4 replies to this topic

[sevengunner]

I've just examined a Savage 1928 with what appears to be the original du-lite finish. However, when angled just a certain way in daylight, a purple streak appears to run diagonally across the rear of the trunnion area on both sides of the receiver.

Upon close examination, there does not appear to be any obvious re-welding of the receiver. The raceways on the inside of the receiver are clean and un-interrupted with what appears to be perfect continuity in the original machining marks. There is not any porosity or uneveness in the receiver surfaces.

I have checked the paperwork, and it indicates Auto Ordnance / Bridgeport CT as the original manufacturer -- but we all know that BATFE often does not check for the accuracy of this kind of data.

Any ideas on what the "purple" discoloration could be:

Normal result of factory heat treatment in the trunnion area?

Residual heat discoloration from early dewat welding to plug barrel chamber?

Botched up cold blue touch-up on surface scuffs that should have been left alone?

Normal aging highlighted, over time, by exposure to environmental moisture?

Extremely skilled reweld on expertly joined receiver halves from post war dewat?

Thanks,

Sven

[reconbob]

Having read your description I'd say you'll never know for sure. When doing black oxide (i.e. bluing or
du-lite) you get a purple color when the steel is not heated to the correct temperature, or not left at that
temperature long enough. A good example would be some rifles where the barrel blues sooner than the
receiver, and you have to leave the assembly in until long after the barrel is ok to get a match. If you have
this discoloration its because you've got a variance in the molecular structure of the steel. It could have
something to do with carbon content, but usually the older Thompson receivers are lightly hardened
from approx the middle of the actuator slot to the front, not just in one spot.

....if the receiver was heated with a torch for some unknown reason you would get a discoloration, but
unlikely it would be a streak....OR....

...this is a long shot - the receiver may have been partially immersed in the bluing salts and had one end
done, then flpped around and had the other end done. The streak could be the overlap...

Usually the machining marks are a good guide, but people are very detailed and resourceful when they
want to be. If the exterior was polished before bluing - it could be that someone just did a perfect job of
covering their tracks....



Bob Bower

[SecondAmend]

Bob,

Thanks for an informed explanation.

Such posts are appreciated.

[amafrank]

Bob pretty well nailed most of the reasons there. Differences in hardness can change the color and welds do change the hardness. I can also say though that I have seen a number of thompsons, maybe 4 or 5 that have some discoloration in the area between the magwell and the front of the receiver. One of them had fairly pronounced darkened streaks running from the ejection port to and through the inspectors mark on the left side of the front of the receiver. The marks were all clear and I knew the history of the gun. It was definately not a reweld. It was in a museum and had been donated there by the GI who carried it in the south pacific
I am leaning toward Bobs explanation of double dipping the receiver in the bluing salts. Funky overlaps. . .

Frank

[sevengunner]

Bob & Frank,

Thank you for taking the time to share your valuable insights, experience and knowledge!

Sven