Feed Your Garand What It Wants: Adjustable Gas Plug Install and Test

An adjustable gas plug allows shooters to safely use any type of 30-06 ammunition.

The story goes like this. After spending years developing a fancy new 30-06 cartridge (the M1) for their fancy new semi-automatic rifle (the “U.S. Rifle, Caliber .30”), the U.S. Army made an unfortunate discovery: the M1 cartridge could shoot well past the safe zones built into exiting Army practice ranges.

Going back to the drawing board, the military developed the M2 cartridge, a throttled-back version of the M1 that would keep errant rounds within bounds.

The rifle, commonly known today as the M1 Garand, was designed to function with the M2, which means that modern commercial 30-06 ammunition often produces higher-than-safe pressures. These higher pressures can bend the rifle’s operating rod, destroying its functionality and seriously decreasing its value.

Now, let me be clear: the safest way to avoid a bent op rod is to use either the diminishing supply of military surplus M2 ball or one of the commercial loads specifically designed for the M1 Garand. But if you’re looking to use a heavier bullet or hotter load for hunting or competition, that’s not going to work. You need a way to decrease pressures, and that’s where an adjustable gas plug comes in.

Adjustable gas plugs allow users to control how much gas from a fired cartridge is redirected back into the piston and operating rod, which in turn cycles the action and loads another cartridge. If all the gas is allowed to escape, the action won’t cycle; if too much gas is redirected, the action will cycle too quickly or too forcefully. Adjusting the gas flow to fit a specific cartridge ensures that the action cycles reliably with minimal wear and tear on the bolt, op-rod, etc.

SEE ALSO: Five Reasons You Should Buy That M1 Garand You’ve Been Eying

This adjustable gas plug from Schuster replaces the factory plug without any permanent modifications to the firearm.

There are several options on the market, but the most common adjustable plug seems to be the Schuster DCM Adjustable Gas Plug. For less than $40, this adjustable plug is easy to install and tune, and can be readjusted for whichever 30-06 loads you want to shoot.

1. Remove existing gas plug. 

First things first. Make sure your Garand is unloaded!

Next, you need to get the stock gas plug unscrewed and out of the way. The plug on my rifle wasn’t very tight, but I’ve heard of units that require some elbow grease. There are lots of tools specifically designed to remove M1 Garand gas plugs, but I just used the tool that came in the buttstock cleaning kit. If you have a wide, thick flathead screwdriver, that’ll also work.

The factory plug can be removed with a special tool or a flathead screwdriver (though the tool is recommended).

2. Install Schuster adjustable plug.

Once you have the stock plug out, simply screw in the new plug. Before you do this, be careful not to adjust the screw inside the plug. It comes from the factory at the correct setting and tightening it could damage the action.

Also, be sure to tighten the Schuster plug before you begin firing (the entire unit, not just the internal screw). The M1 wrench doesn’t work well for this, but a flathead will get the job done. If you don’t tighten the plug, loosening the screw inside the plug will loosen the entire unit.

The adjustable plug simply threads into the gas tube.

3. Tune the plug until the action cycles reliably.

The first round you shoot shouldn’t move the action, so you’ll have to extract the spent casing by pulling back the bolt. With the action locked to the rear and without any cartridges in the gun, reach forward and turn the gas plug ¼ turn clockwise with the provided Allen wrench.

Repeat this process until the action extracts the spent casing and the bolt locks to the rear. I started with 180g Winchester Powerpoint loads, and I turned the plug one full rotation until the action ejected the spent casing on its own. Once you think you have the correct setting, load multiple cartridges and check for reliable cycling.

SEE ALSO: The CMP’s Advanced Maintenance Class for the M1 Garand

After trying the process with the Winchester loads, I turned the screw back to its original position and repeated the steps with the 150g Remington cartridges I plan to use most often. With that load, I only had to turn the screw three-quarters of a turn before the gun started to cycle reliably.

To adjust the gas plug, turn the screw clockwise to give the system more gas and counterclockwise to give the system less.

4. Find the sweet spot.

This can mean one of two things. If you’re wanting to make the action cycle as slowly as possible (and thus, less wear and tear), turn the screw counterclockwise by small increments (I used 1/8 of a turn) to find the exact spot at which the action still functions.

Or, if you’re planning to use this rifle for competition or hunting, you can also tune the gas plug to achieve optimal accuracy. To do this, turn the screw in 1/8 turn increments, shooting a group after each adjustment. Repeat this process until you find the best group.

The gas plug can be tuned to maximize accuracy or reduce wear and tear.

5. Enjoy!

Now that your mind is at ease about damaging your M1 Garand, take it out to the range and start shooting! If you ever want to switch cartridges, you can simply loosen the screw to its original position and start the process from the beginning.

It’s always a good day at the range when I bring my M1 Garand.

Also, for your viewing pleasure, check out this great “How the M1 Garand Works” video from the 1940s.

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About the author: Jordan Michaels has been reviewing firearm-related products for over four years and enjoying them for much longer. With family in Canada, he’s seen first hand how quickly the right to self-defense can be stripped from law-abiding citizens. He escaped that statist paradise at a young age, married a sixth-generation Texan, and currently lives in Waco. Follow him on Instagram @bornforgoodluck and email him at jordan@gunsamerica.com.

{ 22 comments… add one }
  • Thomas Gaffey June 11, 2019, 10:26 am

    when I built my M1 at CMP a few years ago the armorers warned us that any bullet above 180gr MAY bend the op rod, since they see and work on more M1’s than anybody else, I’ll believe them. Also since surplus ammo is still widely available I’ll shoot that unless I want to hand load for something special, like I already do

  • Lou Cranford June 11, 2019, 12:30 am

    Hey, in the top picture the M1 sling is upside down. Better get i t fixed before Sarge sees it.

  • Jeremy June 8, 2019, 11:33 am

    Or you can just shoot commercial ammo with no worries In A properly maintained garand.

    There is no real need to add one of these… they are usually masking other problems.

    • Jordan Michaels June 8, 2019, 2:59 pm

      Hi, Jeremy. It’s true that many modern cartridges aren’t likely to damage the gun, and proper maintenance is key. But some manufacturers offer high-velocity or heavy bullet loads that do increase the speed of the bolt. Will this damage the gun? Maybe, maybe not. But if you’re hoping to hold onto your M1 for the long haul, reducing wear and tear might be worth it.

  • Russell Gordon Schoenfeld June 8, 2019, 2:53 am

    I have a Fulton armory peerless m1 Garand not shot much….only with military ammunition, and the Schuster gas play. I want to be clear. To shut off the gas and stop the cycling of the action I should turn the Schuster valve countercounterwise ? I want to be sure.

    Thank u,

    Gordon

    • Jordan Michaels June 8, 2019, 12:13 pm

      Hi, Gordon. That’s right. Unscrewing the internal screw will release more gas and the action won’t cycle.

  • Scott June 7, 2019, 10:10 pm

    How about a garandgear ported gas plug? It is a plug and play unit with no tweaking needed. I installed one and fired a few boxes of Hornady 165 grain Super Performance without any problems. Regular 150 grain from CMP still works fine as well. Other folks give the garandgear plug a thumbs up based on their comments on calguns…….

  • John Winn June 7, 2019, 5:37 pm

    Uh NEXT QUESTION for you Michael Courtney.

    How EXACTLY does this adjustable gas cylinder “LOCK SCREW” it’s NOT A “PLUG” !!@!

    affect ACCURACY??

    You are OBLIVIOUS to the FACT that NOTHING MOVES in the M1 Gas System, NOT ONE BIT, until the BULLET IS PAST THE MUZZLE!!!

    Between 7 and 12 inches before the system “dwell” time STARTS the op-rod moving.

    Therefore, your claim of TUNING for accuracy is ABSURD (as the rest of your nonsense).

  • John Winn June 7, 2019, 5:30 pm

    Your article is WOEFULLY IN ERROR!!!

    The M1 Garand was developed, tested, and FIELDED with M1 Ball. M2 Ball had ABSOLUTELY NOTHING WHATSOEVER to do with the M1 Garand.

    The M2 Ball round was developed at the REQUEST of the NATIONAL GUARD BUREAU for use with BOLT GUNS.

    The M1 Ball round dates to 1926!!!!! 174 grain bullet at 2750fps!!! FULL POWER !!!

    If you had even the SLIGHTEST CLUE Mr. Michaels, you would READ HATCHER who QUOTES Mr. Garand who states that M2 ball is for “TRAINING USE ONLY.” He said the M1 is designed for the “1926 cartridge” or alternatively to use “M2 AP”.

    Also, there are NO BENDING FORCES acting on the M1 operating rod. THIS IS MYTH.

    Instead of repeating total BS, WATCH THIS.

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

    sheesh.

    • Jordan Michaels June 8, 2019, 2:54 pm

      Hi, John. Thanks for your comment! This is really helpful information, and you’re right — “designed to function with” is likely an overstatement. I think it’s worth noting that, as Hatcher mentions on p. 25-26 (linked below, for readers who are interested), the M2 was substituted for the M1 in 1940. So, if we’re talking about what was most frequently shot out of the Garand in WWII, we’re probably talking about the M2. Hatcher also mentions on p. 25 that even the M1 was throttled down to 2640 fps in 1923.

      To your larger point, it’s true that the Garand action is probably beefy enough to handle many modern cartridges. I know Garand owners who shoot commercial cartridges out of their Garands with no trouble. But some manufacturers make 30-06 ammunition with bullets heavier than 174g and with higher velocities than 2640 fps. We’re also talking about a 70+ year old gun that many people are holding onto as an investment. If you’re looking to make wear-and-tear as minimal as possible, an adjustable gas block might be a good idea. You might not break your operating rod (not “bend,” eh?), but some modern ammo does increase the speed of the bolt.

      These guys even had a double fire shooting 220g bullets: https://www.youtube.com/watch?v=ZQ_F1riBth8

      Anyway, thanks again for your feedback. I was hoping someone would bring this up. Here’s the link to Hatcher’s Notebook, for anyone who wants to read more (check out Chapter III): https://www.amazon.com/Hatchers-Notebook-Revised-Classic-Books/dp/0811703509

  • lefty June 7, 2019, 12:58 pm

    No Garands for southpaws-highly unwieldy and Garand “enbloc” is stupid.I’ll stick with a STG44 or the later FAL

  • TOM BROLLINI June 7, 2019, 10:04 am

    Good article on a gas plug that has been available for decades.

    Should have mentioned that it was invented by Clinton Fowler of VA!

    He has been making M1s shoot good for a long time! We used to take our M1s to him & he would install it & find the best load for that rifle. With that plug, it was interesting to see some of the powder/primer/bullet combos that would shoot better than a minute.

  • Joe June 7, 2019, 9:57 am

    Click on the highlighted words in the article, “Schuster DCM Adjustable Gas Plug with Wrench” and it will take you to Midway sales.

    I have purchased from them before and they appear (to me!) to be quite reputable.

  • Resolute June 7, 2019, 9:25 am

    …and why did you not provide a RETAIL source so that your readers might acquire this adjustable gas plug?

    • S.H. Blannelberry June 7, 2019, 10:35 am

      It’s hyperlinked.

  • Jerry kosik June 7, 2019, 9:09 am

    How do you order the adjustable M1 gas screw plugs? What is cost with shipping?

  • Lyle June 7, 2019, 9:00 am

    In regards to adjustable Gas plugs and CMP competitions – it would be legal to use one in the “Unlimited M1 Garand” category = higher cutoff scores for the achievement medals. As previously stated, they are not legal for the “As Issued” category.

  • AK June 7, 2019, 7:46 am

    Been there…and it works. Just some validation for the author.

  • Lou Knapp June 7, 2019, 6:46 am

    Clear, well-written, helpful article.

    • Jordan Michaels June 8, 2019, 12:11 pm

      Thanks, Lou!

  • Jim Jenkins June 7, 2019, 6:18 am

    You mention competition in your article. Adjustable gas plugs are not legal in CMP as issued matches.

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