I will introduce a controversial point of view.Knowledgable folks with opinions I respect disagree,make your own choice,
A 7mm mag has a tight twist,about 1 in 9.It typically shoots heavy for caliber bullets(I like 160-168).We put a big charge of slow powder behind that heavy bullet riding in tight twist,there is a lot of friction and the slow powder makes for heat dwell time.It is significant enough you do not get real long barrel life with one,wild guess,if you get 4000 rounds,that would be real good,(I said,wild guess!)
You are pushing or exceeding 3000 fps
All those factors working together can make for a barrel all cheezed up with copper fouling,and it won't shoot.
I do not think more moderate cartridges like the .308 or 30-06 typically show as much problem,and not removing fouling may work for them.Like I said,folks that know more than I do just wrote they don't remove copper.
If you do,maybe bore-tec-eliminator,a Montana black nylon bristle brush,a clean,straight one piece rod and a bore guide,try cleaning the copper out of it.I have a couple of decent shooting tight twisted over 3000 fps rifles,and they start to open up after about 50 rds from cleaning.
Just for fun,you might risk buying a box of 50 Accubonds ,150 gr .Try those.From memory,verify with the manual,IMR 4350,H-4831,H-1000,Re19 and 22,someplace in there is a powder that will work.
There are a lot of other fine bullets!!I only mentioned the Accubond because it is tough enough to hold together with a 7mm mag,and typically is very accurate
Add to that,its a Rem production barrel.Is what it is,not bad,but not a hand lapped high grade barrel.Not a big deal,but in my opinion,less smooth and more likely to foul.