1. Condition: Excellent condition means the rifle is well-preserved, with minimal wear and tear. The finish should be mostly intact, the stock should be free of major damage or cracks, and the mechanics should function properly.
2. Rarity: The 1894 octagon barrel variant is generally considered more desirable and rarer compared to round barrel models. Additionally, the 3240 serial number range indicates it was produced in the early stages of 1913, which adds to its collectability.
3. Market Demand: The market demand for vintage firearms, especially well-preserved and original models, has been steady in recent years. Winchester lever-action rifles, including the 1894, are highly sought after by collectors and enthusiasts.
Based on these factors, a 1913 1894 octagon barrel 3240 serial number 674708 in excellent condition and all original could potentially be valued between $1,800 to $3,000. However, it's important to note that the actual value can fluctuate depending on the specific condition, any special features or markings, and the current market trends.
Consulting with a reputable firearms appraiser or dealer who specializes in vintage firearms is recommended to obtain a more accurate valuation.