1907 sling: how long & what type do I need?

[Nashville Stage]

I'm looking to get a 1907 leather sling so that I can learn to use one and also have the knowledge to help our students who come to an Appleseed with one. I'm brand-new to 1907 slings, and am trying to figure out how long of a sling to get for me. If it helps any, I'll likely be using my sling on an M1 Garand, an AR-15, and a 10/22. Obviously, the sling will need to be adjusted between those three, but I'm not sure how to measure the appropriate length that I'll need to order.

For example, I was looking at an Eric Hollis sling https://erichollisllc.com/collections/rifle-slings/products/copy-of-hollis-leather-nm-rifle-sling. He lists several different rifle types and a range of lengths to choose from. I'm not sure what the pros & cons are for the different lengths & options available.

[Oz]

About 10 seconds into this video, Ken Roxburgh will speak to sling length.  (Spoiler: 54" if used on an AR.) 

I find videos of his rifle instruction really interesting, his techniques and ways to express himself (colorfully) and involve the students (lots of "say it with me".)

https://www.youtube.com/watch?v=V80JyfZ4gBQ&list=PLsutmAIyqfOYzLnbBkVi1xFMQi3hPii-1&index=2

[Herme]

I have a turner saddlery sling https://turnersaddlery.com/ts/product/carlos-hathcock-signature-edition-national-match-service-rifle-sling/.  Its 10 years old with little signs of wear or stretching.  Saddle soap and leather oil is supposed to keep it good for decades.

they also make a all weather variant.  I like the all weather but it is a absolute pain in the @ss to remove sometimes.  I borrowed one during a rain event, worked really well.  Couldn't get it off by myself.

Here is another video from the Army Marksmanship Unit.  they have a great facebook site with interesting articles weekly.
https://www.facebook.com/watch/?v=1318640191839378

[maxwell]

As Oz said, 54" will cover an AR (and the Roxburgh video on setting it up is gold). Beware that lengths may not be measured the same way by all manufacturers, though. I'm on the last hole of my Eric Hollis 54" sling, and about 6" from the last hole on my Ron Brown 54" slings, both used on the same rifle-length AR; the M1 Garand sling can be shorter, so you're fine with 54" from either mfg there. Depending on your Ape Index, you might want to err on the side of caution if you get a Hollis sling, since it's easier to shorten a strap than lengthen it.

[Ramblin' Wreck]

Love my 1907 slings. I have two from Turner, one leather and one biothane all weather, and 3 from Eric Hollis. The 54" or 56" should be good for an AR. As stated elsewhere, I'd rather have one too long than too short.
I find the all weather biothane a little to "grippy" and at times is a SOB to get on especially if I'm in a hurry.

https://erichollisllc.com/collections/rifle-slings/products/copy-of-hollis-leather-nm-rifle-sling?variant=6381950697511
Wreck