I have been canning my own for about a year now.
Best thing I started doing.
I have only used ball jars.
Sister recently told me she's been canning for years using recycled sauce jars.
Am not too familiar with canning so asking is that safe?
Others do the same?
Am guessing as long as lid is airtight and doesn't pop should be good?
No, for the same reason you don't re-use your canning lids. The lids on store jars probably won't seal properly.
From the USDA:
Most commercial pint- and quart-size mayonnaise or salad dressing jars may be used with new two-piece lids for canning acid foods. However, you should expect more seal failures and jar breakage. These jars have a narrower sealing surface and are tempered less than Mason jars, and may be weakened by repeated contact with metal spoons or knives used in dispensing mayonnaise or salad dressing. Seemingly insignificant scratches in glass may cause cracking and breakage while processing jars in a canner. Mayonnaise-type jars are not recommended for use with foods to be processed in a pressure canner because of excessive jar breakage. Other commercial jars with mouths that cannot be sealed with two-piece canning lids are not recommended for use in canning any food at home.
If the sauce jar is a Mason jar, and is undamaged, it should be as good as any other Mason jar. The only sauce of which I am aware that comes in a canning jar is Classici, which uses Atlas Mason jars.
The seal must be checked for any canning jar, when you store it, and again when you use it.
You don't reuse lids because that is where the rubber seal is. This does not apply to jars.
+1 for GH's comment. The Classico jars are mason jars, and the lids fit (and seal) perfectly. They are, however, slightly smaller than a real quart jar, so you may end up with odd amounts left over if you are following a recipe. I have been canning for way longer than I want to admit, AND I work for Extension in Missouri, so I consider myself an expert.
Extension is the best place for canning info.
If you are making freezer jams you can reuse these. No processed preserves stored in the freezer will be OK. Its when you get into heat processing that the question of a proper seal is important. You won't get that reusing store lids. And the vast majority of glass jars in the supermarket are considered "single use" jars and aren't thick enough to withstand home processing in water without breaking.
To answer your question: it is safe if the jar doesn't break and the lids seal (they should have the same "button" action as purchased lids, which depresses as the jar cools if there is a vacuum).
Unbroken jar + vacuum + correct processing time = safe.
I have re-used lids with a success rate of about 90%. I usually don't re-use them more than a couple of times. Again, if the jars seal, they're safe; otherwise, it's just a matter of whether you want to risk the occasional non-sealing jar and having to re-process it with another lid, use up the product, or store it in another fashion such as freezing.
Mayonnaise jars are pretty large and thin-walled, it's true. I have used smaller jars from Classico sauce (Mason jars) as well as those from jarred olives, pestos and other sauces. Make sure you give your lids a bit of simmering time so the plastic can relax and expand to then (hopefully) form the seal better.