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March 1st, 2015

Offset Scope Mount Helps Shooter with Vision Problem

offset scope base mountForum member Roy Bertalotto did a real nice off-set scope installation on a bolt gun to help a sight-challenged shooter. Roy explains: “A friend of mine shoots left-handed and has lost the sight in his left eye. I built him a scope mount so he can still shoot left-handed, but now use his right eye.” Roy’s fabrication work is impressive and we praise his efforts to help a fellow shooter stay in the game.

Roy bolted a plate to the existing scope rail on the top centerline of the Rem 700 action. This plate extends a few inches to the right. On the outboard end of the plate, Roy fitted a second scope rail, aligned with the bore. Weaver-based rings are then clamped to the outboard (right side) auxiliary rail.

offset scope base mount

offset scope base mount

offset scope base mount

Be Careful of Canting Issues with Offset Scope Installations
We’re pleased to see that Roy developed a solution for a shooter with an optical disability, but we want to stress that this is a specialized installation that can create some problems with point of impact shift if the gun is not maintained perfectly level. With the amount of horizontal offset (between the scope’s optical axis and the bore axis) built into this rig, if the rifle is canted, point of impact can shift rather dramatically. For a southpaw who is willing to adapt his/her shooting style, it may be better, in the long run, to learn to shoot right-handed if his/her right eye is the only good eye. Likewise, if a right-handed shooter can only see well through his left eye, he may benefit from learning how to hold the stock and work the trigger with his left hand. The shooter could still work the bolt with his non-trigger hand. Changing from right-hand to left-hand shooting (or vice-versa) may require a stock swap if the stock is not ambidextrous.

Permalink Gunsmithing 3 Comments »
July 21st, 2014

Muzzle Brake Performance Tests by Bertalotto

Muzzle brakes are controversial. Some people swear by them, while others swear at them. Still, there’s no question that a good brake can reduce felt recoil up to 45%. And likewise, the best brakes, when installed properly, seem to have no negative effect on accuracy.

VAIS muzzle brake

Roy Bertalotto has done considerable experimentation with muzzle brakes, testing dozens of brake designs on his own rifles over the past few years. Roy’s article, Adventures with Muzzle Brakes, discusses various aspects of muzzle brake design and performance. Roy doesn’t claim that his testing is definitive, but his article is definitely worth a read. Here are some of Roy’s interesting findings:

Exit Hole Diameter
“Best accuracy and effectiveness of the brake was obtained with a hole .020″ over bullet diameter. If the exit hole is too small, such as +.005″ over bullet diameter, accuracy suffers. If the depth of the exit hole is too shallow, the metal around the hole will erode very quickly.”

Hole Placement
“The most effective braking was with a brake 1″ in diameter with a 3/4″ exit hole on each side, just in front of the muzzle. The bullet passes through a cone of 35 degrees before it exits the brake. (Like the tank example), Incredible reduction of recoil. But loud and ugly. Very easy to make since you don’t need a spin fixture or a dividing head.”

Bottom Gas Venting Helps Accuracy
“In my tests, not having holes all around the brake effects accuracy a bit. I believe it does something to the bullet by the air pushed ahead of the bullet creating unequal turbulence in the bullet path. I’ve tried a few brakes where I drilled only holes on the top, test fired, and then completed holes on the bottom and in every case, accuracy improved.” Below are spiral-ported brakes crafted by Clay Spencer.

VAIS muzzle brake

Brakes Work Best with High-Pressure Cartridges
“The higher the pressure of the particular round, the more effective the brake. I have over 20 rifles with brakes. The 220 Swift is the king of reduction. Followed very closely by the 25-06, 6mm Remington, any Weatherby small bore. With a proper brake and a hot handload under a 40 gr bullet, the Swift will move 1/2″ to the rear and 0 muzzle rise! Big boomers with low pressure like 45-70s and shot guns benefit the least.” [Editor’s Note: Roy is judging effectiveness by the percentage of recoil reduction rather than absolute levels of recoil. Obviously if you start with a heavier-recoiling round, the absolute amount of recoil energy reduction is greater. Roy is really talking about efficiency–brakes are most efficient when used with high-pressure cartridges.]

Installation is Key to Accuracy
Roy’s findings are fascinating and suggest that further study of muzzle brakes is warranted. But we can all agree that precision installation of the brake is essential for accuracy. A poorly-installed, mis-aligned brake will degrade accuracy, that is well-known.

Harrell’s Precision has made thousands of muzzle brakes, in many styles and port arrangements. The Harrell brothers offer some good advice for gunsmiths installing brakes: “Muzzle brakes aren’t magic, they reduce recoil by redirecting exiting gas. What’s important is that they are straight and the threads are perpendicular with the base. The only way to get the base and threads perpendicular is to thread, not tap, them on a lathe.”

Permalink Gunsmithing, Tech Tip 9 Comments »
August 10th, 2012

RVB Precision Cleaning Rod Bore Guide for 17 HMR Rifles

When Hornady (and CCI) developed the 17 HMR cartridge, they really hit a homerun. And the rifle manufacturers quickly marketed some nice rifles to chamber this 17-cal rimfire round. But unlike .22 LR rifles which, typically, require very little cleaning, 17 HMRs demand frequent bore cleaning to maintain good accuracy. That’s because 17 HMRs shoot copper-jacketed bullets at 2550 fps velocities.

17-Cal Bore Guides — The Challenge
The problem is, it’s hard to find a well-designed, quality bore guide for 17-caliber rimfire rifles. With many 17 HMR (and 17 Mach 2) rifles, you encounter mechanical interference when you try to use a standard bore guide to protect the delicate chamber edge and the bottle neck area of the chamber. A fixed ejector is in the way. On many 17 HMR rifles, this little “shark fin” ejector is right in line with the chamber and is fixed — it doesn’t retract. Therefore the kind of bore guide you might use for centerfire rifles won’t work in 17 HMRs — it will hang up on the ejector.

Polymer bore guides exist for this type of action, but they are typically open-bottom designs that do not enter and seal the chamber. These open-bottom designs don’t protect the delicate chamber edge or the bottleneck area of the chamber, and they also allow some seepage of solvents out of the chamber. That’s why Roy Bertalotto created his RVB Precision Bore Guide for 17 HMR rifles. The 7075 aluminum tube on his Bore Guide is thin enough to pass by the ejector, yet it is extremely rigid. (Photos below.)

Roy explains: “My bore guide is made of 7075 anodized aluminum tubing, which is totally unaffected by any type of cleaning solution. One end is swagged down to fit completely into the chamber of a 17 HMR rifle. This guides your cleaning rod perfectly to the bore without touching the chamber walls or front edge of the chamber. The tight fit of the bore guide in the chamber also stops cleaning solvents from getting into the action, magazine, and trigger housing.” (Editor: Solvent seepage can do damage. We had a 17 Mach 2 rifle that rusted internally because solvents leaked past an open-bottom bore guide.)

Using the RVB 17 HMR Guide – Once the bore guide is in place, slide the supplied aluminum bushing over the tube, and gently push the bushing into the rear of the action. This centers the guide rod in the action to keep the guide rod tube aligned. Once the guide rod and bushing are in place, you can use a 17-caliber cleaning rod* with patches and/or brushes to clean the barrel. Use the rod normally, but make sure your patches are quite small and don’t apply too much pressure as these small-diameter rods can kink if you try to force over-size patches down the bore.

The RVB Precision 17 HMR Bore Guide costs $19.95 plus $5.00 shipping. To order, email Roy Bertalotto via rvb100 [at] comcast.net. Roy will then send you shipping/payment details.

* NOTE: You really do need a dedicated .17-cal cleaning rod for this job. Most other rods are too fat to pass through the barrel. Dewey Mfg. makes a decent 17-caliber cleaning rod that is reasonably stiff and doesn’t kink too readily. It is available sizes from 7″ to 36″, either bare stainless or with a nylon coating. We prefer the nylon-coated version, in either 26″ or 36″ lengths, depending on barrel length.

Dewey 17 cal caliber bore guide

If you have a high comb on your rifle, you may need extra length to avoid interference with the rod handle. Use this formula to determine correct rod length: Length of barrel + action or breech rod guide length + 2-3″ clearance + high comb if applicable = total rod length needed.

There are other quality 17-cal cleaning rods, but we’ve used the Dewey and it functioned well. The nylon coating cleaned easily and was gentle on the throat and crown. You should clean the coating before and after each use to ensure it does not embed grit or other contaminants.

Permalink Gear Review, New Product 5 Comments »