The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > The Smithy

Reply
 
Thread Tools Search this Thread
Old March 29, 2021, 12:00 AM   #1
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
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.
Attached Images
File Type: jpg Casper (wecompress.com).jpg (345.4 KB, 216 views)
45flaco is offline  
Old March 29, 2021, 08:29 AM   #2
4V50 Gary
Staff
 
Join Date: November 2, 1998
Location: Colorado
Posts: 21,824
Position of the gas port and gas port size is important. You're a pioneer! Keep us informed.
__________________
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!
4V50 Gary is offline  
Old March 29, 2021, 07:33 PM   #3
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 11,653
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.
__________________
"Everyone speaks gun."--Robert O'Neill
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; March 29, 2021 at 07:43 PM.
stagpanther is offline  
Old April 15, 2021, 12:55 PM   #4
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
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.
45flaco is offline  
Old April 15, 2021, 12:57 PM   #5
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
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.
45flaco is offline  
Old April 15, 2021, 12:59 PM   #6
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
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.
45flaco is offline  
Old April 15, 2021, 01:00 PM   #7
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 11,653
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.
__________________
"Everyone speaks gun."--Robert O'Neill
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; April 16, 2021 at 11:38 PM.
stagpanther is offline  
Old April 17, 2021, 11:02 AM   #8
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
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.
45flaco is offline  
Old May 23, 2021, 08:06 AM   #9
lilguy
Member
 
Join Date: December 18, 2007
Posts: 56
Do you have it feeding reliably yet?
lilguy is offline  
Old May 25, 2021, 06:25 PM   #10
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
Feeds wonderfully now. But can't get enough pressure through my homemade gas block to eject the old case. So it's sitting at a CNC shop while some guy designs a better gas block and also a charging handle, since he's already got it I the shop
45flaco is offline  
Old July 21, 2022, 02:27 PM   #11
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
Got tired of waiting for the CNC guy to make a gas block for it.
Took the rifle home, modified some parts from autozone and put an adjustable gas block on it. Gas tube is just 3/16" brake line lol.
But it works beautifully now.
Test fired with 20 rounds of factory Hornady DGS ammo, 10 rounds of 200 grain sierra handloads, and some random cast bullets.
They all worked decently.
Then I loaded up some DGS above max, as kind of a proof test.
Fired 2 of them with gas block turned almost off.
Still cycled, but kicked like hell. Have included a link to that video, will have more organized testing once I'm finished with current job.

https://www.youtube.com/watch?v=bLe0Px2VWv4

The sparks are because my previous gas port at 16" was plug welded, but the proof rounds blew that plug out. Eventually I'll just start over with a new barrel now that I know what distance to put the gas port at.
45flaco is offline  
Old July 21, 2022, 08:31 PM   #12
Shadow9mm
Senior Member
 
Join Date: March 21, 2012
Location: Indianapolis, IN
Posts: 3,947
Wow. Super cool project!
__________________
I don't believe in "range fodder" that is why I reload.
Shadow9mm is offline  
Old July 22, 2022, 06:57 AM   #13
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 11,653
Your's is about the most ambitious and coolest build I've ever seen on this forum--my hat is off to you! Among other things, just getting those bullets to stack and feed from a magazine must have been a major engineering feat in itself. I built a 284 win AR and it works great--but I can't get more than 3 cartridges at a time to successfully feed from a magazine due to magazine bulge.

So what did you end up using for a lower?
__________________
"Everyone speaks gun."--Robert O'Neill
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; July 22, 2022 at 07:02 AM.
stagpanther is offline  
Old July 24, 2022, 09:12 AM   #14
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 21,021
That's cool. Might be the start of a specialty side-business.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
Old July 28, 2022, 07:44 AM   #15
4V50 Gary
Staff
 
Join Date: November 2, 1998
Location: Colorado
Posts: 21,824
Might want to open up the gas port to allow more gas?
__________________
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!
4V50 Gary is offline  
Old September 15, 2022, 06:32 PM   #16
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
Made the lower myself, welded some steel together.
I do have plans for a CNC cut version at some point, as my lower has the buffer tube tower slightly misaligned.

As far as feeding, it wasn't actually a terrible chore, although the lack of factory box magazines was a bit irritating. Using a modified 338 magazine from Wyatt's Outdoors, and it's a single stack so I had to modify the barrel extension much the same as you would see on a .50 beowulf.

Also had to make a new paddle-style mag catch for the new mag. Being intended for a bolt action, there was no way to put a side bolt catch on it
45flaco is offline  
Old September 15, 2022, 06:34 PM   #17
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
I did incrementally open it up, and unfortunately it still didn't like some ammo even at 3/16" port diameter, which is where I stopped. Ended up moving it further up the barrel to get higher pressures, which means I'm now changing buffer weights and spring.
I think the issue is that some H&H ammo is loaded to drastically lower pressure than others.
45flaco is offline  
Old September 15, 2022, 06:36 PM   #18
45flaco
Senior Member
 
Join Date: November 19, 2017
Posts: 134
I've found that it likes factory DGS ammo, loves whatever the hell PPU puts in their 300 grain, and doesn't like Federal at all. I think federal loads to like a 375 winchester/38-55 level, as there's noticeably less recoil and they don't want to cycle. Hopefully the new, shorter gas system fixes this, it seems promising so far
45flaco is offline  
Reply

Tags
375 h&h , varmint rifle

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 02:06 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.08845 seconds with 11 queries