I could use some help.

I have been reloading my factory Hornady brass with H4350 and RL17 for my Ruger Predator.

If I load a 120 grain bullet and create an accurate round of 0.5" @ 100 meters and then switch to a 140 grain bullet, same brand bullet and same powder, it will hit low and left by 4 inches but group just as tight. I can't seem to get 2 different bullet weights to hit in the up and down vertical pattern. It makes shooting 2 different weight bullets in silhouette diffcult. Anyone have any suggestions as to a fix?

Right now im sticking with one bullet weight load for all animals, but would like to shoot a lighter bullet at C-P-T. Any help would be appreciated.

You are using the same weight charge for the heavier bullet?

Different weight bullets are expected to hit at different places, usually only vertical but it can be a horizontal change occasionally. Just adjust your scope to the new impact, no big deal.

No I use my chronograph to keep the rounds in the 2700 FPS range. So the powder charge will change.

I don't mind the round hitting lower just not left or right of the current scope setting of the 120 grain load. I don't want to adjust for windage if I don't have to because of a different weight round for rams. I watch my buddy shoot 107's and 130s and his hit straight down from his lighter bullet load. That's what im trying to achieve. I may just stick with one weight bullet and not worry about it.

Only thing I can think of at the moment is maybe a bedding issue or a barrel harmonics interaction.

I'll check my bedding block. I appreciate the info.

i once tried a light bullet in a 30-30 win for chickens. The load was light too. Grouped great at 50 yards, 9" right!
Gave up and just shot 150's. Best guess was a barrel harmonics thing, too.

Bullets don't travel strait. Nor do they travel in an arch. They travel in a cork screw manner. Imagine a dot as the line the bullet travels but the bullet orbits the dot. That's how bullets fly. Different weights orbit differently.
I had to look up the actual term. Its called YAW.

Many competitors are adjusting both elevation and windage. Got to remember that you moved both when you come off the ram line.

for a different shooting discipline, my light loads grouped up and to the right in an oval pattern. As I approached the best grouping load, the group become more or less round and centered on my point of aim. Different loads even eith th same bullet weight eill group differently...

I shoot 107s for the first 3 and 142s for the rams. I don't care if the point of impact is the same. Left and right are the same but not up and down. Sounds like you may have a bedding problem for the left and right impacts.

Thanks for a the responses everyone. I'm going to check a few things out. Have some good weather coming up and going to send a few rounds down range.

I see that with my 30-30 cast loads. The heavier bullets hang more and more left

I have the same issue with my .260 Rem.
My gunsmith that builds my rifles is a benchrest shooter.
When I asked the question about my ram loads shooting 1 minute left (139 gr Lapua Scenar) vs my CPT load (107 Sierra MK),
he replied that it's all about barrel harmonics/vibration pattern with the 2 different loads. As others have said, mark your adjustments needed to shoot rams, and don't forget to put it back when you go back to CPT.

Yes K Danz I talked to a couple guys that shoot A LOT more than me and they have the same issue with harmonics. I have decided to load up 160 rounds in 140 grain bullets and just shoot my next match and not worry about the adjustment until I have time to play with a lighter load.

Thanks for the reply.

"When I asked the question about my ram loads shooting 1 minute left (139 gr Lapua Scenar) vs my CPT load (107 Sierra MK),
he replied that it's all about barrel harmonics/vibration pattern with the 2 different loads."

Your gunsmith is absolutely correct. The bullet will go in the direction the barrel is pointed during the barrel vibration pattern when the bullet exits the barrel. At that point, bullet ballistics take over. You need to adjust your sights to compensate the different loads.