[Gila Jorge]

Have a 7mm RemMag and shot a nickle sized group with 175gr Fed Premiums
boattails and then installed a new scope and loaned the gun to a friend to shoot
with 175gr Remington Core Lokts and at 50 yards he brought me a targe that evidences key holing. Oh, I had a KDF muzzle brake put on also and they automatically recrown with installation. The brake was in place so their could not have been any damage to the crown. All thats left is ammo....maybe
the gun simply does NOT like Remington ammo....?

[Art Eatman]

Was your nickel-sized group also at 50 yards? And, was the keyholing a full 90 degrees, or was it just slightly off?

It might be that the twist rate of your barrel might not really be right for the longer bullets, and they don't settle down and fly true until beyond 50 yards or so.

Just a guess.

Art

[Jim K]

Was the nickel size group shot before or after the brake was installed?

Jim

[Gila Jorge]

Both before and after the muzzle break installation....but the nickle group was at 100 yards NOT 50 yards. Maybe the problem is short yardage...? I've
heard of problems with 300 Weatherby mags at short range with bullet blow up which certainly would cover keyholing...?!

[MLC]

What kind of rifle is this?
Perhaps the core lokts are longer than the federals and the rifle won't stabilize them properly. 175's at the heavy end of the 7mm, try some 130-150's and see if they work ok( as long as you're sure the muzzle break is not being grazed).
IMHO the muzzle break isn't necessary for the 120-150 grain bullets, so you could try the lighter ones with and without the break.

[Jim K]

Bullets take a while to stabilize in flight, but I would think 50 yards should be enough. Have you tried the Remington loads at 100 yards? ( I am assuming both loads are factory and that reloading errors can be ruled out.)

Bullet blowup is a different matter from keyholing. Bullet blowup happens when a bullet is driven so fast that it simply blows apart from the centrifugal force generated by the rotational speed of the bullet. (A bullet travelling 3000fps fired from a barrel with a 1:12 twist is rotating at 180,000 revolutions per minute.) Blowup is fairly common with high speed varmint loads and thin jacketed bullets.

As for a Remington rifle not liking Remington ammunition, that is entirely possible, but I would look at other factors first.

Jim

[Gewehr98]

When I was working up handloads for 7.62x45 Czech, I had some batches that keyholed at 50 yards. I was also about 200fps shy of what the issue military ammo chronographed at. When I bumped up my handload to match the GI stuff, the keyholing disappeared. If I remember right, Greenhill's formula is also velocity dependent, isn't it?

[Hand_Rifle_Guy]

175 grains is definitely at the top of weight-for-caliber in 7mm. Standard 7mm bullet weight is usually 139 grains.

I seem to remember those Remington Core-Lokts are really long RNSP's. They would require a very fast twist rate to stabilize them properly, something like 1 in 7". Some early factory guns predate the heavy-bullet-for-moose/elk role for the 7mm Mag, and they might have a slower twist than those darn-near-1 1/4"-long jacketed lead hot-dogs the factory loads in response to market demand really want. When bullet OAL starts to get up to 5x the diameter, stability becomes an issue.

[Gila Jorge]

The rifle is a 1976 200th Year Ruger 77R. Originally when I sighted it in
was with 175gh Fed Premium boat tails and three shots could be covered
by a dime. Later, I changed scopes to a Leupold 3.5x10 VariX3 and added the KDF muzzle break. KDF recrowned the muzzle at the time of installation.
I then shot 160gr Fed Prem Partitions. Just last week I loaned the gun to a friend and told him to resight it as it was then shooting 175gr Remington
PSP Core Lokts. That'w when the keyholing was evidenced. First time with Renmingtons.

[Archie]

keyholing is a sign of bullet instability. (Taa-daa!)

Usually, instability comes from underspin. (A LOT of over spin is better than a LITTLE underspin!)

So....
What is the actual muzzle velocity with this rifle and load?
What is the actual twist rate of the rifle in question? The Ruger website says their currect 7mm Rem Mag twists at 1/9.5".

At one time, I loaded up some 357 Magnum ammo that keyholed at 15 yards. The bullets weren't grabbing in the rifling, as far as I could tell. (Lead bullets from an unreliable source. I was broke and they was cheap!)
So... any ammo left? Can you check the bullet diameter to insure they are the correct size? (Not often, but factories make boo-boos too.)

Last, do you handload? How do those work? Do the lighter factory loads work right? What bothers me is your statement about 175s working when you first had the rifle. Putting a brake on it should NOT screw up accuracy. Since the brake is at the end of the muzzle, it can't slow down the bullet to effect the rifling rate prior to release of the bullet from the muzzle.

Gwehr98: Yes, Greenhill is velocity dependent; the spin imparted to the bullet is partially due to velocity.

Hand Rifle Guy: You made me laugh. You are correct, that 175s are at the top of the weight range for 7mm bullets. But I remember the original weight bullet for the 7x57 Mauser was 175. Muzzle velocity was around 2300 with a twist of 1 in 8.8 inches. (No doubt it comes out even in metric.)
At the time, it was a cracker-jack flat-shooting rifle.
I have always found it amusing the 7mm "Magnum" shoots such a small bullet in relation to the 7x57 Mauser. But that is of course, how the ammo maker gets to claim incredible muzzle velocity.
I'm of the old school that believes if one is to use half a peck of powder in a cartridge, one should fling a proper (big) bullet. But I'm a dinosaur.