Building a benchrest rifle

[bradshaw]

Lee explains the difference between neck turning and neck reaming as a measurable result; an answer I haven't heard anywhere. Compared to benchrest, silhouette is like playing marbles on the heaving deck of a pirate ship. Nevertheless, as in bench rest, handgun discipline strives to ride----not be ridden by----whatever conditions prevail.

Lucky the revolver shooter's pumpkin ball tolerates life started in a chamber separate from the barrel.
David Bradshaw

[Lee Martin]

New Range, New Bench – Step 1
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Our existing 100 yard range serves us well for handgun and general rifle work. However it is ill-suited for benchrest shooting. The major knock is its location up-range from the target. Initially I thought we could lower the bench and raise the backdrop but the grade is too steep. The second shortcoming is the top itself. It’s made from plywood and bolts to angle iron. That frame is welded to 3” pipes which are set in concrete. Albeit quite rigid, the wood can buckle over time. It also does a poor job at dampening vibration.

A picture of our current bench:



We’ve decided to build a new range and bench with the following goals:

1) The entire 100 yard span must be level
2) The bench will use a solid, reinforced concrete top
3) This will reside on a large concrete pad
4) A shelter will be constructed big enough to cover the bench, a permanent work table, and be accessible by car
5) The designated area must have room to add an adjacent 200 yard range in time

Recently Dad and I walked our land and found the ideal location. We hope to fire-up the bulldozer soon and clear the space. This’ll also involve pushing a massive dirt impact area, minimum 6-foot high. Based on the layout we can extend to 200 yards, possibly as soon as next year.

Unlike many disciplines, competitive BR doesn’t have a regulation bench. Many shapes exist as depicted here:







I’m most familiar with the first style and will build to these measurements (minus the cinder block legs. Ours will be on 8” pipe):



Step 1 is making the concrete form out of 2 x 4”s and plywood. From the spec sheet we drew the shape on a 4 x 8 foot piece of wood. Replicating the dimensions caused us to add 1 1/2” to account for the edge:







The outline is cut with a circular saw:



Roughed:



Here’s a shot of us sawing and screwing the 2 x 4”s into place. Screws were used over nails so it’ll be easy to disassemble:



Finished form:





Future posts will illustrate each step of the construction (especially my favorite part, the bulldozing). But in case you’re wondering, here’s how it’ll play out:

• The range and impact area are graded with an old D6 Catepillar
• 8” pipes are cut to give a 32 – 34” height. We’re thinking of welding cross members and large metal tabs to the bottom. That way we can anchor it directly to the concrete. The alternative is sinking the posts into the dirt and pouring around them. Two problems with that approach. First, it’s harder to level the pad with three pieces of steel in the middle. Second, if the pad ever needs repaired, I could remove the bench if we go with #1.
• An area, say 15 x 15 foot, will be dugout around the bench.
• We’ll hire a concrete truck to pour the foundation
• Three holes will be cut in the bottom of the form. We'll brace it at the proper height on the pipes and pour our mix. Of course, every step will require careful leveling
• The concrete will be sealed
• The pipe feet are drilled and the entire bench is bolted to the slab
• Using 4 x 4” poles we’ll anchor them to the corners and fabricate the pitched roof
• A sizeable workbench will be installed for gear and reloading.

Even if you’re not into BR, I hope this will be a good range-build tutorial.

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[steve1701]

Hey Lee,

Maybe you should start a new thread titled "Building a Benchrest Rifle Range".

[Lee Martin]

New Range, New Bench – Step 2
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We cleared the first 100 yard span this weekend using our dozer. The machine is a 1957 Caterpillar D6 that dad acquired in 1977. He overhauled the gearing and hydraulics and added a roll cage along with a fresh coat of paint. Almost 40 years later it’s still going strong.

The area we chose had little in the way of large trees; mostly just small pines, uneven dirt, and brush.





View from behind the controls:



Video of it in action:





A shot of its 40-ton winch:



Bulling stumps:



Final grading:



Done. You’ll notice a 6-foot high dirt impact area at the edge.



-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[seancass]

YAY bulldozers!!! I'm a little jealous. Haven't played on a dozer in a while.

edit: Also, super jealous of the home range.

[Lee Martin]

Step 67 – Hardening the Cocking Sear
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Before final assembly we have to harden the sear. It’s a quick process and begins by heating the tab cherry red with a blowtorch. Video of that step along with the oil quenching:



Once cooled, it’s reheated with a propane torch for tempering. The color we’re looking for here is a faint blue:



-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 68 – Final Assembly
____________________________

The action came back from Mahovsky’s and he didn’t disappoint. It cycles beautifully and the tolerances are completely in check. So after god knows how many hours and 17 months, here it is:










There are only three parts in it that aren't hand made by us:

1) The Jewell trigger
2) The main spring
3) The extractor

You’ll also notice I didn’t install the extractor. When we chamber the barrel, it’s easier to test and retest the go-gauge with the extractor removed. That process, along with test firing and bedding is up next.

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 69 – The Scope Base, Underside
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There are a number of excellent benchrest scope bases on the market; most notably those from Kelbly’s and Harrell’s. We prefer making our own though out of aluminum. This allows us to precisely match the dovetail to the rings and equally important the radius of the bridge.

We begin by cutting a one-inch wide strip of aluminum to length (intentionally long of course):



Rough milling to the proper height:



Initial cut for the underside’s valley:



Middle pass complete:





Re-truing the table to ensure it runs dead parallel with the vise:



Canting the head to make the side bevels:









The bottom of the base is now complete. You’ll notice we didn’t radius the underside and this was by design. Trying to match two curvatures is really tough. Instead dad likes to trough or v-block his rails. They’ve worked extremely well and seem to yield more consistent purchase.

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 69 – The Scope Base, Top Side
_____________________________________________________________________

Prior to dove-tailing, the inlets are milled to the desired depth:





A key cutter then makes the angle, which again must approximate the rings:



Right side finished:



Left side done and testing with a ring:



A view of the undressed end:



Another shot of the bottom



The screw holes are indicated, drilled, and counter-sunk:



Using emery cloth and a mild buffing wheel, the base was polished. The front and back edges were also slightly rounded. Here it is ready to be installed:



I chose a one-piece because it promotes between ring alignment. A lot of heavy varmint shooters do the same. The 10.5 pound class on the other hand use split to save a few ounces. If I ever needed to shave weight, mine could be sectioned but I doubt I’d ever need to (weight is normally tweaked through barrel contour and length).

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 70 – The Scope Rings
____________________________________

We normally make our scope rings but in the interest of time I purchased a set of Harrells. These are double screw 30mm’s and medium height:





I should have showed them in the previous post because they’re a must for cutting the base. The dovetail is milled until the ring snuggly slides onto the rail. You want a little resistance but not enough to where you’re forcing it. Harrells are precision machined, matched, and weigh 3.0 ounces/pair (single-wide mediums ~1.7 ounces).

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Markbo]

Hmmmm Surprising to me that you chose squeeze rings with no cross bolt.

[Lee Martin]

May 5, 2015 8:59:04 GMT -5 Markbo said:

Hmmmm Surprising to me that you chose squeeze rings with no cross bolt.

Nearly all short-range BR rifles use plain dovetails. Remember, these things weigh 10.5 - 13.5 pounds and have mild recoil. And while through bolts may be better for heavy magnums, they don't offer the even purchase of a tightly fit dovetail.

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 71 – Barreling Part I
________________________________________

With the action complete it’s now time for barreling. As a reminder, I’m starting out with two 13.5” twist heavy varmint Shilens (0.236” lands):



Using our Harrison lathe, the barrel is rough centered and the cutter is aligned 90 degrees against the tailstock:





3/10” of the breech end is chopped and flushed. I always save these for reference since they specify the rifling:







Now for the important part – utmost to any good chamber is ensuring the barrel is perfectly centered in the lathe (perfectly as in less than a half-thousandth over 360 degrees). That isn’t possible with tubes not cut to the highest standards. The premium-selects used in BR should absolutely meet this requisite.

Light chamfering the end to remove burrs:



A dial indicator is mounted and zeroed on one groove. The chuck is then manually rotated 180 degrees to the opposite side. How far you move it depends on the rifling count. Mine is a six groove, therefore every 60 degrees puts you on the bore.



As you slowly spin the chuck, the indicator moves out and back to zero as it rides over the lands. The goal is to have each groove dead-on zero across all six. To accomplish this, the jaws are precisely adjusted. It’s a tedious task but for an experienced machinist like my dad it takes mere minutes (novices like me take 15 to 20):



The muzzle end must be centered too. Below you’ll see an aluminum spud my dad made and a dial indicator at 12 o’clock. Similar to the chamber side, the bolts are manipulated until the dial stays put on zero over the full rotation:



Clearly if the chamber is crooked to the bore, accuracy goes down the drain.

Re-facing the breech:



-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 72 – Barreling Part II
________________________________________

With the barrel properly set in the lathe, we can thread and chamber. Math time – below are the critical dimensions of our action:

• Distance from the front of the receiver to the bolt’s outer edge
• Distance from the front edge of the receiver to the bolt face
• Inlet diameter & threads

Shown graphically:



Calculation one entails determining the barrel shank length. The distance from the receiver face to the front of the bolt equals 0.942”. They can’t touch and too small a gap can bind the gun if brass shavings or grit get in there. Most benchrest jobs are between 0.003” and 0.010”. I went with 0.005” via a 0.937” shank.

The depth stop on our lathe was set for 0.930” using the breech face as zero. That’s 0.007” short because we want to cleanly machine the ledge in one-thou increments.

The 0.930” gauge, comprised of 0.900” and 0.030” spacers:



The depth stop:



Cutting the shank:





Machined to a diameter of 1.062”:



-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[Lee Martin]

Step 73 – Barreling Part III
__________________________________________

Our action is internally threaded for 16 TPI. The lathe’s gear drive is arranged for that thread:



A small recess is made prior to the ledge. This coincides with the relief in our action:



A dial is attached to the lathe and zeroed just ahead the shank’s edge. When the feed puts the dial close to zero, the drive is disengaged.



First pass on the threads and checking that they’re 16 TPI:







Trying the action on the barrel:



-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"