.224 CF
- 7" for bullets heavier than 80gr.
- 8" for bullets up to 80gr.
- 9" for bullets up to 70gr.
- 12" for bullets up to 63gr.
- 14" for bullets up to 55gr.
- 15" for bullets up to 55gr. driven 4,100 fps or more
- 16" for bullets up to 55gr. driven 4,300 fps or more
The above is a copy and paste from Douglas Premium Barrels.
Bear in mind if you want to shoot lighter bullets the 1-7 and 1-8 will both shoot 55gr. Below that the 1-7 does not do well and may even over rotate 40 gr varmints and cause them to come apart. Personally I have a 9 that is my hunting rifle for varmints. My short barrel is a 7 for defense. It just depends what you are after. If long range or bigger targets you may want a 7. If just shooting bulk ammo or varmints out to 400 a 9 will be fine. If you want over 400 on varmints you may have to move up to heavier bullets. 400 is my max range on varmints so I'm fine with the 9".
Barrel length is just a personal preference as well. For varmints I like the 20"(walking) and 24"(stationary) for the added velocity. For defense I like a 16", giving up a little velocity, energy and sound for a compact size.