In-Shop Barrel Porting And Lapping–In One Process

One of the first things I do when a customer comes in and asks for a barrel to be ported is to find out why he wants it ported in the first place. As you may already know, people sometimes want things just because they’ve heard the latest "buzz word" in the industry rather than for any practical reason. I like to discuss the matter first and find out if the customer is having any accuracy or recoil issues which is fueling his request for the porting.

The first thing I point out to a customer is that any modification to a gun will automatically decrease its resale value, and may make it more difficult to sell. Usually this advice is shrugged off and the request is insisted upon. This is when I try to find out what in particular is causing their request for the porting. If it’s recoil related, I first suggest a change in recoil pad or a change of loads.

Since I have always strived to be a ‘moral’ gunsmith, I try not to do work that, deep down inside, I know is not necessary and will cost the customer an unnecessary expenditure. Case in point: A local retailer sold a rifle to one of my customers and talked him into porting the rifle as well. Since he hadn’t even fired the rifle yet, there was no way he could know if the porting would solve any problem. Personally, I try to be a quality-driven gunsmith and not a dollar-driven gunsmith.

Preparing for the Job With that said, if the job is necessary and agreed upon, here’s how I go about accomplishing two steps at once—both porting and lapping. First I strip the rifle down as much as possible to reduce any chance of damage to the stock, and to lighten the workpiece. For added security, I like to enclose the receiver and as much of the barrel as practical with a gun sock. The gun sock is put on after you’ve determined where your porting holes are going to be and they’re marked on the barrel.

Of course, laying out the holes is a source of controversy. Most gunsmiths would agree that porting does work, but there seems to be little agreement on what arrangement of porting holes works best. I’m not an engineer or firearms designer, but I have come up with an arrangement that seems to work well for me, and my customers say they’re happy with the results.

My design is a seven-hole arrangement that consists of three holes of progressively larger diameters, with two sets of what I like to call "stabilizer" holes in between. I start with the largest diameter hole being closest to the receiver end, thus allowing exit of the majority of the escaping gases. Next in the series is the first set of two smaller-diameter stabilizing ports, which are set off center of the main three ports (see Figure 1).

The next port is the next smaller diameter main porting hole, followed by the second set of stabilizing ports, ending with the smallest diameter main (continued on page 14)

AMGDB16 AG DBI – SPREAD AD, NEW coming directly from Belvoir

AMGDB16 AG DBI – SPREAD AD, NEW coming directly from Belvoir

barrel and set it aside close to the workpiece. Once the lead is flowing, pour a small amount into the barrel to form the primary lap. You should leave a space about an inch or so from the end of the barrel opening. Now slide the cardboard separator into the barrel down to the top of the lap already poured in. Now pour the remaining lead inside the barrel to the top of the barrel and let the lead harden (see Figure 2). Once everything is laid out, it’s time to start drilling.

The strength and stability of your drilling fixture cannot be overemphasized here. Any movement will ruin the lineup of the holes and will easily be visible, thus producing an amateurish job. I secure the barrel in my lathe vise (padded of course), with the centerline straight up and level. I then begin the holes by first using a small center drill. These are very stable bits and will not wobble off center.

They are also very cheap, so I like be overly safe and I buy them in quantity so I can use a brand new one on each porting job. (I’d rather pay $10 for a set of bits than buy the owner anew barrel.) I center drill each of the three main porting holes to get them started. The diameter of the holes is another issue of debate, but I’m of the opinion that the largest diameter hole should not be more than 45 percent of the bore diameter.

Depending on the caliber you are working with, calculate the largest diameter and drill the first American Gunsmithing Association News Take a moment to review the benefits of membership in the American Gunsmithing Association. For openers, you automatically receive American Gunsmith, the Association’s monthly magazine, featuring specific, detailed information on maintaining, servicing, and repairing your—and your clients’—firearms.

Back issues and binders are also readily available. • The Member’s Store: a catalog shop filled with items including shop aprons, caps, shirts, and more that highlight your affiliation with the craft of gunsmithing. • Access to the Association’s Technical Assistance Hotline with gunsmithing tips and answers to hard-to-solve problems and everyday gunsmithing questions. hole closest to the chamber end first.

Don’t forget to check the depth of your drill bit so that you don’t drill all the way through into the opposite side of the rifling! Then drill the second hole with a smaller diameter bit, and finally the last hole with a smaller bit than the second. At this point you can save a step and chamfer the tops of the holes before removing the barrel to realign it for the stabilizing holes. You can chamfer the tops of the holes in a couple of different ways.

You can use a drill bit a couple of sizes larger than the drilled hole, and carefully "start" the bit into the hole so the flared end of the bit chamfers the top of the hole. Or you can use a Dremel tool with a ball grinding bit to chamfer the tops of the holes. Due to the curved surface of the barrel, the chamfered surface will have an oval shape to it. I find this look to be quite appealing.

After the top holes are finished, using the scale on the lathe vise, I rotate the barrel a few degrees to drill the stabilizing holes. Note the degree marking that you use so that you can repeat it for the other side of the barrel. For the stabilizing holes, I use the same size bit for all four holes. Drill two holes on either side of the main porting holes. Chamfer these as well. The lead lap that you have drilled into will keep the burrs to a minimum.

Once the drilling is complete, you will then push the lap • Access to a number of vendors including Numrich Gun Parts, Brownells, Lyman Products Corp., Passport Holsters, and many more offering discounts and services to AGA members. • Book and video discounts from DBI and AGI. • Member savings on car rentals, hotels, motels, and air travel, from some of the biggest names in the travel industry. • Liability Insurance: As an AGA member, you can get $1,000,000 in annual coverage for just $1,000 per year.

For membership information, contact the American Gunsmithing Association Membership Services, Norwalk CT 06854-1631; or call so that the secondary lap (the one that was drilled into) will be pushed forward out of the barrel taking the remaining small burrs with it. Don’t push the primary lap out of the barrel. Push only far enough to exit the secondary lap up to the cardboard separator. Once the secondary lap is out, you can now use your lapping compound on the primary lap to begin the lapping process.

Use an extra fine grit so you will only put a nice polished finish on the inside of the barrel. Finishing Up Once you’re finished, clean everything out, reassemble the rifle, and test fire it. One other option I offer is to do the same porting procedure on a custom-made add-on compensator. This way, the customer’s rifle barrel will not have to be drilled and will thus retain its value, but porting the removable compensator can produce the same benefits.

If you choose this method, remember to drill the hole for the bullet approximately .004 larger than the diameter of the bullet. You can also dress up the exterior of the compensator by turning a couple of V-shaped grooves in the side of it for a nice effect. I also bevel the front and rear of it to give it a professional look. If you have the equipment, this is a valuable service you can offer your customers. And with the prices of machine porting, it can be very profitable for you. ■ AGA Corner