What Does Grain Mean in Ammo?

In ammo, grain is a unit of weight, not a measure of size or power. One grain is 1/7,000 of a pound, or 64.79891 milligrams. When a box says "124 grain," it means the bullet alone weighs 124 grains. The number does not include the case, primer or powder.

The grain as a unit

SAAMI, the US standards body for ammunition, defines the grain as an avoirdupois unit of weight with 7,000 grains per pound, and notes it is the usual unit for weighing ammunition components. NIST lists the grain as exactly 6.479891 x 10^-5 kilogram, which is 64.79891 milligrams. It is a very small unit. Even a 660 grain .50 BMG bullet weighs less than a tenth of a pound.

The word has a second meaning. SAAMI notes that "grain" is sometimes used for a single particle of propellant powder, though kernel or granule is the more accurate term. On a box label, grain always means weight.

Bullet weight vs powder charge

Two different things are measured in grains:

• Bullet weight: the number printed on factory ammo boxes. It tells you how heavy the projectile is.
• Powder charge: the weight of propellant inside the case. Handloaders weigh charges in grains on a powder scale. Factory boxes usually do not print it.

The two numbers are unrelated on the box. A heavy bullet does not mean a heavy powder charge, and you cannot work out velocity from bullet weight alone.

How bullet weight trades with velocity

Within one cartridge, a heavier bullet usually leaves the barrel slower, because the case pressure limit caps how hard it can be pushed. Our two Speer Gold Dot 9mm loads show this clearly. Speer lists the 124 grain +P at 1,220 feet per second and the 147 grain at 990 feet per second, both from a 4 inch test barrel. The lighter bullet is faster. The heavier one carries more mass. See 9mm bullet weights for that comparison in depth.

Across different cartridges, grain weight tells you little about speed. The case size, powder, pressure and barrel length decide that. Aguila Colibri has a 20 grain bullet and no powder, and Aguila lists it at 420 feet per second. FN's 27 grain 5.7x28mm load is barely heavier but is listed at 2,216 feet per second from a pistol.

Our loads by bullet weight

Here is the in-stock range at our Phoenix warehouse, lightest to heaviest, with the maker's listed muzzle velocity where we could confirm it:

• 20 grain: Aguila Colibri .22 LR, 420 fps, primer-powered with no powder.
• 27 grain: FN 5.7x28mm SS198LF, 2,216 fps from a Five-seveN pistol and 2,530 fps from a PS90 carbine.
• 55 grain: PMC Bronze .223 Remington FMJ-BT, 2,900 fps.
• 62 grain: Federal American Eagle 5.56 M855, listed by Federal at 3,020 fps. We also stock 62 grain M855/SS109 from MKE and BVAC in 5.56x45mm NATO.
• 123 grain: Magtech .300 Blackout FMJ, 2,230 fps from a 16 inch barrel, and 123 grain 7.62x39 from Armscor and Precision One.
• 124 and 147 grain: Speer Gold Dot 9mm +P 124 and Speer Gold Dot 9mm 147, 1,220 and 990 fps.
• 660 grain: PMC Bronze .50 BMG FMJ-BT, 2,950 fps from a 36 inch barrel.

Listed velocities come from the maker's test barrel. Your own barrel length and the air temperature will move the real number.

How to choose a bullet weight

• Start with what your firearm's manual or barrel twist rate is designed for. Some barrels stabilize heavy bullets better than light ones.
• Match the purpose. Practice loads, defensive hollow points and hunting soft points are built differently even at the same weight.
• Expect point of impact to shift when you change weight, and re-check your zero.
• Store any weight sealed and indoors. Phoenix summer heat in a car or garage is hard on all ammunition. See ammo storage.

Buying and pickup

You must be 21 or older to order. Orders ship UPS Ground from Phoenix within 2 business days, charged by weight. See where we ship, or pick up in Phoenix Monday to Friday, 9am to 5pm, with ID (480-623-4515).

Bullet grain questions

Does a higher grain bullet mean more powerful ammo?

Not by itself. Grain is only bullet weight. Energy depends on weight and velocity together, and within one cartridge a heavier bullet is usually slower.

How many grains are in a pound?

There are 7,000 grains in one avoirdupois pound. One grain is 64.79891 milligrams.

Is grain the same as caliber?

No. Caliber is the bullet's diameter, such as 9mm or .223 inch. Grain is its weight. Two bullets of the same caliber can weigh very different amounts. Shotgun shells are sized by gauge and pellet size instead; see our 12 gauge buckshot guide.

Does the grain number on the box include the powder?

No. The grain number on a factory box is the bullet weight only. Powder charge is also measured in grains but is usually not printed.

More answers in our ammo FAQ.