The following is a compilation of my observations in collecting Savage 99s sporadically over the last 25 years. This is not a definitive or authoritative history. After all, given a production run length of over 80 years, there are lots of variations and such.
The first Savage 99's were rated for black powder only and chambered for black powder rounds (e.g. 38-55). Those made after a certain point in time (early 20th century) were rated for smokeless powder, but only in low-pressure rounds like the 303 Savage and 30-30. Octagon barrels were popular in the early runs, but I've not seen any made after, say, WWI that had an octagonal barrel.
There was a takedown model that was popular for a while between WWI and WWII, but it appears to have been mostly chambered for the low pressure rounds. Savage introduced a few high pressure rounds like 300 Savage and 250-3000 prior to WWII, and most surviving pre-war examples are of these chamberings. You'll occasionally find a take-down in 300 Savage, but not often.
In the late 50's, Savage jumped on the 308-family bandwagon and (with supposedly minor alterations to the receiver dimensions to improve the stength of the action) began offering 308 and 243 chamberings. Somewhere in the 50's, they started drilling-n-tapping all of the receivers for scope mounts at the factory.
In 1961 (right around the one million serial number mark) they redesigned the action to move the safety from the pistol grip/trigger to the top tang, and to simplify the production and assembly of the FCG. Early post-61 units retained the brass rotary shell holder that was one of the 99 trademarks, but by the mid/late 60's Savage appeared to have changed the rotary from brass over to aluminum. I've heard that the production of the 99 was halted for a while in the 70's, but they were reintroduced in the early 80's with a drop magazine in place of the rotary magazine (again, to make it cheaper to produce).
As best I've been able to tell, the following are the Savage 99 models:
- Model A - seems to be the standard model with standard weight barrel; barrel length varies by chambering
- Model C - I've only seen these in the Series A re-introduced version - standard weight barrel with drop magazine
- Model E - 'economy' version, all post-61 as best I can tell - missing the round counter port in the left receiver wall and with birch or maple stocks instead of walnut; otherwise identical to Model A.
- Model EG - Dunno
- Model F - the 'featherweight' model - thin barrel, at least a full pound lighter than the Model A
- Others - there are additional model variants that have Monte carlo stocks and other such discriminators, but I'm just not all that versed in them because they're not all that common.
I have never found a reliable corrolation between model nomenclature and the stock design, i.e. whether the rifle was a straight-grip or pistol-grip and/or round forearm or schnabel forearm. For example, I've had a Model A that was a straight grip and another that was a pistol grip, and they were not all that far apart in serial number. Earlier models *mostly* had schnabel forearms and most all of the post-'61 versions that I've seen have had rounded forearms, but that's certainly not a hard-n-fast rule.
The single biggest issues to look for in any old Savage 99 is barrel pitting and stock cracks in the top of the wrist behind the receiver's top tang. For whatever reason, almost every Model F I've ever seen (even those made in the late '60's) has had a pretty badly pitted barrel. Having said that, I've got four of them right now and they all shoot MOA with pits and all. The other issue, stock cracking, is a very real issue that is a function of the receiver design. Like most two-piece stocks, the majority of the recoil force is jammed into a fairly small area where the top tang mates with the buttstock. This concentration of stress leads to cracked stocks.
Be aware that there are NO MORE PARTS for these old rifles outside of replacement stocks from folks like Boyds. If something steel on the rifle breaks, the only option is to fix it by cannibalizing parts from another rifle. Since the current Savage coporate entity is NOT the same Savage that produced these rifles, you cannot go back to Savage for any technical or parts assistance.
Still - they're neat rifles. Everybody should have at least one.