I've written that my spirit level front sight and any others I've tried are too sensitive to cant to use-I can't hold the bubble in the middle even on sand bags. That bubble just slides over to the side. I've been told that the vial is "U" shaped and to put the bottom of the "U" up so that the bubble stays in the middle. Mine ain't "U" shaped. I've also been told that the spirit level is necessary for long range slow bullet shooting.
1. Can you hold your bubble in the center when shooting from the bench? Offhand? From X sticks?
2. Do you need to hold the bubble in the center/need a spirit level front sight to shoot accurately? What range?
Maybe I'm wrong on this, although I've shot and seen shot some good long range scores without the bubble.
joe b.

Joe b.  The level vials are really more banana shaped than un shaped so the bend is very slight.  Roll it on a hard surface and you'll see that's the case.  The advice you were given was correct, the vial should go in with the bend up.  That gives the bubble a place to sit when level.  Its best to use some RTV or other adhesive on the ends before replacing the caps.  Scewing in the caps and recoil can both move the level if you don't secure it with adhesive of some type.  Even in the best of sights this is the case.  I have found the Parts Unknown sights to have the hardest levels to get centered properly because their "bend" is very slight. As to can you keep the bubble centered the answer is yes, offhand, off sticks or off a rest, that is if the level is correctly installed in the sight.  GS

Joeb;
I have three different BPCR rifles (one C. Sharps, one Browning BPCR and one Browning Creedmoor). It is no problem (at least, when I am looking at the level) to keep the bubble centered off the bench, off sticks, and even offhand. I DO need the level, as I do not seem to be able to consistently keep the rifle on an even keel without a level.

I your level does not have a "bend" in it, maybe you need a new vial. They are available, but it may be difficult to find one that fits your sight. If the sight is currently available, you might try contacting the manufacturer. Maybe they neglected to put a "bend" in your particular vial. It could be that simple.

FWIW

Dale53

Joe b.,
  I think a lot of people are missing part of your statement. You say that your spirit level sight and ANY OTHERS you've tried you can't keep them centered up. Not to be offensive about it but you might have a problem. OR, the quality of the sights you have access to aren't the best. It might help us to know what make sights you are talking about? All the advice you've been given so far is exactly right.... for a quality sight, and if a quality sight the maker will stand behind it.

  MI's comment about the thickness of the liquid is right on. A friend had this "centering" problem and got a vial with a thicker liquid and it helped a great deal. I think he got it from MVA, but not certain. MVA also has different colors of liquid which makes a tremendous difference in being able to see the bubble.

  To answer your questions in order.....

1. Yes you should be able to hold the bubble centered off the bench, cross sticks, and offhand, altho it's not the easiest thing to do offhand.

2. Yes. To shoot accurately you do need to be able to hold the bubble in the center, or at the least in the same position for each shot. Center just happens to be the easiest. Considering the trajectory of Schuetzen or Shilouette rifles a slight cant either way can throw the bullet off quite a bit either left or right. In Schuetzen we're trying to hold 3/4 MOA at either 100 or 200 yds. If you have a gun that will consistently shoot 1/2 MOA then you only have 1/4 MOA to play with. Someone with better math skills than I have could probably figure out how many degrees off you would need to be to put the shot outside the 25 ring. It isn't much.

  What range is a spirit level useful?.... Of course a lot would depend on what kind of accuracy you want. In Schuetzen we want maximun accuracy in as little as 100 and as great as 200 yds.

  You don't tell us what you mean by long range. I know people who think that 50 yds. is a long ways off.  In the text books long range starts at 800 yds. I don't think you'll ever see a shooter at 800 to 1000 yds. that doesn't have a spirit level sight. Even most of your Shilouette shooters will have them on their guns, and anybody serious about a good score in Schuetzen will also, altho many, including myself would rather use a "sled" as it is even more accurate than a spirit level sight.

  Of course many good scores have been made without a spirit level sight, but it is so much easier keeping things "squared" up that it's foolish not to use one if you can afford it.

PETE

The only spirit level front sight that I own now is on my #16 Maynard. Years ago Mike Stevens made a ?nut? for this sight, the round threaded thing that holds the vial in, and told me that the sight was a ?????, maybe Winchester-I don't remember. He said that Mass Arms Co. didn't make their own. At any rate, the sight is original with the gun, from 1882 or thereabouts.
During my research I looked at and through any spirit level sights at matches, these on Stevens, Winchester and Ballard rifles. Perhaps 6-8 total. I remember the lack of interest in the bubble, and the agreement that it was close to impossible to hold the bubble centered and the sights aligned.
I wrota an article for the ASSRA news on Cant and spirit level front sights, and included that info in my book.
A well-known shooter has contacted me and told me that I was wrong. He's the only dissenting opinion, from the article or book. I find one major error in my analysis so far, and it looks like you guys agree with the well-known. 
I've shot, and seen shot, some very nice groups and scores at ranges to 600 yards with lead bullet guns/single shots. I've shot at Williamsport a number of times and not seen a cant-fixer on these 1000 yard bench rest guns. I don't see spirit levels on CBA match guns, nor on the bull guns used for offhand shooting with irons.
The analysis says that the more the drop, the more important cant is.
I'm still working on it, but it looks like I'm wrong again!!!
joe b.

joe b.,

  Well, this could explain why you can't keep the bubble leveled up. I've never taken apart an old spirit level sight so can't say  how they are made. If they came only with a straight vial you might be up the creek since clearance has to be allowed for a curved vial. The same might have been the case of all those spirit levels you looked at on those old rifles.... if they were original equipment.

  As you can see from the consensus here a spirit level sight is considered very beneficial. There are even a coupla guys at our club who have them mounted on their scopes. Can't recall where I've seen them advertised, but they are for sale especially for scope sights.

  I'll admit that not many use a "sled", but for me it serves two purposes. The most obvious is once you have it squared up you don't have to keep tweaking your gun on the bags to get things level. Makes for faster shooting, something that's pretty slow anyway what with breech seating and preparing the case for every shot. Lot worse with BP! The second is that a "sled" helps control torque. As you increase calibers it becomes almost impossible to control a gun exactly the same as a score/group is forming. The sled allows you t oshoot a more relaxed grip and keep fatigue down.

  I'm not aware of what rules they shoot under at Williamsport or at CBA matches, but it could be that a "sled" is not legal at them. They are under ASSRA rules, and I'm really surprised more aren't using it. There are only two at our club that do. Jacketed stool shooters get around not using a "sled" by having as wide a fore arm as is permitted under the rules and bagging their guns in such a way that it gives almost the same effect. Plus most will also have a "return to battery" stop. If their bags are set up right all they have to do is slide the gun forward and the sights will automatically line up so all they have to do is get their shot off under the same conditions.

  As I said in my last post..... It's very possible to shoot good... even great.... scores/groups without a spirit level, "sled", or wide fore arm, but it is much easier to do so with them if the rules allow. Just gives you one less thing to have to set up for each shot.

  Sorry I didn't see the article or read your book. Maybe I'd have had something to say to.  Hopefully you're getting an earful now. 

PETE