FROM THE GUNSMITH’S BENCH TECH-TALK >> BY DEAN MaiseY SCOPE MOUNTING BASICS Scope rings and bases are essential to the pursuit of accuracy and also to ensure that your precision rifle optics are securely and precisely mounted. One of the main reasons Mounting a riflescope to a rifle scope, in the standard manner, for scope base/ring action (or barrel) in most cases to your centre-fire rifle, such as starts with a pair of rings fitted a Remington 700, Howa 1500, alignment problems is to the tube/body of the scope, Mauser 98 or Winchester Model which attach to a base that is 70, etc. due to assuming that attached to the action or barrel, selecting the mount usually by way of small threaded WHAT WE WANT TO screws. Of course there are some ACHIEVE base/s listed for your rifle variations to this; some actions • Scope secured tightly enough such as Sako, Tikka, CZ, Ruger, so that it will maintain correct in the manufacturer’s etc have an integral base/dovetail alignment/position and not shake rail incorporated into their action loose under recoil. chart will guarantee a design and only require rings to • Scope body aligned to affix the scope. Some expensive the action/barrel as truly perfect fit to your rifle. European scopes have a dovetail/ as possible to minimise the rail on the underside of their amount of adjustment required This is often not the case. tube/body, and some new laser using the scope’s internal rangefinder scopes such as the adjustment mechanism. SCOPE MOUNTING rifle. This is often not the case. Burris Eliminator III scopes have • The two scope rings’ internal PROBLEMS The saying that ‘assumption is their own clamping mechanism bore surfaces aligned with One of the main reasons for scope the mother of all stuff-ups’ is very on their underside. In these each other as best as possible base/ring alignment problems is relevant here. Even if you think cases conventional rings are not to prevent unwanted stressing due to assuming that selecting that you have the correct bases required. For the purposes of or damage to the scope tube/ the mount base/s listed for your or rings for your rifle’s action, you this feature let’s assume we want body when the ring clamps rifle in the manufacturer’s chart must still check when installed to mount a conventional rifle are tightened. will guarantee a perfect fit to your that the bases are the same height Genuine Qualified Civilian Gunsmith, Graduate Colorado School of Trades-1997, Certified D.F. Maisey Gunsmithing Smith&Wesson Armourer-Revolver-Pistol, NZDA Short F-Class National Champion 2010, 2011, 2012 SUPPLYING AND FITTING Rifle barrels by Pac-Nor, True Flite, Bartlein and Shilen. Barnard actions, Stiller actions, Surgeon actions, McMillan stocks, Boyds stocks, PTG custom rifle parts, Jewell triggers, silencers & suppressors, DFM muzzlebrakes. Custom target or hunting rifles built to order. FULLY EQUIPPED DEDICATED GUNSMITHING MACHINE SHOP Includes two ultra-high precision toolroom lathes for all barrel fitting, action truing and custom machining. New CNC machining centre recently added. FOR ALL YOUR PRECISION HUNTING & MATCH-WINNING RIFLE WORK Email: [email protected] / Ph/Fax: 07544 2207 / www.gunsmith.co.nz SEPTEMBER/october 2013 / rodandrifle.co.nz / 57 >>TECH-TALK FROM THE GUNSMITH’S BENCH as each other, are both level with adjustment mechanism. each other, and are not canted or • A stressed scope tube can be >>Technical twisted in relation to each other. the cause of fliers, or variations in Bases that are of differing heights point-of-aim / point-of-impact with can be corrected by shims placed changes in ambient temperature. under the lower base, but the other • A poorly aligned scope may problems can be more difficult result in an inability to correctly to correct. sight the rifle in at all if the A few specialist tooling misalignment is so bad that companies in the US make ‘scope you run out of travel on the Looking down along the ring alignment reamers’, which adjustment turrets. edge of a one-piece base is one quick way of checking will ream the inner diameter of • A scope damaged by poor straightness. A engineer’s the installed scope rings truly mounting may affect its value, steel ruler laid along the top surface is also another method and in perfect alignment with or may even affect or negate its of visual inspection. The base each other. The rings’ lower warranty cover. in the pic here is stressed/ and upper parts will need to be bowed in the mid-section. index-marked so that they don’t OTHER THINGS TO BE get mismatched later on. Once AWARE OF the rings are installed to the bases • Loctite is a great product to they should not be removed again, prevent screws rattling loose, otherwise the alignment can no but there are places it should longer be guaranteed to be true. and shouldn’t be used. Loctite Forget about the ‘lapping bars’ and applied to the base screws and the grinding paste method – it’s too underside of bases is fine, but don’t time consuming for a professional apply it to the screws on the rings Often with one-piece bases there is a gap or contouring error that needs gunsmith – what we want to do themselves, as it can be a real pain to be dealt with to prevent stressing is remove just enough metal to to deal with later. the base or action when the screws are installed. Here JB-Weld get a significant proportion of the • On actions that have the front compound is being used to create inner surfaces of both rings to run screw hole for the front base going a 100% contact and stress-free true. How much reaming depth in directly over the barrel threads, foundation at the rear of the base. is required will be a judgement always ensure that the screw end call for the gunsmith. In extreme does not touch or ‘bottom out’ on cases of really bad misalignment the barrel threads. This may mean the rings may need to be having to grind the screw thread a replaced altogether. bit shorter to ensure clearance. It’s There are some rings that cannot amazing how many broken 6-48 be corrected by reaming though screws and accuracy problems are – Weaver rings with their steel top a direct result of having this front- strap and aluminium lower are one most screw jammed hard onto the example. Others that have soft barrel extension threads. aluminium or vertically split rings • One-piece scope bases can be Burris signature series rings with the posi-align plastic can also be difficult or impossible better than two-piece bases in so inserts; ‘Zee ring’ style shown to ream true. far as they can help to minimise here – to fit the common One easy method of overcoming misalignment, but they are not Weaver style bases. scope base misalignment problems always a foolproof arrangement quickly and economically is to use that you can just screw on and rings with the self-aligning ball/ expect the alignment to be perfect. socket type plastic inserts, such Steel one-piece bases are often as the Sako Optilock or Burris bowed slightly from the stresses Signature Rings. The unique design of the machining processes. of these rings can compensate for One-piece alloy bases are usually all of the misalignment scenarios straighter, but manufacturing possible (within reason) with the tolerances and differences with plastic inserts floating in a ball/ both the bases and the rifle action Close up (top view) of rifle action socket recess while piloting off the itself often mean that some showing how front screw hole is located directly over the barrel scope tube body itself. When the shimming or custom fitting/ threads. The scope base screw must top strap of the rings is tightened bedding of the base may still NOT touch the barrel threads, or the alignment is maintained and be required to prevent the base there will be problems. the scope tube secured. twisting and to ensure that it stays straight and ‘stress free’. Top view of a crooked rear base. This can be due to problems with the WHAT IS THE REASON • Be aware that barrel/receiver alignment of the threaded holes, the FOR ENSURING CORRECT alignment is not always perfect, contouring of the base or the action itself – or all of the above. SCOPE RING ALIGNMENT? and while you may have the scope • To prevent permanent damage and mounts nicely aligned to the to the scope tube body. Misaligned action, the barrel itself may be rings can result in dents or kinks in pointing slightly off-centre. Sorting the scope tube or in extreme cases out severe misalignment in this may even bend the tube body – area can be a major problem. sometimes permanently. • If using Loctite on the underside • A dented or stressed scope tube of bases, remember that this may affect the operation of the product requires a couple of things scope’s magnification (power) ring in order for it to set. Contact with 58 / rodandrifle.co.nz / SEPTEMBER/october 2013 a metal or metallic coating and the absence of air. Occasionally on rifles that come in for repair, I find that the Loctite that has been applied has not gone off or set, leaving a soft, gluggy mess under the bases. This is common if one of the metal surfaces has been painted, or similar. In these cases – or where significant gaps or misalignment errors need to be corrected – then Loctite is not the right product to use.