Because all copper or all gilding metal bullets retain their weight better than lead-core bullets, it's safe to step down in weight and not sacrifice penetration. From a .30 Remington AR, this 110-grain Tipped Triple Shock bullet penetrated 5 inches deeper than the 125-grain AccuTip.
Lead-free bullets are longer than their lead-cored counterparts of the same weight. Keep this in mind when establishing overall cartridge length. Also, some companies suggest that their lead-free bullets be seated a certain distance from the rifling.
Lead-free bullets are long when compared to lead core bullets. The bullet on the left is a .30-caliber, 165-grain Speer Deep Curl, the one on the right a .30-caliber, 168-grain Nosler E-Tip. Not only does this impact powder capacity, it may be an issue with the twist rate of your rifle.
Notice the difference in length of these three 6 mm bullets. The bullet on the left is the shortest and the heaviest—a 100 grain Speer Grand Slam. The middle bullet is the lightest—an 80-grain Barnes Tipped Triple Shock. The bullet on the right is the longest—a 90-grain Nosler E-Tip. All will penetrate to about the same depth in 10 percent ordnance gelatin or animals.