Airsoft Barrel Lapping, a brief overview and theory test. (Part 1)
Whats the heck is Lapping?
Lapping a steel barrel for an airsoft gun involves polishing and smoothing the inner surface of the barrel to improve its performance. The primary purpose of lapping is to ensure that the inner surface of the barrel is as smooth and uniform as possible. This process can offer several potential benefits for airsoft players:
Increased accuracy: A smoother and more consistent inner surface can reduce inconsistencies and imperfections that may affect the trajectory of the airsoft BBs. This can lead to improved accuracy and precision when shooting.
Improved consistency: Lapping can lead to more consistent shots, as there will be fewer irregularities inside the barrel that can impact the BB's path. This means that each shot is more likely to follow a similar trajectory, improving overall performance.
Reduced friction: A well-lapped barrel will have less friction between the BB and the barrel's inner surface. This can help to maintain the BB's velocity and reduce the loss of kinetic energy, which can be especially important in airsoft games where range and velocity are crucial.
Less Maintenance: Lapping can help to remove small burrs, scratches, or other imperfections that would normally cause build up of debris/BB wax residue to stay within the barrel. Having a significantly more polished surface reduces the chances for debris to stick on the inside of the barrel.
At Umbrella our methods involve using a large linear 20mm CNC rail, with mounted hardware as well as a jig to capture the barrel firmly. Using custom resin 3d printed lapping bits we have the ability to rapidly lap barrels as the bits are nearly 6x longer and more 2x more contact surface than traditional lapping bits in the past allowing each pass to essentially being over 12x more efficient than standard lapping bits. The force required to run the bits through the barrel is also significantly higher as well as the bit is designed to expand like a spring within the bore during lapping. Perfect for hard materials such as steel. As you can assume, lapping a carbon steel barrel is significantly more time consuming than lapping a brass barrel.
Testing this theory, we used a simple apparatus to measure static friction, and the coefficient of static friction.
Using a steel cylinder rod, that is 60.1mm in length, and 5.96mm in diameter. It weighs 13.1 grams. Using 2 different steel barrels with the inner diameter of 6.03mm. The steel cylinder is inserted fully and slowly elevated until the steel rod inside breaks through static friction and begins to move.
For Stock 6.03mm barrel #1, the rod begins to move at 13 degrees.
For the Lapped 6.03mm Barrel #2, the rod begins to move at 9 degrees.
We can calculate the coefficient of static friction (μs) between the steel cylinder rod and the steel barrels using the formula:
μs = tan(θ)
Where θ is the angle at which the rod starts to move.
For barrel #1: θ1 = 13 degrees μs1 = tan(13°)
For barrel #2: θ2 = 9 degrees μs2 = tan(9°)
To calculate the coefficients.
μs1 = tan(13°) ≈ 0.2309 μs2 = tan(9°) ≈ 0.1584
So the coefficients of static friction for both barrels are:
Barrel #1: μs1 ≈ 0.2309
Barrel #2: μs2 ≈ 0.1584
The barrel lowers the static friction by about 31%. With a reduction in internal bore friction, its easy to understand how and why we see an improvement in FPS with observable results of ~2% boost in FPS once a barrel is lapped.
There's no surprise to see tighter groupings appear from one of our lapped barrels as reducing internal friction, helps to reduce the interference of the backspin on the BB, providing a more consistent and stable hop as the BB leaves the barrel.