This article contains instructions, advice, or how-to content. (November 2011)
Rifle bedding is a process of providing a rigid and consistent foundation for a rifle’s operational components, by creating a stable and close-fitting bearing surface between the gun’s functional parts (i.e. the receiver housing the barrelled action) and its support part (i.e. the stock) that do not deform with pressure or shift under the shear stress of the recoil from firing. This is for the goal of accurizing the rifle and (to a lesser extent) prolonging the life of the stock.
The bedding process is often an aftermarket improvement and involves molding an epoxy-based material onto the stock recess to fill away the gaps within its contact surface with the receiver (known as glass bedding), and/or inserting a metal cylinder around the action screws to reduce compressive shifting (known as pillar bedding). The receiver and the stock are sometimes fastened indirectly through an intermediate piece (usually made of rigid materials such as aluminium alloy) known as a bedding block, which serves the functions of a pillar, a bedding surface and even recoil lugs. The contact interface on the stock may also be substituted by a metallic bedding frame known as a chassis, which is either embedded into the stock, or even completely replacing the stock like the lower receiver on many modern modular self-loading rifles.
Bedding increases accuracy in part by relieving stress on the action. The rifle's action will rarely sit flush in the stock without bedding. This causes the action to flex when tightening the bolts holding the action to the stock. This flexing results in inconsistency during operation, which accumulates to a loss of accuracy over time. Bedding will create a flush surface for the action and prevent flexing. Bedding also reduces movement of the action in the stock. Without bedding, the action may be more likely to shift after a shot. If the action shifts and does not return to same spot in the stock the rifle will lose the ability to maintain zero.
Prolonging stock life
Bedding can help prolong the life of the stock. Repeated recoil forces can cause movement of the action in the stock. As the action moves, friction can create wear in the stock surface. Eventually the repeated wear can ruin the stock.
Several different bedding methods can be used depending on the type of stock, desired results and level of experience of the person attempting to perform the bedding.
- Full contact bedding of the action with the barrel floated.
- Full contact bedding of the action and the barrel.
- Full contact bedding of the action with a pressure-bearing pad for the barrel.
- Pillar bedding of the action with the barrel floated.
- Full length aluminum action bedding block.
Full contact bedding of the action with the barrel floated is a very common method for long range rifles with a heavy barrel. A free-floating barrel will generally produce the greatest accuracy. However, a pressure pad under the barrel just forward of the action can sometimes improve accuracy by acting on barrel harmonics and reducing stress on the action from the weight of the barrel. Pillar bedding can be used to float the action as well as the barrel, but the process is more difficult.
Generally a slow, hard drying epoxy is used as bedding for a rifle. The epoxy should dry very hard to withstand recoil and prevent flexing of the action. The epoxy should not shrink or expand after hardening. Several epoxies are designed for outdoor use where they need to expand and contract with changes in temperature. These epoxies are not suitable for rifle bedding. Some epoxies are supplied with coloring additives to allow the epoxy color to match the stock color. Most other epoxies are only available in one or two colors. Some epoxies will come with release agent, otherwise cooking spray, car wax or shoe polish can be used instead.
Tools that may be helpful when bedding a rifle are:
Long, replacement action bolts with heads removed, modeling clay, masking tape, electrical tape, inletting tools or Dremel, sand paper, stock vise, barrel vise or suitable holding fixture, cotton swabs, rags and cleaner/degreaser.
To bed the rifle, voids in the action are filled with clay and the metal is coated in a release agent. Epoxy is then applied to the stock. The material is allowed to cure and the stock is removed. When available, a milling machine is used to clean up the excess dried epoxy.
If performed improperly, bedding can destroy a rifle. Mechanical locking occurs when bedding material is allowed to harden in holes or around protrusions on the action. If locking occurs, the action can be permanently fixed to the stock. Extreme measures may have to be taken to separate the stock from the action, possibly destroying one or both. Locking can be prevented by carefully filling all holes and crevices in the action with clay and removing or taping any protrusions on the action. Never apply bedding material on the upper half of the action or anything that is wider at the bottom than the top. Improperly applied or insufficient release agent can cause the bedding material to bind to the metal. If the trigger assembly is not removed prior to bedding, epoxy can seep into the trigger assembly and ruin it.
This article needs additional citations for verification. (September 2014) (Learn how and when to remove this template message)
1 "How to Accurize Your Rifle - Floating and Bedding" by Russ Chastain. "Floating is at its best when used with rifles that have relatively heavy (large diameter) "bull" barrels, because they are less flexible than slimmer barrels. Lighter "sporter" barrels are less stable, and may flex enough during the shot that accuracy will suffer." http://hunting.about.com/cs/guns/a/float_bed.htm