The wrench you are talking about is called a spanner wrench.
They have been around for a couple of hundred years now.
Finding one for a Remington 760 / 7600 is nearly impossible. The only people that would have had one would be a place that was a authorized Remington repair center - and most of them guard them with their lives.
There is no way in he11 that the barrel can come loose in one of them guns.
The factory makes sure that it is tight.
Your best bet is to sell your 7600 and buy a used 760 Gamemaster.
I saw a couple of dozen of them in the last week in my travels and most of them retails for about $350 - $450 depending on condition and options.
Wal Mart is what ruined the gun industry. You cannot tell Remington that you want to buy 100,000 rifles a year and you want to buy them for $50 less than what they would sell them to their other wholesalers and not get all of their blems and rejects.
The origional system ( 760 Gamemasters ) had a series of lugs on the bolt that locked into the barrel and they are a very accurate rifle out to about 300 yards.
They were all full floated barrels and no amount of leaning on the forearms would make them shift their point of aim. You could however cant them in a different direction than what they were sighted in at and make the POA change some. That's just due to a little slop in the rails and the tube and the forearm - not because something is putting pressure on the barrel.
Any wander that you have would be a result of a couple of different things.
1. Poor Scope mounts.
2. Poor Optic's - a cheap scope - or even a good scope that was junk from day one will give you nothing but trouble.
3. A improperly mounted scope.
If you buy a scope and just mount it to the gun and it isn't bore sighted correctly or you use the wrong type of scope mount and the barrel is pointed one way and the scope is pointed the other - it isn't going to be accurate.
4. The wrong ammo for the job. I don't know what caliber that you have but here is some examples.
I own two 30 / 06's and two 270 Winchesters, all model 760 Gamemasters
2 are ADL's and 2 are BDL's.
I have owned at least 10 different Gamemasters in my life - everything from a 35 Remington - my first gun to a Model 6 - 270 my last gun.
I shot 150 gr Remington Core Loc's in the 35 Remington.
I shoot 150 gr hand loads in my 30 / 06's
I shoot 130 gr hand loads in one of my 270's
I shoot 140 gr hand loads in one of my other 270's
Now comes the fun part.
I took a barrel off one of my 760's and put it on a different 760, both were 30 / 06's
One was in mint condition - but was a ADL and the other was my favorite BDL that I wanted to make better - because the blue was missing and I do not plan on selling this gun ever.
The BDL was sighted in first. It was 4 inches high and 3 inches to the left.
I moved the scope and it shot bulls eye's again.
The ADL I shot and it shot 4 inches low and 3 inches to the right.
So what does that tell me? That the action is pointed in the same place and the barrels were pointed in different directions - but that they were identical.
I will also add that when I changed the barrels I also changed the bolts and the parts that connected to the pump and the triggers. Because I knew that the recievers were all machined the same way and the head space would be the same when I switched them.
The ADL had a cheap Weaver 3 x 9 x 40 scope and the BDL has a Redfield Widefield 3 x 9
Here is another example.
I have a BDL 270 and I shoot 130 Gr Hornadys and Winchester bag bullets and it shoots great.
I use 130 gr hand loads - but they are factory duplicate loads - 55.5 gr of IMR 4350.
I wanted a gun for hunting bears and stuff and I didn't want to mess around sighting in between seasons. So I took a second BDL that I had that only had a 3 x 9 x 40 Simmons scope on it and I sighted it in for 200 yards with a 140 gr Hornady Spire Point bullets , hand loaded for that gun and it is sighted in so well that it will put two bullets in the same hole at 200 yards.
It has done it several times since then - with ammo from different batches reloaded 4 years apart. The scope has never been touched.
The other BDL 270 has a 4 x 12 x 40 Simmons scope and you can cover 5 shots with a 50 cent piece at 100 yards. Which is more than good enough to hunt whitetail deer in Pennsylvania.
You would think that the scope with the higher magnification would shoot better than the scope with the lower magnification.
I also have the Model 6 that is a half way gun - almost a Gamemaster and almost a 7600.
It just has a cheap 3 x 9 scope on it and it will shoot, but not as good as any of the 760's !
Now a kid came over one day and he bought a new 7600 Remington with the synthetic stock and 2 boxes of 180 gr Remington Core Loc's and his gun had a $400 tatical scope on it.
Everything brand new, everything bore sighted and mounted in a gun shop by a gun smith.
He shot both boxes of ammo and never hit the target in the same place twice.
Just to make sure that he was not just a bad shot, I took the gun off him and took 3 shots.
It looked llike I was drunk, shooting at a road sign on the first day of deer season.
I tried my hand loaded 150 gr ammo and I could do no better with his gun.
I gave him my 760 / '06 and he shot 3 times and hit the bulls eye twice.
We took that gun of his and the shells back to the shop where he bought it and threw it on the counter.
Demanded a full refund.
Bought a used 760 off the shelf - one of the oldest rustiest looking guns you ever saw and 2 new boxes of 150 gr Remington ammo and a $300 Swift scope and went back to the range and shot the crap out of the bullseye..
The new bolt action in them 7600's were not better than the older model - just cheaper for them to manufacture.
Your only option would be to invest heavily in a reloading outfit and try to develope a load that your gun might like. Working with different powders and different bullets until you find something that is a little more accurate. Or just getting rid of the gun and let someone else worry about how it shoots.
Borrow another scope and some mounts and tryi to see if it would improve the accuracy some.
Taking it to a gunsmith and having the head space checked out along with the barrel - hane them slug it to see what diameter it is and also putting a new crown on the end of the barrel. All which will cost you money. Or just getting rid of the gun and buying a good used one.
I will sell you a set of Weaver Detachable Scope mounts and the rail for $15 + the cost of shipping.