This article written by John Alexander, appeared in the May/June 2012, #217 issue of the Fouling Shot.
Since the tunnel was finished I have fired thousands of rounds through it and measured the muzzle velocity of a good portion of them with practically no extra work. However, some of the original features had to be modified and a certain amount of ongoing maintenance has been required. A couple of times the learning curve included unexpectedly exciting events.
The first part of the original design that needed modification was my method of stopping the bullets. I originally used ten layers of one and a half inch thick scraps from the house construction. Of course they were of soft spruce or fir but I thought that by shuffling the pieces around as the ones in front were penetrated and by moving the aiming points they would stop a lot of bullets before using up my generous supply of wood scraps. I underestimated the penetrating ability of pointed 85-grain 22 caliber cast bullets at modest velocities.
To reduce the frequency of changing targets I use homemade targets with from ten to twenty aiming points. This has the desirable side effect of spreading the impact points around in the backstop. This undoubtedly extend-ed the life of the backstop lumber but that life was still surprisingly short. Early on I went down to change a target and found that most of the 50 or 60 shots fired on that target had fully penetrated the stack of spruce and splattered against the backup steel plate. The lead fragments had been prevented from bouncing back towards the tar-get by the shredded backstop lumber so the only lead that escaped exited parallel to the plane of the steel plate. There was a narrow line of embedded lead slivers up both walls and across the roof attesting to the value of having the steel plate in place.
I had used large chunks of hardwood for backstop material at my previous outdoor range and knew that an 18-inch diameter chunk of oak, hard maple, or elm would stop a lot of bullets before it needed to be replaced. It wouldnt be as easy to handle as wood scraps but it would last much longer. I used up several of these with-out incident. Then during one exchange the chunk of oak got away from me while I was lowering it into posi-tion while standing down in the buried shed. There wasnt much room for evasive action in the restricted space but I did manage to get all my body parts out from under the 150 pound chunk of oak as it crashed down on the target frames with an impressive splintering and flying of broken wood.
OK I thought, that one was now in place but I didnt look forward to replacing it when the time came. These weighty items could of course be lowered and removed easily with a block and tackle or a chain hoist but there was no sturdy tree limbs overhead to hook a hoist to. I decided to build a miniature overhead bridge crane similar to the big ones that moved things around in a factory where I had once worked. My little crane would be handling light loads so it could be made of pressure treated wood and it wouldnt have to travel up and down the bay of a factory so the girder could be supported in one place on posts instead of on rails. I calculated that the girder could be a simple 2 by 6. The post bearing most of the weight would be a 4 by 4 and the other end of the girder would be supported by a braced 2 by 4. The smallest low-cost chain hoist I could find had a one-ton capacity. This gross over design is bad engineering, but other than being unhandy to hang on the trolley, it works fine. To support the hoist and move it along the girder I built a trolley of plywood and heavy-duty casters. Although using my crane doesnt produce as much weight training nor as much excitement as the previous method, it works as planned and the heavy chunks of shot up hardwood can now be easily fetched out and a new chunk lowered gently into place in a manner befit-ting an elderly shooter.
Since the tunnel was finished I have fired thousands of rounds through it and measured the muzzle velocity of a good portion of them with practically no extra work. However, some of the original features had to be modified and a certain amount of ongoing maintenance has been required. A couple of times the learning curve included unexpectedly exciting events.
The first part of the original design that needed modification was my method of stopping the bullets. I originally used ten layers of one and a half inch thick scraps from the house construction. Of course they were of soft spruce or fir but I thought that by shuffling the pieces around as the ones in front were penetrated and by moving the aiming points they would stop a lot of bullets before using up my generous supply of wood scraps. I underestimated the penetrating ability of pointed 85-grain 22 caliber cast bullets at modest velocities.
To reduce the frequency of changing targets I use homemade targets with from ten to twenty aiming points. This has the desirable side effect of spreading the impact points around in the backstop. This undoubtedly extend-ed the life of the backstop lumber but that life was still surprisingly short. Early on I went down to change a target and found that most of the 50 or 60 shots fired on that target had fully penetrated the stack of spruce and splattered against the backup steel plate. The lead fragments had been prevented from bouncing back towards the tar-get by the shredded backstop lumber so the only lead that escaped exited parallel to the plane of the steel plate. There was a narrow line of embedded lead slivers up both walls and across the roof attesting to the value of having the steel plate in place.
I had used large chunks of hardwood for backstop material at my previous outdoor range and knew that an 18-inch diameter chunk of oak, hard maple, or elm would stop a lot of bullets before it needed to be replaced. It wouldnt be as easy to handle as wood scraps but it would last much longer. I used up several of these with-out incident. Then during one exchange the chunk of oak got away from me while I was lowering it into posi-tion while standing down in the buried shed. There wasnt much room for evasive action in the restricted space but I did manage to get all my body parts out from under the 150 pound chunk of oak as it crashed down on the target frames with an impressive splintering and flying of broken wood.
OK I thought, that one was now in place but I didnt look forward to replacing it when the time came. These weighty items could of course be lowered and removed easily with a block and tackle or a chain hoist but there was no sturdy tree limbs overhead to hook a hoist to. I decided to build a miniature overhead bridge crane similar to the big ones that moved things around in a factory where I had once worked. My little crane would be handling light loads so it could be made of pressure treated wood and it wouldnt have to travel up and down the bay of a factory so the girder could be supported in one place on posts instead of on rails. I calculated that the girder could be a simple 2 by 6. The post bearing most of the weight would be a 4 by 4 and the other end of the girder would be supported by a braced 2 by 4. The smallest low-cost chain hoist I could find had a one-ton capacity. This gross over design is bad engineering, but other than being unhandy to hang on the trolley, it works fine. To support the hoist and move it along the girder I built a trolley of plywood and heavy-duty casters. Although using my crane doesnt produce as much weight training nor as much excitement as the previous method, it works as planned and the heavy chunks of shot up hardwood can now be easily fetched out and a new chunk lowered gently into place in a manner befit-ting an elderly shooter.
The tunnel itself has required no maintenance. It has neither settled or frost heaved and the clean gravel bed it sets on eliminates any potential drainage problems.
The only other periodically required maintenance is at the other end of the tunnel. The small nine-volt battery in the Chrony has to be changed and new baffles must be installed periodically because the high velocity gas and unburned powder grains eventually erode them. Also, the low pressure cast bullet loads leave some unburned powder grains which accumulate in the first few feet ahead of the muzzle.
The only other periodically required maintenance is at the other end of the tunnel. The small nine-volt battery in the Chrony has to be changed and new baffles must be installed periodically because the high velocity gas and unburned powder grains eventually erode them. Also, the low pressure cast bullet loads leave some unburned powder grains which accumulate in the first few feet ahead of the muzzle.
I noticed these on the Chrony the first time I pulled it out of the tunnel to replace the battery. It didnt take too much high level reasoning to understand that a muzzle flash might ignite this unburned powder and turn my tunnel into a very long gun barrel with interesting but unpredictable and probably undesirable side effects. To avoid this unwanted phenomenon, I routinely got out the shop vacuum and all my extension tubes and vacuumed out the first eight feet or so of the tunnel when I changed batteries or light bulbs in the Chrony. I dont like to clean rifle bores and avoid it as much as possible. Cleaning out this larger bore was even more irksome and involved reaching into the sooty tunnel as far as possible with the vacuum cleaner extensions, a dirty job I didnt enjoy. Maybe as a result of my distaste for this chore it didnt get done very often.
I found out that the frequency of my maintenance schedule was inadequate one day after fifteen years of uneventful shooting. As I touched off a shot there was a loud whoof and everything in sight turned a brilliant orange. It was quite dramatic and took half a second to realize what was happening. In a second it was all over, my plastic foam bulkhead had been blown out of the end of the tunnel and the brilliant orange had turned to smoke. My sloppy maintenance had finally caught up with me. The fire had been just a flash and had done no damage to the Chrony or the tunnel surface.
Oak chunk being lowered into place.
Although this nifty combustion method of removing the unburned power was much quicker and easier than vacuuming, it didnt seem prudent to depend on it and I vowed to reform my slipshod maintenance practice.
Other than the regular chores of replacing the back-stops, batteries, and light bulbs and vacuuming out the unburned powder, the tunnel has been maintenance free for 19 years. If you happen to have the right situation and enough land, you may want to consider building a shooting tunnel as a luxury addition to your basement.
I am looking forward to again enjoying the conve-nience of shooting from my basement this winter. I hope the efficiency of experimenting with cast bullet loads within twenty feet of my reloading bench will help me develop the ultimate 22 cast bullet for the coming com-petitive season. I will then be able to torment all my friends who insist on shooting the wrong caliber.
Other than the regular chores of replacing the back-stops, batteries, and light bulbs and vacuuming out the unburned powder, the tunnel has been maintenance free for 19 years. If you happen to have the right situation and enough land, you may want to consider building a shooting tunnel as a luxury addition to your basement.
I am looking forward to again enjoying the conve-nience of shooting from my basement this winter. I hope the efficiency of experimenting with cast bullet loads within twenty feet of my reloading bench will help me develop the ultimate 22 cast bullet for the coming com-petitive season. I will then be able to torment all my friends who insist on shooting the wrong caliber.