Made 60's-70's. 100-300 USD
Potential to 1 MOA
Average condition 225-275 depending on engravings and such
If you are talking about the bolt action. Just queeze the trigger before riding the bolt back. It should come straight out. This is of course providing the rifle has been cleared and safe to work on.
Your rifle which was made by Mossberg and is there model 800B will bring between 100-275 dollars,depending on overall condition and a good bore.
The Mossberg Model 151-K was made for two years only: 1950 and 1951.
Do not attempt to use other than a Mossberg bolt made for that rifle.
This rifle was built by Mossberg and was labeled the 800B. The "B" series was sold thru Montgomery Wards and other large reatilers. All Mossberg model 800 .243 rifles manufactured had a twist rate of 1 in 10. So I believe it is safe to the twist rate is 1 in 10.
No sn data in the public domain I know of.
They were made over several years. For more detailed information on them research the Mossberg 800b.
A Mossberg 22 rifle such as the Plinkster depending on the condition is worth around $150-200.
It is the rifling in a mossberg rifle barrel.