There is a lot of jargon when it comes to the world of archery which will inevitably be confusing when you head out to buy a compound bow. Some of these terms are cams, limbs, risers and tillers which all describe 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.

When drawing a bow, especially if you owned a longbow or a recurve bow you would have noticed that it takes a lot of strength 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 design of the compound bow has been done to decrease the draw weight towards the end of the drawstroke giving the shooter more time to aim and release the arrow. To take the explanation further, as the bowstring is drawn back the weight increases steadily until you reach a certain point at which time the cam system steps in 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..

The let-off rate of early compound bows was around 35-50% but these days it is more in the region of 75-80%, with some bows featuring an adjustable let-off. 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 it allows the arrow to move more easily 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. We might just take a quick look at the meanings of actual let-off and effective 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 work out let-off you need to be able to measure two things: the minimum weight during draw and the maximum draw weight. You would expect the numbers to be the same whether you’re pulling the bowstring back or letting it down, but they’re not. 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.

Where it pays 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 your fingers and you are left with a destroyed compound bow.

A last word on let-off is for the trophy hunters out there who want 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.

So now, when you go out to select a compound bow and you see the let-off figure you will understand the significance of the numbers. The higher the number, the lighter the draw. You’ll only know whether it will help or hinder your shooting accuracy through trialling the bow.