LaBounty Bolt Fixture

The LaBounty bolt fixture, action truing sleeve and receiver mandrels are a set of tools used in the process of accurizing bolt action rifles.  You may have heard of accurizing rifles, sometimes referred to as blueprinting, but not fully understood what is involved or how it is done. The following is a brief description of the process and the reasons behind each step of the process.

The explanations that follow are for bolt action rifles. There are some things that can be done to improve the accuracy of other types of rifles, but these tools are designed for bolt actions.

Let’s talk about theory. When a cartridge is fired a lot of things happen.  All that pressure and bullet engraving into the rifling and accelerating from zero to 3,000 fps in 24 inches creates all sorts of complex vibrations that are transmitted to the barrel and action.  The theory is that if the vibrations are uniform from shot to shot, then the muzzle will be in the same position each time a bullet exits.  What are the factors that would lead to variations and what can we do to lesson them? Consistency is the goal.

  • Ammunition must be as uniform in pressure as possible.  The cartridges must be the same in length dimension to the headspace datum surface. Ideal is a slight resistance to closing the bolt handle. The head of the case must be square with the case body, i.e. at a right angle to the center line of the case. The seating depth of all bullets must be uniform.
  • The stock must be bedded properly.
  • The trigger pull must be of target grade quality.
  • The scope and mounts must be of high quality and properly mounted.

The following are things that are sometimes wrong with factory rifles, but can be brought into tolerance with the LaBounty Bolt Fixture and related tooling.

  • The bolt face should be square with the bolt body.  Assume that the bolt face is not square with the bolt body. The base of the cartridge will conform to the angle of the bolt face upon firing.  If the base of the cartridge is not square, it would be possible that the two angles would match, or be turned 180 degrees from matching, thus producing an extreme gap. Since the orientation will be random, there will be randomness in the vibrations.
  • Ideally the locking lugs are at right angles to the bolt body and in the same plane. They seldom are.  The thinking is that if the lugs are not bearing evenly on the locking lug abutments, and the ammo is never exactly the same pressure, then there will be a difference as to when the non-bearing lug makes contact to share the load. Since this will vary from shot-to-shot because of the different pressures, then it follows that the vibration pattern will not be consistent.
  • The locking lug abutments in the action body should be in the same plane and at a right angle to the center line of the action’s bolt raceway. They seldom are. If they aren’t, then we will have wasted our time squaring the locking lugs.
  • The bolt face should be square to the center line of the bolt body. You probably get the idea by now…

The reality is that few, if any, production rifles have perfectly square bolt faces, locking lugs in precisely the same plane, and action locking lug abutments square to the bolt raceway.

LaBounty Precision Reboring Inc.’s accurizing tools consist of a suite of tooling that address the above enumerated problems.  The first tool is a fixture to hold the bolt so that the locking lugs and bolt face can be easily machined into being at right angles to the center line. Additional tooling for holding the action for truing its front face at right angles to the bolt raceway and squaring the locking lug’s abutment is available.  Once you have used the LaBounty Bolt fixture you will find that you can machine a bolt in less than 15 minutes, depending mostly on your ability to use a four-jaw chuck for the dialing in process. I have opened up four Mauser bolt faces to magnum size in under fifteen minutes.  Check out the following pictures for a quick overview.

This picture is a Mauser bolt having the back of the locking lugs trued with a carbide tool bit in a boring bar holder. Fortunately, most Mauser lugs are quite close. They are case hardened, so we don’t want to go through the case.

This is the bolt fixture in the four-jaw chuck being dialed in.  The arrow points to the brazed joint between the bolt body and the locking lug piece.

One of the problems with the Remington 700 series bolt is that it consists of five pieces.  The three pieces we are concerned with are the bolt head, the bolt body and a steel washer that is sandwiched between the bolt body and the bolt head. These pieces are furnace brazed at high temperature with a copper alloy. (The other two parts are a steel cross pin that goes through the bolt body and the head to align them and the bolt handle.) Sometimes it seems that the factory doesn’t get the bolt head and body accurately aligned.  This creates a condition where the locking lugs are not at right angles to the center of the bolt.  Look closely at Remington bolts and on most of them you can see this joint.  You must dial in the bolt on the bolt-handle side of this joint.  If the bolt head piece is cocked at an angle to the bolt body you will never get it dialed in properly.  When the body is dialed in behind this joint, then when the back of the locking lugs are machined, they will be at right angles to the bolt body.

There are other methods of doing the above work.  Let me caution you; don’t ever use a method in which you use the firing pin hole as a center for your lathe tailstock.  Firing pin holes are seldom concentric with the bolt body.  Also, it is way to easy to swage a small 60 degree bevel on the edge of the firing pin hole with the tailstock pressure.  That leaves a recess for primers to flow into, which is not good.

ACTION TRUING SLEEVE AND MANDRELS

The bolt fixture takes care of holding the bolt to perform the necessary machining operations.  The action truing sleeve is a sacrificial piece of tooling that has a hole diameter that is a close fit on the outside diameter of the action.  By mounting the action on a mandrel that is a close fit in the bolt raceway, and the sleeve onto the front receiver ring, and then placing the whole unit between centers in the lathe and turning the sleeve, then a surface that is concentric to the bolt raceway is created. (Look at the picture below). The front face of the sleeve is also machined.  While it is mounted on the mandrel, the front face of the receiver is also trued.  Remove the complete unit from the lathe and remove the mandrel from the action.  Do not disturb the sleeve.  Chuck the action/sleeve unit in a four-jaw chuck, the tang end into the spindle, leaving about one-eighth of an inch of the sleeve protruding from the chuck.  Dial in the sleeve both on the diameter and on the front face of the  sleeve. With an appropriate boring bar, the locking lug abutments can now be trued to a right angle with the bolt raceway.

The two arrows are pointing to the two screws that bear against the mandrel. These screws clamp the action to the mandrel.  On the opposite side of the truing sleeve is a hole for a screw that threads into the front guard screw of the action, thus attaching the truing sleeve to the action.

This is the action mounted in the truing sleeve and dialed in, ready to machine the locking lug abutments with a boring bar. The arrow points to the front of the action.