4 ms·
Fun, unrleated fact. Transsonic is very bad for rifle accuracy, as it tends to be somewhat unpredictable. For most rifle calibers this isn't a big deal, because
by ashtonkem 5y ago
Fun, unrleated fact. Transsonic is very bad for rifle accuracy, as it tends to be somewhat unpredictable. For most rifle calibers this isn't a big deal, because they spend their entire flight time in the supersonic flight regime. But for 22lr, this is an issue because even the fastest 22lr around is going to be subsonic within 100 yards or so for reasons[0]. The result is a shot that’s laser accurate until 100 yards or so, and then suddenly becomes unpredictable beyond that. So "match" 22lr ammo tends to be subsonic even out of the barrel.
0 - The reasons are due to maximum allowable pressures, and barrel rifling. At max pressure for a 40gr bullet you’re going to get maybe Mach 1.1, maybe. If you want to go faster without increasing pressure above spec, the solution is a lighter bullet. But lighter bullets often like different rifling, and virtually all off the shelf 22lr barrels come with 1:16 rifling, unsuitable for extra light bullets. Also, lighter bullet get pushed around by the wind more; you’d often rather compensate for more drop than wind, since drop is more predictable.
- nautilius 5y agoWhat kind of pressures do you have in a barrel?
- ashtonkem 5y agoLots! The maximum chamber pressure allowable for a given civilian caliber is set by one of two regulatory bodies, SAAMI (US) or CIP (EU). In some countries firearm barrels will be tested (“proofed”) at 125% of set pressure to ensure consumer safety, and then stamped with a proof house specific mark. My understanding is that the US doesn’t require this, but any imported barrels will be stamped. Specifically CIP sets the maximum pressure of 22lr at 24,646 psi. An extremely high number considering, but pretty pedestrian compared to other cartridges. For example NATO sets a maximum pressure of 62,366 psi for its primary rifle caliber, 5.56x45mm. It’s genuinely amazing that rifle barrels don’t regularly explode, to be honest.
- nautilius 5y agoOh wow, that is a lot! Thanks!