Origins of the Blowback System: Its Trials and Triumph

By Louis A. Garavaglia

If any autoloading system has proven itself over the past 100 years, that system is the simple blowback. It has worked with pocket pistols taking cartridges as diminutive as the 2.7mm Kolibri, and (in the case of the Model 1910 Winchester) with rifles firing a 250-grain bullet at a velocity of more than 1,850 feet per second. With special modifications, it has worked with even heavier loads. The writer’s Astra M600 pistol, a simple blowback chambered for the 9mm Luger cartridge, has fired well over a thousand rounds without a hitch. And some of these loads, packed in 25-round cartons with faded labels printed in an undecipherable language, ejected the fired cases, shall we say, vigorously. Moreover, a friend’s Astra M400 (the 600’s slightly bigger brother) has gone through several thousand rounds of the powerful 9mm Bergmann-Bayard cartridge, also without malfunction. Both guns still work well and give every promise of continuing to do so.

As many readers know, in a true blowback action the slide or bolt remains closed during the moment of high pressure chiefly because of its mass and consequent inertia; there are no delaying or locking devices to hold it. Simply stated, the slide and bullet move away from each other upon discharge, but if the slide is, for example, 60 times as heavy as the bullet, then the slide’s rearward velocity is only about one-sixtieth of the bullet’s forward velocity, so the bullet has cleared the muzzle before the slide can open appreciably. (In the all-important initial stage of opening, incidentally, the recoil spring has little to do with this process.)

Again, few if any firearms designs have proven more successful than the blowback. As a Heckler & Koch brochure states the case: “Let us accept the fact that, when it comes to an automatic weapon bolt, a system consisting only of a mass and a spring cannot be surpassed for its simplicity and ruggedness.” But when the blowback system was first formally proposed, it met everything from strong skepticism to outright derision. Its designer, Capt. J. P. Morgan of Her Majesty’s Royal Artillery, learned the hard way what other pioneers before and after him learned—that any new and different idea may be championed by a few, but it will be regarded doubtfully or scornfully by most others. For Morgan, it was the old story, with an added twist; not only was he 25 years ahead of his time, but he applied his idea to the wrong type of gun.

Morgan first presented this idea to a meeting of the Royal United Service Institution in June of 1870. His paper was entitled “A Proposal for a Very Heavy Gun of Novel Construction.” In 1870 the gun was, in all probability, a true novelty, and it was certainly heavy, because the captain initially applied the idea not to a hand-held firearm but to a 15-inch cannon! Nevertheless, his principles were sound. He led into his subject gently, first noting that the heavier the breech, the less stress and strain on other parts of the gun. In citing several examples, he said:

“The relief which a heavy mass affords in receiving and absorbing the force of a blow admits of many familiar illustrations ... but perhaps the most singular instance of this law may be found in a case which excited much wonder in the last generation, namely, that of a man who was accustomed to exhibit himself sustaining a very heavy stone on his chest while lying on the floor; several large sledge hammers were freely used upon the stone, but although so much force was applied, there was no injurious effect upon him who submitted to such an ordeal. The relief afforded by simple weight in these examples gives just the same immunity in a gun.”

Then Morgan got to the point, a point which had taken him 14 years of experiment to reach:

“[My] principle consists in receiving the longitudinal strain [of the discharge] on a solid block of metal not rigidly connected with the rest of the gun ... When the gun is fired, the shot and breech move in opposite directions, with velocities inversely as their weights. The shot will thus have left the bore long before the breech is opened. I have taken the breech as 56 times the weight of the shot.”

Understandably, the discussion which followed Morgan’s talk did not even touch on the idea he had presented. It was too new, too radical. And, as one of his listeners commented, it was a subject that required a great deal of consideration before an intelligent opinion could be rendered.

How well Morgan had worked out his plan is shown by a modern comparison. The blowback Astra 600, chambered for the 9mm Luger cartridge, has a slide which (including all the components that recoil with it) weighs 13 ounces, or 370 grams. Assuming a standard 9mm load with a 115-grain bullet, the Astra slide assembly then weighs very nearly 50 times as much as the bullet. Morgan’s “slide” weighed 56 times as much as his projectile, but his projectile was proportionately heavier.

Morgan, of course, was convinced of the accuracy of his deductions, but he realized (as all arms designers come to realize) that the real proof of his theory lay ultimately not in mathematical formulas but in a shooting example. By March of 1871 he had completed such a gun, a firing model about 26 inches (66 centimeters) long from breech to muzzle. This 26-inch length was roughly that of a barreled action for a standard military carbine of the day, but no carbine even chambered the load that Morgan’s model did: a 12-ounce (340-gram) projectile backed by a two-ounce (57-gram) powder charge. In other words, the gun used an 875-grain powder charge to fire a projectile weighing more than 5,200 grains!

By the time Morgan finished his model, the objections to his plan were becoming well known. Apparently, the one voiced most often was that the breech would somehow manage to open while the projectile was still in the bore, with disastrous results due to the high pressure involved. In June of 1874, however—four years after he had first presented his idea—Morgan, now a major, had the chance to publicly answer his critics. Again he appeared before a meeting of the Royal United Service Institution, ostensibly to give a talk on the then-current controversy between breech-loading and muzzle-loading for artillery pieces. Inevitably the talk swung back to his design, and this time he could claim that “the method of its action has since been successfully demonstrated in a firing model.” He then compared his gun with more conventional breech-loaders, including one locked at the rear by interrupted threads. (Coincidentally, a rifle using this method of locking, the Ward-Burton bolt-action, had recently undergone field trials with the U.S. Army.) In comparing one system with the other, Morgan said:

“Instead of being kept in its place by the tenacity of the threads of a screw, [my breechblock] is kept in position [simply] by the mass of metal behind it. This is a most important difference. Tenacity is a quality that is limited in amount and liable to failure under repeated strains of great amount; but, like time and space, the resistance of mass can be calculated upon with certainty at all times. When tenacity fails there is a violent explosion, but the resistance of mass increases as the pressure increases, and it is practically impossible to move a heavy mass in a very short time ... nor can [my] breech ever get jammed, because the result of the explosion is to open it harmlessly after the shot has left the bore ... .”

To no one’s surprise, a spirited exchange took place once Morgan had finished his talk:

A MEMBER: “How much powder have you fired in that model, and was there any escape [of gas]?”

MORGAN: “Two ounces, and twelve ounces of shot. It was fired at Elswick, Mr. Rendel looked at it, and he admitted that there was no escape whatever.”

ANOTHER MEMBER: “Major Morgan fires two ounces of powder from his model, but he cannot judge from that how [a bigger gun] would answer. His idea is clever, but I do not understand how he can count upon its proper action in practice. He says that the breech-piece comes back to the loading position with perfect ease; it is so beautifully managed, that the shot goes out and the breech-piece comes back, and everything is all right, and nice and quiet. But from our knowledge of gunpowder we cannot presume on these things. ... It might be vice versa; for example, should the breech-piece move before the shot which has to take the rifling leaves the bore, there would be a great escape of powder-gas. ... I do not see what useful purpose it serves ... to propose to supersede [our other guns] by a novel system which is only represented by a model which has fired two ounces of powder ... .”

MORGAN: “I have been so wearied with this objection that the only thing I can say is that guns, like everything else, must obey the multiplication table, and I am prepared to prove by the multiplication table that the shot will be out of the bore before the breech opens. ... I have been so wearied with similar objections that I have almost felt irritated at times. Some have said the shot will drop harmlessly out of the muzzle, and all the danger will be from the escape of the powder behind. I have said in reply, only make a gun and stand in front [of it] when it is fired, and I will stand behind.”

It was a good argument—that the real test of a new design was not on the drawing board but in its actual performance. Obviously, no one took Morgan up on his offer. And gradually, others came to see things his way. In 1879, a civil engineer named James Longridge, already noted for his work with big guns, stated the following publicly:

“In my paper recently read at the Institution of Civil Engineers, I described a system of construction for breech-loading and exhibited a small gun which had proved perfectly successful. ... I have no hesitation in saying that the system is theoretically right and that it would prove the most efficient as well as the most economical of any that have come under my notice. It is in principle the same as the system advocated by Major Morgan ... .”

Although public opinion eventually turned in Morgan’s favor, his big blowback cannon was apparently never built. And not until the 1890s did the blowback system, when applied to handguns, begin to gain widespread acceptance. The first U.S. patent to spell out the principle, issued to Louis Schmeisser (assignor to Theodore Bergmann) in October of 1895, said in part that “a breech bolt bearing against the rear end of the barrel, the weight of which is a certain multiple of that of the projectile, is given a motion by the gas-pressure which is correspondingly slower than the lighter projectile.” Eighteen months later, the great John Browning, using somewhat similar wording, patented a blowback pistol of his own. In many ways, Browning’s pistol set the pattern for the millions of blowback arms to follow. Yet the true father of the principle is a man little known today: Captain J.P. Morgan, Royal Artillery.

AUTHOR’S NOTE: As given in the HK brochure, the actual formula for computing the mass of a blowback bolt is: (projectile mass + 0.5 x load mass) x projectile velocity = bolt mass x bolt velocity.

This article first appeared in Small Arms Review V22N2 (February 2018)
and was posted online on December 22, 2017


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