I don't think there are any spoilers in this but here's a warning regardless. I want to quote the larger passage for context as well as to point out several of the other men use their ramrods as rests to aim rifles. I believe (and this is just a best guess) that the rifles in question are the Colt First Model Ring lever rifles. This guess is based on the fact that they are revolving rifles in 1849 and that seems to have been the only one on the market.
"[Glanton] reholstered the gun and stood his empty rifle upright against the saddle and held it with his knee while he measured powder down the barrels.....He was watching a rise to the north where a band of mounted Apaches were grouped against the sky.
They were perhaps a quarter mile distant, five, six of them, their cries thin and lost. Glanton brought the rifle to the crook of his arm and capped one drum and rotated the barrels and capped the other. He did not take his eyes from the Apaches. Webster stepped from his horse and drew his rifle and slid the ramrod from the thimbles and went to one knee, the ramrod upright in the sand, resting the rifle's forestock upon the fist with which he held it. The rifle had set triggers and he cocked the rear one and laid his face against the cheekpiece. He reckoned the drift of the wind and he reckoned against the sun on the side of the silver foresight and he held high and touched off the piece..... [he hits the target but only wounds the man]
Glanton turned in the saddle without taking his eyes from the indians and held out his rifle to the nearest man. This man was Sam Tate and he took the rifle and reined his horse so short he nearly threw it. Glanton and three rode on and Tate drew the ramrod for a rest and crouched and fired. The horse that carried the wounded chief faltered, ran on. He swiveled the barrels and fired the second charge and it plowed to the ground.....
Glanton had drawn his pistol and he gestured with it to the men behind and one pulled up his horse and leaped to the ground and went flat on his belly and drew and cocked his own pistol and pulled down the loading lever and stuck it in the sand and holding the gun in both hands with his chin buried in the ground he sighted along the barrel. The horses were two hundred yards out and moving fast. With the second shot the pony that bore the leader bucked and a rider alongside reached and took the reins. They were attempting to take the leader off the wounded animal in mid stride when the animal collapsed."