The Tubegun in F-Class - Part 4
by Germán A. Salazar
This final installment of the series is simply a confirmation that the work John performed on the rifle and our various ideas about what to do all worked well. There aren't any additional developments presented here.
As I mentioned in Part 3, today we went to the weekly 500 yard match at the Phoenix Rod & Gun Club and gave the various modifications a good test. Conditions were breezy with the temperature just under 100, so a very nice day by summer time standards in Phoenix.
The bipod clamping block worked perfectly, never moving even a millimeter. Between sighting in the rifle, firing the match and shooting a few extra rounds at the end, I fired 80 rounds of .308 with 190 gr. bullets. That was as good a test for the clamp's holding power as it needs; I'm satisfied that the moving bipod problems are now behind us.
The scope base modifications were a complete success as well. I lowered the elevation setting on the scope by 20 moa from last week's setting and it only took a few clicks to zero it in. There is now plenty of elevation travel left to go to 1000 yards, as well as enough down travel for 100 or 200 yards - although 300 yards is the shortest range at which we shoot.
Just as important, the windage zeroed very close to the center of the scope's adjustment range, just as we had hoped. This confirms that our slope calculations and John's milling work were on the money and that Gary's instructions on the windage problem as well as John's work on the rings worked out perfectly.
The change from medium height rings to the high rings was also just right. I was able to move the cheekpiece up a little and get the amount of cheek pressure that I normally use while maintaining a comfortable sight picture. The high rings are the ones we modified as described in Part 3.
There isn't much else to say without turning it into a match report, which isn't my intention, but the scores were good for the conditions: 198-8X, 198-9X, 195-4X (591-21). That was enough to win F-Class overall, but second place finisher Christine Harris (587-26) turned in a 199-11X for her last string in F-TR, so the pressure is always on around here!
I'm satisfied that the tubegun and its accessories are now properly sorted out for F-Class shooting from 300 to 1000 yards. All that remains is for the shooter to perform up to the rifle's capabilities...
The Tubegun in F-Class - Part 3
by Germán A. Salazar
And now, for the rest of the story...
The day began early for John who showed up at the shop while I was in the dentist's chair 20 miles away. By the time I made it down there, he had already made the first item on our list, a stubby and hollowed out adjustment bar for the butt assembly. John did a very nice job on the bar, he even duplicated Gary's circumferential reference lines to ease adjustment repeatability.
The back side of the bar is solid and is drilled and tapped for an attachment screw as well as drilled for a roll pin that comes through the butt plate to prevent rotation. All of this was duplicated exactly as on the original.
Scope Rail Counterbore
The Tubegun in F-Class - Part 2John Lowther very kindly volunteered his time, skill and machinery to attack a few small concerns to optimize the CSS (Eliseo) tubegun for F-Class shooting. As I noted in the first installment, the bipod mount needs additional grip to keep from sliding forward under recoil. Additionally, the scope base needs to be tapered because in its current flat configuration, I won't be able to get enough elevation travel from my Leupold scope to go to 1000 yards. In reality, my problems aren't with the tubegun, but with the bipod base and the scope that I use with it. Nonetheless, we have to make everything work as a system and that's just what we'll do.
by Germán A. Salazar
by Germán A. Salazar
While we're in the shop, we'll look for a place or two to trim an ounce or two of weight; that's always useful for an F-Class rifle teetering on the edge of the permitted 8.25 kilos. My rifle, with a Krieger Heavy Palma contour barrel is right on the limit, so creating a small margin is just prudent planning.
Bipod Clamp Bar
The first item on our agenda was beefing up the bipod's attachment to keep it in place. Before I even arrived, John was already busy and had begun to make the piece we'd discussed. This is an aluminum bar to go inside the handguard which will provide a lot more clamping surface than the two small flat nuts that came with the bipod. This arrangement won't work with a conventional rail (nor is it needed) but it's just the ticket with the large, but curved, inner surface of the tubegun handguard.
John milled the sides of the bar down a bit, planning on the center fitting into the rail slot from the inside. When I arrived, he saw that the bipod base plate already had that protruding surface, so we simply decided to reverse the orientation of the new bar. Two holes were drilled and tapped for a 10-32 thread, spaced two inches apart. The photo at left shows the long piece of stock with some holes drilled and tapped and the base plate on for a trial fit.
Once everything lined up properly, the bar was cut to the length of the base plate and a piece of non-slip friction tape was applied and cut to size. This will further add to the clamping power of the new piece.
The finished bar with the original lock nuts in front for comparison. Because the bar is quite a bit thicker than the lock nuts, we used longer screws to allow for a bit more torque without fear of stripping the threads in the aluminum bar. The handguard will be sandwiched between the base plate and the bar. Between the added clamping area, more clamping power and the textured surface, I'm confident that there will be no more bipod slippage.
The picture at left shows the installed bipod base with the new bar in place.
Scope Rail Tapering
The next item to address was the scope base which could use a bit of taper to allow me to zero the Leupold scope at 1000 yards. Currently, when zeroed at 500 yards, there is approximately 19 moa of upward elevation travel remaining in the scope. For a .308, the required elevation from 500 to 1000 yards is on the order of 29 moa. Obviously, without some work, this combination won't work when our long-range season begins in November.
Although the tubegun scope rail isn't tapered, the mounting surface in the tubegun sleeve is tapered, accomplishing the same objective. My sleeve has 0.020" taper, newer ones have 0.035" taper. The 0.020" taper amounts to approximately 10 moa of additional elevation over a perfectly flat mounting surface. Our plan was to add another 20 moa of taper to the rail, thus allowing a 1000 yard zero on the Leupold with plenty of room to spare. Cutting too much taper creates the possibility of being unable to zero the scope at shorter distances; however, my scope was at 33 moa elevation at 500 yards, so even taking 20 moa from that (leaving it at 13 moa at 500 yards) would leave enough to zero all the way down to 100 yards.
Some of you may be asking: "Just what is 20 moa?" A circle has 360 degrees, as we learned in school, and each degree can be further divided into 60 minutes of angle (moa). Therefore, 20 moa is 1/3 of a degree. That doesn't sound like much, but it sure has a big effect as the distances involved increase. A bit of trigonometry (which I will skip here) tells us that if we want to achieve a 20 moa slope, then the height of the scope base must change 0.005818" for every 1.00" of length. We'll round that off to 0.006" per inch, then multiply by the 6.5" length of the base contact surface, yielding a result of 0.039". That is how much lower the base needs to be at the front of the contact surface than at the rear to create a 20 moa slope.
Time to get to work! John looked at the scope base's very irregular shape and pondered how best to clamp it to the mill table. Any slippage of the piece while the mill is running could ruin it, or worse, send it flying into one of us. Although clamping the front end was simple, because no cutting would take place there as it is a cantilever over the handguard, the rear was not so simple. Clamping right down on the rear of the base was out because that would cover a portion of the surface that had to be milled.
John's solution was to make a small aluminum fork which would slide over the back of the base and allow unimpeded access to the base surface. The picture above shows the fork being milled and the picture at left shows the finished fork and how it will slip over the base. Bear in mind that when being milled, the base will be upside down, so the fork will bear against the Weaver rail portion of the base.
In the picture at left, you can see how the fork was used to clamp the base. Additionally, note that there is a feeler gauge under the very front of the rail, this was used to create the needed slope.
Although our calculation of 0.039" taper to induce the 20 moa slope was based on the 6.5" length of the base's contact surface, when it came time to clamp everything down, we realized that the best place to shim the base was right at the front. Because the total length of the base is 10", it was simple enough to calculate that the shim at the front needed to be 0.060" to maintain the 20 moa taper.
John spent about 15 minutes carefully setting up the depth of cut so that the mill would just barely cut at the back end of the base and cut the targeted 0.039" at the front of the base contact surface. The real work was in the calculations, the setup, the checking and double checking. Once everything was set, it was a matter of letting the mill run and work its way up the rail. After the cutting was done, we measured and found that we were within 0.001" of our target number. Not bad at all, and perfectly acceptable considering the slight imprecision involved in shim placement.
A careful look at the base in comparison to the handguard will show the taper that we created. Click the photo to enlarge it if it isn't readily apparent.
So an evening's work by a skilled craftsman (I mean John, of course, all I did was get in the way and take pictures) produced solutions to two problems. In Part 3 of this series we'll look at pinning the scope base to the tube to prevent any possibility of loosening under recoil with heavy loads and a heavy scope, and we'll look for some weight saving opportunities.
Click here for Part 3
The Tubegun in F-Class - Part 1
by Germán A. Salazar
The tubegun has truly changed the face of Highpower shooting over the past five years or so. Specifically, the CSS (Gary Eliseo) tubeguns, which are made for a broad variety of actions and configurable to single-shot or repeater, have truly helped the sport to grow. That's not just idle talk, the two principal factors that made the tubegun so important to our growth are the ease of transition for AR15 shooters moving into a bolt-action rifle and the absolutely ridiculous length of time it currently takes to get a stock from the conventional stock makers. My last conventional stock took well over two years from order to delivery (plain fiberglass); one of my friends has now been waiting four years for a simple wood stock for a Smallbore rifle. By contrast, tubeguns, which are largely CNC machined, are delivered in a reasonably short time - weeks or a couple of months at most.
Notwithstanding the foregoing, the tubegun would never have attained its present success if it weren't for one simple fact - they are brutally accurate. I have three CSS tubeguns, two with the Borden Tubegun Special action; one chambered in .308 and two in .30-06 and they are my favorite prone rifles due to their accuracy and great ergonomics. Great accuracy, great ergonomics and honest availability - those factors are just as appealing to an F-Class competitor as to a prone shooter, and indeed, the tubegun is making solid inroads into F-Class.
When I began shooting F-TR a few months ago, however, I didn't begin with the tubegun because I didn't want to chew up what I knew was a fantastic barrel while I learned the ropes of F-Class shooting. Instead, I used an older, conventionally stocked rifle and it worked well; but I'm now ready to give the tubegun a try in F-TR.
|Bag Rider on CSS Tubegun stock|
Unfortunately, the scope setup didn't go quite as smoothly. I mounted my Leupold BR36 at the range right before the match and discovered that my rings were too low for comfortable viewing. After struggling with it during the first string, I temporarily solved the problem by removing the adjustment wheel. This allowed the cheekpiece to drop a little lower and I was able to get through the match with a greater degree of comfort. Obviously, the correct solution will be to use a set of high rings in place of the current medium height rings.
|Bipod slid to the end of the fore end|
Before beginning the third string, I tightened the bipod support bracket; however, it loosened once again during the string with the inevitable increase in vertical dispersion resulting. Subsequent examination revealed the source of the problem: the two small plates that grasp the interior of the rail just don't have enough surface area in contact with the tubegun's curved inner rail section to provide the necessary friction to resist movement. Although this hasn't been a problem with the flat rail in my conventional stock, it is definitely a problem here. Over the next week or so, I hope to make a long, reasonably wide plate that will go inside the tube to replace the two small clamping plates; that should increase the clamping area by a factor of four or five.
The scorecard tells the whole story - a strong beginning before the plate began moving, not discovered until the end of the second string, more loosening in the third string along with increased wind dispersion. Hopefully, next time we'll at least eliminate the mechanical problems and be able to once more focus properly on the wind.
By the way, if you want to download the scorecard form, plot sheets or other club resources, they are available on our club website http://www.desertsharpshooters.com/
F-Open competitor Chuck Gooding with his Clark Fay built 6BR Panda. Chuck is tough competition and keeps me trying hard just to get close to his scores. Clark also does the metal work on my rifles.
Click here for Part 2
A Chapter of Accidents
by Hap Rocketto
As the supervisor of a high school academic department, which includes both chemical labs and art supplies, I find safety an issue that is always in the back of my mind. In the 18 years since my school opened my department has had only a few minor cuts and burns to report. They inevitably occur during one short lab when we teach the kids how to cut and bend glass tubing. Hot glass looks no different than cold glass and glass is brittle so when you mix those conditions with 14 year olds inevitably some skin will be scorched and some blood will flow.
In the many safety bulletins that I read I note that shooting rarely, if ever, shows up on accident lists. It should come as no surprise that this is the case because legitimate firearms owners are well aware of the inherent possibility of accidents with guns and respond accordingly with great responsibility. The shooting sports are very safe. However, I am reminded of some unusual injuries at ranges.
In the 1960s my brother Steve ran the rifle range at Camp Wakenah, the local Boy Scout Councils’ summer camp. I succeeded him in that post when he moved up to, if you can believe it, the position of waterfront director. There he was in charge of a half of a dozen well-muscled bronzed young men who taught swimming and boating. He was even bronzed himself, but that is another story. It turns out that in the five years that we ran the range it incurred the second highest accident rate at the camp.
We never had a shooting accident, however, while the youngsters were waiting to shoot they whiled away the time working on handicraft projects. Many of them had recently bought razor sharp whittling knives and neckerchief slide kits at the camp trading post. While they waited they took out the knives and furiously flailed away at white pine, yellow poplar, and their fingers. Our ready line accounted for dozens of stitches each summer.
The most dangerous area was the handicraft lodge itself. There the boys sat hacking and hewing at lumber and limbs from morn ’till night. The wooden floor was a rust brown color from many years of soaking up scout’s blood. The floor was always covered with wood chips, saw dust, and blood easily reminding one of a butcher shop. Perhaps the only other area that could match it was the scaffold in The Place De La Revolution upon which the guillotine stood during France’s Reign of Terror. Fed by tumbrels full of aristocrats, instead of Boy Scouts, the French abattoir barely outdistanced the handicraft lodge in bloodshed.
In the early 1980s Mark Lasrich and my brother Steve traveled the summer shooting circuit together. When this Laurel and Hardy team ended up at Perry, in 1983, the accident rate soared. About two days into the NRA Championships Lasrich’s glasses fogged up during a rapid sitting string and he tore off his glasses to shoot the last shot. The averages of having a punctured primer are astronomical. Lasrich beat those odds and was rushed to Magruder Hospital. The damage was slight but he had to wear an eye patch for the rest of the week forcing him to withdraw from the rest of the tournament.
The next day, Steve, who is a brilliant theoretical and practical physics teacher, decided to leap off of one of the shooters’ trolleys that were provided to move competitors and equipment around the ranges. A quick calculation, based on the estimated speed of the vehicle, momentum, acceleration of gravity, and mass, informed him of the speed that he would need to avoid falling. He started pumping his legs and leaped from the cart forgetting that his mind is much more athletic that his body. Released from the Magruder emergency room with his left elbow in a bandage and his shooting at Perry finished he joined Lasrich on the disabled list. The two stalwarts did not let the rest of the week go to waste. They spent the few days remaining exploring all of those obscure places at Perry that we wish we could visit but never have the time.
Everyone in the free world witnessed me being shot between the eyes during the Wimbledon Cup Match in 1976 (ricochet in the pits), but few people either saw, or heard of, this little incident that involved my brother few years later. Steve was sitting on the bench next to the phone after scoring a Leg Day rapid-fire string at Perry. A strong wind was blowing and it dislodged the scoreboard on the target to his left. The scoreboard flew across his point and struck a member of the pit crew to his right a sharp blow to the head. The target puller dropped like a pole-axed ox as blood began to gush from his head like Spindletop.
As a result of good training and responsibility there are precious few shooting injuries. Most are generally shooting related injuries, but Leg Day is always Leg Day.