Bullet keyholing ????

[Bulseyetom]

I recently purchased a Sharps Borchardt smithed by CC Jackson in the 50's to a 219 Improved Zipper with a Heavy Varmint contour barrel. For a 60 year old barrel with god knows how many rounds it shoots lights out, or at least most of the time. The bore by eye looks good and I have scrubbed it with JB's and I am assuming the twist to be a 14 twist as that was the twist of the day for such competition rifles. I am using the load provided by the previous owner which was worked up by the original owner who competed with the rifle. To make a long story short, about 1 shot out of maybe 20 keyholes but the bullet is always within an inch of the group at 100 yards. I shot a five shot group several weeks ago that I never noticed until I got home had a keyholed bullet as it was just a large ragged hole. What would anybody guess is making the odd bullet do that when at least 90% of them are shooting around 3/4 moa? I haven't weighted the bullets but they are all new 50 grain flat base bullets that are shooting lights out in my Ruger #1 223. I am not going to rebarrel just yet as I am just shooting at the range and it is very accurate for the most part but am really curious as to what is going on. Thanks for any help. Tom

[BadgerBob]

Congrats on the find! Im still working on mine, there a really cool single shot. I think if it where my rifle I would check the throat first, an improved Zipper could easily burn a throat out, who knows how many rounds have been shot through that old gun. Im thinking you should post some pictures, you just don't run into those old guns very often.
Bob

[Bulseyetom]

Bob, I will try to do that. It is a really nice old rifle with a trigger to die for. I have some 60 grain bullets I am going to try as they are longer and I might be able to reach the lands. If I ever do anything to the rifle it will be restocked to a sporter instead of a heavy varmint in maybe 25-35 Ackley. I still can't complain when a rifle shoots 95% of the bullets 3/4 moa or less at 100 yards. Tom

[17 Nickal]

Have you slugged the barrel?? It could be .228"

[george ulrich]

older 22 barrels were ,228 groove dia. but if is stabilizing some bullets check o.a.l. of bullets, going to a longer ie 60 gr is the wrong direction. longer bullets require faster twist to stabilize..

[Daryl]

Many of those older barrels were also .223" and with a 16" twist. If you are on the ragged edge of stabilization for any given bullet, you might get the odd keyhole, before they ALL keyholed.

Something else that caused keyholes in my short swift, was driving bullets too fast for their construction. The rifle still shot around an inch, but there would be 2 to 3 keyholes in every group, with lead swirls around some of the holes.

Bore condition can add to that as well - slightly rough will be tougher on the bullet jacket than glass smooth would be.

[Bulseyetom]

I thought that going to the longer bullet might help because the jump into unworn lands might be less if the throat is worn much. Maybe I should also try to find the next slower node to see if that helps. Nothing to lose here so will try all suggestions and see what happens! I also have tons of 40 grain bullets for my Bee that I might try. Thanks to all. Tom

[Old Hawkeye]

Might not be key holing at all. I had some shots on paper that first appeared to be keyholed, but it was just the way the paper was responding to the bullet impact. When I took my finger to the back side of the target and smoothed things out the holes were perfect circles. Really had me fooled for awhile. You might check that out before you go searching for other answers. Not saying that's what it is, but just eliminate that possibility first.

[Old Hawkeye]

Originally Posted by george ulrich

older 22 barrels were ,228 groove dia. but if is stabilizing some bullets check o.a.l. of bullets, going to a longer ie 60 gr is the wrong direction. longer bullets require faster twist to stabilize..

The only "older" 22 barrels I'm aware of that were .228" were for the 22 WCF (Winchester Centerfire), a black powder round that was the precursor to the 22 Hornet.. All 219 Zippers as well as all the other 22 centerfires were .224", except some of the pre WWII Hornets which were .223". Can't imagine someone rechambering a 22 WCF to 219 Zipper to end up with a .228" bore, although stranger things have happened I'm sure. No way it could shoot 3/4" groups with 95% of it's shots if it was a .228 bore, as the bullets would rattle down the bore & not engage the rifling.

[BadgerBob]

The 22 Savage High Power was a .228 barrel also but most of them where skinny little Savage 99 barrels, I have run across at least one that had been re-chambered to Zipper, but the guy knew what he had and shot 70gr .228 bullets.

Bob