.22-caliber Lightweight Disco Double: Part 3
by Tom Gaylord, a.k.a. B.B. Pelletier
Okay, all joking aside — today, we’ll look at the performance of the Lightweight Double Disco that Lloyd Sikes built. Lloyd tested this exact rifle when it was still in its factory original condition, so we can compare that to the performance of the rifle after the conversion. I was pleased to see that my chronograph results and Lloyd’s are very close.
Before the conversion, the stock Benjamin Discovery accepted a fill to 2,000 psi. From that fill, the rifle got 21 shots of .22-caliber Crosman Premiers at an average 845 f.p.s., which works out to an average 22.7 foot-pounds. Lloyd did get more shots in his string, but he discounted all those that were not within 4 percent of the average velocity. That’s a subjective choice, but it’s what drives the numbers Lloyd is giving us for the factory rifle. The maximum velocity spread in this string of 21 shots was 40 f.p.s., with a low of 820 f.p.s. and a high of 860 f.p.s.
After the Lightweight Double Disco conversion, Lloyd shot the same Crosman Premier pellets on a similar 2,000 psi fill and got a string of 33 shots at an average 849 f.p.s., for a muzzle energy of 22.9 foot-pounds at the average velocity. Again, this number includes all shots that fell within 4 percent of the average velocity. The maximum variation in this string of 33 shots was 34 f.p.s., with a low of 831 f.p.s. and a high of 865 f.p.s.
The shot count made possible by the Lightweight Double Disco conversion went from 21 to 33 shots. The average velocity did increase by 4 f.p.s., but I wouldn’t concentrate on that because these numbers will change a little each time you record them. Essentially, the gun shot this pellet the same before and after the conversion — it simply got more shots after.
What did I get with Premiers?
I filled the rifle to about 2,100 psi because I wasn’t sure that my best pressure gauge agreed exactly with Lloyd’s gauge. I wanted to start in a slightly valve-locked posture and move up into the power curve as I went, and that’s exactly what happened. Here’s my shot string.
1-20 21-40 41-end
802 856 836**
822 856 832
817 852 828
826 852 825
831* 857 824
831- 855 820
833 857 816***
837 853 STOP (47 shots)
– Slowest shot in acceptable string
+Fastest shot in string
* First gauge photo
** Second gauge photo
*** Third gauge photo
If I accept the shots in this string starting at No. 5 and continuing through No. 41, I get 37 shots. They’ll have a maximum spread of 29 f.p.s., with a low of 831 f.p.s. and a high of 860 f.p.s. If I’m more critical and start with shot No. 8, which went 837 f.p.s., and still stop at shot 41, the total is 34 good shots, with a maximum spread of 24 f.p.s. The low in this string is 836 f.p.s. and the high is 860 f.p.s.
Do you see how this works? It’s entirely subjective. I’m deciding what to accept and what to reject. Once I start accepting shots, though, I keep on shooting until the last shot in my acceptable string has been fired. I can’t ignore any shots in that string because I won’t be able to chronograph my shots when I’m shooting in the real world, away from the chronograph.
You must pick the starting and ending points that you feel are best for what kind of shooting you want to do. That’s why a chronograph is so essential to the owner of a PCP. If I were to shoot this same string again with the exact same starting pressure, which is very difficult to control, I might get numbers that are similar but slightly different from these.
Next we will look at the performance with .22-caliber H&N Baracuda pellets. Lloyd tested the rifle with them, but I didn’t have any .22-caliber Baracudas on hand, so I substituted the Beeman Kodiak, which is the same pellet under a different name.
With the Discovery in factory trim on a 2,000 psi fill, Lloyd got a string of 22 shots that averaged 717 f.p.s. They produced an average muzzle energy of 24.2 foot-pounds (compared to the 22.7 foot-pounds produced with Premier pellets in the factory trim). Heavier pellets will almost always produce more energy in a precharged rifle. The maximum velocity spread with the Baracuda pellet in the factory Discovery was 29 f.p.s. The low was 697 f.p.s. and the high was 726 f.p.s.
The Lightweight Disco Double conversion running on the same 2,000 psi fill with Baracudas gave a string of 38 shots that averaged 713 f.p.s. The low was 699 f.p.s. and the high was 729 f.p.s., so the spread was 30 f.p.s. The average muzzle energy was 23.9 foot-pounds.
Baracudas got more shots per fill than Premiers
With Baracudas, Lloyd got 22 shots per fill in factory trim and 38 shots with the Lightweight Disco Double conversion. In both cases, the rifle gave more shots per fill with the Baracudas than with the Premiers. My thinking is that the heavier, slower pellet holds the valve open a bit longer and is able to go to lower pressure before it falls off the power curve.
What did I get with Beeman Kodiaks on a 2,000 psi fill (refer to the first photo of the pressure gauge to see where I actually stopped the fill)?
1-20 21-40 41-end
702 712 701
699- 720 693
707 716 695
714 718 696
709 714 683
719 726 STOP (45 shots)
– Slowest shot in string
+Fastest shot in string
While this string has fewer shots than the first one with the Premiers, there are actually more usable shots here because I learned where the needle on the gauge had to be in the first test. No air was wasted at the start of this string. I would accept everything from shot No. 1 through shot No. 41, giving me a total of 41 usable shots, with a spread of 29 f.p.s. The low was 699 f.p.s. and the high was 728 f.p.s.
I got more usable shots from Beeman Kodiaks than from Premiers, just like Lloyd did with H&N Baracudas. Our data seems to agree very closely. Lloyd’s low velocity was 699 f.p.s. and so was mine. Lloyd’s high was 729 f.p.s. and mine was 728 f.p.s. How is that for consistency? As I said, the H&N Baracuda and Beeman Kodiak are the same pellet.
Analysis thus far
The Lightweight Disco Double increases the useable shot string significantly, even though the rifle is no larger nor heavier than a factory Discovery. You can tell from a glance at the onboard pressure gauge if the rifle is still on the power curve, so there’s no need to count the shots.
All of what you have seen to this point was done with the stock Discovery striker spring (0.035″wire, 0.289″ OD, 1.99″ long , 16.5 coils) in place. But Lloyd also provided and tested a heavier striker spring (0.041″ wire, 0.300″ OD, 1.78″ long, 19 coils) that gives both the factory Discovery and the Lightweight Disco Double conversion more power.
To see what the heavier striker spring can do with Baracuda pellets in the Lightweight Disco Double, Lloyd recorded that the average velocity climbed from 713 f.p.s. to 764 f.p.s. That is an energy increase from 23.9 foot-pounds to 27.5 foot-pounds. The total number of shots dropped back from 38 to 25 shots. This shows how the Disco Double allows the power to be increased, and the total shot count to remain the same as the less powerful factory gun.
I haven’t reported on the trigger, yet. You may recall that I had Lloyd install an optional trigger from a Benjamin Marauder. Lloyd told me in a message that it’s set for a light first stage, and then an extremely light second-stage pull. I found at first that it was so light that I pulled straight through both stages without recognizing stage 2. But when I adapted to it, it’s really not as sensitive as a 10-meter target pistol trigger. Stage 1 takes 14.4 oz. of effort; and stage 2, while recognizable, does not increase the number on the electronic scale. It’s on the order of 10 grams or less.
So far, I’m delighted with the Lightweight Disco Double. If it turns out to be accurate, it could become my go-to PCP!