An angle isn't going to help - save your money. Check the muzzle for damage as rc advises - with the q-tip test. Sometimes it helps to see any little bit of caught cotton if you use a magnifier to look for it. ANY tiny burr can effect your accuracy.
"You might want to try a good copper solvent and see what comes out blue!"
Juk, rcmodel has given you the key to the biggest and most common destroyer of rifle accuracy.
Shooting jacketed bullets, HP or FMJ, or any other point will leave a nearly invisible coating through a rifle bore, usually concentrated toward the muzzle.
You can't normally see it by shining a light through a bore but if you haven't developed a method of cleaning that goes after copper with a vengeance I think it's safe to say that your bore is heavily contaminated with copper.
Ever been to a benchrest match? If you can find one go there just to watch the competitors clean their rifles. They'll be using bronze brushes, as many as fifty strokes after 25 shots, or each ten shots, or each five shots according to the individual beliefs of each shooter. However many strokes each shooter uses
you'll think that they're nuts for as much as they clean their bores.
They do it because they've learned that COPPER DESTROYS their chances of firing winning groups.
Get yourself a good copper solvent bore cleaner. I've liked Butch's Bore Shine and Hoppe's Benchrest but any good one will work. Put some on a patch and get your bore wet with it. Bronze brush the bore several strokes then walk away leaving the bore wet.
A while later go back and run a clean dry patch through. It WILL come out blue (some call it green but it looks blue to me). Put some more patches through. Each one will come back with blue, usually less of it with each patch. Don't think you're done.
Many times with a bore that's nearly clean of copper a soaking and then dry patch will look like it came out clean. Watch while that patch turns blue right before your eyes, or go grab a cup or something and when you come back your clean patch will be blue.
That blue patch means that you aren't finished getting your bore clean.
If you want the best accuracy a barrel can give you you can't have ANY copper in the bore.
(Some barrels just don't shoot. Some barrels shoot hunting accurate and good enough for lots of folks. If you're trying to make your Ruger shoot 1/4 MOA it won't happen no matter what you do).
The old standby Hoppe's No. 9 is a powder cleaner and doesn't help with copper.
nuff?