Wednesday, 25 May 2011

The Switch Barrel

   For the last couple of years I have been running what is commonly known as a switch barrel on my F-T/R rifle. Basically it allows for removal and reinstallation of the barrel with basic hand tools and with no, or very minimal, shift in zero. As some of you more astute readers may have noticed in a couple of the pictures from my first blog, a hex is machined on the muzzle of my rifle. 

This hex varies in size with the barrel diameter at the muzzle and can be as small as 5/8” for barrels that are turned down for front sight bands. The hex allows a simple end wrench or socket to be used to loosen and tighten the barrel into the action by hand. This really isn’t a new concept since bench rest shooters have been screwing barrels on and off by hand with no tools for many years but it is rare to see it in F-Class.

  So that is the switch barrel in a nutshell. But what are the real facts of the matter when it comes to....GASP! .... taking the barrel off your rifle and then putting it back on again? I have been asked about shift in zero and barrel loosening by many folks while talking about the switch barrel and how I use it and so I decided to write this piece to bring out the facts as I have observed in my own rifle. Mind you, this isn’t a scientific study replete with reams of data and years spent testing. It is merely a collection of observations and some semi-scientific testing on my own rifle. So….let’s get to it.

  Why in the world would you want to be able to pull and reinstall your barrel anyway? The first answer is quite simple. Traveling with your rifle. 

   Whether you fly or drive, being able to put your rifle into a compact case is a boon to the traveling shooter. The airlines have pretty strict rules concerning overall outside linear measurement on luggage and the penalty for going over is very stiff….something on the order of $150 each way for “oversize” luggage.  If you drive, a compact case is easier to get into and out of a car. I drive a pickup, so it’s a moot point most of the time. But on those occasions when I fly, like the upcoming Creedmoor Cup in Ireland or the FCNC, the smaller case is a blessing. Getting a 30” or longer barreled action into a case that will pass the “62 inch rule” is a pretty tall order and I have yet to see one that I would trust with my gear that actually meets that rule. They all seem to come in just a tad short and require a step up to the next bigger case. This all based on the use of a mil-spec composite case like a Storm or Starlight or Pelican. I wouldn’t trust my gear to anything but a Storm case, personally. The baggage goons haven’t hurt a thing inside yet. 

The second reason for a switch barrel is caliber changes with multiple barrels. 

  If you shoot a 308, like I do, the .473” bolt face will accommodate a wide variety of cartridges from the magnificent 6BR Norma to the venerable 30-06 Springfield. Having the ability to easily change barrels to a different caliber makes good economic and ergonomic sense to me.

   Let me explain that last statement. If you have a stock and action that fits you and you shoot it well, you can effectively make it into multiple rifles with the addition of a different barrel. Obviously a barrel is much cheaper than another barrel, action and stock, so there you have the economic component. Having a common chassis for the various calibers allows the shooter the familiar “feel” of a rifle that has been fine tuned to his or her personal tastes, so there’s the ergonomic component. In my view it is a win-win situation.

  What about the all important question of shift in zero? While I had never seen much of a change on my rifles, there were small changes from barrel removal. How much, you ask? Good question, because I had never really measured it until now but I figured it was in the neighborhood of les than ½ minute. I decided to make the test simple and brief. Shoot a 5 shot group, pull the barrel (actually unscrewed it a couple of turns) and reinstall it exactly as it was. I would then shoot another 5 shot group without adjusting the scope to see if the point of aim and point of impact shifted.

   At my local range, I did just that, much to the amazement of the local guys who though I had lost it when they saw me loosening my barrel. The groups were shot at 100 yards with a ½ to ¾ minute westerly wind. The accompanying photos show the actual groups.

 The “flyer” in the baseline group is the 1st shot which was the result of missing the wind value. This group is just about ¼ minute high.

  So I unscrewed the barrel a couple of turns and retightened it to line up the index mark I had made on the barrel. All it took was a couple of medium raps on the t-handle and socket with a hammer handle to seat it to the mark.

The second group results are interesting. 
The first shot went high and the next two went slightly low and last 3 went to the same group. This group is also just about ¼ minute high as well. Curious, I shot another 5 shot group to confirm the second result and it was, in fact, also ¼ minute high. 

So I re-zeroed my scope.  J
The reason for the point of impact movement?...... I have no idea. Anything I say would be pure speculation and I will leave the explanation to the engineer types. 
It is enough for me that it is what it is and that the rifle shoots in the middle  with minimal fuss after barrel reinstallation.

  So what does this non-scientific test prove? On a strictly scientific level, it proves nothing. For me, it confirms what I have seen and believed since trying the switch barrel. The two gunsmiths that I trust, Larry Racine and John Whidden, both told me that the switch barrel system would return to a very close zero with no problems. As I said earlier, I had never actually tested, quantified and verified the zero questions. Now that I have, I can safely submit to my readers that the system is extremely reliable and repeatable. A few fouling shots after reinstalling the barrel and the sight is spot on. I believe that the real key here is getting it back to the same spot with an index mark instead of a torque wrench.

  The INCH action lends itself very well indeed to the switch barrel system due to the dual locating diameters machined before and after the threads on the barrel shank. This design captures and aligns the barrel with the receiver very precisely in 2 locations versus only one in front of the threads as is common practice.  I believe that is why the INCH returns to exact zero where my other rifle didn’t.

  The barrel loosening question is moot, since my rifle and every other rifle I have ever seen has a right hand twist barrel and that causes a slight tightening effect with each shot. Removing the barrel on my rifle always takes a bit more torque than seating it.

  So…is the switch barrel for you? Maybe and maybe not. It can be a great benefit to the traveling shooter and a money saver for the shooter wanting to shoot different calibers on the same chassis.
I hope that the data outlined above will help you to make an informed decision on the matter of the switch barrel.

Warren Dean