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M1 Carbine Blank Adapting FAQ

Written: 7/29/2007
Author: Chris Guska


Q: How do I blank adapt my M1 Carbine

A:  There are currently 3 options available to M1 Carbine owners.
 
1.) Use a military – surplus clip on style adapter.
2.) Drill and tap the barrel for a set screw
3.) Chose another weapon to use.

Q:  How does the M1 Carbine blank adapter work?

A:  The M1 Carbine is a semi-automatic gas operated rifle.  Essentially when live ammunition is fired, the gasses of combustion are trapped behind the bullet as it makes its way down the barrel.  Roughly 4 inches from the chamber, some of those gasses are re-directed through a hole in the barrel into the gas cylinder, which push on a piston head.  That piston head pushes on the operating slide, which cycles the action of the Carbine.  When firing blanks, there is no bullet to trap gas behind and no way of creating the requisite pressure to push on that piston and cycle the action.  The blank adapter reduces the opening (aperture) at the muzzle, trapping gases momentarily, long enough for the requisite pressure to be built and operate the action.

Q: Why would you want an “adjustable” blank adapter?

A:  Not all blanks were created the same.  Some blanks have more powder, or faster burning powder than others.  These blanks are considered “hotter” and create a higher pressure of gasses in the barrel.  With higher pressures, a smaller aperture at the muzzle is no longer needed to cycle the blanks.  Being able to adjust the size of the aperture in these circumstances is preferred, as less wear is put on the rifle, in addition to less stress is being put on the threads that hold the BFA on.  High pressures and an aperture that is too small will cause the BFA to be blown off the rifle.

Q: How do you gauge the safety of a blank adapter?

A: It depends.  Everyone has their opinion on what is best and what is safest.  Much of the safety factor of blank adapters depend on a myriad of factors, including but not limited to:  The type of front sight on your carbine (only matters with the clip on adapter) The condition of your rifle, barrel, threads and gas system, The age of the adapter, The history of the adapter (how many blanks were fired through it, as well as what kind of blanks), The proper installation of the adapter (has it been over-torqued into the barrel previously?  Has it been accidentally cross threaded?  Is it properly tightened down?  Is it insufficiently tightened down?  Have additional means of securing the adapter been used such as Loc-tite? )

Finally, the last factor in safety is YOU, the user.  Safety begins and ends with the user.  Blanks are dangerous.  Blank adapters are only as safe as their user.

All of the blank adapters listed will safely function properly, with the correct blanks, with the correct aperture.  No one adapter is truly “safer than the rest” or “unsafe”, all have been safely used for years.  It all comes back to you, the user.

Q: I don’t want to “destroy”  a piece of history, is there any way of adapting my carbine without drilling & tapping the barrel?  

A:  Yes.  You can either use the clip on adapter, which is very obvious and looks ugly, or buy a new commercial replacement barrel, and have a gunsmith swap your original barrel for a new replacement of no historical value.  This will allow you to carefully preserve your barrel in a climate controlled inert gas vault for the sake of history.

Over 6 million carbines were made for the US military.  Although every single last one of them will carry historical significance, not all of them will carry “collectors” value. 

Most carbines you find are pretty run of the mill, and somewhat used and abused.  These gun’s weren’t babied during their lives.  Those carbines that saw use overseas in foreign militaries, such as Korea, have been heavily used. 

Additionally, carbines that have been “import marked”  on their barrels are virtually completely rendered “shooter grade” and not desired by collectors. 

Many of the Korean carbines have barrels that are virtually shot out.  The rifling is heavily worn, and the crowns of the barrels are far from perfect. 

These guns are perfect candidates for drilling and tapping.  Their accuracy and use as shooters are marginal at best.  Their “collector” value is close to nil.    If you take the time to “restore” the gun, it still wont be desireable to true collectors, as it’s a put together parts gun, and not truly original. 

Basically, get over yourself, if you have a truly collectable M1 carbine, why are you even considering running blanks through it.  Chose another weapon, or buy another carbine that isn’t as “perfect”. 

Civilian production carbines are also available, of NO military historical significance that you can drill and tap, and gleefully run blanks through all day… That’s another article in and of itself. 

Q: I heard that if I drill and tap my carbine, it’ll totally destroy the accuracy of the barrel.

A:  True and false.  If done properly, drilling the barrel re-crowns it, essentially returning the muzzle wear back to 0.  If done improperly, not true to the axis of the bore, yes it can negatively impact accuracy.

Also ask yourself, how often do you really shoot your carbine?  Do you shoot your carbine in matches?    How serious are you about accuracy?  Maybe you should consider either shooting another gun in those carbine matches (an AR15, or mini 14), or just getting another M1 carbine and putting a brand new match quality barrel on it…

Q: What does the military have to say about blank adapting the Carbine?

A: The M1 carbine was not adapted for blank fire by the US military during WWII.

Q: Whose blanks are the best?

A: It depends.

Unfortunately, blanks aren’t a standardized product.   A .30 Carbine blank is not the same from everybody, the brass that the blank is made from may differ, the primers used may be harder or softer from some manufacturers, the powder types may be slightly different as well as the powder quantities.  Some blanks are made from special purpose .30 carbine blank brass, some blanks are made from turned down and formed .223 brass.

It’s really subjective.  Basically – Ask your unit where they get theirs, and whose they like.  Try and find a vendor that is local, shows up to the events that you do.  You want someone local, who will A.) be at the events you’re at so you can buy them there, have a consistent source, and save on shipping B.) will be able to field questions and complaints in person, hopefully they will make things right if there is a problem C.) help you troubleshoot your weapon if there are problems.

Try and be consistent in who you buy your blanks from, as it will save you a lot of headaches in potentially re-configuring your weapon.

There are 2 main types of blank adapters available on the market currently.

Danish Surplus / Military Surplus
Threaded barrel set screw

 

1.) Danish Surplus / Military Surplus

Photo from Sarco-Inc

 

How does this attach: This adapter twists onto the barrel, and is held around the front sight with spring tension

Adjustability:  This adapter is not readily adjustable.  It could be made adjustable with significant modification.  It would need to be drilled and tapped for a set screw.

Safety:  This adapter is not designed to use modern reenactor .30 carbine blanks.

This adapter was designed to use red plastic cased blanks produced by several NATO countries, notably Norway.   These red plastic blanks are SIGNIFICANTLY weaker than the current production blanks.   

I do not consider these blank adapters safe for use with current production blanks without modification.  

Additionally, this type of adapter was designed to fit on the barrel with milled or thin cast front sights.  There are thee types of front sights, Milled, Stamped and Cast.  The adapter WILL NOT FIT PROPERLY ON STAMPED FRONT SIGHTS. The adapter may fit on some cast front sights properly; conversely it may not fit on all cast front sights.  Some cast front sights are the same dimensions of the stamped sight.  Many WW2 production sights were stamped, keep this in mind. An ill-fitting adapter is unsafe to use. 

Here is a photo detailing the 3 types of front sights.

 

Aesthetics: This adapter has a large visual impact.  It significantly extends the length of the barrel and is easily seen.  You will most certainly remember and be able to quickly see if the adapter is on the rifle; there is no confusing this for anything else.

Cost: $10-25 Online.

Sarco - $9.95  http://www.sarcoinc.com/m1c.html

Tools needed to install / maintain:  None.

 

2.) Threaded barrel set screw

 

How does this attach: This adapter directly screws into the muzzle of the barrel.  The barrel has been drilled, then internally threaded with either a 3/8ths inch NC (national coarse – 16 threads per inch) or 3/8ths inch NF (national fine – 24 threads per inch) tap.  Screw in correct aperture set screw and tighten with Allen wrench.

Adjustability:  This adapter is readily adjustable.  This type of BFA utilizes a common set screw that has been drilled with the desired size aperture.  The number of plugs and size of apertures may vary with who blank adapts your rifle.  This is a permanent modification to your rifle! If you need additional size plugs that aren’t provided by whoever adapted your rifle, you must purchase and drill them yourself (this is a common hardware store item, see the M1 carbine Blank Adapting instructions for more info).  If you lose the set screw, or need a different size aperture, you may be in luck if others in your unit use 3/8 set screws in their weapons and may be able to borrow one. Make sure to know whether or not the set screws are NC 16 or NF 24, as this makes a big difference, they are not interchangeable.

Safety:  I consider this type of adaption to either be the best or the worst.  Why the best and the worst? It all depends on who does it, and how it is done.  If done properly, this can be one of the safest, most cost effective methods and actually improve your rifle.  If done improperly, it can be very dangerous, and destroy a barrel, and potentially the rest of the weapon.  A properly done job will have the barrel being drilled true to the axis (perfectly centered) of the bore, which will re-crown the barrel, and allow for a consistent amount of metal remaining for the threading operation.  An improperly drilled barrel will be off the axis of the barrel, or potentially hogged (hole is ovoid and not perfectly round).  The threads must be deep enough so that the entire plug is countersunk into the barrel, with a few threads additional in case the screw begins to work its way out.   This process can either leave a barrel as shootable as it was before the adaption if not better, or just totally wrecked.

Remember - Adjustable is good!

You can drill more set screws as needed, and they should be inexpensive ~25 cents per plug.  If you leave the screw at home, or Allen wrench, you might be out of business for the day, unless others in your unit use set screws and can loan you something that works.

In the event of a catastrophic failure these adapters may be sent down range as a projectile.  Set screws have a tendency to loosen over time, make sure to check and tighten the set screw before every use.

It is good practice to remove this type of blank adapter after every use, not only for cleaning of the rifle, but to ensure that the plug does not corrode or fuse itself in place.  Additionally, since this adapter is not visible at a glance or looking at it from the side, it is a good safety practice to remove it so there is no chance of accidentally leaving the set screw in when going to live fire the rifle.

Aesthetics: This adapter has a minimal visual impact. It maintains the original gas cylinder lock and profile of the barrel.  It is virtually invisible except from looking down the barrel.  This is a permanent modification, and the threads are visible at the muzzle when a set screw is not installed.

Cost: Varies.

The cost can vary – gunsmiths can charge in excess of $100 to do the modification, to people in your unit may be able to do it for virtually nothing.  Take the time to ask questions as to how the process is completed to meet your needs and desires.

Tools needed to install / maintain:  Allen wrench

 

 

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