Rubber Gun Plug ID Help

[whiskydown]

What are these for? Packaged 1953. 
 

Plug side is tapered and measures 72mm to 74.5mm, too small for 3”. 
 

 

[whiskydown]

Two more pics

[opus5150]

Pretty sure these are made to plug the 40mm AA guns while at sea.  Keeps water out of the barrels and can be fired through when needed.

[whiskydown]

They could fit the cone at the end of a 40mm bofors. 
 

The package says gun blast tube plug. I think blast tube is an aviation term for a tube on a barrel protecting the plane from muzzle blast.

[whiskydown]

Someone in an artillery FB group said they were a 40mm bofors gunner and the barrels had canvas covers, they never saw a rubber plug. 

[917601]

On 12/6/2021 at 10:01 PM, whiskydown said:

Plug side is tapered and measures 72mm to 74.5mm, too small for 3”. 

It would help if you could write down ALL the numbers /letters on the packaging. Your picture is blurry. That said, the plug size matches closest to a 75mm or 76 mm ( 3” inch gun). It is not necessarily to small or large as a gun bore size does not take into account the brass/ bronze driving band ( which makes the projectile much larger diameter at the driving band). Make sense? Example, a 75 mm gun projectile body will be 75mm at the base, 80 plus mm around the driving band. The barrel at the muzzle  will have two dimensions, lands will be smaller than the grooves. The key is running the nomenclature and numbers.

[whiskydown]

I tried it in a 3” M5 barrel and it’s too small.

 

Package info:

 

S.O. NA-181 EXH. A MODEL

ITEM 1465-100 QUAN. 1

CONT. NOa(s)51-642-1

PART R94-NA-181-61155

PART NAME: PLUG-GUN BLAST

TUBE EXPENDABLE

[robinb]

According to the contract information they are navy aviation related.

[Quest Master]

Contract NOa(s)51-642-i (third line of text on package) is the government contract number with North American Aviation for the NA-181 Project, FJ-2 "Fury" Navy/USMC fighter aircraft.