12 gauge Ballistics question with 1 ounce solid lead slugs ?

[blackpowder1]

Hi all around !

I am not very familiar with the ballistics of solid lead shotgun slugs. I sighted my Benelli M2 at 15 yards to hit center with 1 ounce slugs. It took some dialing in, but now the POI is dead center. Yesterday, I extended the range to 25 and 50 yards respectively. The slugs were rising with increasing distance. POI was 3" high at 25 yds and 5" high at 50 yds. The iron sights sit 1,5" above the bore center line. I would have expected the POI to be lower with increasing distance due to the considerable weight of the slug. Can someone enlighten me as to why POI is higher at greater distances.

Many thanks ! Blackpowder

 

[Steve Rose]

Given that the sights are above the bore axis the projectile comes up to meet the line of sight (see the bore axis in the picture) at 2 distances (in your case first at 15 yards) then as gravity takes over the projectile starts to drop to cross the line of sight at some greater distance. Extend your target out to 75-100 yards and you will find that the slug does intersect, then fall below, your sight picture some where beyond 50 yards.

 

Edited October 19, 2024 by Steve Rose

[blackpowder1]

Many thanks for this explanation. It makes perfect sense. So, I will leave my sight adjustments to hit what I aim at at 15 yards, as this is a reasonable distance one can expect in most self defence scenarios. At distances of 25 and 50 yards, I can just aim below the mark accordingly because I know to aim 3" or 5" lower. If I shoot at greater distances, I guess I will have to find out by trial and error where the projectile again crosses the line of sight on it's way down, right?  

[Steve Rose]

2 hours ago, blackpowder1 said:

Many thanks for this explanation. It makes perfect sense. So, I will leave my sight adjustments to hit what I aim at at 15 yards, as this is a reasonable distance one can expect in most self defence scenarios. At distances of 25 and 50 yards, I can just aim below the mark accordingly because I know to aim 3" or 5" lower. If I shoot at greater distances, I guess I will have to find out by trial and error where the projectile again crosses the line of sight on it's way down, right?  

Exactly. Actual shooting at a target at various distances is the best way to learn your gun and choice of ammo's trajectory.

[Copo9560]

You might want to adjust the sights to be right on at 50 yards.  The difference at 15 yards will be far less than 5 inches off.  This approach eliminates the need to compensate under potential high pressure situations.