30-30 flight path weird

[Macdsl]

Okay, for those more knowledgeable than myself on the old trusty 30-30, I have a head scratcher. The rifle is a lever action mosberg (Winchester copy) that shoots really quite nice. The issue is with the POI. All ammo is federal. Zeroed it with 150gr soft points at 100 yards then tried some of the 170gr to see the difference. POI at 100 yards with the 170gr are now almost 4” higher?! I don’t get it. Wouldn’t the 170’s have more drop than the 150’s with no change to the sights? I can hit the gong at 200yards with the 150’s all day but can’t make a hit with the 170’s, next time out I will have a spotter to gauge where I’m hitting.

So tell me how a heavier grain bullet is hitting a higher POI?

[catnthehat]

Originally Posted by Macdsl

Okay, for those more knowledgeable than myself on the old trusty 30-30, I have a head scratcher. The rifle is a lever action mosberg (Winchester copy) that shoots really quite nice. The issue is with the POI. All ammo is federal. Zeroed it with 150gr soft points at 100 yards then tried some of the 170gr to see the difference. POI at 100 yards with the 170gr are now almost 4” higher?! I don’t get it. Wouldn’t the 170’s have more drop than the 150’s with no change to the sights? I can hit the gong at 200yards with the 150’s all day but can’t make a hit with the 170’s, next time out I will have a spotter to gauge where I’m hitting.

So tell me how a heavier grain bullet is hitting a higher POI?

Could be nothing more than the way the 170 and the 150 site in the chamber and the way the bullets react coming out of the barrel , the way the barrel harmonics change
My 215's in my 303 brit have a higher point of impact at 100 yards than my 150's.
Cat

[Macdsl]

Yes, weird for sure. Never seen this before so that’s why I asked. Trying to get it dialed in for a nice light deer anchor.

[rugerfan]

Just pick one load, sight in with that and stick to it. Probably not the case here, but the higher point of impact with heavier bullets is common in pistols, the heavier and therefore slower bullet spends longer in the barrel, giving the pistol more time to move upward with recoil before it exits the muzzle.

[elkhunter11]

Could be harmonics, or the muzzle rises more due to recoil, before the 170s leave the barrel.

[Dean2]

What you are seeing is very common and relates to ballistics.


All projectiles fired from any gun begin to drop the instant they leave the barrel. The line of sight is above the barrel so we must elevate the barrel so that the projectile crosses the line of sight, traveling in an arc. The projectile thus crosses the line of sight traveling in an arc above it. All this while, gravity is working to pull the projectile back to earth. Both projectiles will hit the ground in exactly the same amount of time regardless of velocity from zero the basically infinite, the difference is the faster projectile will travel further in that same period of time. Eventually, the projectile again crosses the line of sight, this time traveling from above it to below it. The point where they cross this second we call the Point of Impact.

A faster moving projectile will have a lower arc (trajectory) and will cross the line of sight farther from the muzzle than a slower projectile. Thus the POI will be slightly lower anywhere along the line of trajectory.