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I am looking for some advice on reloading,
If you have set your rifle/scope and get good results with 55 grain bullets and have been given some 69 grain bullets (1 in 7 twist rifle) to try.
If you adjust the amount of powder for the heavier bullet so the ftps are the same would the poi be the same as the 55 grain bullets.
Cheers

Sam

Generally speaking, heavier bullets will impact higher.

No. At short ranges the difference would not be noticeable, but as range increases the greater mass/section ratio will result in better velocity retention of the heavier bullet (all other things being equal). You won't notice unless you are an expert at distances under about 200 m, but at 1000 you will miss the target.

One not quite trivial consequence of this is you can use any ammo that fits in the gun on the zero range at Bisley to establish where your sights are pointing, because over 71' 7" the velocity difference between your best handloads and something that barely makes it out of the barrel has almost no effect on the bullet drop.

Learn your way around a good ballistic calculator, then you can answer these questions and many more.
Here's one: JBM Ballistics - Trajectory Calculation

A quick comparison with a couple of arbitrarily chosen bullets at those weights, assuming a particular calibre, 3000fps MV and default sight-height & environmentals gives you a difference of half a minute at 300, 3 minutes at 600 and over 15 minutes at 1000 yards. Substitute your own bullet data, velocities and environmentals to get a useful comparison. Remember, garbage-in garbage-out; use G7 BC values, and where they're available consider using the values measured by Brian Litz in preference to the manufacturer-claimed BCs.

You are making a big assumption though:

shotgun sam wrote: ↑Wed Nov 03, 2021 9:31 pmIf you adjust the amount of powder for the heavier bullet so the ftps (sic) are the same would the poi be the same as the 55 grain bullets.

By simply adjusting the charge to obtain the same muzzle velocity with the heavier bullet you could:

• Exceed safe pressures.
• Exceed case capacity.
• De-tune the load so badly it isn't worth shooting.

What is the application, and why do you want to match the trajectory of the other bullet? Are you trying to match a ballistic reticle, or battle sights graduated by distance? For a hunting application the JBM calculator can also give you values like maximum point blank range for a given vital-zone radius, plus the danger space. Regardless of the application you should, of course, develop the load for the new bullet from scratch by reference to published load data from a reliable source. If you really need to match the trajectory then consider the following:

• At shorter distances the trajectory will be close regardless of bullet and velocity.
• You might be able to develop a load where the trajectories are close at one chosen longer distance, but:
  • It is unlikely to occur at the same muzzle velocity as the lighter bullet.
  • You may need to use a different powder.
  • You might not achieve optimum or acceptable accuracy at the charge which results in trajectory intersection at your chosen distance.

I think sometimes we overthink these things.
I shoot 75grn HPs for fox out of my .243 Tikka. But occasionally if the opportunity arises I can load a 100 grain SP and providing the Roe/Munty is less than 100yds (which normally it is on the land I shoot on) then I am only looking at around an inch difference, which is not even worth thinking about.
Target shooting over longer distances will obviously make a difference, but surely if that is the case then you would simply sight in with whatever ammo you are using????
My 75grn bullets are loaded with 45grns of h414 (still have a tub) and the 100grn bullets are loaded with 40grns H414.

The best thing to do it to have DOPE or come-ups for each bullet weight at 50 or 100yd intervals (or at whatever interval you prefer). Have these written down preferably on the rifle somewhere and refer to it as you need and dial in the change.

fps being the same they may have same poi but purely by chance!
Most standard type of cartridges such as 223 308 etc in my experience seem to have very similar elevation settings to get in the black on a NRA target out to 600 yds.
That will definitely be different weights of bullets flying at different speeds.
I am with rox on this. I am a massive fan of the JBM ballistic software. Its free and a lot of it is compiled by Bryan Litz.
Stick with known data for your bullet - cant beat N140 or N150 in 223 - chrono 5 rounds then build a drop chart out to whatever your max distance will be.
I shoot a lot of 260 remington and have used many styles of 6.5mm bullets over the years.
At a 1000 and even 1200 two different bullets - say 123 and 136 - can be within a couple of minutes elevation. Not by design just how it panned out.
As it happens the Lapua 144gn fmj has a very high BC but drops badly at 1000 plus.

Thanks for all the replies
Sam