I've used various metals for caboose parts, including brass, phosphor bronze, nickel silver and stainless steel.
I've also used these metals in etchings, machined parts, investment-cast parts, and raw stock.
And now, I'm designing 3D models that allow me to have even more grab, railing and ladder details at the cost of being a bit thicker than either etched or wire parts.
So, what's more important?...near scale grab and end railing diameters or more details??
When looking at prototype photos of caboose (UP mainly) grabs and railings, as well as visiting preserved museum pieces at the Utah State Railroad Museum in Ogden, where I've taken hundreds of photos and measurements to incorporate into my UP caboose models, it's pretty plain that actual scale-sized grabs and railings are most likely impractical in N-scale, with many railings/grabs being in the 3/4" dia. neighborhood depending on how many coats of paint are on what I'm measuring. Prototype photos show these details to be very fine...much finer than any wire or etched N-scale versions I've ever applied to my models.
3/4" diameter translates into 0.00468"...or rounded off to 0.005" in N-scale...not including another mil (if you're lucky) for paint thickness, sooo...logically, 0.006" N-scale grabs SHOULD look prototypical, but they don't, so my memory is probably failing me as to the actual diameter of the real details.
However, for what kind of metal works "best' for grabs, ladders and end railings for N-scale cabooses, cars and motive power, since I'm not ham-fisted and handle my models with reasonable care, I've never found a durability problem using any of the aforementioned metals, and I used brass & phosphor bronze for the majority of detailing on my cabooses since both metals are hard enough, readily available, easily bent, and easily soldered.
I've also used NS etchings for some details, and I don't have a problem with that metal either, and I don't find a discernible difference between it and brass/bronze parts in any aspect other than availability.
I regularly use various alloys of Stainless Steel stock for specialized applications, particularly for unpainted grabs on my passenger equipment to represent prototype Nickel-plated grabs on passenger motive power and some premier passenger cars...and it works GREAT, and also looks great for shiny silver grabs.
Lately, I've been using it (0.006" polished Stainless Steel wire) for grabs on models that get painted, but I break the polished surface with 400 grit sandpaper, simply pulling the wire through a folded piece of sandpaper a few times before cutting and bending. Also, I've never had a problem with cutting it with my not-hardened flush cutters.
What I like about stainless for painted grabs, is that if the paint wears off a bit for cars that are regularly handled, the metal underneath looks like steel, rather than yellow brass/bronze since prototypically that's the way it is.
If the need arises for soldering stainless stock or etchings, which happens on my scratch-built D-Type signal masts (made of Surgical Stainless Thin-Walled Hypodermic Steel), I just use Superior No.71 Stainless Soldering Flux Paste, which is readily available here:
https://www.hnflux.com/page21.html at H&N Electronics Soldering & Brazing Flux and makes soldering brass/bronze, NS to Stainless simple. I also use their 96/4 Tin/Silver Silver-bearing solder since it's 5 to 6 times stronger than "regular" old electrical solders.
Frankly, I've NEVER used a "primer" for painting any of my metal models. For my metal stock I'm going to use for fabricating grabs and end-platforms, I simply pull the wire or shapes through 400grit sandpaper a few times to scratch it sufficiently to give the paint something to grab on to, making sure that my assemblies are completely wax, grease and oil-free by removing these residues with 91% IPA and generous applications of Heptane (Bestine/Beacon-Solvent-Thinner) which does not affect plastic at all.
In the past, I've brush-painted my grabs and end-platforms on my cabooses, but this adds considerably to their diameter, as much at 3 mils (or more) depending on the paint, which sort of nullifies making grabs out of 0.006" stock when the end-product will be near .010" or thicker after applying paint with a brush.
Now, I airbrush them...if possible BEFORE installing them into their matching mounting holes, but if not, then carefully masking them off before painting the car body, then, when the car body is thoroughly cured, removing the masking from end-platform railings/ladders, cleaning with Bestine, masking the car body (wearing Nitrile gloves) and airbrushing the attached end-platforms....and I do not use any primer whatsoever...and I've NEVER had a problem with paint adhering to my metal constructions or models if I've run the stock through 400grit sandpaper before cutting, bending, soldering and assembling...then thoroughly cleaning with a powerful, yet plastic-friendly solvent.
Photo (1) Here's a pic of one of my superdetailing projects, using 0.006" brass wire for the grabs on this old Hallmark "Welded UP Caboose" model, converting it into a pretty accurate model of a UP CA-8...notice the relatively small diameter of the grabs on this unpainted progress shot...
When painting the model, I airbrushed it with Scalecoat II, baked it at 175deg for half an hour, then, using Scalecoat II, I brush-painted the grabs and end-railings...
Photo (2) Here's the nearly-finished model with its brush-painted grabs and end-railings. The grabs & end-railings are noticeably thicker, and the details on the investment cast portions are obviously obscured: 
Although I thought the model looked much better than the stock-box model with it's hugely oversized grabs running boards, I never was happy with the increased diameter of the grabs and end-railings on this model, with their one coat of airbrushed body color paint, and then another coat of brush-applied red paint.
Although not detailed to the extent of my Hallmark brass CA-8, I kit-bashed a Micro Trains "Wooden Caboose" into a model of an actual UP CA-Class caboose, removing and replacing the cast-on grabs with bent 0.006" brass ones...but, since these prototypically were the same color as the body.
Photo (3) Kit-bashed MT "Wooden Caboose" turned into a specific UP CA Class caboose with its cast-on grabs removed and replaced with 0.006" wire, then airbrushed:
You'll notice that the grabs on the freight car red MTL CA-Class UP caboose, with a single coat of airbrushed paint are much smaller in diameter than the previous airbrushed-then-brush-painted grabs on the Hallmark CA-8.
Although I'm sure there are differences in the way various metals accept paint, in my experience, using good cleaning procedures, good handling procedures and quality model paints...I find no difference in the way my models of various construction materials and build-techniques retain their painted surfaces...and I never use primer, which adds thickness, obscures details, adds an additional step and, since I have never had a paint problem on my metal models, would not have "improved" adhesion nor durability on any of my painted project over the last 55+ years.
As far as "profile" is concerned...meaning a rectangular cross-section vs round... Sometimes, in N-scale (and smaller) it's near impossible to actually bend up grabs or end platform details...such as "Ladder Grabs" on the noses of E and F units with wire, and only rectangular, etched grabs are either available for properly representing these complexly bent style of grab-irons. So, I live with the rectangular cross-section. The same goes for caboose end-platform cross-sections, because very often, the metal shapes for these railings are a combination of rectangular (or other metal shapes) that transition into round cross-sections...so BOTH square and round cross-sections are prototypical, but only one profile is incorrect since both rectangular AND round profiles is what is correct.
Typically, grabs on the sides of the end-railings...and vertical supports, have a round cross-section, with horizontal portions and ladder sides being rectangular. Ladder rungs can be either rectangular or round, depending on the specific prototype. If there are other attachments, such as air pipes, vertical brake wheel shafts...these are round. Other attachments, such as gussets, platform mounting girders, brake wheel housings and supports...these are shapes made from sheet metal and are not round.
Sooo...making end-platforms more correct, to incorporate both round AND rectangular AND constructed non-round components can be accomplished by making an etched "kit", allowing insertion of round wire into appropriately sized holes in the etching, and engineering housings (with half-etched bend lines) to accept round wires and/or mounting tabs/holes on the rest of assembly, all to be soldered together.
In my case, the most obvious use of a "kit" would be in two positions on my end-railings, these being (1) the ladders, with thin profiles (the thickness of the non-etched metal) and the profile and thickness of the side profile, with mounting holes where the round or etched rectangular rungs will mount, with the ends being snipped off after soldering and representing rivet-ends or bolt-heads on the outsides of the ladder rails. (2) The second location would be the horizontal components of the end-railings, the top of the railings being rectangular, with holes where the vertical round wires protrude through and are bolted on, and the large, horizontal end-girder...a "C" channel with holes where bottoms of the round vertical components go through and are bolted securely...with rivet-heads where the back of the "C" channel is bolted to the steel frame, and where the platform steps are bolted on.
If I was willing to pay for precision etched details for my cabooses (which I am) I want to use the potential of the medium, which allows me to design a "kit" that gives me a much more prototypical "look" than a mere one-piece bend-up etching gives me, and I'll have both rectangular and round components where they would prototypically be.
Additionally, it would be quite easy to etch assembly/positioning jigs for holding and spacing the kit components when assembling and soldering...in the same fret.
Yes, both designing and assembling this "kit" would take a bit more time, but the results could be phenomenal...and it shouldn't cost much more than a simple one-etch fret, except if rivet details and bend lines are wanted.
I've thought about this a lot, and now that I've found a professional etcher only a few miles away, this is one project that will finally come to fruition in the near future if my resin 3D prints turn out to be too large or too fragile.
Hope this gives you something to think about...
Cheerio!
Bob Gilmore
