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Old March 29, 2021, 12:00 AM   #1
45flaco
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375 H&H AR

Hey guys. Built my 375 H&H AR, now just have some minor work to do before hopefully test firing this weekend.
Just need to make a handguard, install detents, safety, and FA, and grind feed ramp a bit.
Its a left side, forward charging piston.
Handle does reciprocate, as it is directly attached to the piston.
Gas port is 18 inches from the back of the barrel extension, gas port is 0.082", because I figure the 375 has a lot longer pressure curve, and piston rifles don't tend to need as much gas to operate anyways. If it doesn't work, I'll drill it out a bit. But I don't think it will be necessary.
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Old March 29, 2021, 08:29 AM   #2
4V50 Gary
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Position of the gas port and gas port size is important. You're a pioneer! Keep us informed.
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Old March 29, 2021, 07:33 PM   #3
stagpanther
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An AR in 375 H&H?? You have a wilder imagination than I do!! I'm assuming you must have started with something like a noreen lower that gets you into non-standard cartridge length? I can't even imagine how to engineer a magazine to work with that. Did you take a look at the 375 Ruger? Easy to work with cartridge (though pretty wide so there may be an issue with bolt face).

That said, I love your idea--I would have never have thought of that.
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Last edited by stagpanther; March 29, 2021 at 07:43 PM.
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Old April 15, 2021, 12:55 PM   #4
45flaco
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So, it chambers a roudn from the magazine, fires, but doesnt eject under its own power. Basically a magazine fed straight pull currently.
@stagpanther, I actuallybdidnt start with a Noreen. I would have liked to, but their rifles cost more than my truck. So I started with 14 dollars of 1/8" steel flat and some castle nuts for a lower. The magaxine is from Wyatt's Outdoors, although any 3.850 CIP/AICS magazine will work, even the savage ones with a little modification to the locking tab.
I did think of 375 ruger, but Ive done a bolt rifle in both calibers, and the 375 H&H just feeds much smoother. The H&H is longer, more tapered, and has a minimal shoulder, which means it feeds beautifully in prettyvmuch any rifle. The main benefit of the Ruger is that it fits a 3.34" magaxine. But since Im doing everything custom, that wasnt really a concern.
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Old April 15, 2021, 12:57 PM   #5
45flaco
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Quote:
Originally Posted by stagpanther View Post
An AR in 375 H&H?? You have a wilder imagination than I do!! I'm assuming you must have started with something like a noreen lower that gets you into non-standard cartridge length? I can't even imagine how to engineer a magazine to work with that. Did you take a look at the 375 Ruger? Easy to work with cartridge (though pretty wide so there may be an issue with bolt face).

That said, I love your idea--I would have never have thought of that.
If I had started with a Noreen lower, the 375 Ruger would have likely been my go-to, as I think they make a 3.34" length action.
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Old April 15, 2021, 12:59 PM   #6
45flaco
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Quote:
Originally Posted by 4V50 Gary View Post
Position of the gas port and gas port size is important. You're a pioneer! Keep us informed.
Yoy are correct, gas port placement was a lot more important than I thought. Im used to building AKs, where I just pick a piston and gas tube length that looks cool, and drill port accordingly.
I have sinced moved the gas port to 15.5", standard rifle length. And am trying tp rework the piston.
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Old April 15, 2021, 01:00 PM   #7
stagpanther
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So you haven't actually achieved auto-feed/cycling with it?

Quote:
375 Ruger would have likely been my go-to, as I think they make a 3.34" length action.
The ruger does work in a conventional long action--and is also a fairly straight-forward case design--except it is "fat" and my guess would require some artful work on a magazine to work. It would also need a magnum type bolt, I'm not familiar with such a thing in AR's.
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Last edited by stagpanther; April 16, 2021 at 11:38 PM.
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Old April 17, 2021, 11:02 AM   #8
45flaco
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Quote:
Originally Posted by stagpanther View Post
So you haven't actually achieved auto-feed/cycling with it?

The ruger does work in a conventional long action--and is also a fairly straight-forward case design--except it is "fat" and my guess would require some artful work on a magazine to work. It would also need a magnum type bolt, I'm not familiar with such a thing in AR's.
Have not got it cycling. Right now it's a straight pull. I have a huge dislike of the 375 Ruger after trying to build a bolt action for it, and it took a LOT of work to make it feed. Whereas 375 H&H took nearly zero effort to work in a mosin, and the AR was maybe 10 minutes of polishing a feed ramp and bending a 338 LM magazine's feed lips to fit. Feeds smooth as glass.
The 375 Ruger could use the same bolt head as the H&H, as it was meant to be a mini action knockoff. They're both 0.532" rim diameters. But since it's only advantage is fitting in a standard action, I'd rather opt for smooth feeding and extraction, and the worldwide availability of the old H&H.
The difference in cost between making a 3.34" AR and a 3.85" is about 3/8 of a cent of sheet steel.
Both would be full custom, as I'm building anyways, not buying.
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