ideal ratio of length to diameter on suppressors?

[waterhouse]

Is there some sort of ideal ratio of length to diameter on suppressors?

Most 5.56 cans on the market seem to be 1.5" in diameter by 6.5-7" in length. I know soundtech had the Fatboy, which was closer to 2" in diameter and about 5", but these are not popular dimensions amongst the different manufacturers.

The sight height on an AR is pretty high, so it doesn't seem like added diameter on the can would be any sort of issue, but it would be nice to have a shorter can on something like an SBR while still maintaining high DB reduction. Do the baffles just not work well if they get too tall, or is it that baffles have to be a certain width to work and shortening the can would cut down on the number of baffles?

If I'm doing the math correctly, a 6.8" long can with a 1.5" diameter (YHM Phantom, for example) has a volume of about 12 cubic inches. If the can's diameter is increased to 2", a length of 4" would give a volume of 12.5 cubic inches, a greater volume in a suppressor that is almost 3" shorter.

Is there just not a market for this sort of thing, or is there some part of the design process that makes short, stocky suppressors poor performers?

 

[MisterPX]

I beleive there's more to it than just "volume". Gas escapes behind the projectile as well, and it the can isn't long enough, that gas won't have time to burn up. Case in point, if it were just volume, then we could have a 4" diameter can, that's only 1" deep. Same volume, but wouldn't work for crap.

 

[Crosshair]

Well, for diameter you are often limited in how big you can go because you don't want to block the sights. As for length, you need to have enough do you can have several expansion chambers. You have the added difficulty of a larger diameter can needing thicker baffles to resist the higher forces because of the larger surface area.

MisterPX is right, you will have better suppression from a longer skinny can than a short fat one. You want the propellant gases behind the bullet to dissipate inside the suppressor. A certain amount is going to "follow" the bullet through the holes in the baffles as the gases are traveling forward at the same velocity of the bullet. The gases will only have enough time to spread out a relatively small amount before they hit the blast baffle, so once you get the can large enough in diameter, you gain more by making the can longer to add more baffles than by continuing to increase the diamiter.