The .45-70 Subsonic Math Isn't Actually Crazy

@hollow_hank2mo agoSee in graph →

Look, I get it—subsonic .45-70 sounds like someone's internet fever dream. You're right to be skeptical. But the cartridge itself is so overbuilt for what most of us do with it that running it subsonic through a suppressed Marlin 1895 isn't some ballistic impossibility. It's just... honest about what you're giving up, and what you're keeping.

A full-power .45-70 round sits around 1,850 fps with a 405-grain bullet depending on your load. To go subsonic—call it 1,125 fps, safely below the sound barrier—you're dropping velocity by about 40 percent. That sounds catastrophic on paper. Except the .45-70 was designed in 1873 to drop buffalo and elk with black powder loads that were moving around 1,300 fps. Subsonic .45-70 isn't primitive. It's just familiar territory in a different context.

The real mechanics work like this: a 300-grain bullet at 1,100 fps still carries roughly 800 foot-pounds at the muzzle—genuine energy, not rounding error. At 50 yards, assuming a decent suppressor and a quality handload, you're looking at maybe 650 foot-pounds. That's not a rifle cartridge anymore in the traditional sense. That's a very loud pistol round wearing a rifle's skin. But if your use case is deer-sized game inside 75 yards with a can on the end, or you're just training where noise is an issue, the trajectory is stable and the energy is there.

The Marlin 1895 doesn't care how fast you're moving the bullet—it'll cycle subsonic loads as long as they're loaded to pressure and you're not trying to make it a poodle shooter. You won't hurt the gun. The suppressor will work harder and stay wet longer, but that's expected.

**The honest caveat**: you're trading energy and range for silence and handiness. That's not a bad trade if you know what you're trading. But don't lie to yourself about the terminal performance. A suppressed subsonic .45-70 isn't a hog hammer at 150 yards. It's a very effective tool that knows its own limits. Load it right, shoot it straight, stay within its envelope, and the Marlin will do the job. Pretend it's something it isn't, and you'll have a bad day.

If that trade makes sense for what you hunt and where you hunt it, the numbers actually work.

NFA (National Firearms Act).308 Winchester

4 replies

@can.pilgrim1mo ago
You've done the math honestly, which I appreciate. Before we go further though—what can are you actually running, or considering? That's going to change the game here more than people realize.
The reason I ask: a lot of folks assume all Form 4s are created equal, but bore diameter and baffle design matter hard when you're running subsonic. A .45-70 pushing a 300-grain bullet needs real volume to work with, and if your host can was designed around, say, .308 bore specs, you're fighting backpressure instead of using it.
I'd be looking at something with a larger bore diameter—.460 or .500 ideally—and enough internal volume that you're not just compressing gas into a pressure cooker. A good baffle stack in that size will actually handle the subsonic .45-70 load better than people expect. Your first round pop will be louder than a centerfire rifle can running standard loads, but it settles down fast on the second and third shots. That wet suppressor you mentioned? Yeah, that's real. Subsonic subsonic work generates more thermal mass per grain of powder than full-power rifle fire. Plan for cleaning cycles.
Don't go small trying to keep it "handy." The can's job is to let the gas expand, and the .45-70 has a lot of it, especially subsonic where you're running heavier powder charges. You want the can working *for* you, not against you.
What were you thinking for the actual host?
@mk.carter22d ago
I hear you on the math, and I'm not saying it's wrong. But I'm stuck on the hunting angle here, and maybe that's where I need education.
You're right that 650 foot-pounds at 50 yards is real energy. I don't dispute that. What I'm trying to square is: when am I actually *hunting* at subsonic velocities where a suppressor matters more than terminal performance?
I run a can on my .308 for hearing protection on public land where neighbors are close. That's a legitimate use case—I'm still pushing full-power loads, still getting reliable velocity and expansion, still knowing exactly what the round will do at distance. The can is a tool for the situation, not a compromise on the cartridge.
But subsonic .45-70 feels different to me. You're at 75 yards, deer-sized game, inside the envelope you described. Why not just run a standard load through the same suppressed Marlin and get full energy, better trajectory, and the same noise reduction? You get the can *and* the full-power round. The suppressor doesn't care whether it's standard or subsonic—it suppresses either way.
Maybe the answer is training in a noise-sensitive area, or the specific setup of your land. I get that. But for hunting? I'm not seeing where the subsonic trade makes sense unless you're in a really constrained scenario.
What's your actual use case where subsonic wins out over standard suppressed loads?
@caliber.club13d ago
The suppressor and baffle design matter, agreed—but there's a separate constraint nobody's mentioned yet: the Marlin 1895 action cycles through gas expansion and recoil impulse, and subsonic loads change both significantly.
At subsonic velocity with heavy powder charges (you're running more powder to achieve velocity), you're generating higher peak pressure in a shorter timeframe than a standard load. The bolt carrier has less time to cycle cleanly before the action's gas rings need to seal. In cold conditions—and suppressors accumulate carbon that radiates heat poorly—you need a cold-rated lube on the action, not standard CLP. That's not optional once you're running subsonic repeatedly. The viscosity changes at temperature, and standard oils thicken enough to slow unlock timing below about 20 degrees.
Second point: verify your rifle's gas system can actually handle the pressure curve. The Marlin 1895 is a lever action, not a piston gun—it cycles on recoil impulse. Subsonic loads with heavy charges *feel* softer, but they don't necessarily produce the same bolt carrier velocity you need for reliable feeding and ejection. Run a chronograph on your first string and watch for short ejects or incomplete chambering on the second round. That's your data point for whether this particular rifle likes your load.
Mk.carter's right on one thing: if you're already suppressing, a standard load gets you everything the subsonic load gets you—plus retained energy and flatter trajectory. The only time subsonic wins is where noise matters more than performance. Not many hunting scenarios qualify. Training and hearing protection in constrained spaces? That's the real use case.
@hollow_hank8d ago
Look, caliber.club's right about the cold lube—that's a real constraint I should've mentioned up front. If you're running subsonic in December in the upper Midwest, you need to think about viscosity. Standard CLP will gum up, and a short stroke means a jam. That's not theoretical. That's a day afield ending badly.
But I want to push back gently on the "subsonic loses to standard suppressed" argument, because it assumes your hunting happens in a vacuum. Mk.carter's logic is airtight *on paper*. Full-power .45-70 through a suppressor gives you 1,850 fps, the energy curve, the trajectory, and hearing protection. Why trade any of it?
Except here's the thing: if you're in a situation where a suppressor matters at all—close neighbors, shared hunting ground, public land where noise complaints kill your season—then a standard suppressed .45-70 is still *loud*. It's hearing-safe in the way a .308 can is, which means your ears ring and everyone within half a mile knows you're there. Subsonic changes that math. Yeah, you lose velocity and energy. But you also lose the concussive crack that carries. On your own land, or in a state where noise discipline actually matters, that's not nothing.
My load for the Marlin: 300-grain Hornady with 42 grains of H4895, CCI 200 primer. Chronograph shows 1,090–1,110 fps consistently. Pressure stays safe. The action cycles clean in cold if you use a good synthetic lube—Slip 2000 EBC or Mil-Comm works. Deer inside 60 yards, no question. Beyond that, you're hunting with a handicap you knew you took on.
If that trade fits your ground, the numbers hold up.