#123 - Answering Questions from Listeners
00:36:12 | This week Bryan and Mitch will answer some questions asked by listeners. The topics covered include Bullet Stability, Twist rate vs Muzzle Velocity, Engraving Force, Rate of Deflection, and more. Have a question? Let us know!
Would you be willing to do a podcast on the comparison between gas guns and bolt guns in regards to accuracy and precision for the LE community. It is a constant debate and although there are pros and cons to each it would be a great topic for discussion.
Im a Sniper TL in Texas and there is always a push for agencies to rid the community of bolt guns.
I am trying to get to the bottom of a question that I can’t find any good answers to and this video has given more to think about. I have been doing a LOT of testing with subsonic ammunition in multiple calibers and I am at the point now where I am being limited by my understanding of external ballistics and fluid dynamics or the price of equipment needed to get further insight. The summary of my findings so far is that the longer a subsonic projectile gets, the more dispersion increases. We already know that 22LR subsonic can be extremely precise with dispersion under 1 MOA but that same does not seem to hold true for heavier or longer projectiles like in .300 Blackout and 8.6 Blackout. 8.6 Blackout seems to be affected the most since the .338 projectiles are very long. I have found that decreasing the velocity improves the dispersion significantly. I am wondering is this due to normal shock due to supersonic airflow? As an example, with a 20 shot sample of each: at 1056FPS the dispersion was 3.6MOA but at 900FPS it dropped down to 1.9MOA. Is this a problem that can be solved by a different bullet design or is this some kind of inherent problem at subsonic speeds (like normal shock)?
I know you guys are currently working on Air rifles and hopefully that work will translate to subsonic centerfire cartridges but any insight you can provide would be greatly appreciated.
A significant factor here can be dynamic stability. It’s much harder to predict, but like gyroscopic stability, it is lowest (least stable) near the speed of sound and generally speaking, a longer bullet (relative to caliber) will be less dynamically stable as well. There are a lot of factors to consider here, but dynamic stability can certainly be a contributing factor. You should also consider the barrel time/recoil relationship. Your examples also track that you get worse dispersion with larger, heavier recoiling subsonic loads. This effect should not be ignored either as more recoil means the rifle can move more before the projectile exits the muzzle.