Only ever handled the 30mm ,buddy just showed me this and asked if I could maybe find something out about it. Apparently this friends cousin or something
Sound like it has powder in it but no primer and looks like it's been hit multiple times so I'm thinking it's just a dummy filled with sand for weight ?

it was my understanding they don't have primers because they are electronically set off , primers are a major weak spot in a case for pressure as well as another place to let moisture in

add in triple based propellants and not typical small arms stuff need the different ignition

since 20mm are mostly for gun instillations like on ships , in air craft , and such power to run them isn't an issue

even some of the crew served stuff that does have primers has a electronic ignition as well because hang fires are not good in a gatling gun

ahh also they may be considered a destructive device as they are a rifle over 50 cal so I wouldn't expect anyone to pipe up with their collection of 20mm rifles

They are electric ignition as Greencountypete said. That looks like the 20mm valcan used in the mini/gatling guns on aircraft. There are a few shoulder mounted rifles floating around but not very many. The tip in the gray color indicates armor piercing rounds. They came in the gray(armor piercing) blue( dummy) red ( tracer) and green ( exploding) to my knowledge. Friend of mine was airforce and I have a few decom rounds in my collection. Talking with buddies they can really eat up whatever is on the receiving end.

These pictures are of a 20MM Dummy round that I traded for 1977 while deployed. The air winger told me they used them to set the guns up on the Cobras. This one is marked 20 MM Dummy round M51A.

Knew a gunsmith back in the 70's had a gun shop in CO. He had an anti tank gun from WWII. If my memory is correct it was Finnish. Had a stock for each shoulder and was about 8 feet long. It was fired prone. Had two rockers on it and could be pulled over snow. Thing musta weighed 100 pounds. If I remember right there were primers in the case. Was an FFA item and so was the ammo. No clue where he got it. I shot it a couple times. Recoil was manageable with all that weight and a stock for each shoulder.

He collected big stuff. Had a double rifle I thought when I saw it was a shotgun. Something nitro express. That one hurt when you pulled the trigger.

In Nam our Cobra gun ships had 20 mikes on them along with a whole other assortment of weapons. Some of the C model Hueys were fitted for them as well. When fired as statee above electronically it could slow the chopper down quite a bit.

Bryce

Handled a lot of 20 and 30 mm while I was in the USAF. Hated sorting those by lot numbers. Would have to cut a stencil and paint the nomenclature along with the lot code and qty.
What a pain. We'd get a 1 or 2 rounds with the same lot number and we'll they usually ended up not passing g inspection due to a loose projectile. A good rap on the cement floor made it so. IYAAYAS

Very interesting thanks for all the information everyone I'll tell him not to shake it lol

Boss Paul was a BB Handler, check with him.

Have had one marked 20 mm Dummy for 50+ years, looks like Bob56's

It's been 53 years since I was a BB stacker (461). Cross trained to EOD (464) in 72.

I really can't tell which 20mm that is. It could be AP or it could be HEI.

What's this critter I have?
My mics ain't handy at the moment but looks to be 1-3/16th to 1-1/4 bore.

The HE rounds always reminded me of a load of fireflies thrown into the jungle