Rifles 103: Parts Selection & Assembly
Precision Assembly.
Precision derives not only from shooter technique but equally from proper barrel performance, action torque, optic type, optic mount type & torque, and overall assembly.
Barrels should be no longer than required to achieve AMIV at max hunting range. Their chambers should be tightly machined to SAAMI specs for off-the-shelf loads, or to specific round reamers for handloading. Their rifling can be achieved by button, cold hammer forge, or cutting - accuracy is possible with all methods. The manufacturer should be known for quality blanks and excellent stress-relieving, which improves performance when hot. The gunsmith or company chambering the barrel should have a reputation for meticulous work. The profile of the barrel is primarily important in terms of weight and thread pattern compatibility. If the barrel is properly stress-relieved, heat should not overly affect performance within a 10-shot string, even if the barrel is thin. Barrels should be threaded for suppressors, even if that requires the gunsmith to thread in 1/2x28 and permanently install a “flare” to 5/8x24. Thin barrels are not an excuse to ignore suppressors.
Actions should be torqued to manufacturer specification. When aftermarket stocks or chasses are being used, ensure torque specifications have not changed. When torquing, ensure the recoil lug is seated in contact with its receptacle by tapping the butt against the ground. Some actions have integral rails of a proprietary nature (Tikka) or partial or full picatinny. Those which don’t will require the addition of Picatinny scope base sections in order to mount optics. These scope bases must be torqued correctly, with threadlocker, and must include recoil mitigating pins or other mechanical connections beyond simply screwing or gluing. Integral rails will always be stronger.
Degreasing screws is of paramount importance prior to torquing the action, mounts, and optics. See a tutorial here.
The Optics.
Optics are aiming devices, not telescopes. Quality of glass is secondary to robustness and “tracking” (the true nature of the adjustments made by turrets). Seek objective 3rd party testing or personally follow this drop test procedure prior to trusting an aiming system. Optics known to hold zero include:
SWFA 6x, 10x, or 3-9x
Inexpensive, hard to find, bulky turrets (except the 3-9), indestructible
Nightforce (any model)
Known for reliability and true tracking.
Choose a SHV, NX8, or ATACR based on preference and budget.
Only the Mil-R reticle is usable for hunting.
Trijicon (any model)
The 3-18x44 Tenmile FFP in Mils is the best blend of weight and capability in the Trijicon range
Credos lack parallax focus, Tenmiles have one. You decide if that matters.
Lightweight for mag range, glass quality, and durability.
Maven RS1.2 2.5-15 SHR-Mil
Single best choice for most applications.
Good clarity, most usable reticle (by far), durable.
Leupold Mk4HD 2.5-10 TMR-illum
Durability is promising, but design is new. Has passed some drop tests and failed others.
Great eyebox and glass, good bold center-dot reticle.
Locking elevation, capped windage - good turret configuration. No parallax.
Optics should be mounted in quality rings or monolithic mounts whose internal diameters are known to be true and whose mounting interface includes recoil abatement beyond simple attachment screws such as studs or lugs. The rings as well as the action interface should be temporarily threadLocked, torqued to manufacturer spec, and then drop tested as above to ensure solidity. Torque is not a figure that transfers between ring types, and threadlocker affects torque values. Without drop testing a particular full setup, there is no way that trust can be established. Using known combinations is helpful but not the whole answer.
The Stock.
A rifle is “built” once it has the ability to reliably place rounds on target at maximum hunting distance. The last component in this equation is the interface between the rifle and shooter, which is the stock or chassis in which the barreled action rides. Broadly speaking, these fall into two categories: traditional stocks and modular chassis. In either case, 5 fundamentals should be met:
Negative Comb
As the rifle is fired, it will recoil backwards into the shoulder of the shooter, while the shooter’s cheek is in contact with the comb of the stock. If the stock is flat or positive at the comb, this recoil will move the shooter’s face off the line of the target and disrupt his recoil management and tracking through the scope. If the comb is instead slightly negative, the rifle will drop away from the face in recoil, not disrupting the stock weld or sight picture as greatly.
Negative Drop at Heel
The rifle’s bore should draw a straight line back to the top of the recoil pad at the shooter’s shoulder. This line might intersect below the recoil pad or at its top, but should not intersect above the recoil pad. Many stock designs place this boreline above the recoil pad, causing more muzzle flip than is necessary and hampering recoil management and target tracking through the scope.
Parallel forend
A forend whose line is parallel to the barrel aids in pointing while shooting offhand, and in shooting from supported positions. Under recoil, the rifle should track straight backwards without influence up or down from a sloped forend.
Near-Parallel Toe
The rifle should ride smoothly on its rear support bag, supported by a gentle slope from the toe to the grip. This enables small elevation corrections by moving the bag fore and aft, but doesn’t unduly move the rifle off target upon recoil.
Vertical Grip w/ correct trigger reach
The hand should rest naturally on the grip in a vertical position to pull the rifle into the shoulder without exerting any sideways torque. There should be a comfortable position for the thumb to rest on the same side as the hand, since looping the thumb over the top of the grip results in inevitable torque. The reach from the comfortable gripping position to the trigger should result in a near-90 degree index finger angle.
For a light stalking rifle, a standard wrist instead of a vertical grip may be preferable so long as the trigger reach is still natural.
Stocks are preferred by shooters who want a more traditional feeling rifle, or those who use a scabbard. They are comfortable to touch when cold as they are generally made of carbon fiber or fiberglass. The lightest stocks are lighter than the lightest chasses, though many stocks are heavier than ultralight chasses. Most stocks require manual bedding by a skilled gunsmith, via skimming, pillars, and some custom inlet fitting. This step should not be skipped.
Chasses are preferred by shooters who prize adjustability, accessory attachment, and shorter overall length (due to folding mechanisms). A chassis doesn’t require manual bedding, instead mating to the action via interaction with a bedding block attached through torqued screws. They are often more expensive than stocks to buy, but are less expensive when factoring in manual bedding, fine inletting work, and extra parts.
While stocks can accept bottom metal in either BDL or DBM format, all chasses use detachable magazines and do not require extra purchase of bottom metal. The most common magazine formats are AICS and AW. Both can feed reliably and AICS is as common a format as STANAG is for AR-15s. These magazines may rattle, which can be an annoyance for hunters, though this is usually mitigated when there is spring pressure from loading, or by the use of electrical tape or small o-rings. There are many proprietary bottom metal types from many manufacturers, and few of them play nicely. It is mandatory to understand the relationship between bottom metal, magazine type, action compatibility, and stock inlet in order to assemble a trouble-free system.
The Accessories.
Though accessories aren’t strictly part of a rifle, the rifle components chosen will explicitly limit the accessories which can be used.
Sling studs or QD cups are required on the stock/chassis in order to use a sling. An extra sling stud can be used to mount certain bipod types (like the Harris). Sling studs do, however, get in the way of front rests (for shooting) and gun bearers (which are better than slings for holding rifles whilst hunting).
ARCA rail can be molded into a chassis (XLR and MDT), attached to a stock via T nuts, or attached to a chassis via M-Lok. It enables mounting to tripods and certain bipods (MDT, Atlas).
Picatinny can be mounted or recessed into chasses and stocks. Many bipods still mount to Picatinny.
Spartan Javelin adapters are small magnetic Quick-Detach recesses for certain tripod heads and detachable bipods. Gunsmith adapters can be installed into most carbon fiber stocks, and external adapters can be attached to sling studs or m-lok or picatinny.
Muzzle brakes can reduce felt recoil 50% at the expense of increased noise, blast, and concussion.
Suppressors can reduce felt recoil 30% and also decrease noise to hearing safe levels depending on the cartridge and suppressor in question. They are the single most important rifle attachment, bar a scope.