Part 2 of 3, of John Alexander's artilce was published in the Mar/Apr 2012, #216 issue of the Fouling Shot.
Once the tunnel had been constructed and backfilled with the shed, target frame and bullet catcher at one end and a shooting bench anchored to the concrete base-ment wall at the other end, the next thing was to learn how to make it work. I was unable to find any informa-tion about a shooting tunnel of this small size. There were probably similar small tunnels somewhere but as far as I find out it was unique and with any unique design, performance is uncertain.
I worried that shooting through such a small tunnel with corrugated sides might affect the bullets trajectory. I had read Harold Vaughns book Rifle Accuracy Facts and noted his remarks about the effects of tunnels on the bullets flight, especially bullets in the transonic range. I was also concerned about the noise. After all we were in an area where shooting was prohibited and I wasnt the only one living in the house. I was fairly certain the fifty yard tunnel would successfully reduce the noise that escaped the shooting shed. I wasnt so sure about noise in the house.
I tested the tunnel by firing several groups with high speed 22 long rifle ammunition. The average for the groups was similar to the results I usually got when shooting groups with the same rifle and ammunition out-doors. It appeared that the small tunnel with corrugated sides didnt do anything to a bullets shock wave that degraded accuracy at least to the shock wave of 22 long rifle bullets.
The sound problem was harder to solve. A 22 rimfire didnt produce enough noise to be objectionable but when I started shooting my cast bullet loads it was appar-ent that additional work was needed. The fifty yard tun-nel and the wooden target shed absorbed most of the noise emitted from the shed and because our nearest neighbor was over three hundred yards away through the woods this wasnt going to cause trouble. But at the shooting bench it sounded as if I were shooting inside a large steel tank or at least what I thought it might sound like to shoot inside such a tank.
My first attempt to dampen the sound at the base-ment end was to make a removal bulkhead with a hole for the rifle barrel and line of vision. I hoped that this barrier would keep most of the report in the tunnel. The bulkhead was of three inch thick Styrofoam and tightly fitted to the pipe. It reduced the sound level in the basement but the empty tank tone was still there and still unpleasant.
Once the tunnel had been constructed and backfilled with the shed, target frame and bullet catcher at one end and a shooting bench anchored to the concrete base-ment wall at the other end, the next thing was to learn how to make it work. I was unable to find any informa-tion about a shooting tunnel of this small size. There were probably similar small tunnels somewhere but as far as I find out it was unique and with any unique design, performance is uncertain.
I worried that shooting through such a small tunnel with corrugated sides might affect the bullets trajectory. I had read Harold Vaughns book Rifle Accuracy Facts and noted his remarks about the effects of tunnels on the bullets flight, especially bullets in the transonic range. I was also concerned about the noise. After all we were in an area where shooting was prohibited and I wasnt the only one living in the house. I was fairly certain the fifty yard tunnel would successfully reduce the noise that escaped the shooting shed. I wasnt so sure about noise in the house.
I tested the tunnel by firing several groups with high speed 22 long rifle ammunition. The average for the groups was similar to the results I usually got when shooting groups with the same rifle and ammunition out-doors. It appeared that the small tunnel with corrugated sides didnt do anything to a bullets shock wave that degraded accuracy at least to the shock wave of 22 long rifle bullets.
The sound problem was harder to solve. A 22 rimfire didnt produce enough noise to be objectionable but when I started shooting my cast bullet loads it was appar-ent that additional work was needed. The fifty yard tun-nel and the wooden target shed absorbed most of the noise emitted from the shed and because our nearest neighbor was over three hundred yards away through the woods this wasnt going to cause trouble. But at the shooting bench it sounded as if I were shooting inside a large steel tank or at least what I thought it might sound like to shoot inside such a tank.
My first attempt to dampen the sound at the base-ment end was to make a removal bulkhead with a hole for the rifle barrel and line of vision. I hoped that this barrier would keep most of the report in the tunnel. The bulkhead was of three inch thick Styrofoam and tightly fitted to the pipe. It reduced the sound level in the basement but the empty tank tone was still there and still unpleasant.
I next decided to try to interrupt, or at least confuse, the sound waves and perhaps change their tone by adding a couple of baffles. There was nothing scientific about this. I simply made a bracket that held two three-inch thick Styrofoam pieces that loosely fitted the pipe with a hole in the centers to fire through. One baffle was positioned perpendicular to the axis of the tunnel and the other one was held at a 45-degree angle. Eureka!
The report was reduced and the tank tone was gone. Hearing protection was still needed but the noise in other areas of the basement was tolerable and the first floor and the padding and carpet above apparently dampened the noise that reached the rooms above enough to prevent Janet, my usually tolerant wife, from objecting.
The report was reduced and the tank tone was gone. Hearing protection was still needed but the noise in other areas of the basement was tolerable and the first floor and the padding and carpet above apparently dampened the noise that reached the rooms above enough to prevent Janet, my usually tolerant wife, from objecting.
Basement end of tunnel with bench, rests and Styrofoam bulkhead in place. Another concern that others have mentioned is whether the results from shooting at fifty yards would be a true indicator of what a rifle and load would do at longer distances. Because my principle motive for building the tunnel was to be able to test rifles and cast bullet loads this was a critical question but one I was confident that I already had a partial answer for.
Styrofoam baffles that solved the objectionable tin pipe sound and reduced the report. At my shooting range at our previous house I had both a fifty and hundred yard backstop. When it was very windy or troublesome mirage was present I often shot at fifty yards. I repeatedly compared the group sizes at 50 with those fired, in good conditions, at 100 yards and satisfied myself that, on average, groups at 100 were no more than twice as big as those at 50. If any-thing, they seemed to average a bit less than twice as big at 100. I suspect this proportional relationship does-nt hold true at longer ranges for all loads, but 50 yards seemed to be every bit as good at determining what a load would do at 100 yards as actually shooting at 100 yards maybe better for a marginally effective wind shooter like myself.
The next thing on my wish list was a chronograph set up in the tunnel so I could collect velocities with min-imum fuss. I looked at the chronographs on the market and decided that a Beta Model Shooting Chrony with the remote control panel and a lighting fixture would fit in the tunnel and work, as well as keep the cost down to about$100. Of course the chronograph screens and lighting fixtures needed to be ten to fifteen feet into the tunnel and I didnt want to have to crawl into the tunnel every time I needed to replace batteries or light bulbs.
To solve this problem I mounted the screens and light fixture on a eight foot 1 x 8 that can be pushed into the tunnel and then pushed further ahead by the bracket for the baffles. Pulling on the power cord allows me to fetch the board with the screens and lights back out for battery and light bulb replacement.
To solve this problem I mounted the screens and light fixture on a eight foot 1 x 8 that can be pushed into the tunnel and then pushed further ahead by the bracket for the baffles. Pulling on the power cord allows me to fetch the board with the screens and lights back out for battery and light bulb replacement.
Chronograph screens and lights mounted on board for inserting into tunnel.
Completed shooting shed and long handled target holder. Changing targets requires a trip to the shooting shed. To minimize the time and effort spent changing targets I use a target with from ten to twenty aiming points. When shooting five shot groups I can fire as many as 100 shots between target changes. To make target changing easier I attached a long handle to the piece of plywood bracket that holds the targets. This allows me to remove and replace targets without climbing down into the shooting shed.
This set up worked and has served me well for almost twenty years with thousands of cast bullets mak-ing the trip to the target. Details of the maintenance of the tunnel will be discussed in part three.
This set up worked and has served me well for almost twenty years with thousands of cast bullets mak-ing the trip to the target. Details of the maintenance of the tunnel will be discussed in part three.
