I'm looking at a winchester 670 for my grandson that has a long crack that appears by the photo to run from the rear of the trigger guard back into the butt. Its a good sized crack but not very wide. I do a lot of woodworking and have done a lot of furniture glue-ups, but am wondering how best to address this crack. Thanks for sharing your experience and ideas on how to attack this if I buy it.

It can be fixed. I like to open up the crack so can get glue down into it. I thin the glue and use compressed air to get into the bottom of the crack. I use surgical tubing to clamp it tight. Sometimes a dowel or screw is warranted but not always.

thank you mr. forner: How would you open this type of crack? I use titebond for all my furniture gluing: any problem using that for this one?

The 670's were a blind magazine version of the M70
Most of them had Birch stocks and were prone to cracking in the recoil lug area.
Once that happened then cracks would start from the bolt handle and rearguard screw

Fixed many of them a few decades ago and always used Acraglas

J Wisner

There is some glue called "Hot Stuff" , runs like water into any crack.

I'd also recommend looking for the cause of the crack. Years ago I repaired two with cracks that were caused by poor bedding of the recoil lug. The rear trigger guard screw was actually taking the recoil.
When you're done with the crack repair look at the recoil lug.

thanks all for your help. Only other question would still be how I might open the crack a bit to get glue down into crack.

This is the hot stuff:

https://www.caglue.com/Hot-Stuff-Original_c_15.html

I would try spreading the crack a little by wedging something into the stock where the trigger goes through. Pour in this stuff, remove the wedge, then clamp the stock.