Keyholing?

[lcclower]

What makes cast bullets keyhole? 38 spl wadcutter loads.

[Dieselhorses]

Lead is too hard probably causing inadequate obturation (bullet fit in bore). Bullet needs to "seal" bore thus preventing gases from bypassing. (Somebody chime in if that's not right.)

[Winger Ed.]

(Somebody chime in if that's not right.)

That, and maybe a undersized boolit could do it.
The boolit wouldn't stabilize, and fly sort of like a football that wobbled and didn't 'spiral'.

[hoodat]

Maybe give us the sized diameter, load, hollow base or solid, firearm, range, --- one or some of these things will be the reason. Something is waayy wrong if you are having that problem at any reasonable range. jd

[243winxb]

A slightly oval hole is normal for 38s.. A true keyhole is undersize bullet diameter or bullet skidding from using very soft/pure lead.

High pressure may cause it also.

[nicholst55]

Wadcutters lose stability beyond about 50 yards, so if you were shooting farther than that, that could be the reason.

[rintinglen]

The number one reason is a poor fitting, undersized bullet, especially if cast hard. However, a perfect wadcutter, of ideal alloy and hardness immaculately prepared and sized will still lose stability at ranges much past fifty yards resulting in greatly enlarged groups.

One other thing besides the bullet is the revolver itself. If you have an undersized chamber throat or two, you may have a condition where you get 4 or five good shots, and one or two keyhole shots. If this "5 +1" pattern occurs often. Doug Guy is the fellow to make it right. He will hone the chamber throats for you and make them as close to identical as you can measure. I heartily recommend his work.

[45DUDE]

If a hbwc an overcharge of powder can send the end down range and the rear stuck in the case.

[lar45]

Or a blown skirt on a hbwc.