What is reboring?
Reboring is the process of cutting a new rifled bore in an existing rifle or pistol barrel. This new bore will be of a larger caliber than the original and will be new and fresh in all respects
How is a barrel re-bored?
Specialized tooling and equipment are used. The machine tools look similar to an engine lathe and the cutting tools themselves are attached to steel tubing. The first step is counter-boring. This is akin to a roughing cut on a lathe and removes the bulk of the material from the bore leaving it a few thousandths of an inch under size. A special cutting tool called a counter-bore which is attached to a steel tube is pulled through the barrel. Cutting oil is pumped through this tube under high pressure and the steel chips are carried out the rear of the barrel by the flowing oil. Finish reaming is next. Feed rates and cutting speeds are adjusted and a finish reamer is substituted for the counter-bore and the bore is brought to final size using the same technique. The smooth bore is hand lapped and then placed in the rifling machine. The barrel is rifled by cutting a series a helical grooves in the bore. This is done using a single-point hook cutter. Each pass removes about one ten thousandth of an inch of steel (.0001") from one groove and then the barrel is indexed and another pass made in the location of the next groove. A six groove barrel would require six of these cycles to create grooves only one ten thousand of an inch deep. A typical groove in a small arms caliber is four thousandths (.004") deep, meaning that forty passes down each groove are necessary to bring it to final depth. When the grooves are cut to the proper depth the barrel is removed from the machine and hand lapped again. The lapping processes assure a very uniform bore dimension and a surface finish that is smooth and free from radial tool marks.
Why should I rebore instead of installing a new barrel?
There are several instances in which reboring is advantageous. All of the external features of a barrel are retained when it is rebored. These may include sights, quarter or full length ribs, special profiles such as octagon, scope blocks, dovetail cuts on the underside of the barrel, coned breech, extractor cuts, engraving and bluing or other special finishes. The expense of duplicating these features when installing a new barrel are avoided when an existing barrel is rebored. A new barrel may not match the profile of your old barrel. Thus it will not fit the existing barrel channel in your stock. Re-inletting your stock or re-profiling your new barrel are not necessary when reboring. Fine double rifle barrels may be rebored at a small fraction of the cost of replacement. A cast bullet shooter may want to experiment with a groove diameter slightly larger than standard, or a non standard twist rate.
What is meant by a "family" of cartridges?
Many cartridges have been developed by changing the caliber of an existing case by simply necking it up or down. This changes only the bore and neck diameter. The case body, shoulder location and angle all remain the same. Any group of such cartridges is said to be in the same "family". When reboring a barrel to another caliber in the same family the headspace remains unchanged and re-chambering may be performed using only a "neck & throat" reamer. Most of these conversions require little or no alteration of the feed surfaces to achieve reliable function. One family includes the following popular factory and wildcat chamberings: 25-06, 6.5-06, 270 Winchester,30-06 Springfield, 8mm-06, 338-06 and the 35 Whelen. Another is: 264 Winchester Magnum, 7mm Remington Magnum, 30-338, and 338 Winchester Magnum. There are numerous other examples.
Are there any limitations to what caliber I choose?
Yes. When your barrel is rebored material is removed resulting in thinner walls. Several things need to be considered. The contour of your barrel, any cuts or holes in your barrel such as dovetails for sights, spring or forearm mounts, holes for scope bases, quarter rib dowel pins or screws etc. These all need to be measured and the final wall thickness calculated. The walls need to be thicker near the breech/chamber where pressures are greatest. Ruger drills the quarter rib mounting holes extremely deep on their Number 1 rifle. Some lever actions have deep cuts on the underside of the barrel which limit your choices.
Do you lap your rebores?
Yes. Each bore is hand lapped after being finish reamed. This extra step removes the radial tool marks left by the reamer and brings the smooth bore to a very consistent diameter along its entire length. The barrel is then rifled using the single point cutting method after which it is hand lapped a final time. The resultant bore has excellent uniformity of diameter and twist rate with a very smooth surface finish which lays in the direction of bullet travel. This finish reduces copper and lead fouling to a minimum and results in a bore which is slow to carbon foul and easy to clean.
What kind of accuracy can I expect?
Each barrel leaves our shop with a bore that is consistent in diameter and twist rate with a fine hand lapped finish. These are two traits of many that contribute to accuracy, and the only two over which we have control. Reboring will do little to straighten a crooked bore (although some crooked barrels shoot pretty well). A bolt action that has an out of square bolt face, crooked barrel threads, only one bolt lug bearing, poor bedding or any other problems known to cause poor accuracy will not shoot very well even with the best of bores. If you are considering a rebore to correct an accuracy problem it is wise to eliminate as many other potential causes as possible before reboring or rebarreling. A gunsmith familiar with action accurizing/blueprinting techniques can identify and correct many problems. This will allow one of our rebores (or any good barrel) to shoot to it's potential. With this in mind, you may expect your newly rebored barrel to shoot as good as when it was new, many times they shoot better and almost always foul less. Performance equal to the better cut-rifled aftermarket barrels is common
Do I need to break in my rebored barrel?
You should treat your barrel the same way you would a newly installed high quality aftermarket barrel. We have had good results following the same guidelines offered by the better aftermarket barrelmakers. A bore with a fine lapped finish free from radial toolmarks (as ours are) will typically only metal foul until the newly cut chamber throat has broken in. A quick look at a new throat with a borescope will reveal an abundance of radial toolmarks. These need a few shots to smooth them up!
Is a new forcing cone included with a revolver barrel rebore?
No. Our basic rebore for revolver barrels is a rebore only. All remaining caliber conversion work is to be completed by you or your gunsmith.