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I was doing some target 22 target practice and had three different brands of ammo, supersonic Thunderbolt 35 grain, Aguila 40 grain subsonic and Aguila 60 grain subsonic.

The Thunderbolt was the loudest due to the sonic boom, but the 40 grain was noticeably quieter. The exact same setup of rifle and suppressor remained the same for all of them.

Why would the 60 grain subsonic be louder than the 40 grain?

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I've worked extensively with the Aguila subsonic .22LR loads. Out of a full-length (i.e., 18") barrel the 40gr runs about 1035fps while the 60gr barely breaks 900fps. So both are soundly subsonic.

The 60gr is an unusual load in which the bullet is crimped in a .22 Short case. It's easy to recognize, in contrast to the 40gr which looks like most other .22LR ammo. (60gr is on the left in the following photo):

Aguila subsonic 60gr and 40gr rounds

As James Jenkins guesses, the 60gr load uses more powder, and holding all else equal more powder produces more gas volume and "uncorking" pressure, and therefore more muzzle blast – i.e., more noise at the muzzle. For the following photo I pulled four different cartridges and weighed the powder charge. The Aguila 60gr has 0.9gr of powder, whereas both the Aguila 40gr subsonic and a CCI subsonic load have only 0.6gr of powder. (For further comparison, the supersonic CCI 40gr "Mini-Mag" has 0.8gr of powder.)

.22LR ammo dissections

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Assuming both the 40 and 60 grain are actually subsonic (the projectile does not break the sound barrier) and both have similar muzzle velocities, you should expect the 60 grain to be louder.

It takes more energy (gun powder) to get the heavier 60 grain projectile to the same speed as the lighter 40 grain projectile.

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  • They are both subsonic, but the weird thing is that the case on the 60 is shorter with less room for gunpowder than the 40 midwayusa.com/product/2506135961/…
    – Charlie Brumbaugh
    Commented May 17, 2019 at 14:28
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    @CharlieBrumbaugh case length isn't super relevant to powder load with modern powders. Most handgun cartridges are only filled ~20% full because smokeless is so high energy compared to black powder and other older charges. Interestingly enough, you can make a .38 cartridge with the same power as a .357 very easily - there's plenty of room for powder. It's just exceedingly unsafe to do so because you can chamber the round in a .38, which isn't meant to handle the muzzle pressures that a .357 round produces.
    – Monica Apologists Get Out
    Commented May 17, 2019 at 14:48

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