January 04, 2011
Have you ever read an article in which the writer indicated with great authority that to achieve the best performance the barrel of a particular rifle should have a specific number of pounds of upward pressure on it? For years when I would read something like that I was absolutely mystified as to how the heck you could set upward pressure on a barrel. I fully appreciated the fact that some guns do tend to shoot best with a bit of upward pressure on the barrel, but how you could get a precise amount of pressure was beyond me. Until an old friend showed me a trick with a water bucket.
Common business cards can be used to initially determine if your rifle will benefit from upward forearm pressure on the barrel.
But before I get into that, let's take a look at how we determine if a gun would benefit from upward pressure, and most importantly, just what is this "upward pressure" and how is it created?
For quite a few years it has been widely promoted and accepted that a rifle will tend to shoot best if the barrel is free-floated. Free-floating simply indicates that the barrel has no contact with the forearm beyond the receiver or perhaps the first two inches or so of the barrel chamber area ahead of the front of the receiver. Beyond that point there is a gap between the barrel and the stock. You could take a piece of paper, fold it around the barrel, and slide it back to the receiver or chamber area. There would be a clearance between the barrel and the forearm.
The idea behind this is that as a gun is fired, the barrel will move about; it will vibrate or move in a specific pattern. By allowing this free movement to take place the muzzle of the barrel will always be in the same place or position at the moment the bullet exits the bore. That in turn means that the bullet has a much greater chance of hitting the same spot on the target downrange. If the barrel were in five different positions for five different shots, then you would have hits at five different points on the target. Consistency of barrel position at the moment the bullet leaves the bore is critical for accuracy.
If upward pressure is needed, the barreled action is removed, the location of a pressure pad is marked, and a Dremel tool is used to remove wood for the base of the pressure pad.
An added advantage of free-floating a barrel in a wood stock is that the barrel is not influenced by the movement of the stock as it swells or twists as it absorbs or loses moisture or is bent by sling pressure.
Most gunsmiths generally agree that free-floating a barrel is a darn good idea. When working with a rifle to get it to shoot its best, I will start off by glass bedding the action and free-floating the barrel. I then head for the range and do some very serious testing. More often than not, the rifle does quite well, and that's the end of the story.
When Free-floating Isn't Enough
But in perhaps less than five to 10 percent of the rifles, I run into one that will not shoot well after my initial accurization work. At that point I look at the possibility that this rifle may need some pressure on the barrel. In these cases a pressure point in the stock may help to stabilize or dampen erratic or nonsymmetric barrel movement.
Reid uses Bedrock glass bedding for building pressure pads, and he says to be sure to place enough glass bedding in the barrel channel to ensure contact with the barrel.
This can be tested easily with nothing more than a bit more shooting at the range and a few business cards! Just loosen the guard screws so that the barreled action can be lifted up a bit from the stock. Then take two or three standard business cards and place them under the barrel about an inch in from the tip of the forend and tighten the guard screws. Another shooting session is required, and at that point more often than not I see some improvement in performance. Those business cards are a cheap, quick, and easy way of determining if upward pressure on the barrel is appropriate for a rifle.
By the way, it is extremely important when tuning a bolt-action rifle that the guard screws always be tightened with consistent pressure. The best way to do this is to use a torque wrench. While there is no hard and fast rule about how tight guard screws should be, generally about 50 inch pounds will work well. If you don't have a torque wrench, then do your best to be consistent in tightening those screws.
But we don't want to leave our rifle with a stack of business cards under the barrel, so we need to pull the barreled action from the stock. I then take a marker and draw a 3/4-inch square centered in the bottom of the barrel channel about one inch from the tip of the forend. Once I am satisfied with that, I take my trusty Dremel tool with a small round cutter and cut down about 1/16 to 1/8 inch inside this square. That gives me fresh wood to bond with the bedding compound.
With the rifle upside down in a padded vise, the water bucket is hung from the barrel ahead of the forearm tip and the trigger guard screws are tightened.
You can use virtually any brand of bedding compound, but I like the Miles Gilbert Bedrock glass bedding kit. It costs less than $16 and is available from MidwayUSA, Dept. ST, 5875 W. Van Horn Tavern Rd., Columbia, MO 65203; 800-243-3220; www.midwayusa.com. This kit provides enough material to fully bed several rifles or make up goodness knows how many pressure pads in a forearm. It is especially handy for this type of work because you can make it quite thick so it will not run when you use it.
I mix the bedding compound and place a small amount in my relief cut. I want to make sure there is enough so that when the barrel is back in place it will always contact the bedding. I also make sure there is plenty of release agent on my barrel!
The barreled action is placed back in the stock, and the guard screws are partially tightened. The rifle is
then clamped upside down in the padded jaws of my vise. The vise is only on the stock, and the vise jaws do not contact the barrel.
A simple bucket of water of known weight (generally about six pounds) is used to regulate the amount of upward pressure on the barrel.
It's Time For The Bucket
I then take my water bucket in which I have a measured and weighed amount of water. I generally will start off with a total weight of six pounds including the bucket. The bucket is hung from the barrel just ahead of the end of the stock forend. This six-pound weight will be pulling the barrel down, away from the stock. Keep in mind that the total amount of upward pressure will be the weight of the bucket plus the weight of the barrel. The guard screws are then fully tightened. At the same time the pad of glass bedding is setting up forming a solid pillar between the barrel and the stock.
If you don't want to use water, you could use lead shot, sand, or anything else that you find easy to work with.
After the bedding sets up after about 24 hours, I remove the bucket and pull the barreled action from the stock. I normally have to do a bit of cleanup work around my pad of bedding just to make it look nice and uniform. Then it's back to the range for another testing session. More often than not, the results will be a marked improvement over my last shooting session.
Some guns will respond better to more pressure, some work best with less. By using this "water bucket" technique, I can easily vary and control the amount of weight I hang off the barrel. The amount of weight I use to pull down on the barrel when the rifle is upside down will result in an upward pressure on the barrel of approximately the same weight when the bedding is cured and the rifle is right side up. Again, some rifles respond to more upward pressure, some respond best to less pressure. Like developing handloads for your favorite rifle, the process of finding that "best" or optimal amount of upward forearm tip pressure will by necessity require experimentation.
If I find that I must change the amount of upward pressure, it's not at all difficult. If I want to increase the amount of upward pressure, I just roughen up the top surface of the pad, clean it with solvent to remove any trace of release agent, and add a bit more bedding material. I then reposition the rifle upside down with the increased weight on the barrel. If I want to decrease the amount of upward pressure, I will need to cut out the existing pad with my Dremel tool and then apply a bit of bedding. I then reposition the rifle upside down with the lesser amount of weight on the barrel.
Forearm tip pressure is not always the cure to inaccuracy. However, this simple procedure will enable you to accurately adjust the amount of pressure you bring to bear against your barrel with nothing more than a common water bucket!
Until next time, good luck and good gunsmithing!