I was guessing the gun was moving a lot from shot to shot. Any inconsistency in form would make the rifle recoil differently and therefor effect groups.
When working on fundamentals, it is very important to really focus on hand (And the amount of force or energy you are gripping the stock with)...
I do not see the lighter weight M's being great for bone on a mule deer myself either.
On the other hand, a 7mm 180 grain M I wouldn't be afraid to hunt elk with (Still stay away from heavy bone), and mule deer at about any angle.
I am not suggesting it is the best bullet for elk, but I wouldn't...
It wasn't the wind.
Were you shooting off of a bi-pod in previous range trips, when it was shooting good?
I wouldn't use a slick fabric myself with a bipod, unless it was something like my JOYPOD-X...Which is a completely different cat.
https://sebrests-usa.com/joypod-x/
Shot an antelope with a 223AI XP-100...Probably the same performance level as a 223 rifle with 75 grain A-Max. Bullet did it's job.
A 75M or 80M will work great on deer.
80 M works great on hogs too with my 22 Creed XP pistol...Again, slower MV's than what you would get with a rifle.
88M's...
Started with the 284 Win in the early 90's, center-grip XP-100.
Mine have all been 9T.
I have run from 140's-180's.
The 180's are on my F-Open Rifle (30" barrel).
140's to 168's in 15.75" to 18" barrels.
I had 3 recently, and I am down to 2 right now (Sold a XP-100).
H-4831sc has been the powder...
@FOTIS ,
Beyond some traditional handguns and some 22lr's, I don't use iron sights for any big game.
Even some of my semi-auto pistols and revolvers have some kind of optic on them.
I have taken a few pd's beyond a 100 yards with a S&W 44 Mag, using irons, but that is the exception to the rule
Used to use them-I don't any longer for game.
For me, they were inconsistent in performance...Sometimes opening up and performing well, and sometimes penciling.
At those distances, even a reduced load will have enough impact velocity to perform.
Since she is recoil sensitive I would consider 22 Creed or 22GT, 6 GT or 6mm Creed, and the 25 Creedmoor.
Depends what is minimum caliber where she will be hunting