OK, I'll try to un-lingo that.
The bolties (bolt-action rifles) in game are standard 98 Mauser and Mosin type rifles.
Both of these are designed so that, while the bolt is moving forward and feeding a new cartridge (aka "round"), the rim of that cartridge actually slides up under the extractor (on a Mauser, that
claw-looking thing on the side of the bolt) and is held in place. The extractors are NOT designed to just click over the rim of a cartridge which is already in the chamber. This is called controlled feed.
Shoving the bolt home on a chambered round really stresses the extractor, and will eventually cause the extractor to break. This is a very bad thing. The Mosin bolt design might be more tolerant (it was designed for use by poorly-trained peasants, after all), but it's still not something you're supposed to do.
On to the subject of topping off: on most modern
detachable magazine-fed weapons, "topping off" (also known as a tactical reload) involves chambering a round and then filling the magazine to capacity. For example, an AR goes from 30 rounds (29 in magazine + 1 in chamber) to 31 rounds after a tactical reload. On a Mauser or Mosin, you load up five rounds from a stripper clip (filling the magazine to capacity), and then closing the bolt takes that fifth (top) round and chambers it.
To "top off" (as in get 5 + 1), you would have to actually load five rounds into the magazine (like normal), then press those rounds down and directly chamber a sixth. On many/most rifles, internal clearances are such that you can't actually push the top round in the magazine down far enough to close the bolt anyway; even if you can, chambering the sixth round will be either very difficult (you would have to remove the bolt, slip the cartridge rim in place on the boltface, and then reinsert and close the bolt while holding down the fifth round in the magazine; the obvious problem here is that your finger will be in the path of the cartridge on the bolt) or impossible (you can't close the bolt on top of the full magazine anyway).
Thusly, "topping off" for 5+1 loading on the bolt-actions currently in game is impossible.
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Even on a bunch of "push" feed rifle designs (like, say, the Remington 700, which is a very popular platform for modern sniper rifles), the magazines are dimensioned such that you can't actually push loaded rounds down far enough to close the bolt on top of "full" magazines. The Remington page lists the .30-06 version of the 700 as having a four-round magazine—you can in fact fit a fifth round in the magazine
with the bolt open, but closing the bolt will chamber that round. I think Savage does the same thing with their rifle spec sheets.