Obtaining a high quality barrel doesn’t necessarily have to imply high costs and large amounts of money from your pocket. In face, you can rebore a rifle barrel using a few simple tools. This technique is possibly one of the best ways to improve your barrel. While specialized gunsmithing tools and equipment are required for such operations, we have provided a step-by-step walkthrough to make this process as easy as possible.
It can be advantageous to undergo this process in certain situations. For one, when you rebore a rifle barrel, you ensure that all of the external features of your barrel remain. Whether you have special profiles, full length ribs, sights, coned breeches, extractor cuts, engraving and special finishes, a rebore job will not impact any of these features of your rifle barrel. Installing a new barrel would require that you duplicate the features of your old barrel (and involve massive costs), a simple rebore ensures that you get the best out of your rifle at only a fraction of the cost of replacing a barrel.
How the Rebore Gunsmithing Process Works
You may not be familiar with the term “reboring”. It represents the process of using your existing rifle (or pistol barrel, depending on the situation) and cutting a new rifled bore in it. Such modifications will result in a new and improved bore of a larger caliber than your initial weapon. Before you consider a rebore for your rifle barrel, remember that each manufacturer has a particular mix of steel for each type of factory barrel. While the majority of steels cut smoothly, there are some situations when they do not.
If the steel contained in a weapon’s button barrel isn’t sulpherized, for instance, the cut is most often rough. Sako uses unsulpherized steel. Other manufacturers use steel which has soft and hard spots alongside the barrel and in these weapons, making the cut not as smooth as one would desire. For instance, older Winchester firearms use such steels. Rebored Winchester barrels often have small tears in the bottom of the groove. Barrels constructed of steel high in vanadium don’t cut ideally either.
In the case of an “old-brown” gun, as collectors call it, reboring is the ideal gunsmithing solution.
The first step in any reboring process is completely disassembling and inspecting the rifle. Drift the sites out, from left to right and then use an action ranch to remove the barrel. The bore is drilled and reamed for the larger diameter. Hand lapping then removes the reamer marks. Counter boring requires particular gunsmithing tools to be used (a counter-bore) so as to remove the bulk of the material found on your bore. At the end of the process, the bore should be left a few thousandths of an inch under-size. After counter-boing comes finish reaming, when a finish reamer is employed to bring the bore to its final size. The technique is similar to counter boring: the finish reamer is attached to a steel tube which is pulled through your riffle’s barrel while cutting oil is continuously pumped at high pressures through the tube. When you have your smooth bore, it is placed inside a riffling machine where helical grooves are cut into the barrel. Finally, when all the required grooves have been cut, the barrel is taken from the machine and undergoes another process of hand-lapping where a uniform bore dimension is assured.
With the finished barrel, you can now proceed to chambering. Center it in a 4-jawed-chuck and hold the mussel end in a spider. Ensure that the reamer is in perfect alignment with the bore. Use oil to cut the chamber, making sure to back the reamer out and clean out the chips. You can always test your progress with a go-gage. It should end up just flush with the bike of the barrel. After finishing this step, you can proceed to re-crowning the mussel. The last step is taking care of the outside edge of the barrel. Place the cutter on the outside of the barrel and reverse the rotation.
If you also wish to bring the breach block from rim fire to center fire, drill a new hole in the breach block and construct a new firing pin. Make sure to also work with the extractor (as it too must be modified to work with the higher magnum case).
Size and Caliber Limitations
During the reboring process, the resulting barrel will have thinner walls. Considering that the barrel has to have the thickest walls near the chamber and the breech, where the pressures are highest, your choices somewhat limited. Where the length of a barrel is considered, most reboring procedures are done on barrel longer than 20 inches and shorter than 34 inches.
Gunsmithing Accuracy Modifications
The best part about reboring a rifle is the fact that there aren’t accuracy limitations. After reboring, your rifle will be at least as good as (if not better) than a factory one. The barrel’s diameter and twist rate are consistent with those of a fine hand lapped finish. Remember that reboring your rifle will not straighten crooked bores. Granted, there are some crooked barrels which still shoot quite nicely, but reboring can’t work miracles. When a bolt action has both out-of-square bolt faces, crooked barrel threads, bad bedding, or other problems, reboring is most likely not going to improve its accuracy, even if it is performed divinely.
All things considered, a newly modified barrel will most likely foul less and shoot better than before.
Image Source: gunsmith.co.nz