The Remington 405 doesn't generate the harsh recoil that the lighter bullets do even when pushed at the same velocity.
Never the facts get in the way of an amusing but completely erroneous claim. The laws of physics have not been repealed and you have not found the secret to perpetual motion or free energy or anything of the kind…
The fact is that given a 405g bullet and a lighter bullet pushed to the same velocity, the heavier 405g bullet will introduce greater recoil with a faster impulse.
These following handloads are all chrono’d loads from my 22” Marlin 1895, with recoil and recoil velocity calculated with “Point Blank”, assuming a 7.5 pound rifle/ammo combination.
Let’s start with the 405g at Remington’s 1330fps Trapdoor velocity and assume 30.0g powder (which is probably light):
Recoil / Recoil Velocity / Load
19.5fp / 13.0fps / 405g Remington @ 1330fps (assuming 30.0g powder, which is probably light)
17.4fp / 12.2fps / 300g hardcast @ 1366fps, 49.5g Varget
Or, let’s bump the 405g up to Marlin velocities:
Recoil / Recoil Velocity / Load
45.0fp / 19.7fps / 405g Remington @ 1982fps, 48.8g H4198
42.6fp / 19.1fps / 350g North Fork @ 2183fps, 51.0g H4198
39.0fp / 18.3fps / 350g Speer JSP @ 2067fps, 50.5g H4198
36.6fp / 17.7fps / 300g Speer UCFN @ 2247fps, 54.5g H4198
31.4fpe / 16.4fps / 300g Speer UCFN @ 2075fps, 51.0g H4198
28.6fp / 15.7fps / 300g Barnes XFN @ 2004fps, 47.0g H419
Pretty clearly, the 405g load is generating more recoil with a faster impulse in all cases, often significantly so and quite contrary to your claim.
For my plinking, though, I prefer this:
7.2fp / 7.9fps / 300g hardcast @ 1167fps, 13.5g HS-6
The heavier bullets are more accurate because that's what the guns were designed to shoot.
Actually, that is not necessarily the case. The most accurate loads in my rifle have been with the 350g North Fork.
The Remington 405 will work just fine up to about 2000 fps. I agree a 405 cast bullet is good too and that's what I'll mostly be using. If I wish to shoot long range I'll haul one of the dozens of other rifles I have out of the safe that are more suitable for that job. I don't have to impress anyone I just want a freezer full of meat. The Speer 400 grain bullet is also suitable for the .45-70 but it's more expensive.
I’m actually more concerned about wounding an animal and having it get away than I am filling the freezer. The load I hunt with is better suited to my needs than a Trapdoor load.