Direct scope mounts seem like a reasonable, simplest and most logical idea of all mounts. Mostly, direct mounts are made as two piece mounts in most cases. Naturally, there are exceptions, for example DNZ mounts, which are known for single piece direct mounts.
Direct mounts can be recognized by the fact that each piece / ring is made from one single part and by the fact that such mounts are mounted directly on the rifle. Such mounts are usually mounted either on dovetail that is part of the receiver or directly on the mounting surfaces and on prepared (in advance) holes, drilled in the receiver.
Advantages of direct mounts can be found in
simple design and therefore – they are reliable because of small number of parts.
Small number of parts also means less chances of failures if everything mounted correctly.
If direct mount is made of two pieces, it might be hard to install it on the rifle. This is because it is often very hard to achieve perfect alignment of both rings (especially if the rifle is not made precise enough).
If it comes to strain because of poor alignment of both rings, it can flex the scope or even damage it. We would suggest to use a help of a skilful gunsmith who should mount them as they should be mounted.
What else does not go in favor of direct mounts, is the fact that they are always only fixed and if they are quick detachable, they are usually not repeatable.
On the market, there are both – aluminium and steel mounts. It usually depends on what you need and what material is the receiver made of. If mount is made of one piece, there can also be a problem with linear thermal expansion. This occurs two piece mounts too, but it causes more problems on one piece mounts. Temperature changes around the mount and the scope create linear thermal expansion of the materials.
In extreme cases – taking your rifle from cold weather outside to a heated room in the house (big difference in temperature of the environment) causes higher linear expansions than normal. Therefore, linear thermal expansion causes material strain which can be followed by damage on the scope or mount. The bigger the length of the one piece mount is, the bigger the linear thermal expansion is (and it causes bigger problems). Linear thermal expansion basically represents how much will some material change in length when heated (or cooled) for each degree of temperature changed. Note: Thermal linear coefficient of expansion for aluminium is approximately twice the value of steel (or iron).
This info in theory means that in real life aluminium stick will expand twice the size, compared to the steel stick with the same dimensions, when heated for one degree of temperature. In other words: An equal temperature change will produce twice as much change in the length of a bar of aluminium as for a bar of iron or steel. Problems with linear expansions might occur when we have a aluminium direct mount installed on the steel receiver. Their different thermal linear coefficients of expansion can cause strain in screws that hold together mount with the steel receiver on the rifle. In worst case, these screws can brake or get damaged in other ways.
Lapping procedure during mounting process of direct mounts, is always needed. It is the easiest way to achieve 100 % alignment of both rings, while reducing material stress and deformations of scope and mounts, caused by the strain in materials.
Alternative to lapping process might be bedding of the scope. Usually, one of these two methods should be applied to mounting procedure of direct mounts.
Direct mounts might be very handy (because of its simplicity and rigidness) on rifles with dovetail on the receiver. Most known representatives of such rifles are Tikka’s, Sako’s, CZ 527’s, CZ 550/557’s etc. One of the most popular dovetail dimensions is also 11 mm wide dovetail. This is used small Tikka’s (T1x), SIG Sauer 200 STR and so on.
Correctly mounted direct mounts might be very appealing because of its slim and elegant design, yet they are also very robust and rigid. Their popularity is also connected to affordable prices, but have in mind – you might consider about the additional cost of the gunsmith’s work to it!