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So you finally bought your first AEG, gas, or bolt airsoft gun and the next thing on your mind is shooting it. Before you can do that, you’ll need some bbs, but which weight should you buy? There are numerous weights of bbs out there available for purchase starting with weights as low as .12 gram all the way up to .88 gram carbon steel bbs. The majority of the bbs sold today are .20 gram. As you go up in weight, you will go up in price and down in quantity of your bag of ammo. But who cares about the weight of the ammo you buy? Most people want the most for their money, so why not go with the cheapest .20 gram bbs you can find?

There have been numerous field studies performed that deal with specific bb weights related to accuracy, fps, and range. Since these are the three main areas of study for airsoft ballistics, we should look at them more in depth than just recording data trends from the field. Although this method of using statistical data to form a trend best represents actual effects in these three areas, is it possible to apply science and physics behind these findings to further knowledge in these specific areas?

The answer is yes. The study outlined in the following paragraphs shows the effects of three variables on airsoft ammo. These three variables are time, fps, and distance. The main reason for this study was to find downrange velocities of certain bb weights at varying distances and specific time intervals. This particular study uses a theoretical airsoft gun firing at 85m/s (278.87 fps) and compares the relations between .20 and .25 gram ammo. It can be altered to any muzzle fps as well as any ammo to show the desired results on the tables and graphs from only two inputs (bb weight and initial m/s). This study not only includes the effect of specific bb weights and initial muzzle velocities but also uses an exponentially changing drag coefficient and corresponding interval velocity to account for the drag forces that act on the bb during flight. Without these drag forces, the bbs velocity at every distance would be constant. We know this is now true because it hurts much worse to be hit by a bb from 10 feet versus 100 feet away.

The spreadsheet below has many columns of numbers and formulas that are important to the study, but not directly relevant to understanding the final result. They are all in SI units, not English, so do not be confused. The final results are in English units since most of us prefer and understand a measure in feet versus meters. This first sheet shows a .20 gram bb fired at a theoretical stock fps of 85 m/s (278.87 fps). For those interested in details, the variables from left to right are mass of bb in grams, initial velocity in m/s, time, total distance traveled in meters, coefficient of drag, area of bb perpendicular to velocity flow, the density of air at STP (standard temperature and pressure), force of drag in Newtons, acceleration in meters per second^2, velocity in fps, time, and total distance traveled in feet.

This sheet shows the effects of a .20 gram bb fired at 85 m/s (278.87 fps) over a three second time period with 0.1-second time measurement intervals. Although we know that a bb fired from a stock gun at an almost horizontal shot will not stay in the air for 3 seconds, it is important to show the trend involved with this length of time. This length of time will not affect our final results because they are located all within a 1 second time frame. The last three columns are what we are interested in. They show, from left to right, the bb velocity in fps, the time corresponding to the velocity, and the distance in feet at the same time.

The same variables are used in the sheet for .25 gram bbs. Please note that the same theoretical airsoft gun is used, so the initial velocity is reduced (from 85 m/s to 76.02 m/s) to account for the heavier bb that retains the same amount of joules of energy. If this is not easy to understand, Covert of Canton has the formula for joule energy and a link to an online joule calculator on their website that can be found here http://dan.mahonstudios.com/covertofcanton/insidepages/about.cfm

Again, we are interested in the last thee columns of data. Since all of this data is hard to understand, this data is formed into three separate charts that relate these three variables to each other graphically.

As you can see in the first graph we have constructed, lines for the .20 and .25 gram bbs are visible. This graph shows the relation of the data calculated in the two previous spreadsheets. Specifically, it shows the relation of velocity versus distance. The conclusion drawn from this graph shows that .20 gram bbs have a much higher initial velocity and they retain that velocity until they reach around 50 feet. This is the point at which the .25 gram bbs retain their energy longer and better, which results in a lengthier sustainable fps. Since the .20 gram bbs have a higher initial velocity, the drag force applied to the bb is much higher. Since they are lighter than the .25 gram bbs, they cannot retain their momentum as long; therefore, they lose velocity at a more rapid pace than their heavier counterparts. Also, the loss of momentum relates to the stability of the bb during flight through the air, which in result is the reason why .25 gram bbs are more accurate at longer distances.

The next graph shows the relation of velocity versus time applied to the .20 and .25 gram bbs:

This graph is illustrates the velocity of each bb over specific time intervals. Here, it is again obvious that the .20 gram bbs, since they are lighter, have a higher initial velocity. Again, due to the drag forces involved with higher velocities and the lower weight of the .20 versus .25 gram bbs, they will lose their velocity and drop below that of the .25 gram bbs after only 0.25 of a second. This is very important to us in the area of specific shooting conditions. If you are playing close quarter battles or assaulting, it might seem more feasible to use .20 gram bbs rather than .25 gram. This is because they travel faster to your target as long as the flight path from muzzle to target will take less than 0.25 of a second. If you are support or sniper based, this would recommend using .25 gram bbs because they retain their velocity longer at lengthier flight time intervals over 0.25 of a second.

The final graph shows the relation of distance versus time:

This graph is important to us because it shows the distances attainable with .20 gram versus .25 gram bbs based on a time-oriented scale. It is somewhat hard to see but for the first 0.5 of a second, the .20 gram bbs will reach their target quicker. This will be the case from 0-90 feet as shown on the graph as an intersection of the two lines. At this point, the two bbs will both reach their target at the same time. After this time, the .25 gram bbs will travel further quicker because they do not lose their momentum as well as velocity as quick as the .20 gram bbs. This shows that for shots less than 90 feet use .20 gram bbs, for anything over, this study would recommend .25 gram bbs.

The results found in this study do not include airsoft shots that are made far from horizontal. This means that shots made up or down a large incline would skew the results due to the earth’s acceleration due to gravity affecting the acceleration due to drag. This could be incorporated into the study but is very negligible for most airsoft shots that are not shot at a steep initial angle. Also, hop-up is not used here to determine range or drag because there is simply not a formula in physics that simply states “for hop-up calculations.” Hop-up will not effect the drag because drag is only related to cross sectional area, which is unchanging during flight since we have a solid, round bb. The effects of hop-up on range are very noticeable, but here, we do not have an ultimate range, solely intermediary values. Since both bb weight cases are treated the same way, the results with hop-up would also yield similar results.

Overall, the important results to us are as follows:

• Shots made within 50 feet will have a greater ending velocity with .20 gram bbs.
• Shots made over 50 feet should use .25 gram bbs for stability and velocity retention.
• BB flight times under 0.25 of a second can use .20 gram bbs for a higher velocity.
• BB flight times over 0.25 of a second should use .25 gram bbs because velocity and momentum is conserved better.
• Shots of less than 90 feet can use .20 gram bbs for a faster shot time.
• Shots made over 90 feet should use .25 gram bbs for a quicker, more stable ammo flight path.

The main reason for this study was to find out if .25 gram bbs are actually better than .20 gram bbs and at what velocities, times, and distances this is true. All of this information might sound like another language to some people, but this study was important in understanding the question at hand and has supplied very useful information that is easily comprehendible through simple graphical interpretation.

The previous spreadsheets and graphical depictions are very useful when determining the correct weight bbs to use with specific initial velocities. If you would like a copy for personal use, please direct your email request to the email listed below.

This information is fully protected under the copyright of Covert of Canton © Copyright 2005 www.covertofcanton.tk. Any partial or full reproduction of this article is strictly prohibited without full consent of the author. Any reproduction requests, personal spreadsheet requests, questions, comments, or concerns can be directed to Zinger084 AT hotmail.com

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