When it comes to the world of archery you will run into a lot of jargon which could become confusing if you’re new to the sport. Some of these terms are tillers, cams, risers and limbs are describing actual parts of the bow, other terms, such as draw length, IBO and draw weight refer to the performance of the bow. Let-off is one of those features that you should understand.
The design of the compound bow has been done so that the draw weight decreases at the end of the drawstroke allowing the shooter more time to aim and release the arrow. To explain further, as the bowstring is drawn back the weight increases steadily until you reach a certain point at which time the cam system takes over and it eases significantly so that by the end of the draw the shooter is only holding a fraction of the weight they were at the start of the draw.
In the past when you drew a bow, specially if you owned a longbow or a recurve bow you would have been struck by how heavy it was to draw the bowstring back and then hold it while aiming for any length of time. Traditional bows have the most draw weight at the end of the draw which means it is particularly tiring if you try to hold the bow drawn for any length of time.
The let-off rate of early compound bows was around 35-50% but nowadays the norm is more in the region of 75-80%, with some bows coming with an added feature of being adjustable. So a bow with a 70 lb draw weight and 80% let-off will converts to a draw weight of only 14 lbs.
It’s not always a good thing to have use a bow with super-high let-off at full draw because there is an increased likelihood to experience arrow movement whil in the shooting position. You need some resistance to maintain a good natural alignment.
The let-off is listed by bow manufacturers as a percentage in their literature, sometimes you might see two numbers advertised next to the Let-off statistic. They will be “Effective” and “Actual” let-off. Let’s take a look at the difference between effective let-off and actual let-off.
Quite often when a compound bow’s specifications are listed by a bow manufacturer you will see two figures next to the Let-Off heading. It may read something like Let-Off 65% Actual 70% Effective. What this is referring to is the disparity in draw weight change between drawing the bow as well as the change in weight when letting the bowstring back down.
To calculate let-off you need to be able to measure two things: the maximum draw weight and the minimum weight during draw. These numbers differ depending on whether you are drawing the bow or letting the bow back down. As complicated as the second figure sounds, it’s the actual let-off or the let-off experienced when drawing the bow that you will be most concerned with. The figure you’re most likely going to see, though is the effective let-off.
A potentially crucial time to remember the impact of effective let-off is after drawing the bow while letting it back down without an arrow fitted. There is a high incidence of accidental dry-firing taking place caused by the high effective let-off and the surprise with which it catches people unprepared. The sudden change in weight can rip the string out of unsuspecting fingers and you may be left with a shattered compound bow.
A final word on let-off comes with regard to the significance for those wanting their trophy listed in the Pope and Young Club’s record books. Only trophys taken with a bow that had a let-off lower than 65% were included until recently. This has since been changed in 2004 so that those taken with a higher let-off will be listed but an asterisk will be placed by the hunter’s name.
With any luck the previous explanation will help you when you go out to buy a compound bow and you see the let-off figure you will understand the significance of the numbers. In a nutshell the higher the number, the easier the draw. You’ll only know whether it will help or hinder your shooting accuracy through trialling the bow. Finding out about other pieces of equipment such as the bow stabilizer will also help.