5 lbs
The Henry lever action rifles do not have an adjustable trigger. A competent gunsmith could improve the function but to answer your question, no........
On some of the older rifles, they had a set trigger. You would pull it first to set the other trigger. The second trigger would be a hair trigger. It would have a very light pull. The first trigger was supposed to keep from accidentally firing the rifle as you were aquiring the target.
I don't think Browning can modify trigger pull on their rifles due to liability, but you can contact a retired Browning Gunsmith who does excellent work on pull.
7-8 Ilbs
Length of pull is that distance from trigger to end of stock butt. Most generally, rifle and shotgun stocks are provided with 13 3/4" from the factory, as this is felt to be the average length of the average adult male's requirement for comfortable grasp of the firearm and for trigger manipulation.
The military weapon, AR-15, should have a trigger pull of 5.5 to 8.5 pounds and should be free of creep. Creep is the rough movement between the trigger pull and hammer release.
If you are asking strictly about BB guns and not rifles, pellet guns or pellet rifles then I would have to say it most likely is the "IZH-Baikal Drozd BB Gun." It fires at a rate of 541 feet per second. It will fire 1, 3 or 6 shot burst at the pull of the trigger. However Pellet guns and Pellet Rifles are more powerful.
5-7 lbs
Part of the firing mechaism prevents the hammer from falling again until the trigger is released to reset it. Without it, you would have the possibility of firing more than one shot per pull of the trigger.
It is supposed to.
This will vary from gun to gun. An M16 Military rifle has a trigger pull of about 5 pounds, it is a single stage trigger which mean steady pressure on the trigger will release the sear and fire the weapon. A two stage trigger requires the shooter to take up slack in the first stage of pulling the trigger and then apply slightly more pressure to the final process of releasing the sear. In the M14 rifle and M1 Garand the two stage trigger is still about 5 pounds. In hunting rifles most are single stage triggers ranging from 1 to 4 pounds. An Olympic Target rifle or pistol may have a trigger with a pull of just a few ounces, while a combat pistol may have a trigger pull of around 5 pounds. Uncle John Foremost Hunting.com
AVERAGE 12.2 pounds double action, 5.2 lbs single action.