40mm Bofors Question

[Godwin Hampton]

Roger,

I find it inspiring that 70 years after its' launch, there is so much awe and respect for the Bofors L60. Good engineering will live on after the engineers have passed on!

[Mats]

It's always nice to hear that someone can make sense of my writing.


Here's a cross section of the gun housing, which shows the feed pawls, the two feed rolls and the loading tray.

[herr-pear]

Mats:

The cross section drawing REALLY brought everything into focus for me.

You have my everlasting thanks.

In return, the only thing I am reasonably knowledgeable (although not an expert) on that fits this forum is the Bren Gun. I have fired them and have a complete but non-operational one, and have spent much time in study. If I can be any help on that subject, please ask.

Roger in Vegas

[Godwin Hampton]

Roger,

There are many parallels between the Bofors and the Bren, and not just that they both start with a 'B'!

The barrel cooling system, the design and engineering quality, the fact that they were adopted by the British Armed Forces in time of great peril and then used into the Seventies, etc., etc.

Do you happen to have a complete list of all the spares and tools which would accompany a Mk.1 Bren? Especially interested in all the bits that were supposed to be in the spare parts tin.

[herr-pear]

Godwin:

I have answered your question in a Private Message as that would be Off-Topic for this thread.

Roger

[Rob Fast]

Yes, my gun barrel is still pinned and deactivated, but capable of firing blank 2 oz. black powder cardboard plug blanks. I have cut off some old Bofors shells to a 6 inch length, loading by hand through the top, no rammer involved. If I would use a full length shell and the rammer with no tapered head inserted in the shell, it just gets caught up and bent up in the barrel opening. I am having a heck of a time getting the shell rammed all the way into the barrel, so the breech face can clear the primer on closing and firing. Why are things so tight? Have the old brass shells expanded at their base? The shell has to be rammed into the hole to the max before the breech face will clear, and the extractors release. Maybe thing are just not clean enough down in the hole? Any thoughts? Thanks Rob

[Mats]

Rob

Let me first say that I don't own one and I never worked with the Bofors 40 mm on a professional basis, but I'm a member of historical association that operates two L/60. I have fired maybe a dozen blanks at various events.

The blanks we have used, have been official army issue blanks. They work just fine if you first operate the hand lever and then push the blank in the case discharge opening, and make sure that you hear the click when the rammer levers engages the rim of the case. These blanks does not generate nearly enough recoil to operate the gun, so you have to repeat the procedure with the hand lever for each shot.

As far as I understand, the blanks are made from ordinary used brass, filled with about 0.4 kg black powder, then topped up with saw dust and sealed with resin or something. I belive that the secret is that the mouth of the case is crimped to make the opening maybe 30 mm in diameter. When fired, the cases opens up, so we haven't been able to reuse them. But as our supply of blanks are drying up we now plan on start crimping the used blanks and reloading them.

[Alex Blair (RIP)]

Originally posted by Rob Fast
Yes, my gun barrel is still pinned and deactivated, but capable of firing blank 2 oz. black powder cardboard plug blanks. I have cut off some old Bofors shells to a 6 inch length, loading by hand through the top, no rammer involved. If I would use a full length shell and the rammer with no tapered head inserted in the shell, it just gets caught up and bent up in the barrel opening. I am having a heck of a time getting the shell rammed all the way into the barrel, so the breech face can clear the primer on closing and firing. Why are things so tight? Have the old brass shells expanded at their base? The shell has to be rammed into the hole to the max before the breech face will clear, and the extractors release. Maybe thing are just not clean enough down in the hole? Any thoughts? Thanks Rob

Rob..
Get your brass preped for priming and loading...
Before you are ready to prime aneal your brass casing..Get it cherry red...let cool and then either ram the cooled casing into the breech or turn out a dummy breech block and size your casing on the bench by pressing it into the breech mold...
use some G-96 on the casing and pop it out after sizing..then prime and load it and it will slide right into the breech..All brass has to be resized before reloading..anealing it makes it easy and keeps the brass from cracking...
(Even if it is cracked ,repair it with bronze welding rod...)
It is not worth repairing small casings but big casings are worth it..I wouldn't suggest repairing cases for full pressure live rounds but low charge blanks should be ok...

[Godwin Hampton]

Rob and Mats,

Handloaders who reload fired cartridges first re-size them by pressing them into special dies. Various companies produce dies for a whole variety of cartridge designs, some long obsolete but requested by reenactors.

The pressure of the charge on firing expands the brass, but it immediately contracts enough to free itself from the chamber for extraction. It might then not fit into another chamber with less wear in it. If re-used without re-sizing, it might even jam in the chamber!

Even blanks, with their lower pressures, still have a large area of brass to work on, so the force is still considerable.

I am positive that the commercial die manufacturers like Lyman do NOT make them in Bofors L 60 size! What can be done is to try and obtain the chamber part of a cut-up L 60 barrel, and turn the cartridge rim recess in a lathe to make it deeper. The cartridge is then forced into the chamber, using a hydraulic press. The press will probably also have to be used to push it out again.

To feed propely automatic weapons need the projectile to guide the front end into the chamber. In fact blanks made for automatic rifles have a cartridge with a neck as long as the complete round, crimped after filling to resemble the bullet.

For the Bofors to feed automatically the cartriges should have a fair amount of sand in front of the charge instead of the sawdust. Roughly the weight of the projectile, and with a fairly powerful charge. Remember, action and reaction are equal and opposite. Check first if this can be done legally! Why use black powder, and not smokeless to avoid the corrosive by-products?

[Rob Fast]

INST. TESTING STRAIGHTNESS OF BORE NO 4 MK ll
COLLIMATOR
FOCAL LENGTH 6 INS.
DISTANCE BETWEEN BEARING CENTRES 6 INS.
M.S.G. 1943 REG. NO.56 C

WHAT WAS IT'S APPLICATION? DID IT FIT INTO THE BREECH? MISSING THE EYEPIECE? Thanks Rob

[Brad Mills]

Rob and all...

Does any one have photos of "Blank" rounds for the 40mm Bofors? I know the ones Gunner had made up were full length casings, not short ones.

What can one use for primers?

[pekelney]

See:
http://maritime.org/doc/index.htm

40 MM Antiaircraft Gun, OP 820, 1943. The maintenance manual for the dual Bofors 40mm gun.

40 MM Mount Mk 4, OP 1329, 1947 describes the very widely used quad mount for the Bofors 40mm gun of WW II.

40 MM Antiaircraft Gun, TM 9-1252, 1951, is an Army service manual for this widely used single Bofors 40mm anti-aircraft gun of WW II.

40-mm Automatic Gun M1 (AA), TM 9-252, 1944, is an Army service manual for this widely used single Bofors 40mm anti-aircraft gun of WW II.

40-MM Wet Mount Assemblies (Single), OD 5853, 1947, describes modifications to the Army single Bofors 40mm gun for use on submarines. The manuals for the gun are in the ordnance section below.

rich

[pekelney]

See also:
http://maritime.org/doc/#guns
Scroll down and there are 4 Bofors 40mm manuals.

rich