Chainrings and chain tension

Unshipped the chain from my fixed bike (Specialized Singlecross) yesterday going at ~20mph downhill. Fortunately I was going in a dead straight line so I quite serenely skidded to a stop. Chain was mashed up and a real censored to remove, but I got it all untangled eventually and walked the remaining couple of miles to work.
I know why it happened - chain too loose, but the trouble is there's a huge variation in tension as the cranks rotate. I'm about to try the Sheldon method to help even things out, but I'm none too optimistic that it'll make much of a difference. I've now tightened the chain, but it's a bit tight at its tightest point in order for it not to sag too much at the loosest point.
I'm guessing it must be the chainring that's the problem as I've tried a sprocket I had on another bike where the tension was nice and even and it makes no difference.
So can anyone recommend a chainring that's not too expensive that's more likely to be round than oval?
And does anyone else with a Singlecross have this issue?
Thanks.
I know why it happened - chain too loose, but the trouble is there's a huge variation in tension as the cranks rotate. I'm about to try the Sheldon method to help even things out, but I'm none too optimistic that it'll make much of a difference. I've now tightened the chain, but it's a bit tight at its tightest point in order for it not to sag too much at the loosest point.
I'm guessing it must be the chainring that's the problem as I've tried a sprocket I had on another bike where the tension was nice and even and it makes no difference.
So can anyone recommend a chainring that's not too expensive that's more likely to be round than oval?
And does anyone else with a Singlecross have this issue?
Thanks.
More problems but still living....
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What make of sprocket are you using. If it a Cyclo- one, then bin it as they are just a bit of punched metal and almost always off centre.
Many chains will wear unevenly especially if not looked after to well, and once they start to go, every little stretch from there on in will appear magnified
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Gears - Obscuring the goodness of singlespeed
PZ.
+1. Just got one of these last week and they really are fantastic for the money. Miles better than the FSA Vero ring of cheese it replaces. I finally have consistent tension and a silent drivechain. Bliss.
Like PapaZita says, they're quite chunky and well built, with nice tall teeth so unshipping chains should be a thing of the past. Reversible too so should last twice as long. I'm very impressed and will be buying another when this one wears out.
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More stuff:
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Gears - Obscuring the goodness of singlespeed