Precision lead balls are very popular among knowledgeable airgun shooters because the spherical shape cannot tumble at long distance. The spherical shape also makes these projectiles faster and easier to load. "Perfect Rounds," are especially popular as a substitute for the steel BB, but have a higher impact."BB" is now an official caliber, listed as .177 or 4.5 mm, but actually having a maximum diameter of .175", a minimum diameter of .162" and a weight of only 5.3 grains for steel BB's. The diameter is approximately .177 with a weight of about 8.0 grains for equivalent lead airgun shot (with a maximum shot start force of 22.5 lbs.). Precision lead balls thus fit the gun's bore much better and waste less air. The .25 Perfect Rounds produces amazing penetration and high muzzle energy in magnum .25 caliber air rifles. However, they are not a good choice for use in guns with magazines.