I'm telling you that I've read that DB taught Sheila how to shoot,years before the massacre. She was born and brought up on a farm surrounded by guns of all kinds. Sheila KNEW how to shoot and had been to a few shoots herself.
It's not my fault if you only read biased information to suit YOUR way of thinking.
The one reading biased information is you. You read accounts from books which don't proved any evidence while I go the sources. Only DB would know for sure whether he taught Sheila to shoot unless someone else were present. There are no witnesses who claim they saw DB teach her to shoot nor doe she claim he did.
Secondary evidence would be a claim he told someone he taught her to shoot which would set the stage for him saying the person was lying or misunderstood and then it comes to credibility. There are no witnesses who say he told them he taught Sheila to shoot nor are there any witnesses who say Sheila told them DB taught her to shoot.
If you were not biased beyond all reason and actually objective like you claim to be then you would look for witness statement to events and not make claims unless there were a credible witness who says they witnessed what you are asserting.
You have no witnesses though who saw DB teach her or a witness told by DB or Sheila that DB taught her. That is the only evidence that could be brought to bear and thus where a rational objective party would look.
As a practical matter being taught how to use a double barrel shotgun would not enable someone to know how to use the murder weapon because they function differently. So even if DB had taught her to shoot a shotgun it would still mean little but there is no evidence that supports your claims. You are the one being biased and closing your eyes to the truth not me.