At 20 yards and off a decent rest, what are reasonable to good groupings? Would grouping to an 1" of center bullseye be considered decent to good with fieldpoints?

1 inch at 20 is pretty good.

A lot depends on the bolts with crossbows and you will find even ones from the same box they may consistently hit to different paces close to the bull but some might be right while others are left and consistently do that. I mark my bolts on the fletching with a sharpie. There may be 2 or 3 that always hit the bull and those are the ones I will use hunting.

The most consistent bolts out of the box I have had are no longer available Parker Redhots, those rom my parker would hit the small yellow dots on a Rhienhart 18-1 target to 70 yards from my x-bow consistently. I would shoot 5 bolts at the 5 dots and generally always hit my dot out to 70 yards and killed hogs a little beyond that with it. Those would do that with 125gr heads but the groups would open up some with the 100 gr heads.

Crossbows speed rating is with their bolts with 100gr points, generally they will shoot a little slower but more accurately with a bit heavier bolt even going from a 100gr head to a 125gr head can help that. Some of the bolts like Piledrivers are also heavier and get better accuracy for that reason. I do not mind giving up a little speed for better accuracy.

At 20 I cannot shoot mine two or more at the same dot. Too expensive. That said I've never shot it at game. Too uncivilized of a weapon.

Kmon is spot on. With the right equipment and a little practice, you can get very accurate. And as passthru said, at 20 yards you can ruin a lot of arrows. I shoot 2 xbows that shoot 400fps. At 40 yards you can be inside a fifty cent piece on either.

A reasonable question, DQ. When I started with my xbow just a few years ago I tried to ask that question on here. It seemed like I never could really get that good of an answer. I will tell you what my experience is. I am admittedly inexperienced with a bow of any type but I am fanatical about doing everything I can to be very accurate. I have a high end xbow and I shoot off a very solid rest.
In my situation a 1" group at 25 yards is very doable and I wont go serious Trophy buck hunting without that type accuracy because theres just no need to cause its doable(at least with my equipment.) I use the standard Mission arrows/bolts that come with my Mission bow. I havent tried other bows but Ive been told that most/many(?) xbows are very accurate but its the arrows that are not always accurate.
I mark each arrow and keep meticulous records of where each shot hits per each arrow until Im comfortable how each specific arrow groups.
Some out of the same box will group less than 1" while others will group several inches. I just note which are inaccurate and use them to shoot at unimportant stuff.
***Some arrows will group within 1" but they will not be shooting to the same point of impact as others that shoot 1". ***
I just keep shooting and keeping records until I find "enough" that shoot 1" and also shoot to the same point of impact.
Kmon helped get me started and he is always a great member to listen to on all archery stuff.

I've had a xbow for few years now & hunted a little with it. Fun to shoot & accurate. Here is something I've come to a conclusion on. If you want to do a lot of practice & you want your hunting arrows to go where your practice arrows go, you need to use mechanical broadheads & use their practice head. I was an avid bowhunter in my younger days & I always used fixed broadheads. Very hard or impossible to get a practice point arrow to hit where a true broadhead arrow goes. Besides, fixed broadheads eat-up a target faster too.

Just IMHO & YMMV. Good shooting & good luck!

Good info in my experience!

Bullets I will shoot for groups they are gone after one shot. Arrows and bolts I will shoot to small different targets for each shot, they are reusable and easy to destroy by shooting one with another.

I use one of these https://www.rinehart3d.com/catalog/18-1-archery-target/ for most of my shooting, plenty of target dots to shoot at that are the same size. Shoot 5 bolts in each of those 5 dots and you can see group patterns well enough IMO and if you can hit each individual dot at ranges 20 to as far as you can shoot With some bolts I and one crossbow I have 70 yards I have and can do that.

IMO if you can keep your shot in that about 2 inch circle out as far as you will shoot be that 20, 30, 40 yards accuracy will not be your issue for not getting your deer or hog with your archery equipment. Within those ranges anyway. Other things like animal moving can sure come into play though which is why 30 yards is as far as I care to shoot a deer with my Bow or crossbow and 20 yards with the recurve. Hogs are a different story, they do not tend to "jump" the string aka react to bow noise causing a miss or bad hit like deer do. I still prefer using a bullet on hogs as I have broken or lost abut half the bolts and arrows shot at hogs.