With less than 2 weeks before the state championship in the rifle class in CLAS, my rifle has suddenly started shooting keyholes at 50 yards all over the target off a benchrest. The load has been exceptionally accurate for the last several years, 37 grains of Leverevolution powder with a 150 grain Hornady RN. Prior to this, using a scope I could get a 1 inch group at 100 yrds. The load is a fairly stiff one but is also the most accurate and knocks down the 200 yard rams with regularity. Any ideas? I'm cleaning the barrel as clean as possible as a first step, any other ideas?

Cleaning is certainly the first step. If possible, get a borescope view to assess the condition of the bore and throat.

Has anything else changed? Primers, bullets, powder, crimping (or not)? Look for what's changed. Keyholing is often caused by undersized bullets - have you measured the later lot?

Make sure your latest lot of powder looks correct. You wouldn't be the first person to get something different than what you expect.

Check the crown for a nick or bump.

quote:

Originally posted by p dog shooter:
Check the crown for a nick or bump.

Good catch, I missed that one.

One of my long time hunting buddies had an old Savage 99 in 250-3000. It had been handed down a couple of generations and was a first year production gun in that caliber. He shot the you know what out of it. It started key holing so he cut about 1/2" off the muzzle, recrowned it and it was back to it usual excellent accuracy.

The first thing I would do is clean the barrel REALLY, REALLY GOOD, with J&B Bore Paste...

Then shoot it and get back to us...

Measure the diameter of your bullets. Seems impossible, but undersized bullets (or bullets with bad bases) can cause this problem. For it to be a fouled bore as a cause, the metal fouling would have to be extreme...


.

Make sure you get any metal fouling out of the grooves.
Slug your bore. Check the groove dia.
Marlin Microgroove are known to be on the large side.
See if it has tight or loose spots.

Find some .310 cast bullets and try a known good cast bullet load with the larger bullet.

If your bore happens to be .310, .311, or .312
you might think about using a RN bullet in those diameters.

I have never seen copper or powder fouling with smokeless powder cause keyholing, It can cause accuracy problems in guns with rough bores.

I would change bullets and see what happens. I would also try a different box (lot) of the same bullets. I would use new brass etc for no other reason than to have a startng place to eliminate the causes. Its definitely and investigation and you have to remove the obvious, when that's done and the problem still exists, its time for a new barrel.

It is rare indeed with a 336 or 94 actually needs a new barrel, hell 99.9% of them shoot as good with a trashed barrel as they did when the gun was new..Low velocity rounds normally just need a rifling to hang onto and it need not be crisp...I have owned so many old Win. and double rifles that shot so good and the bores looked like the inside of a tramp steamers pipes.

quote:

With less than 2 weeks before the state championship in the rifle class in CLAS, my rifle has suddenly started shooting keyholes at 50 yards all over the target off a benchrest.

Well???? What happened? How did you do?