Bullets Key-holing

Warthogga10,

There are several things that can cause keyholing, and excessive crimp can be one of them. It's sometimes caused by an undersized bullet for the bore, and sometimes from overdriving the bullet, which usually applies to cast or plated bullets. That simply means so much velocity that the bullet strips through the rifling, rather than riding it and spinning properly.

Excessive crimp can cause the bullet to swage down smaller in diameter than it was when seated and before the case was crimped. It only takes a couple thousandths to make it too small for the bore and will cause keyholing.

The 95 grain bullet is pretty light for the 9mm, especially if you're driving it pretty fast. It also doesn't have much bearing surface, so it would be more likely to swage down from the crimp. With the 9mm, you should be taper crimping and then only enough to remove the belling of the case mouth that you put on to seat the bullet.

If less crimp solved your problem, then you probably guessed right at the cause of the keyholing. I've seen it in 9mm several times and that was one of the causes.

Hope this helps.

Fred

9mm seems to be the most fickle caliber of all time when it comes to lead bullets.
The best results I have achieved were by using lead sized to .357".
But slugging will tell you what diameter will shoot best in your gun.

I have found by slugging several 9mm barrels that the bore seems to taper toward the muzzle. With jacketed this is okay but with lead bullets they should be sized for the largest portion of the barrel.

To properly slug a 9mm barrel drive the slug from the breech at least 1.25 but no more than 2.0 inches into the rifling. Then drive it back out towards the breech.

Undersized bullet seem to be a bigger problem in barrels with an odd number of lands and grooves.

Kind of dumb newbie question (we all had them at one point eh?)

I understand what keyholing is but how can you tell it is happening?

non round holes in your target - cardboard or heavier, not paper. paper lies about such things.

thanks pauli.

I would assume crap accuracy would happen also?

I had a Beretta 92FS inox compact that 9mm that would reliably keyhole with any hardcast lead bullet no matter how hard it was. the first 20 rounds would shoot fine, and then the bullets would start to hit the target sideways leaving a keyhole profile in the target.

Upon removing the barrel and inspecting it I discovered that there were shreads of lead hanging from the rifling, I have never seen anything like it in years of reloading cast bullets. THe manual also specifically said no lead bullets should be shot in it.

It shot wonderfull patterns err groups with jacketed and plated bullets. My theory is that the twist rate was a touch fast for lead.

You may want to check your barrel for excessive leading, like it may be a smoothbore in spots by now.

If I knew how to post a picture on this forum, I could show you what they look like. I was given some stiff 45-70 cast bullet loads for my Marlin 1895 and they tumbled so bad that they hit sideways at 25 yards and it was next to impossible to hit a target at 100 yards.

Yes, accuracy suffers from keyholing and tumbling bullets. When I was rangemaster for our department back in the late 1970's, the 9mm was brand new and about half (300 or so) of the officers were carrying them. I had put in a purchase request for practice ammunition for the 9mm's, since I loaded all the practice .38's on an automatic press. I had specified the manufacturer I wanted, but the purchasing dept. had bought from the lowest bidder. All the rounds keyholed and tumbled. At 7 yards the bullets hit the target sideways and at 50 yards it was next to impossible to hit a silhouette target with them.

I packaged them up and wrote a memo stating that the only possible use I could see for their "low bid" ammunition was to put it in a coffee can and fill it with concrete and use it for a boat anchor. The purchasing agent about had a heart attack and said I couldn't tell a vendor that his product was only good for a boat anchor. I just told him to read the memo again, since I all ready had said that and told him to forward it to the vendor and then get me the right ammunition. No problem after that.

Fred

Keyholeing can be attributed to many things.

too heavy a bullet for the rate of twist of the gun,

too soft of a bullet and "skidding" in the barrel,

not enough bearing surface to get the bullet spinning.

"soft" loads just not driving the bullet fast enough.
(usually with long heavy bullets)

not enough rifling. worn or poorly made barrel.
or an oversized barrel

I once saw a Maverick (not the mossberg brand but the very low priced pistol of that name) come into the shop and the guy complained that it shot like crap, we said what do you expect from a 69 dollar gun. (he had not bought it from us) when i looked at the barrel with a bore light you could see scratches like some one had run a rifleing button thru the gun but there barely enough rifling to detect by feel with a dental pick.

finally we got a 36 cal ball of soft lead and it would drop right in and with hand pressure on a pencil you could push it through.

I would get your bore checked. you might find that you are a little big there too.

Upon removing the barrel and inspecting it I discovered that there were shreads of lead hanging from the rifling, I have never seen anything like it in years of reloading cast bullets. THe manual also specifically said no lead bullets should be shot in it.

Click to expand...

Probally has polygonal rifling. DO NOT SHOOT LEAD THROUGH POLYGONAL GUNS!!! IT CAN RESULT IN DANGEROUS PRESSURE BUILDUP AND QUITE POSSIBLY BLOW YOUR GUN APART IN YOUR HAND!

In my 9mm's, tumbling has always been caused by soft bullets. Try adding more tin and/or antimony to your alloy. As was said, sizing to .357 may help too.

Warthogga10,

The difference between polygonal and cut rifling is that polygonal is rounded, with no pronounced edge between the lands and grooves. On the other hand, cut rifling has sharp edges between the lands and grooves.

Cut rifling is what you're used to seeing when you look down the barrel of your rifle or pistol, since it's easy to see the lands standing out from the grooves. With polygonal rifling, you can still see it, but everything is rounded. Once you see one, you'll notice the difference.

Hope this helps.

Fred

Lead bullets and polygonal rifling can lead to gas blow-by. The gas gets past the bullet in the "corners" or low spots of the rifling. This can lead to gas cutting of the bullet, and lead buildup near the lede.

Some pistols with non-standard rifling (notably the Glock) can fire out-of-battery and also have poorly supported chambers. What can happen is the lead buildup causes the cartridge not to fully chamber. The gun will still fire with the cartridge not well-supported and the slide not locked, and KA-BOOM.