Author Topic: Bullet Inaccuracies or Key-Holeing (Read 456 times)

Chuck White · « **on:** May 03, 2006, 03:44:21 AM »

A thought just hit me while reading replies to "204 Reloading"!

I know that the rate of twist in the barrel controls the bullets flight!

I'm wondering if it (in that case) is the weight of the bullet, 40 vs 32 grains that causes the heavier 40 grainer to keyhole, or is it the longer bearing surface of the bullet (the actual bullet-to-barrel contact) that causes the instability of the bullet!

If it's the weight, we can't do much about it, except use the weight that our barrel likes!

If its the bearing surface, could we for example use a boat-tail bullet which would have a shorter bearing surface and shoot 40 grainers with the same accuracy as the 32's?

Questor · « **Reply #1 on:** May 03, 2006, 07:08:09 AM »

Length probably has more to do with it than anything else. I'm surprised you're getting keyholing in such a new cartridge that should have been developed with (long) plastic tipped 40 grain bullets in mind. Are you using some kind of reduced load? That could have an effect on it too.

Dusty Miller · « **Reply #2 on:** May 03, 2006, 11:05:35 AM »

Questor is on the right path here. Try some progressively hotter loads and see if somewhere along the way the keyholing comes to a halt.

Chuck White · « **Reply #3 on:** May 04, 2006, 01:17:36 PM »

I have heard others say that they got keyholeing with 40's and extremely accurate groups with the 32's!

Then there were others who said that both the 32's and the 40's were very accurate in their guns!

The load that I got the keyholeing with was the factory load, that's the part that puzzles me!

Questor · « **Reply #4 on:** May 04, 2006, 01:19:06 PM »

Chuck:

What kind of gun is it?

Chuck White · « **Reply #5 on:** May 04, 2006, 01:21:54 PM »

Sorry, I should have said earlier, my rifle is a TC Encore with a 26 inch factory barrel!

Lone Star · « **Reply #6 on:** May 04, 2006, 02:46:34 PM »

The two most common causes of keyholing are insufficient twist rate, and a greatly oversized bore/undersized bullet. Neither should occur with factory ammo in a factory rifle, but sh*t happens. The rifle may not have the correct twist rate or bore diameter-T/C buys barrels from various sources and they may have gotten an out-of-spec batch. It is very doubtful that the bullets are too small, but even factory ammo gets incorrectly loaded. Chronograph the load and see what the muzzle velocity really is.

Questor · « **Reply #7 on:** May 04, 2006, 03:11:58 PM »

TC stands behind their products. I had to send a .223 barrel back because it wasn't crowned right. They took care of it right away.

Try some factory 40 grain ammo just to make sure it's not your loads.

Describe the problem to them and tell them the group size. If it's, say, 2.5" at 100 yards they will be quick to agree that it's not suitable accuracy for a barrel designed for a prairie dog cartridge.

Lone Star · « **Reply #8 on:** May 04, 2006, 03:38:42 PM »

Quote

Try some factory 40 grain ammo just to make sure it's not your loads..

The loads which gave the trouble were the 40-grain factory loads... !! :?: !!

ron haralson · « **Reply #9 on:** May 04, 2006, 04:38:27 PM »

Try Greenhill's formula:

bullet length = 150 diameter square/twist rate.

If your heavier bullet exceeds this length by much, bullet length is probably the problem.

Lone Star · « **Reply #10 on:** May 05, 2006, 04:15:08 AM »

Quote

Try Greenhill's formula...

This tells him nothing - the factory loads won't work in a factory barrel.... :roll:

Questor · « **Reply #11 on:** May 05, 2006, 07:00:26 AM »

Chuck:

Just call TC and tell them you're shooting factory 40 grain ammo and tell them your group size. That's the next thing to do.

Chuck White · « **Reply #12 on:** May 06, 2006, 01:38:52 AM »

Thanks Guys;
I kind of thought that calling TC would be what everything narrowed down to!

I do appreciate all of the replies!

Thanks; Take Care;