Accurizing Your Firearm: Part 2 - Abed and Afloat
In the first part of this series, we took a production line pre-2006 Winchester Model 70 out of the box, cleaned it up a bit, mounted a 3x9 scope on it and subsequently took it to the range for a bit of paper punching. Now you can't knock a consistent group of under three inches at 100 yards, but you'd expect better than that if it had been a custom gun. And I just knew the Winchester could be tweaked to custom gun performance with a bit of effort and investment.
In the test firing, I noticed that the spread in the bullet consistently crept upward and tended to the left, suggesting that the barrel was likely touching the barrel somewhere between the muzzle and the chamber. As the barrel heated up from subsequent firing, the metal expanded and changed the way the barrel reacted when the shot went off, in this case causing the point of impact to wander up and left. To push the accuracy up another notch, the pressure point would have to be eliminated.
The next step was to open the wood-to-metal clearance in the fore-end of the stock and glass bed the action.
To understand the reason for free floating a barrel, it's important to understand the fact that a gun barrel does not in the true sense of the word, direct a bullet to its target. Rather, it flings the projectile.
When the primer ignites the gun powder, the bullet is rammed down the length of the barrel under tremendous pressures, forcing it to accelerate to three to four times the speed of sound and, at the same time, imposing a spin by way of the rifling. The sum total of all these forces causes the barrel to vibrate and at the moment the bullet leaves the gun, the muzzle actually whips around in an ellipse that can be as much as two inches in diameter in the case of some of the thin barreled sporters.
Provided this vibration and barrel whip occurs exactly the same way every time, the gun will theoretically throw the bullet in exactly the same way every time. Changing the bullet weight, style and the rate of powder burn will change the way the barrel throws the bullet because the pressures change, but more on this in Part 5 of this series. The second reason that a gun can vary the way it slings a bullet is that the pressure exerted externally on the barrel might be inconsistent. And here we come to the tacky controversy over barrel bedding.
It's been raining for days and everything is drenched. Do you really know where your gun is shooting?
Full Glass Bedding
One school of thought suggests that a rifle barrel should be in constant, continuous and even contact, preferably from chamber to muzzle. This is achieved by a painstaking process of applying a substance--inletting black if you're a gunsmith and machinist's blue if you're not--to the barrel and attaching the barreled action to the stock. When the barreled action is removed, the blue will have rubbed off onto the wood of the stock at all high points.
These points of contact are carefully sanded down and the barreled action is again reattached to the stock to check for high points. The process is repeated over and over until the barrel is in uniform contact with the wood which is then sealed against moisture. Because it is extremely time consuming and labor intensive, full barrel bedding is rarely found in production guns.
That's no great loss, maintains the other school of thought. While the concept is theoretically sound, it leaves no room for less-than-perfect workmanship or the eventual changes in the wood due to humidity and natural warping. Hence the overwhelming popularity of floating barrels over bedding them.
Two methods of floating barrels are used. Many production line rifles are pressure floated, usually by resting it on a ridge that runs the length of the forearm from chamber to schnabel or else by resting the barrel on a slightly raised portion usually located toward the front end of the channel. The technique works surprisingly well more often than not. If your gun throws entirely satisfactory groups at the range, there's really no need to fiddle with the floatation.
The second method is to completely free float the barrel so that it does not make contact with the fore-arm at all. The free space is minimal, usually not more than the thickness of a sheet of paper and the reasoning is that if there is nothing touching the barrel then there is nothing that can change the way the barrel throws the bullet.
Few production rifles can honestly boast a full floating barrel since the process takes time and that cranks up the cost of the firearm. Instead, they prefer to pressure-bed the barrel. The process unfortunately does not take into account the eventuality that moisture might get into the wood to swell it and, in so doing, change the pressure on the barrel. Nor does it allow for barrel expansion due to temperature. While synthetic materials are less prone to swelling caused by humidity, the expansion of the barrel due to changes in temperature can nevertheless result in changes in the way the barrel slings the bullet and so the importance of a full floating barrel applies to synthetic stocks as well.
To determine whether a barrel is fully free floating or only partially, take a piece of thin writing paper and run it down between the barrel and the fore-end. If it's fully free floating you should be able to slide it smoothly to about two inches from the action. At this point the barrel increases in diameter to enter the action and it should be the only area where a free-floated barrel actually touches the stock.
To determine whether the barrel is fully free-floated, slide a piece of
paper or a dollar bill between the forestock and the barrel.
If the paper jams anywhere else along the barrel and the rifle shoots groups that would do a shotgunner with buckshot proud, it needs help.
The first step is to determine the points of contact between metal and wood; in the case of a well used gun, these points should show up as polished areas in the barrel bed, but if we're working with a new rifle, we'll need to mark the areas where the paper is pinched on the outside of the forearm before you remove the stock. On a bolt action rifle, the two screws holding the stock to the action are usually located in front of and in back of the magazine.
On most rifles, the lug holding the stock to the barrel is located just forward of the magazine.
How It's Done
Gunsmiths use special tools to work on the barrel bed, but there's no need to fork over a lot of hard-earned money for the sake of one or two guns. A hardwood dowel of the appropriate size-usually about 3/8 inch diameter, but this will change with caliber and barrel beefiness-and a sheet of 80-grit sandpaper will do the job nicely. Simply wrap the sandpaper around the dowel and proceed slowly to avoid taking off an excessive amount of wood. By the same token, take into account that you'll have to apply new sealant, so sand the full length of the channel to remove the old varnish and provide sufficient tolerance for the new coating.
Put the gun back together to make sure that all the high spots have been eliminated and that you have continuous clearance between the wood and metal down to the chamber. If your paper binds anywhere along the length other than near the chamber, slap a short piece of painter's tape to the outside of the stock to mark the area and take the barrel off again. Apply some candle soot-literally take a lit candle and quickly run the flame across the matching portion of the barrel to deposit a thin layer-to the problem area and reattach the barrel to its stock. Now when you take it apart, the soot should have rubbed off onto the high point. Sand, reassemble and test. Once you're satisfied with your workmanship, remove the barreled action one final time and proceed with the process of sealing the exposed wood. A good, high grade outdoor polyurethane will do the job nicely. I used the rub-on variety to absolutely prevent any puddling of the sealant prior to drying. Two coats are plenty. Let the polyurethane set completely, preferably overnight or longer, reassemble the gun and do the paper test one last time. The test sheet should slide all the way down to the chamber encountering no resistance.
Glass bedding the action is somewhat more complicated. Essentially, the process encases the recoil lugs and the action in a resin bed so that these parts are not affected by the movement and distortions of the wood reacting to humidity, heat or recoil. Most medium priced guns these days are glass bedded at the factory; those which are not should be left in the hands of a competent gunsmith since the process is both exacting and messy.
Now all that's left is the gratification of taking the gun to the range to punch some paper. Frankly I was keen to see how a few hours of tinkering and a minimal investment of money had improved the accuracy of my out-of-the-box, production class Winchester Model 70. Essentially, you could stop at this stage and be reasonably confident in the gun's ability to shoot where you want it to. But there are a few more improvements you can make to fine tune it into becoming the kind of gun most hunters boast about. In the next issue I'll look at ammunition and how you can squeeze that five shot group down to about an inch.
George Gruenefeld has been hunting big game for over four decades and his travels have taken him to several continents. Most of the time, though, he concentrates his efforts on the Prairies and mountains of Western Canada.