Bullit Keyholing?

[BOOM BOOM]

HI,
I've got 2 questions really.
I was out shooting some of my old unquenched WW loads and got 2-3 keyholes per 100 rounds fired. Now I know this is common if one is fire forming brass in wildcat cartages W/ undersized bullets (25/06 in a 7mm/06 wildcat), or if the rifling is too fast or slow for the bullet wt.
But why would i get only 2-3 keyholes out of 100 rounds.
2nd I noticed that after about 50 rounds the point of inpact started to rise &
kept rising slowly w/ each successive group. I guess it could be because of bore leading but accuray did not deteriate.

[44man]

You never said what caliber, boolit or powder you are using. Some powders like 4227 are very heat sensitive and the point of impact can change as the gun heats. Usually it is a lowering of the point of impact as velocity goes up from heat. The raising of the impact is sort of a mystery unless your sights are moving or you are changing your hold. This can be caused by a reduction in velocity also due to leading which creates friction in the bore even though pressure increases. Another thing is poor bedding on the barrel or screws loosening.
I had a strange happening with a TC 30-30 years ago. I was using a cast GC boolit and the accuracy was super. I have several nickels with holes in them from 100 yd's. I ran out of gas checks so I tried some without them. Every single boolit keyholed at 50 yd's. That loss of a tiny amount of drive area changed a tack driver into a slug.
If you are borderline on stability and your velocity is changing due to heat sensitive powder, leading or some other reason, you sure can get some keyholes. Let us know if you find a reason.

[Junior1942]

Boom, if you'll look closely at the other holes some of them will probably be slightly oval in shape. That shows a bullet with yaw.

[Willbird]

I have seen 405 grain 45/70 boolits keyhole when I leaded the bore from using liquid earwax (I sprayed the boolits with mineral spriits before coating, prolly not enuf lube)


Bill

[BOOM BOOM]

HI,
I belive these loads were w/ eather green dot or 700X . They are about book max loads. Each group shot had all the same cases in the group. There were some bullet holes touching but I did not notice any holes made by yawing bullets.
Only the 3 keyholed ones .

[Bass Ackward]

HI,
I've got 2 questions really.
But why would i get only 2-3 keyholes out of 100 rounds.
2nd I noticed that after about 50 rounds the point of inpact started to rise & kept rising slowly w/ each successive group. I guess it could be because of bore leading but accuray did not deteriate.

Boomer,

Well. Now you might have just discovered why some people believe that hard bullets shoot more accurately then soft. And why cast is usually shot with faster powders.

When a bullet has a defect, pressure on the base will push it closed. But since most molds are base pour, the voids occur at the top of the mold or .... the base of the bullet. When one part of the base is pushed farther forward than the other, your base is no longer square. The size and location of the void and the amount of pressure determine how far out of square it will actually go.

When this bullet gets to the crown, gas excapes at a much faster velocity than the much heavier bullet. Since it occurs from the short side, it causes jet propulsion in the opposite direction. As the base totally clears the crown, this force pushes the base away from the early break. Sometimes this merely causes the bullet to yaw and it later stabilizes because of bullet rotation. Sometimes the effect is so great that stabilization never takes place and you can get a keyhole.

A harder bullet has more strength to resist pressure. So ..... you get less fliers from the same quality bullets that are soft. Faster powders tend to peak early and then drop as the bullet moves toward the muzzle. Even if the base is defective, there is less pressure / force available to cause deflection. So .... a larger percentage of bullets stabilize sooner and thus shoot better. Virtually all bullets have some amount of yaw at the begining.

One other thing you stumbled on to. Just because a bullet leads, does not mean that groups will automatically go south. I have actually seen groups improve in a small amount of cases. But leading causes a change in friction which will change pressure. Change pressure, you change velocity, and point of impact.

Of coarse there are a lot of other possibilities, but this is my .... guess since the amount of key holes were so few.

[BOOM BOOM]

HI,
Thanks, that sounds like the answer to my question/problem. The groups did seem to improve afterabout 50 rounds, and the point of impact seemed to rize.

[44man]

Bass, very good way to explain it.

[BOOM BOOM]

HI,
I was shooting up some old low vel.(1300'/s approx.) 7mm/06 168gr. gc. bullets, about 13gr. 700x loads w/ air cooled ww, prior to working up a new load useing dacron filler.