1978 Ruger M77 Changing POI , Tumbling Rounds

EasTex

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Nov 15, 2021
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Location
Canton, Tx
I've inherited a pristine old M77 in 30-06, starting to see why it was never shot. Took it to 100 yd Range with the scope that was on it, shooting Core-Lokts and it wouldn't pattern at all. One round wouldn't be on paper, next was high right, next was low left. Put 10 rounds through it before I decided the scope was trash.

Got some different glass that functioned fine on another rifle, and took it to a 25 yd range.

The first few rounds weren't on paper, got a few rounds to land but they were all over the place too and not grouping at all. Some were on target, some flying past on left or right, and some kicking up dirt in front of the target, and this at 25 yards !

Down to the target, and there were three shed jackets resting against the paper inside the bullet hole. The target was paper on a shot out cardboard backing, nothing solid at all and you could push your finger right through the backing easy. Somehow it shed the jackets just on the paper, and gentle enough to leave it resting against the paper.

The holes it did punch weren't really round either, most of them were jagged tears like you threw a rock through the target and just kind of knocked a hole in it.

The barrel looks great with a bore light, everything is crisp and clean, nothing stands out as a problem.

Shooting Core-Lokts both times, but two different boxes purchased a year apart.

I'm seeing these older M77s are infamous for bad barrels, but this is bad bad !

Any thoughts on whats going on ? Is the bullet just tumbling the whole way ? Is there anyone out there that works on these old Rugers ?
 
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I imagine that the twist is standard 1-10", so I wouldn't think that would be the problem. I'd confirm the twist. And yes I'd inspect the bore and give it a good cleaning. I'd check the crown but bullets coming apart suggests a rough bore. But you say it looks clean and the rifling looks sharp. I'd try some different ammo. Maybe some Ballistic Tips. They have tougher jacket than core locks.
 
Any thoughts on whats going on ? Is the bullet just tumbling the whole way ? Is there anyone out there that works on these old Rugers ?
Any real gunsmith should be able to help you. Beware of the "wanna-be's". It doesn't take a 'specialist' to work on a Ruger 77. It is always best to have the rifle/shotgun/ handgun in hand to diagnose the problem(s).
 
The rifle should be checked. If it still shoots poorly then switch scopes.

A checklist for the rifle:

clean barrel

Check to see if action screws are loose.
Action screws should be torqued to an inch pound value.

Ruger M77 of that era use a blind hole for front action screw. Check front screw hole for bedding material or bottoming out. Either will have you thinking the stock is tight when it is not. This will cause point of impact shifting.

Ruger rings not seated properly in integral bases

Imperfection in crown

Screw holes in wood stock too small, drill larger so sides of action screw won't touch

Bolt handle touching stock

Mag box must not bind

trigger group must not touch stock

Trigger guard must not touch trigger

Rugers come with a fore end pressure point in barrel channel, sometimes this needs to be removed. If action isn't bedded that would also help. All my Rugers have been bedded with barrel floated.

Hope this helps
 
I've seen those accuracy fixes on the net and they do seem to help. But this tumbling issue seems to comes from the jackets and core separating. That's common from fast twist bores with certain types of rifling, or certain jacketed bullets. I've yet to hear of this happening with core locks. Two separate boxes of core locks so that seems to rule out the ammo. But I'd try some different ammo first. Then look at that bore. It might need some lapping.
 
That should not tumble, time to go through it, take apart, inspect clean and torque everything including checking barrel torque. Of course check and adjust barrel channel in stock.
 
The rifle should be checked. If it still shoots poorly then switch scopes.

A checklist for the rifle:
I appreciate you taking time to make that detailed checklist. I will look at each of these points before I take it somewhere.
I purchased new Ruger rings for the second scope, but neither of the scopes was new. The second scope I know for sure was fine on the last rifle it was on though.
 
I'll try to pick up some different rounds and see how it behaves. I was a little worried about shooting it more, it was behaving so erratically.
I guess the jacket may be seperating from the bullet as it leaves the gun ? I can see how that would throw the rounds everywhere, and why the jacket itself would stick in the paper once it got to the target.
 
What about a chamber cast and a muzzle cast to examine what is there. With the chamber cast include 2-3" of the barrel and for the muzzle you only need 1-2" to see if there is damage there.
 
I have seen many neglected rifle bores that tend to really deteriorate in their mid section, including rust and heavy carbon build up. Running a tight patch down the bore should alert you to this possible problem if it is there,
 
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