Contact the Remington Custom Shop
Most barrel split from bore obstructions. Count your self lucky you are alive.
Check the date code on barrel ;) There's information on the Remington Society of America, check related links.
The bullet will rotate one full turn in ten iches.
Yes they are interchangable.
Would have to at least know the model and condition would be a huge plus for determining value, also it's a .35 Remington not mm. Probably is a model 8 or 81. Well unless it's a .35 Whelen and that would be a more modern rifle like a 7400.
Remingtons are dated by a letter code on the left side of the barrel, not the Serial number.
The weight is 7.5 lbs
You won't get you answer by serial no unless you call the factory. However you will from the barrel codes listed on the Remington Society of America here: http://remingtonsociety.com/rsa/questions/barrelcodes
You can request one from Remington for free at their web site.
I have paid $469 for a new, synthetic, 30-06 carbine (18 1/2" barrel) from my local gun shop Bulls-eye (Lawrenceville, GA).
What year was my Remington 7400 30-06 made ser#B821945, the barrel has KQ just in front of the receiver. Donnie dmso7357@aol.com May 1978. In General I believe serials starting with A are the first half of 1970, B the second, C first half of 1980's etc etc.
$500