So I have done a few write ups on various DD subjects posted to the NFA guns Facebook. Just answering some of the common questions I get and having a conversation. I will cross post over here for the non Facebook people
Let’s talk 20mm. I get a lot of questions regarding various 20mm guns so I am just go to pass on a little knowledge I have accumulated over the years. I consider myself reasonably knowledgeable on the subject but always learning. Yes I do have a few biasses.
The Lahti: Lahti’s are probably the most common and in my opinion undervalued. Chambered in 20x139. They are a fun, simple gun. They are pretty rugged but not super high quality. Kind of like a big sten. They are pretty hard on brass. Case mouth gets beat up on extraction. Recoil is very manageable. When my daughter was 15 she put 15-20 rounds down range in semi auto mode with no issue. Barrel is pretty much fixed so it is kind of difficult to move around. If you found one with a demilled barrel they can be chambered in the 20mm lahti/Vulcan. Basically the lahti/vulcan is a 20mm Vulcan that has had the rim machined to match the the 20mm lahti so no modifications to the bolt face. This will also insure you do not load a 20mm Vulcan in to the lahti as the Vulcan is higher pressure than the lahti. Mag capacity is reduced to 7.
Solothurn: the solo is the nicest of the 20mm guns. Also chambered in the lahti 20x139. It is a beautiful machined gun with almost every piece on the gun serial numbered to the gun. It is as nice as the best of the Swiss made guns. Typically solothurns will cost twice as much as a lahti. They break down so they can easily be moved in a car and easier to store. Because every part of the gun is actually serial numbered and fit to the gun spare parts are way more difficult. It is a pleasure to shoot.
Hispano: full auto 20mm chambered in 20x110. Closed bolt auto cannon. They are primarily an aircraft gun so if you want to shoot it off the ground you pretty much build a ******* mount and fire control. There are like 20 different variants with some parts being interchangeable but not all. Makes it a pain in the ass when you find a pile of parts and have no idea what varient they go to. There are post samples and transferables floating around. Ammo is tricky. Cases are available but typically require a lot of work. I hate autocannons.
Oerlikon: another full auto 20mm. Fires the 20x110 Oerlikon. Slightly different than the Hispano case. Advanced primer ignition gun. Like a big Mac. They are super hard on cases and typically blow the mouth out after firing. Oerlikons are a naval gun and typically mount and cradle is harder to find than the gun. Cases are difficult because they are damaged after firing. There are transferable and post sample examples. I hate autocannons
Carl Gustav 20mm recoilless: if it was safe this one would be the coolest. The precessor to the recoilless guns and bazooka. There are a handful of guns and live ammunition unfortunately the ammunition is 80 plus years old and there is no room for error. Powder breaking down could be a major problem. Light weight gun. Huge case. Fantastic back blast. Extremely difficult to reload the ammunition and internals have a life span. As you shoot the gun and wear the internals the gun begins to recoil forward. Guess that is opposite of recoil. Maybe we call it coil
Anzio Ironworks: bolt action 20x103 Vulcan The most modern on the list. Simple bolt gun. Barrel unscrews so it is easy to move and store. Fires the easy to find vulcan round. Don’t believe they are being made anymore with less than 100 made. If you brake a part a new piece can probably be machined without loss of value on the gun. Also can be suppressed but who buys a cannon to make it quieter?
Riker 20mm: Mike Riker build a handful of 20mm guns based off a large pressure test receiver. Simple falling block design with spring recoil system mounted on the soklov wheeled mount. Has a lanyard slap
trigger. Looks like a small cannon. The most cost effective way to get in to 20mm world. Easy to shoot fun for all ages
Vulcan/m39/mg151/mk12/etc. not going to get in to these unless someone has real questions
Ammo: remember you will be spending real money on dies and a new press. Vulcan dies are the easiest to find. There is pretty much one person that makes all the big dies. Sometimes it takes months to get them. Remember most of the cases are berdan primed and will have to be converted to boxer primed. 20mm Primers are currently a problem. Not a lot available. 50 primers can be used but require a 50 primer pocket and usually
A black powder booster to light a full load of powder. Vulcan projectiles are pretty common and need to be slightly modified to work in the lahti. Also note they are not all that accurate. Military standard us 3moa. Not a high ballistic coefficient either. Designed to put high explosives over a large area.
Vulcan cases are pretty common costing between $2-6 a piece. Hispano $5-10. Oerlikon 3-10, Carl G 25-50. Thé 20x139 brass is $20ish. There is some new machined steel and brass cases that are nice but have a limited life compared to drawn brass cases.
Live ammo can be found for all of the above. The Vulcan is electric primed and bullets have one hell of a crimp. You pretty much end up cutting the live rounds apart to get the projectile off and maybe salvaging the powder. In my opinion they are only worth the value of the projectile. 20mm lahti run between 40-70 each depending on who’s selling. Most are AP. Live Hispano and Oerlikon 15-30. Recoilless 100-150.
Hope this book explains a few things. I am sure i am forgetting a few things but this is a good start.