I was looking at purchasing a ruger blackhawk and the guy said the throats were reamed to .4525 by a gunsmith. now i feel like a idiot for not knowing why or what the purpose of that is for could i have  a explanation ?

they've been known to be undersized which can degrade accuracy

This. Ruger is known for undersized throats.

I had a BH that had .4510 throats.

This is especially important if you shoot cast bullets. Undersized throats will swage down the lead, and then the bullet will not obturate to the bore, which can create significant leading.

If you ever use lead bullets, I would suggest sizing to .453, this way no gas escapes around the bullet as it is leaving the cylinder.

I have to deal not only my Ruger 45's, but my Dan Wesson .44 and my S&W .44 Mountain Gun. So far it has only helped.

I thought Ruger fixed this a couple of years ago.

Nope!  

They are still sending out revolvers with .451" barrels and cylinder throats of anywhere  from .450" to .454" or larger and they call it "within our spec".  
What a joke.



As to the OP's question:

If the throats have already been fixed i would consider it a bonus.

Yep, as far as I can tell, Ruger is still boogering up the throats in their 45's.
They are undersized and inconsistent.

They have also begun selling revolvers with oversized barrel diameters.
I would love to buy a Toklat, but not with the possibility of barrel groove diameter up to .456".

The undersized cylinder throats can be fixed, but not the barrel, unless you ream the throats to .4555" then cast and
size your own bullets to .457".

Why does Ruger refuse to manufacture a functional .45?

The bad news is, Ruger tends to undersize the chamber throats of their .45s. The worse news is, that while they were making the throats undersize, they sometimes also made them oval, tapered conical, S shaped, you name it. The good news is that they are typically sufficiently undersize that a .4525" reamer will clean up the errors resulting from manufacturing allowing the gun to shoot much better. Ask me how I know.

I could not chamber .452" long wide flat bullets in 4 of the 6 chambers of my Redhawk.
( number 1,2,4 from the left).



I slugged my chambers and  barrel.  
The barrel was .4512" with a very slight constriction a the threads.
The throats had various diameters, with the tightest being .4510".



I had 'Cylindersmith' ream the throats to 0.4525".  Now, I can chamber and shoot 0.452" Pb bullets with little to no leading.

In my previous post, I forgot to mention.  They guy who posted "Ruger has fixed the problem" was somewhat correct.
Apparently, Ruger is attempting to respond to complaints about underdimensioned throats.  Now, some throats can be a large as .457".
A huge amount of gas blows by the projectile in the cylinder causing huge loss of velocity and leading problems.

Just checked my new 5242 Blackhawk. Both cylinders, .45ACP and .45 Colt, all the cylinder throats measure right about .460".

With .45 ACP cylinders, I don’t think it matters too much if the throats are oversized. My S&W 25-2 is 0.456”, one of my .45 ACP cylinders for my NMBH is 0.455” while the chambers for my 625s are right at 0.452”. All shoot well in .45 ACP. I think what is going on is that the case is so small and the primer so relatively powerful that the bullet is blown into the forcing cone before the powder charge burns and gets up to pressure. The bullet is already sealing the bore and there isn’t any significant blow-by to damage the bullet.

In .45 Colt, with the much bigger case, oversized chamber throats can make a big difference. The large case attenuates the blast from the primer and the larger powder charge also soaks up a bit of the blast. The bullet is then getting blow-by from the powder gases as it is hitting the forcing cone. Not good.

Not on my 4-15-2014 built one it wasn't.

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