Chrome lined barrels

We all know that most 99s were chrome lined. How was that done? Couldn't have been a sleeve.

It was done by a process known as hard chrome electroplating.

Just mask off everything you don't want chromed. Usually wax will do or can be more elaborate. Our plating shop does selective plating all the time as part of the repair processes we use.

The main trick is the chrome wire electrode run up the dead centre-line of the bore and strung between insulators at either end. This is the ONLY way you are going to get deposition on the INSIDE where you want it.

The barrels are hung vertically in the tank and there is usually some mechanical agitation and sometimes heating to maintain a flow of the "bath" through the bore.

That sounds a bit complex and needing some skill to manage. Maybe some practice.

Health warning re. chrome plating:

One of the less pleasant by-products of hard-chroming is a nasty substance called "Hexavalent Chromium".

Th US navy has spent a prodigious sum searching for an alternative to hard-chroming naval guns. Not sure whether they have succeeded.

I had to go look...

Quote:

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Originally Posted by Bruce_in_Oz

"Hexavalent Chromium".

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Health Effects

Adverse health effects associated with Cr(VI) exposure include occupational asthma, eye irritation and damage, perforated eardrums, respiratory irritation, kidney damage, liver damage, pulmonary congestion and edema, upper abdominal pain, nose irritation and damage, respiratory cancer, skin irritation, and erosion and discoloration of the teeth. Some workers can also develop an allergic skin reaction, called allergic contact dermatitis. This occurs from handling liquids or solids containing Cr(VI) such as portland cement. Allergic contact dermatitis is long-lasting and more severe with repeated skin exposure. Furthermore, contact with non-intact skin can lead to ulceration of the skin sometimes referred to as chrome ulcers. Chrome ulcers are crusted, painless lesions showing a pitted ulcer covered with fluid.