Savage makes some outstanding rimfire rifles that offer an excellent value for the money. Occasionally I’m asked about machining them for customers. Normally I’ll pass, but the owner of this B.Mag .17 HMR managed to talk me into it.
Before we get started, let’s take a look at the Savage B.Mag Thumb-hole Target as it comes from the factory:
What a great looking little rimfire. Let’s make it look even better!
Basically what the customer wanted to do was to add a brake and fluting on the barrel. While I’m unsure of the recoil advantages of the brake, the aesthetics will certainly improve from this project.
Before we get to the work, please take a look at the following disclaimer:
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Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.
Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.
I ordered the following tools and parts from Brownells to complete this project:
Stripped B.Mag action in hand, I got to work.
This project is two separate operations; muzzle brake installation and barrel fluting. I decided to begin by installing the brake.
This barrel comes from the factory with an 11 degree target crown and no threads. The customer supplied a brake with 1/2-28 threads that was the same diameter of the barrel. The nice thing about small diameter actions like the one found on this B.Mag, is they are easy to set up in the lathe.
This is my lathe (when it was new, it is way filthier now). It is a Precision Matthews PM-1440GT. I’ve found that it does everything I could ask of it exceptionally well.
To hold the barrel in the lathe’s chuck, I wrapped it in .010″ thick plumbing tape. I find this gives ample protection to the barrel surfaces.
Next, I have to dial in the barrel on a 4-jaw chuck in my lathe. I don’t have a range rod in .177″ caliber, but I do have a pin gauge set that is in .001″ increments. I select the ground pin that has the tightest fit and use it to indicate in the barrel. I start with a .001″ indicator and follow up with a .0001″ indicator.
I use a high-speed steel 35 degree profile tool to turn the tenon. I like to make them .002″ under the major diameter.
Next, I use a threading tool to cut the threads at a 28 TPI pitch. In this case, I am using a carbide threader; it works well, provided I run at a high enough spindle speed. As always, when threading into a shoulder, care must be taken to prevent crashing the lathe.
I come back with my profile tool to clean up the shoulder.
A test fit shows this brake from MAC’S GUNWORKS NWP No Timer Muzzle brake fits great. The surface finish is a little different, but I think that it actually accents the rifle very well.
A view of the brake installed with the barrel off of the machine. The diameter of the brake was the same as the barrel. The customer ordered it this way. Normally I like to see them oversized because the bore may not be concentric to the barrel, in this case it is and the two parts match well.
Another look at the freshly cut threads!
So, it is off to flute the barrel. Straight flutes could be cut with a rotary table and a tailstock on a knee mill, but I’m cutting helical flutes. In this case, I’ll be using something that is not found in every shop: the 4 axis mill.
A few notes, I like helical flutes on round actions. Unlike straight flutes, they don’t require indexing. With a barrel action like this, finding top dead center to start with would be extremely difficult. In this case we only wanted to cut flutes on 8″ of barrel, starting it on one side of the roll marks and ending it just short of the muzzle brake.
This is how I begin to set up for fluting. The 4th axis is to the right and the tailstock is to the left. I held the barrel in the 4th axis chuck using some tape to protect it and drove the tailstock’s live center into the muzzle brake.
Next, I set up some angle blocks to eliminate chatter. This is a fairly long and skinny part. If I start machining it without support, the chatter would be horrendous. By placing the blocks against the barrel and tightening them down, the vibration is mitigated. Since the barrel is only touching on the round part of the diameter, the 4yth axis can still spin the barrel.
I cut the flutes with a 3/8″ 4-flute carbide ball nose end mill. I programmed this run by hand. It is 6 flutes, 8″ long, with 360 degrees of twist over the distance.
This is how it comes off of the machine.
This is one great looking barrel and brake combination!
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