I want to store my pistols and revolvers on my gun safe's door. Its inner surface is sheetmetal.
Finding affordable and adjustable pistol cradles is a challenge.
I considered SlatWall and the louvered steel bin hanger system but rejected them, usually because the pistol cradles available were too expensive, too deep (I don't want the pistols to hit my safe's shelving) or simply not a cradle.
The best, most flexible wall-mounted cradle was the HOLD UP at Amazon.
(
https://www.amazon.com/Hold-Up-Displays-Handgun-Storage/dp/B0764GW723?crid=2WNTHMIV2GX1D&keywords=hold+up+gun+display&qid=1540835117&sprefix=hold+up+gun%2Caps%2C198&sr=8-11&ref=sr_1_11 )
But they are $12.33 each. That would be $270 for 22 guns. Ugh.

Then I spotted the display wall behind a Sig video. It had vertically adjustable T-Slots with cradles that looked great.

Moving to eBay, I found a supplier that sold T-Slot that takes 1/4-20 hex head bolts. Four, 48-inch sections for $60. Pricey, but they work great and got here really fast. Low profile (3/8" x 3/4") and pre-drilled for mounting with flathead 6-32 machine screws,
(
https://www.ebay.com/itm/Lot-4-48-Aluminum-T-Track-3-4-x-3-8-Accepts-1-4-Hex-1-4-5-16-T-Bolts/152038683416?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 )
I mounted the T-Slots to the door with just two 6-32 x 3/8" flathead machine screws. I could add more later, but honestly, the two held fast. That way I can easily adjust the T-Slots left or right if necessary.

The cradle hooks I settled on were the Roos Small Hook from Amazon.
(
https://www.amazon.com/gp/product/B01KMBW8R4/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 ) 4 for $18.

The Tornado also work.
(
https://www.amazon.com/Tornado-00500-Small-U-Hook/dp/B0050PHTLS/ref=pd_bxgy_60_img_3?_encoding=UTF8&pd_rd_i=B0050PHTLS&pd_rd_r=6d4eac86-dba1-11e8-822f-6d69579ae4b5&pd_rd_w=na52g&pd_rd_wg=IXxiH&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=6725dbd6-9917-451d-beba-16af7874e407&pf_rd_r=FEAH6PZ2QM1E6JFHWRRX&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=FEAH6PZ2QM1E6JFHWRRX ) $6 each

To widen the hooks so they could cradle a pistol or revolver, I had to bend the steel hooks apart.
I built a simple tool from a scrap 1"x1/2"x12" aluminum bar (if you have an old Ford "F" monkey wrench, that would work too) and mounted a large Crescent wrench into my vise to hold the hook.



I now could bend each hook quickly and easily to receive a given pistol or revolver, small or large. Interestingly, almost all full-size and compact pistols have about the same distance between the web of your hand and the front of the trigger guard. Only tiny mouse guns like the Beretta Pico were shorter. The giant FN FNX 45 and the P-10 C both fit the same cradle.

I squirted black hot-melt glue onto the exposed steel and nut so I couldn't scratch the pistol. The door looks textured because I mounted some thin rubber tool box liner to the door earlier and have fussed with various mounting systems for a couple of years.
I can now safely store around 22 pistols on my small 21x55-inch safe door's interior surface. The best part is that I can rearrange the door easily using only a 7/16" socket wrench if my collection changes. Well, more like "when."

Costs:
$60 for the T-Slot
$90 for 20 Roos hooks
$5 for 3/4" 1/4-20 bolts, nuts and 3/8" flathead 6-32 screws
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$155 Total