All text and photographs that follow are copyright 2014 and are not to be copied or used without the author's (me) written permission. As usual with my "in detail" essays, this is going to take me several days and multiple posts to complete. I try to provide useful information on subjects that I have wanted information about for many years but could not find. My thinking is that, if I wanted such information, I'm sure that others must have as well and these posts seek to provide that service for people who are in the same boat I was in. Hopefully, I will succeed and not bore you folks to death in the process. As always, if I do not provide information which you seek, please do not hesitate to contact me and I will gladly help you if I can. As you look through this, you will notice that I have covered up the serial numbers. I hated to do this but I feel that the current political climate in this country necessitates such actions....it's very sad to feel this way. I'm starting this one with a little History because I needed to write something in an effort to keep my mind busy. If you don't care about the background or simply hate my writing/rambling thoughts, just skip to the pictures and have at it! Thank you for your time and good luck getting through this without falling asleep.
When most people think of roller locked rifles, they think of the German arms manufacturer Heckler & Koch and their G3 rifle. To a slightly lesser extent, Spain's Cetme comes to mind as well. Both of these rifles are direct descendants, more final products really, of the prototype STG45 designed by Mauser Werke in the waning days of WWII.
The STG45 was Mauser's answer to Germany's quest for the next generation of infantry rifle. It was an amalgam of two classes of small arms, seeking an efficient balance between the ranged capability of the full sized rifle and the close range volume of the submachine gun. It was also designed to make extensive use of stamped parts in an effort to speed up the manufacturing process and conserve precious resources. Additionally, it eliminated the need for a gas piston and associated parts, hereby simplifying the design and making it more reliable at the same time.
To this end, it employed a delayed blowback system using a trunnion with recesses machined into it, a bolt head with moveable rollers that would lock into those recesses and a wedge shaped camming piece that controlled how long those rollers kept the bolt head locked into the trunnion. These parts, working in unison against the rearward forces created by the detonation of the powder in the cartridge, kept the breech safely closed until the bullet had exited the barrel and pressures had dropped to acceptable levels. Mauser called it a "half locked" design and, while locking rollers had been employed in previous firearms (most notably the German MG42), this novel setup was something never before seen. Whereas the STG44 had revolutionized the concept of military rifles, the STG45 revolutionized the design of that concept. It was set to be Germany's new "Storm Rifle" replacing the STG44 and entirely eliminating the need for both a standard long range rifle and a short range submachine gun.
By the spring of 1945, multiple advanced prototypes had been assembled and mass production was on the horizon but the war ended before the project could be brought to fruition. But, in a vein similar to many of Germany's technologically advanced projects, this was not the end of the STG45. In the late summer of 1950, Mauser engineer Ludwig Vorgrimler moved to Spain, taking much of the firm's STG45 development data with him. The result was the CETME rifle and, because of Belgium's refusal to allow a German firm to build the FN FAL under license, the HK G3. The rest, as they say, is History. But there is another History; one most people are unaware of involving the Swiss manufacturer Schweizerische Industrie Gesellschaft (SIG) and its own roller lock derivative of the STG45 known as the SIG 510.
The Swiss have always been known for producing extremely high Quality firearms that employ advanced design characteristics as well. Proof of this is readily seen in the well known K31 straight pull bolt action carbine which was accepted for service in 1931. This carbine was built to the highest Quality standards of any rifle in the world at that time and common issue examples rivaled the best sniper rifles of other nations. Dating back to the latter part of the 19th century, the straight pull bolt design was lightning fast to operate, smooth as glass and extremely durable. It was also very expensive to produce. That last part didn't bother the Swiss. In fact, spending lavish amounts on the Quality of their equipment was standard fare. What DID bother them however was their eventual realization of the fact that the self loading select fire rifle was the way of the future. By the early 1940's, they were already at work on various designs, ranging from fairly typical gas piston systems to blow forward actions. In the end though, all were found wanting for one reason or another. But the emergence of Mauser's half lock design must have really impressed SIG engineers. Exactly how or when they became aware of it, whether it was through the original STG45 project or through continuing development being carried out in France and Spain post war by ex-Mauser engineers, I do not know. What I do know is that, by the early 1950's, SIG was working on a roller lock design of their own. The culmination of this effort was the SIG 510-1.
Accepted by the government in 1957 (two years before Germany accepted the G3) as the Sturmgewehr 57, the 510 had the honor of being Switzerland's first standard issue select fire rifle. In some ways, it was very similar to the STG45 and Cetme designs. The basic operating principle was the same and the rifle made use of sheet metal stampings for the majority of both the receiver and trigger housing. Beyond that, the Swiss had parted ways with the German and Spanish designs and had, as usual, created a firearm that was characteristically "Swiss". Whereas the Cetme was originally designed for an intermediate sized round and had been modified to accept a full sized cartridge, the 510 had been intended for use with the standard 7.5x55 cartridge from the outset. Because of this, the various components of the 510 appear somewhat massive when compared to their German and Spanish counterparts. This is especially apparent when comparing the bolt heads, rollers and locking wedges. The trunnion is located outside as opposed to inside the receiver for this reason as well. There are many other details about this rifle that bear mention and that is part of the reason for this work. But the main reason is to provide careful and detailed first hand information about this interesting and, unfortunately, seldom encountered rifle in the hope that others will find it useful whether it be for research or just plain 'ol curiosity.
The example that we will be studying is the "Americanized" version of the SIG 510-4. Chambered in 7.62x51, it is called the 510-7 by SIG but is known here in the United States as the American Match Target or AMT and it is marked on the top of the trunnion as such.
For scale and comparison purposes, many of the photographs will also include various parts of an HK91, itself the civilian version of Germany's G3 rifle. One of the common misconceptions about the SIG is that it is a large and ungainly rifle. Visually, that certainly appears so what with its look of cobbled together boxes and tubes. In reality though, it is quite slender and actually about the same length as its German counterpart and significantly shorter than its Belgian/Austrian and American contemporaries as can be seen below:
In fact, the first time I saw one in the flesh, I was immediately struck by how small it appeared for a .308 battle rifle. It almost looked as if it was a miniature of the many 510s I had previously seen only in pictures. It is heavy though. It would be prohibitively heavy were it not for the fact that SIG used aluminum for some of the less critical parts such as the barrel jacket, bipod legs and butt plate. This is not to say that the 510 is in any way cheaply made of fragile. On the contrary, it was built to the highest standards, using heavy gauge steel that is both spot welded AND brazed for maximum durability. Upon even the most casual inspection, it is immediately obvious that both cost and ease of manufacture were not a serious consideration. Rather, reliability, durability and longevity were the driving factors behind the design. As you would expect of a Swiss made product, fit and finish approaches the realm of art. Machining marks are almost nonexistent, bluing and phosphate are near flawless and inspection stamps are usually as clear as if they were engraved (the serial numbers are in fact engraved). The walnut stock and forearm are impeccably finished as well. Simply put, the SIG is the highest Quality military firearm I have ever encountered.
But I have droned on long enough. In my next post, we'll begin to get to the good stuff...pictures! Later, we'll start ripping stuff apart and look at the guts and other assorted goodies. We might even have a sword fight using the AMT and HK91 as our swords!! Well, maybe not that last part but we will have fun looking at all the cool metal bits and rolling thingies! Believe it or not, this post took me a looong time to type because I'm a slow hunt and peck type of guy so I'm done for the night. I think slowly too. I'll be back at it soon though. Thanks for your time and Gute Nacht!