How about these...
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The replicas we made are copied from these .50's.
This is a pretty little issue on a replica, but if you are trying to make it look like they did when it was delivered to the USAAF or how it might have looked ready to escort bombers...
The AN/M2 had a lighter barrel than the ground versions, with barrel shroud which both reduced gun weight and raised rate of fire. The end of the barrel is what we see on the outside of fighters. The barrels (at full scale) have a 0.5" ID and an OD of around an inch, were Parkerized to anywhere from black to dark grey to dark green-grey. When they were new, the bore and crown (the chamfer from the bore) were bright as a rubber plug had been inserted in both ends of the barrel to prevent phosphate coating the bore and chamber. In use with chlorate based priming used in US military ammo until well after WWII, the priming left corrosive salts on the bore. If left alone, it corroded the bore. In use, the guns were removed and cleaned after firing, and bores were scrubbed with solvents. This tended to leave the front faces of the barrels close to the bore brightened too, but not the OD. So the barrel itself should be dark grey to black, with it partially worn off on the front face.
In the photos extant from WWII, the dark metal barrels with the crown bright are visible while the front face is sometimes bright, and rarely, the OD is bright. The shround usually appears dark when new and then brightened from handling and use.
The way I would expect that the barrel would all be bright while in service is if the ground crew failed to wipe a thin coat of oil before reinstalling the gun, allowed it to rust (Parkerizing holds oil and waxes, which prevents rust unless one washes it clean with solvent and fails to put some oil back on it), and then were told to "clean the rust off that gun" and ended up polishing off the Parkerizing along with the rust. In replicas and static displays, you might indeed see hard chrome or stainless parts to make it easier to keep it looking nice.
If you want it to look like they did when delivered to the USAAF, the barrel itself would be dark satin grey to black with the bore and crown (chamfer) bright. The exposed portion of the shroud at the muzzle apprears to not have been phosphated, and so might be bright when new;
If you want it to look as it did while fighting, the front face would have some polishing near the crown and perhaps some scraping of the phosphate from the OD. Shrouds would likely have a patina as seen in the photo below;
And if you wanted it to look as it would after neglect in the field and then cleaned up later by polishing to remove corrosion (and thus susceptible to rusting quickly afterwards), you would make the barrel and bright bright.
A point in these photos - the two guns being cleaned are the same. The third gun had a different shroud as that gun set further aft in the wing for ammo feeding. The muzzle end of the barrels are not visible here - the shrouds pictured compress the coil springs when installed in the wing and slide aft along the barrel a short distance, exposing the end of the barrel. Notice the somewhat rusty look of the part of the shroud exposed when installed where it has no phosphate coating and was exposed to chlorate priming salts and the weather...
All of this is why when I walk by so many warbirds, both real and reproductions, where so much effort has gone in,with magazines, linked belts of ammo, reproduction guns, etc, I shudder bit as the guns neither look as-issued nor as they would look while fighting and being maintained in the field.
Billski
