I have the 16" Alexander 7.5 twist barrel
will it stabilize the 140s or is it just not worth the effort ?

Depends on which 140gr bullet, flat base yes it will, VLD could be an issue but could work perhaps.

Look around the 6. Grendel forum using the search engine in this link, just put in 140 in the search and you will find a good bit of info LINK

I am sure with that twist it would work but it’s going to take up powder space to fit magazines so won’t be moving very fast...

I would expect with that barrel length somewhere in the 2100 to 2200fps for velocity from the Grendel keeping it at AR pressures.

This is about what I would expect with the limited volume you would trade bullet weight for velocity

I like the following site.

https://bergerbullets.com/twist-rate-calculator/

I usually just pick a berger bullet in the same, or close weight, and as similar of style bullet as possible. According to this thing, probably not enough stability. I tried 130 gamechanger in a 1:8 and I couldn't get faster than about 2250 with RL15. Never shot well even at 100 when 123gr shined.

I use that fairly often as well. you can input your bullets length weight, BC.... in but also it does not work well with flat base bullets so they have a chart for their flat based bullets.

A total tangent but I have never loaded a flat base bullet. Got some lighter varmint 22's l wanna try. Everything has been a boat tail that' I've loaded. Probably making a mountain out of a mole hill but I was concerned I was gonna screw up brass when seating. Heck, I screwed 3 Lapua cases seating bt bullets in my 308.
Read a dorky ballistic article once saying that flat based bullets have a higher bearing surface for a given weight. They concluded believe it aids in faster stabilization and more consistent muzzle velocities when compared to bt bullets of the same weight, mostly 22cal..
So basically it great at shorter ranges (like less than 300) but without a boat tail it had poor performance as it went down range. Again vs same weight w/bt because of the aero dynamic advantages of the bt. For me specifically, our 1:8 should be more than stabilize most of the flat base bullets I've seen.

But yes, this and their ballistic calculator are 2 of my favorite tools for reloading.

Chamfer the inside of the case necks and you have no problem seating flat based bullets. Flat base bullets have their place just High BC is not a strong point for them. I have killed deer and pronghorn at over 500 yards with 160gr Nosler Partitions which are basically flat base bullets. You loose velocity quicker with FB bullets than Boat tail bullets but they can be very accurate.

My most accurate rifle gets flat base bullets, you do not see many choices for a .172 diameter bullet that are not flat base. Sighted in where it is I can hold on fur of a coyote to 325 yards and kill it with 0 hold over or scope adjust, of course it helps when it leaves the barrel at 4250fps.

Bullets have changed since Finn Aagaard and John Wooters were writing their gun/shooting/hunting information but neither were that fond of boat tail bullets for hunting, but the boat tail bullets of the 70s and 80s were not nearly as good as the ones we have now.