Whelanlad, back in the day when the second dump of M96 and M98 Swede Mausers came into Canada, you couldn't find ammunition or cases to save your life.
There was some old DOC ammo and a bit of surplus that had been pulled apart for the components, but it was all Berdan primed, with corrosive primers.
When the surplus dried up, there was nothing, and none of the manufacturers in North America were making it.
I had purchased several of both models and really came to appreciate what they could do, with ammo they liked.
I had read about the Boers in South Africa having an ammo supply problem and how they contacted a manufacturer in Germany or Belgium to manufacture ammunition for their M93 rifles originally chambered for the fine 7x57 cartridge.
It was a huge order, and the Boers were short of money, so they took a "deal" where the manufacturer had a large quantity of 7.65x53 cases in storage that they wanted to move out of inventory. So they resized all of the cases in and ended up with an overall case length of 54mm, and a 7mm case mouth diameter.
They did some testing and felt they were safe to use in the 7x57 Boer rifles. Those rifles were made for military purposes, with rather large chambers. They sold this ammo to the Boers, and it created some issues, mostly because of the generous "freebore." There were issues on the battlefield with Kabooms.
I decided to do something similar, with 308 Winchester cases. and came up with a cartridge with a slightly smaller base diameter and short neck when resized, trimmed. The overall length of the cases was about 2 mm shorter than the original 6.5x55 case called for and well under minimum length.
I shot a lot of these cases without incident, but I wouldn't recommend this unless you're desperate for components.
I eventually was given several hundred "blank" 7.62 Nato cartridges, and these could be trimmed, neck resized, and fireformed to proper overall case lengths.
Some people will moan and wail about the undersize rim/base diameter, but when fireformed, all was well.
The issue with having cases with less than minimum length is twofold.
One, the shorter case neck will allow part of the chamber to be exposed to ignition gases, which really isn't much of an issue IMHO.
The other issue, which is what the Boers ran into, is how much "freebore" will your rifle have with the bullets you intend to load.
If there is too much freebore and the diameter is generous, under certain conditions the bullet can cant before entering the leade, which could lead to a kaboom.
In your case, where you will be only a few thousandths under the minimum spec, IMHO, there will not be any issues to worry about, other than it may have a negative effect on accuracy when the bullet enters the leade after leaving the case mouth.
Some firearms, such as Tikka, have very tight freebore diameters to the leade, which allows short bullets to enter the leade concentric with the axis of the bore.
If you have a rifle with close to or even right on maximum spec diameters, accuracy may not be up to your needs.
Back in the early days of metallic cartridge design, "loooonnnnggg" necks were the norm, as were long for caliber bullets.
The reason the necks were long was to hold the bullet true to the axis of the bore by holding the bullet until it established itself in the leade.
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