Mostly wondering what these factory rifles are capable of
It varies, widely - much more widely than a custom-built target rifle. Almost all custom built target rifles will shoot 1/2-MOA or less, and if not they are broken and need to be fixed.
A typical good factory rifle might be able to deliver 1MOA, on average, more or less. But there are many, many factory rifles out there with which there is nothing "wrong" which deliver 1.5MOA or 2MOA. By "wrong" I mean nothing that is clearly out of the factory's specs and standards, which they will acknowledge as a manufacturing fault and fix.
There are some factory rifles which deliver better than 1MOA, honestly and consistently. There's nothing at all unbelievable about a 3/4 MOA factory rifle (though they're also not as common as people claim!).
There are even some factory rifles which deliver 1/2MOA, honestly, consistently, and on average. These are exceptional rifles - all the various tolerances and variabilities happened to line up "just right". These are quite rare, but they do exist.
When you shoot a group with a rifle, the result (group size) is a result of the combination of several factors:
- how well the shooter aimed and fired each shot
- how accurately the rifle+ammo is shooting
- whether or not the scope is moving between shots (internally, or in its mounts, etc)
- whether the scope has been properly adjusted and used (zeroing out parallax, for one)
To shoot a 1MOA group, you need to do all of these things reasonably well.
To shoot a 3/4 MOA group or a 1/2 MOA group, there is *much* less room for error in each and every one of these factors.
Before you blame your ammo/rifle/scope, you might want to test yourself - see if you can take a known-good target rifle (say, a rifle that the owner is able to get sub-1/2-MOA groups from), shoot say five 5-shot groups, and see if the groups are closer to 1-MOA (in which case, you now know that it's worthwhile to focus your efforts on improving your shooting technique) or closer to 1/2-MOA (in which case, you know that your shooting technique is not responsible for your ~1-MOA groups with your rifle, so you can productively look at the other possibilities).
If that's not possible, see if you can find a known-good shooter to shoot some groups with your rifle+ammo+scope. If he delivers substantially better groups than you do, you have one answer. If he delivers substantially the same size groups as you do, you have another useful and worthwhile answer.