil finish that improves with a light rubdown of Ballistol. The holographic curl grain runs the entire length of the stock, though it’s hard to see in some places. There are 4 checkered panels — 1 on either side of the forearm and 1 on either side of the pistol grip. The pistol grip has a slight palm swell on the right side. When coupled with the high, sculpted cheekpiece, that makes this rifle for right-handed shooters, only. A thick ventilated rubber buttpad adds some length to the overall pull that measures 14-1/2 inches.
[Special note: Pyramyd Air is now stocking Ballistol in 16-oz. and 4-oz. non-aerosol cans. I use these to fill plastic spray bottles that I keep in several places. Buying it in bulk lowers the price. The link I gave takes you to the new cans.]
The metal parts of the rifle are finished commensurate with the wood, but the finish is not even. There are steel parts (barrel, part of the receiver tube, various bands, etc.) that are blued steel with an average bluing, and there are aluminum parts (receiver and reservoir tube) that are highly-polished with a deep black finish. The look is attractive, but not uniform.
The barrel is not free-floated. A forward band connects it tightly to the reservoir. That might cause vertical walking of the pellets as the pressure drops, so that’s something I’ll watch for.
The gun is filled at the front, under the muzzle. In the days when the Shamal was new, there were no quick-disconnects for any precharged airguns. Each gun had its own proprietary hose with whatever connection thread pattern the makers thought was good. When you bought a gun in those days, it was important to also buy a fill device that you knew for certain would fit. I had such a fill device when I owned the rifle the first time, but the gentleman who sold it back to me asked if he could keep it since it fit another precharged airgun he owns.
He gave me an adapter Dennis Quackenbush made that threads into the rifle’s fill port and has a male Foster quick-disconnect coupling on the other end. With this adapter installed, the rifle can easily be filled by a number of fill devices because Foster fittings have become the PCP fittings of choice over the past 10 years. I left the old fill hose and clamp with the previous owner and screwed in the Quackenbush adapter to the fill port. It works perfectly, and I’ll leave it on the rifle all the time.
With the adapter installed, it’s impossible to put the elaborate Air Arms muzzle cap back on the rifle. While it finishes the look of the gun, it had to be completely removed to attach the old-style fill hose coupling anyway, so I’ll just leave it off the gun.
The muzzle cap (bottom) had to be removed every time to attach the original fill hose, but now I just leave the Quackenbush adapter permanently installed.
Back in those days, precharged airguns didn’t have pressure gauges built in. You had to keep track of the number of shots fired and know when to fill your gun. I’m used to doing that, and it doesn’t bother me.
Usually, I have the manufacture’s literature to go by or I know nothing about the gun at this point in the testing process, but I’ve owned this rifle before and know what it was doing then. In the 1998 timeframe, this rifle was able to produce about 20 foot-pounds with .22-caliber Crosman Premier pellets. The average velocity it got back then was somewhere in the 790 f.p.s. range, which gives a muzzle energy of 19.82 foot-pounds. A heavier pellet might raise that by a couple foot-pounds, but this is a 20 foot-pound airgun. In those days, that was considered very respectable, but today it seems rather weak. We’ve seen my Disco Double deliver the same pellet about 50 f.p.s. faster, on average, which translates to a muzzle energy of 22.4 foot-pounds.
The trigger is adjustable, though I’ve never experimented with it to discover how it works. I’ll do that for the next report and give you the particulars.
It’s set up very nice as it is, and I saw no reason to change it in the past. But it brings up an interesting observation.
The old against the new
Now that the Shamal is back, I’ll be comparing it to the Disco Double I recently reviewed for you. The power is about the same, and both rifles are single-shot .22s. The Disco Double has the better trigger, but who can say how the rest of the test will compare?
by Tom Gaylord, a.k.a. B.B. Pelletier
This is a third look at the Disco Double shooting at 50 yards. All I’ve managed to do so far is demonstrate the Disco Double is very consistently mediocre with the best pellets — JSB Exact Jumbo RS domes. However, the last time I was out at the range with this rifle, I finally did what the builder, Lloyd Sikes, has been telling me to do all along. He said to tighten the 6 screws on the 2 barrel bands or hangers, and this time I followed his directions. Guess what? Four of the 6 screws were loose! Imagine that! I tightened them and knew the rifle would reward me for the effort.
It was no surprise when shot the best 10-shot group ever with the rifle. Ten RS pellets went into 1.195 inches at 50 yards. But I was 3 shots into a second group when the bolt handle broke off in my hand during cocking. That ended the day for this rifle.
As soon as I returned home, I emailed Lloyd, who put a new bolt and handle in the mail right away. I really wanted to finish the test before leaving for the Ohio airgun show (which is this Saturday), so I disassembled the rifle. I ran into a problem getting the old bolt out, but a call to Lloyd set me on the right path and soon the job was done.
The new parts arrived the following week, and I had them in the rifle inside an hour — though another call to Lloyd was necessary. He was most helpful, and I resolved my problem with a minimum of fuss. The rifle went back together, and I was ready to return to the range.
This time, I took the opportunity to mount a new UTG 6-24X56 scope scope in place of the UTG True Hunter 3-9X40 scope I took off. Naturally, the target image was much larger with this scope, which just made my job easier.
I tried several pellets that I’ve tried before, but once more this rifle demonstrated that it likes the JSB Exact Jumbo RS pellets the best. Since the rifle had been taken apart for the bolt repair (i.e., both barrel bands had been removed), I was back at the beginning on the first group. I had the front band about where it had been before (from the screw marks in the paint), and the first group of 10 went into 1.28 inches at 50 yards. That was marginally better than the 1.317-inch group I’d gotten during the previous full test, but not quite as good as the one group I shot just before the bolt broke (1.193 inches). All the screws were tight, so now it was time to move the front barrel band.
In case you don’t understand what moving the front barrel band has to do with accuracy, it comes down to harmonics. By changing the location of where the barrel is anchored, I changed how the barrel vibrates during the shot. I did a huge 11-part test of this effect a few years ago. You can read about it here.
I moved the front barrel band backwards about a half inch and tightened the 3 screws once more. Then, I fired another group of 10 shots. This time, 10 RS pellets went into 0.816 inches. That’s pretty telling, don’t you think? Of course, I have no way of knowing if I have the barrel band adjusted perfectly — all I know is that it’s better than it was before.
A second 10-shot group went into 1.506 inches. Oops! Was that supposed to happen? Its difficult to say, but perhaps I wasn’t concentrating while shooting this group. I simply don’t know. Stuff happens to me, just like anyone else!
So I shot a third 10-shot group. This one measures 0.961 inches between centers. That’s better.
What I can tell you now is the that Disco Double is able to put 10 pellets into less than an inch at 50 yards under ideal conditions. I’ve shown you everything that’s happened, and I could go on and continue to test this rifle until I have it shooting its best. I probably will, in fact. But the lesson is what I’ve shown you today.
The Benjamin Discovery is an inexpensive PCP that can put 10 pellets into less than one inch at 50 yards under ideal conditions. The Disco Double I am testing for you here has a lot of extra work done to it and is not as inexpensive as the basic Discovery. However, this is the air rifle I wanted. It’s small, it’s accurate, it has a wonderful trigger and this one gets a load of shots on a fill of just 2,000 psi. That’s everything I wanted in a PCP.
Best of all, this rifle weighs no more and is no larger than a standard Discovery. Despite the additional air capacity, I had to sacrifice nothing. That was the real reason I had this air rifle built. Lloyd Sikes has a wonderful thing going here. If you’re interested in what he can do for you, find him at Airgun Lab.
by Tom Gaylord, a.k.a. B.B. Pelletier
This is a second look at the Disco Double at 50 yards. On this day at the range, the wind was quiet, so it was a good day to test.
I didn’t do anything to the rifle before this test because I didn’t have any time to stop long enough to clean the bore. So, it went uncleaned. I may have promised to do certain things before the next test, but all I actually did when the time came was grab the rifle and go back to the range.
I used the same black single sandbag you saw in the Daisy model 8 test earlier this week. The Disco Double perfectly fits the long groove of that bag and feels more secure than if it was in a conventional rifle rest.
The first group was made with 10 Beeman Kodiak pellets, and they were on target since I’d already zeroed this rifle at 50 yards for the earlier test. They initially stayed together, and I thought the rifle might have turned the corner. They then began to fly farther and farther apart. In the end, 10 pellets went into 1.837 inches — hardly a group worth mentioning. When I checked back to the previous test, though, I noted that this same pellet had made a group that was 2.458 inches at 50 yards; so as bad as it is, this was an improvement.
Okay, that wasn’t the brilliant opening I was anticipating. Even though the same pellet beat the last group by half an inch, it didn’t seem like the time to gloat. Next up were the JSB Exact Jumbo RS pellets — the most accurate pellets in the first 50-yard test.
The first group was another teaser. It looked small through the scope. It wasn’t until I measured it that I found out it went over an inch. Ten RS pellets went into 1.317 inches at 50 yards. That’s smaller than the smallest group from the previous test. There, 10 RS pellets went into 1.3418 inches at 50 yards. This group is similar, but it’s not crushingly better by any means.
I now have 2 groups — each of which is better than the same pellet in the previous test. One is significantly better; the other is only better by a whisker. What does that mean? Rather than try to answer that question, I decided to shoot another group. Surely, this one would be conclusive!
The next 10 RS pellets went into a 1.773-inch group. That was the hands-down worst group of both days of testing for this pellet. On the same day, shooting under the same conditions with the best pellet, I got both the best and worst groups this rifle had fired to date.
I’m sure someone can make sense out of these results — but I’m not that person! After 2 days of testing at 50 yards, I had not proven anything except that I can’t make this air rifle shoot — yet!
I considered shooting some more groups; but after looking at these results, I thought this wasn’t the day. Sometimes, the bear gets you!
I think what I’ll do is drag the Disco Double to the range every time I go and try to shoot different pellets each time. Maybe then I’ll stumble across the magic pellet that turns this rifle into a shooter. After testing similar rifles, I’m convinced this gun can shoot — I just haven’t yet discovered how.
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, we’ll look at the Disco Double out at 50 yards. I used the best pellets from the 25-yard test to speed up this test. No sense going over the same ground twice.
The first pellet I tried was the JSB Exact Jumbo RS. It did the best at 25 yards, plus it’s so light, at 13.43 grains, that it gives the rifle a little extra zing.
The rifle arrived at the range filled to 2,000 psi, so I went right to work. I clicked the scope up 5 clicks in elevation to account for the greater distance and began shooting. The day was surprisingly cold — about 28 degrees F. My trigger finger had very little feeling, yet I was able to feel when stage 2 engaged on the trigger every time. That’s important on this rifle because the trigger is very light on stage 2.
There was no wind on the range, which made this a perfect day for shooting a pellet rifle. The first 10 shots went into 1.558 inches between centers. That’s not as small as many 50-yard groups you’ve seen me shoot, but let’s keep testing.
Next up were .22-caliber Crosman Premiers. The first 3 shots went into 2.269-inches and I stopped shooting. These pellets weren’t going to work at 50 yards.
JSB Exact, 15.89 grains
Next up were the heavier 15.89-grain JSB Exact Jumbos that looked promising at 25 yards. They produced a 10-shot group that measured 1.778 inches between centers. It was a little larger than the JSB RS pellet group at 50 yards, just as it was a 25 yards. So far, no prize.
The last pellet I tried was the Beeman Kodiak, which just did fair at 25 yards. Here at 50 yards, they put 10 into 2.458 inches. That’s hardly accurate! I almost stopped shooting this group when I saw how the shots opened up; but I thought that after doing that with the Premiers, I ought to let one go the distance just to show you what it looked like.
Back to the JSB Exact RS
I wasn’t finished with the testing just yet. The rifle was topped off at 2,000 psi again, and I went back to the pellet that was giving me the best results — the JSB Exact RS. The next group of 10 was the tightest of the session, at 1.318 inches between centers. I’d adjusted the scope for the Kodiaks, so this one landed below the bull.
I then shot 2 more 10-shot groups with the RS pellet. The first measured 1.522 inches, and the second measured 1.543 inches. When I examined the target after bringing it back from downrange, I saw a pattern. The RS pellet wasn’t giving tight groups, but they were very consistent. Out of 4 groups, the total variance was 0.24 inches — from 1.3 to 1.5 and change. That’s pretty consistent.
What do we know?
We know this Disco Double can put 10 pellets into 0.365 inches at 25 yards. And with the same pellet, we know that it opens up to about 1.5 inches when the distance is doubled. We know it was warm when the 25-yard target was shot and cold when the 50-yard targets were shot.
And that’s about the only difference — other than I did remove the TKO silencer after shooting 25 yards. I think what I will do next is the following.
1. Clean the barrel.
2. Shoot 5 groups at 25 yards with the JSB Exact RS pellet.
3. Clean the barrel again.
4. Shoot another 5 targets at 50 yards.
One last feature I want to show you is the special optional barrel band Lloyd makes for the Disco Double. It has a Picatinny rail on the bottom, allowing you to attach a bipod at just the right spot with very little extra weight added to the gun.
When I originally tested the .22-caliber Benjamin Discovery rifle in 2007, it was a pre-production prototype that was made out of a Crosman 2260. I shot several approximately half-inch groups at 50 yards with Crosman Premier pellets, but they were 5-shot groups. Now, I’m shooting 10-shots groups that I know are going to be larger. I didn’t use the JSB Exact RS pellet because it didn’t exist back then.
I believe this lightweight Disco Double has more accuracy than we’ve seen to this point. I think it must be capable of shooting at least one 1-inch group out of 5 at 50 yards. So, the test continues.