UNDERSTANDING TITANIUM

Titanium is a naturally occurring metallic element that when formed into an alloy is regarded for its high strength to weight ratio and exceptional heat resistance. It seems however that despite its better attributes there is a general misunderstanding of titanium and its use when applied to firearms parts or equipment – primarily in regard to weight.

Firstly, titanium is not as light as most believe. Type 6AL4V titanium weighs in at .160 pounds per cubic inch (lb/in3), 4130 steel at .284 lb/in3, and 6061 aluminum at .098 lb/in3. In a nutshell, we can say that titanium is almost half the weight of steel, and aluminum is two-thirds the weight of titanium by volume. Once again: aluminum is actually lighter than titanium by volume. Another important consideration then is quantity. If you are designing a mechanism that uses a number of the same part and weight is a concern, or you have multiples of the same items to carry, it’s good to know you could have two titanium parts for every one steel part; three aluminum parts for every steel part, and so on.

An area where titanium’s light weight compared to steel should be especially avoided is firing pins, strikers, etc. These are typically advertised as improving “lock time”, which is the interval between when the shot breaks and the primer is ignited. In the M4 (and thousands of other modern firearms) the travel of the firing pin is so small as to make the need for a reduced-weight firing pin unnecessary. Likewise the mass of the firing pin plays a role in how consistently and with how much force the firing pin strikes the cartridge primer; reducing mass of the firing pin could result in loss of reliability with certain types or brands of primers. If there is a sufficient need to reduce lock time, a reduced mass hammer and stronger hammer spring will likely provide a better result.

Note that the above does not necessarily apply to some types of belt-fed guns like the M240 or M249, which utilize an open-bolt operating system. In these systems, lock time can be illustrated as the time it takes for the operating group to travel forward and strip and fire a round. Titanium could be used here to reduce the mass of the bolt carrier resulting in increased forward velocity (a lighter bolt carrier will move faster, resulting in reduced lock time). The consideration again is more mass = more force to overcome debris in the receiver / strip rounds off the belt = higher reliability. Weight of moving components in semi and fully-automatic guns is always an important balance in the design phase.

Other uses of titanium include derived coatings such as titanium carbide and titanium nitride. The main benefits of these are improved surface finish and surface hardness properties. Many of these coatings were developed for other applications (to increase life of machine tooling, for example) and have migrated across other industries. While there is no real disadvantage to using these coatings in gun parts, their utilization should be carefully considered by the manufacturer as they add thickness (albeit extremely small; roughly .0002 inches usually) to the outer surface of whatever part they are applied to. Unfortunately the full benefits of these coating are seldom realized, as the heat and friction in the areas they are most used seldom comes close to their design threshold. Other than making the coated part subjectively easier to clean and potentially less prone to wear, it is often relegated to jewelry.

In all cases of titanium versus aluminum discussion, titanium is certainly the stronger metal. So much so that it takes higher temperatures and much higher force to forge a titanium part compared to an aluminum (and even steel) one, in addition to other special handling requirements. Care must also be taken during machining to avoid “work hardening”; a kind of premature tempering caused by friction of the cutting bit against the material. Some titanium alloys can be heat treated, however this takes specialized equipment and processes due to titanium’s inherently low carbon content, and the result is typically not optimum compared to a heat-treated steel part for the same application (an M4’s bolt lugs, for example).

The important thing to consider is that just because a part or accessory is made from titanium does not necessarily mean it is better than its steel or aluminum counterpart. If weight is of utmost concern, a little investigation – and an inexpensive digital scale – can go a long way to validating if titanium is right for the job. Conversely there are certain applications where titanium could be utilized that have been historically overlooked; these are component areas that a few designers including myself are researching for potential further development. Look for more information on those projects in the future.

Sentinel Design LLC