How to Easily Calculate Rifle Recoil
The Big Four ballistic parameters that effect rifle recoil are: Bullet Weight, Bullet Speed, Powder Charge Weight and Rifle Weight. There are more parameters that contribute to total recoil in a rifle, but the big four have the most significant consequences when you change them. With some very helpful online tools and some simple math for the more inquisitive among you, it is possible to predict more or less what will happen to rifle recoil when you make changes to one or more of these parameters.
This is an easy way for the average shooter without an advanced math degree to predict what will happen to the recoil felt thru his or her rifle, when any of the big four parameters are changed. Read on, and discover the answers...
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Things You'll Need
- A rifle
- Ammunition, either off-the-shelf or hand loaded
- Among the ammunition, various bullet weights, powder charges and a way to look up bullet velocity, or a personal chronograph to check the speed of the bullets first hand
- Some curiosity as far as practical application of ballistics
Instructions
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If you click on any of the Recoil Calculator links at the end of this article, they will take you to your starting place. That would be where you enter the details of your favorite hunting or target load and the weight of your rifle, and that will give you your baseline recoil for your rifle and favorite load. Anytime you make a change to Bullet Weight, Powder Charge Weight, Bullet Speed or Rifle Weight, you can come back to the Recoil Calculator and plug in the changes and recalculate. For those who want a little more insight to how these changes effect recoil, read on...
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Let's talk a little bit about recoil to make sure we are all on the same page. This is an article for shooters, not ballistics experts, so I may be using general terms that may not be 100% accurate as far as the study of ballistics is concerned, but it will get the job done properly for most all readers. Recoil is that push you feel against your shoulder after you pull the trigger. There is a big, controlled explosion and burning of gun powder in the rifle chamber and barrel, that is pushing a lump of lead and a lot of gases out the barrel at hundreds or thousands of feet per second. As Sir Isaac Newton told us, "To every action, there is an equal and opposite reaction." The action is the bullet and gases coming out of the barrel, the reaction is the motion of the rifle butt that pushes against your shoulder, that is what we call felt recoil, or just plain old recoil.
The recoil we feel can be significantly reduced by well designed factory installed or after-market recoil pads on the butt of the rifle, or also by using a semi-automatic action rifle. The good recoil pads absorb a lot of the recoil energy, and turn it into more of a push than a hit. The reason the semi-automatic action reduces felt recoil compared to a fixed breech rifle that has a bolt, lever or break-open action, that is shooting exactly the same ammunition, is that part of the recoil energy is used to automatically eject the fired round and reload the next round.
In addition to these external recoil absorption methods, when we make significant changes to Bullet Weight, Bullet Speed, Powder Charge Weight or Rifle Weight, these also have profound effects on felt recoil.
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For those of you who would like more specifics about how these changes effect recoil, lets define our rifle for this article: Bolt Action, 8lbs. Lets define our ammunition: 100gr Bullet, 50gr of Powder, and traveling at 2000fps. Accordingly, our rifle produces 6.3fp of recoil with the ammunition described. (gr = grain - 7,000gr = 1lb); fp = foot/pounds; fps = feet per second)
Each ballistic parameter effects recoil in a very specific manner.
Adding bullet weight increases the recoil % by the added weight % x 1.
So, if you start with a 100gr bullet, and increase the bullet weight by 20% (to 120gr), the % increase in recoil is 20% = 7.675fp recoil in your rifle after the change.
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Adding bullet speed, increases the recoil % by the increase speed % x 1, it has the same result as adding bullet weight.
So, if you start with a bullet traveling at 2,000fps, and increase the bullet speed by 20% (to 2,400fps), the % increase in recoil is 20% = 7.675fp recoil in your rifle after the change.
Bullet speed is changed by adding or reducing bullet weight, or by adding or reducing the powder charge while using the same powder, or by changing to a different powder.
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Adding powder charge weight increases the recoil % by the increase powder %, just like adding bullet weight or speed.
So, if you start with a 50gr powder charge, and increase the powder charge by 20% (to 60gr), the % increase in recoil is 20% = 7.675fp recoil in your rifle after the change.
By adding or reducing the powder charge, or by using a different powder, you will change bullet speed.
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Finally, adding weight to the rifle DECREASES the recoil % by the increased weight % x 0.84.
So, if you start with a 8lb rifle, and increase the rifle weight by 20% (to 9.6lbs), the % decrease in recoil is 20% x 0.84 = -16% = 5.285fp recoil in our rifle after the change.
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In summary:
Increase Bullet Weight, Bullet Speed, or Powder Charge Weight - Recoil increase = % change x +1.
Decrease Bullet Weight, Bullet Speed, or Powder Charge Weight - Recoil decrease = % change x -1.Increase Rifle Weight - Recoil reduction = % change x -0.84.
Decrease Rifle Weight - Recoil increase = % change x +0.84.If you change more than one parameter at a time, the effects on recoil are cumulative. For example, if you increase bullet weight by 10%, and increase bullet speed by 10%, and increase powder charge weight by 10%, then increase rifle weight by 10%, the outcome would look like this: Bullet Weight +10% recoil, Bullet Speed +10% recoil, Powder Charge Weight +10% recoil, Rifle Weight -8% recoil. The grand total would be: 10+10+10-8 = 22% increase in recoil (7.69fp) after all the changes were made.
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Tips & Warnings
When experimenting with different loads in any rifle, if you reload your own ammunition, always follow the powder and bullet manufacturers recommendations.
When experimenting with off-the-shelf ammunition used in a semi-auto rifle, managed recoil loads or reduced charge loads may not cycle the semi-auto action.
Warning: All figures presented in this article are approximate. Although there are standard formulas for calculating recoil, the different recoil calculators may produce different results. Use the figures as a good guide only, not an absolute.
