The idea of a single trigger to double guns cannot be said to have
occurred to anyone as an original conception, since it was natural that
at the first attempt to build those toys (as Colonel Thornton considered
double guns, when he was upon his celebrated Highland tour), the
inventor must have exercised some ingenuity to supply these first double
guns with two triggers. It was as natural to attempt to make double
barrels with one trigger as for a duck to swim. First, because single
barrels were the fashion, and second, because single-trigger double
pistols were made and were successful. It was, however, at once
discovered that the action of the double pistol would not do; it let off
both the shoulder gun’s barrels apparently as one. For a century
afterwards repeated attempts were made to overcome this double
discharge, and many patents were taken out on the strength of the
inventor having discovered “the real, true cause” of the involuntary
discharge of the second barrel, by the pull off that was intended to
actuate only the first. However, the problem remained commercially
unsolved until Mr. Robertson, of Boss & Co., of St. James’s Street,
overcame the difficulty, and took out a patent, about 1894, for an
action that prevented the unintentional double discharge. The great
success of this action led to some hundred patents being taken out
between that year and 1902. But most of them were afterwards dropped,
and found not to effect the prevention of the double discharge for which
they were designed. As a matter of fact, the reason of the involuntary
discharge of the second barrel was not understood, not even by Mr.
Robertson, who had, by trial and error, arrived at a perfect system of
overcoming the difficulty, without being aware of what really occurred.
In the autumn of 1902 the author contributed some letters to _The County
Gentleman_, which explained the difficulty; but his discovery, for such
it has proved to be, was hotly disputed in a correspondence led by some
of the leaders of the gun trade. This was by no means wonderful,
although it is disconcerting for a discoverer to be treated as “past
hope” when he is so unfortunate as to make a find that can do him no
good, but ever since must have saved much in work and patent fees to the
gun trade.
The accepted view of involuntary pull prior to this discovery was that
after the shot from the first barrel, recoil jumped the gun away from
the finger, and then the shoulder rebounded the gun forward on to the
stiff finger, which, being struck by the trigger, let off the second
barrel. The author for some time previous to 1902 had become conscious
that this explanation was open to question. However, it was not until he
sat down and worked out the times of recoil and finger movement, that he
felt safe in challenging so generally accepted a statement. But this
calculation proved to him that, so far from rebound causing the
unwished-for “let off,” the latter occurred in one-twentieth of the time
occupied by the recoil backwards. However, the author’s powers of
persuasion failed to convince everybody, and for this reason the editor
of _The County Gentleman_, with the assistance of Mr. Robertson, of Boss
& Co., and of the late Mr. Griffith, of the Schultze Powder Company,
formed a committee of experts to test the point by chronographic
examination. Results were published in _The County Gentleman_ on
December 6, 1902, and were to the effect that the second discharge came
in one-fiftieth of a second after the first discharge, but that the
recoil backwards, before rebound could occur, took from four different
shooters respectively .32, .29, .34, and .38 of a second, or, roughly,
an average of one-third of a second. So that it was demonstrated that
the rebound from the shoulder had nothing whatever to do with the
involuntary pull. The true and now always accepted cause was as the
author had stated it to be—namely, that the recoil jumped the trigger
away from the finger in spite of the muscular contraction that still
continued after the let off of the first barrel; that this muscular
contraction continued to act and again caught up the trigger, as soon as
the pace of recoil was diminished by the added weight of the shoulder,
and so the finger inflicted a heavier blow or pull on the trigger than
in the first pull off. In the first pull it was finger pressure, in the
next it was pressure acting over distance, and was measurable in
foot-pounds, as work or energy is measured. This proved to be the
correct solution.
Consequently, a good single trigger is one that prevents this finger
blow from discharging the second barrel. It is impossible to prevent the
blow itself, but quite easy to prevent it letting off the second lock.
There are at least three principles employed for doing this.
The first is called the three-pull system; it is based on the necessity
of either the voluntary second pull, or involuntary blow (as the gun may
be loaded or unloaded), for intercepting the trigger connection which
the subsequent release of the trigger allows a spring to place in
readiness to receive the third trigger pull, and act on the second
tumbler; this pull in the unloaded gun is observed to be a third pull,
and in the loaded one is only observable as a second pull, because the
second has been given involuntarily, and not consciously.
The double-pull actions are different in principle. Most of them are
based upon a lengthening of the time between the first let off and the
connections with the second lock coming into position for contact with
the trigger. In other words, they are time movements, based upon the
knowledge that the second pull, or impact of trigger and finger, came
very quickly, and that to delay the intermediate connecting link between
trigger and second lock until after this unconscious impact rendered it
inoperative.
A third system is somewhat different, but is also a timer action. It is
based upon having a loose or nearly loose piece, which is partly
independent of the gun, and either by its lesser motion or want of
movement, during the jump back of the recoiling gun, gets in the way of
a further trigger movement, until the recoil of the gun is over, and the
weak spring can replace the independent piece in its normal position
again.
It has been said that the greatest advantage of a single trigger is the
facility with which it can be removed and double triggers substituted.
But this is merely what those gun-makers have said, who, being obliged
to have a single-trigger action of their own for those who ask for them,
have been too proud to pay a royalty for a good one, and have not felt
quite safe in recommending their own to good customers.
The real advantages of a single trigger are many. First, one does not
have to shift the grip of the gun for the second barrel. As explained
above, recoil occupies one-third of a second, and one does not want to
add to the jump of the gun during recoil by partly letting go, nor to be
unready at the end of it, by still having to move the right-hand grip in
changing triggers. In practice, the single trigger is also much the
quicker. It is not necessary to say anything about cut fingers and their
avoidance by the use of single triggers. But a wonderful advantage is in
the more correct length of stock. If one’s gun-maker gave one a stock an
inch too long, or short, in double triggers, he would be thought not to
know his business. There is only one best length for everybody, but
every double trigger has two lengths of stock, one an inch longer than
the other.
The author is told that there are still some very bad single-trigger
actions being made, but that is quite unnecessary when the best can be
employed by paying a royalty, as some of the best gun-makers are in the
habit of doing, or were, until the recent action Robertson _v._ Purdey
was settled.
Probably it would be more correct to say that the principal advantage of
a bad single trigger is that it can readily be exchanged for a good one.
The author would not on his own authority speak of bad single triggers,
because he has tried most of them, and had difficulty with none.