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Recently, we have been debating the possibility of inner barrels flexing (or moving) while our airsoft guns are be being fired. If the inner barrel is made out of soft material, there is possibility of flex. If the inner barrel is made out of hard material, it can still move within the tolerance of the external barrel. The inner barrel is not glued into place for easy maintenance.
We became concerned when my friend used a bore laser sight in the inner barrel. To his surprise, the inner barrel flexed quite a bit just from touching the bore laser sight.
We decided to test how much effect a loose inner barrel has on accuracy and precision. The application will be hand-held indoor CQB scenario, not gun-on-the-vise shooting competition. This article documents the test and the results.
We downloaded the following free target from Evike's web site. This target has inches markings. But Evike provided a raster (JPG) image, not a vector file. Therefore, when we printed the image on our laser printer, the target wasn't to scale. However, the 7" mark was almost exactly 7 centimeters on our print out. Therefore, it provides a good relative measurement.
This target worked so well in our previous test, we plan to use this target for our future tests as well.
For this test, we used an APS ASR107 M4 URX Raptor. The APS ASR107 M4 URX Raptor is an excellent candidate for this test, because it has a mock silencer. The end of the inner barrel sits on the muzzle tip. The mock silencer can be easily unscrewed and removed to eliminate the support for the inner barrel (see photos below). The inner barrel is a 275mm hardened steel 6.04 tightbore barrel, which is a good candidate to see if barrel motion deteriorate accuracy/precision. The stock hop-up unit has been adjusted to be accurate and precise out to over 30 feet in an outdoor environment. APS ASR107 M4 URX Raptor Review
We will use the Barska Red Dot Scope on the URX Raptor upper receiver (see photo below) for this test. The Barska Red Dot Scope has been zero in at over 30 feet in an outdoor environment. Barska 30mm Red Dot Scope Review
We used Evike Professional Grade 6MM Airsoft BB (0.20 g) in this test. 0.2 grams is the most common weight BB's. In an indoor controlled environment, BB weight should make very little difference in the outcome of this test (but sounds like a good test for another day). Evike Professional Grade 6MM Airsoft BB (0.20 g) Review
The controlled environment is a dim garage to eliminate external atmosphere factors. The target trap is located 20 feet from the shooter. The shooter will hand-hold the shots to simulate real combat situation versus using a gun vise. 10-rounds will be fired into the target trap in semi-automatic mode. The shooter is free to take as much time as possible (within reason) to make accurate shots. Aim is performed with a single eye open (in order to reduce error) with the red dot directly on the center of the target (no manual adjustment of the shot is allowed). The red dot brightness is set to 1 in order to keep the MOA as small as possible, but highly visible this dim environment.
The first test is conducted with the gun in complete stock configuration (with the mock silencer). Test result is shown below. Grouping is well within a 4cm x 2cm rectangle at 20 feet; very precise for CQB environment.
The second test is conducted without the mock silencer; the 275mm inner barrel sticks out, all by itself. Test result is shown below. The grouping is a 5cm x 3.5cm rectangle. Not only is the grouping worse, but noticed that the inner barrel is also sagging; the BB pattern is almost off the target.