AA gun "coppered"

[Rockdoc]

I've come across a throw-away comment in the War Diary of 90th AA Section where it says "Gun lapped owing to coppering." Given that lapping is an engineering finishing technique using very fine abrasive, is the comment referring to the careful removal of a build-up of copper from the driving bands in the rifling?

The term didn't appear in the Beta Search so I'm wondering whether this is a common problem or not. It's the second time coppering has been mentioned in one of the Diaries I'm working on, though not at the same Section.

Keith

[TonyE]

Yes, it refers as you rightly presumed to the copper fouling of the barrel from the driving bands of the shells.

It is a very comon occurrence; I do not know whether they had such things in WWI, but de-coppering rounds were developed later to "scour" the bore and remove the coppering. It was also prevalent in machine guns.

Regards

TonyE

[Rockdoc]

Thanks, Tony. When you lap something you tend to use a tool that is very, very close to the size you want to finish the job at so my guess would be that there would have been a tool on a long pole that could traverse the length of the barrel and was a close fit to the bore or, if that was where the problem built up, to the rifling grooves. The reference in the Diary indicates that the work was done on site rather than at the IOM Workshops but whether it would be done by the gunners or by Workshops staff it doesn't say, which probably means they did it themselves. If it was a common problem then the gunners would undoubtedly be trained in the technique. Either way, it took hours of work to complete it.

Thanks again,

Keith

[johnreed]

This was and is a problem which occures today, this is aliviated by the inclusion of foil sheet sewn into the charge bag on which vapourises the copper deposite.

John

[Rockdoc]

Burning foil sheet removes copper? I wonder how that one works? Thanks for the info. It's all grist to the mill.

Keith

[welshdoc]

http://www.reade.com/eastern-region-(usa)/769

[Rockdoc]

Ah! Right! A Thermite reaction would explain quite a bit. The high temperature would certainly soften deposited copper and might allow the minute traces left after each firing to be swept out with the exhausting gases but, importantly, the brief exposure of any given point in the bore would prevent the hardening of the steel being affected and increasing the wear rate.

Keith

[welshdoc]

Sorry about the link but no comments but the family just arrived and I had to be barman. Im guessing its the oxidization reactions which are important and Im presuming its alluminium fiol used. Anyway back to the drink. have a good christmas and dont get too oxidized

[Rockdoc]

Thanks again, Doc. Aluminium, as the article says, is extremely reactive - less so than magnesium (or phosphorus and sodium but you don't see them as metals outside a lab) but much more than most metals although even iron can do it under the right circumstances. Going back 40 years or so to O-level Chemistry, we had direct combination of the elements demonstrated to us using iron filings and flowers of sulphur. They were mixed and heated in an ignition tube and, once started, the reaction became very vigorous and the glowing mass of iron and sulphur fairly soon melted the glass tube and ended up on the asbestos sheet underneath. Pyrex melts at about 700C, btw. By comparison, a Thermite reaction can melt steel - at something over twice that temperature - if the components are placed against it. Our teacher had, in previous years, demonstrated the same thing with finely-powdered aluminium and sulphur but he'd been banned from doing that by the time I was there because it used to explode and blow all the glass out of the fume cupboard.

Health & Safety? What was that?

Keith