Does sandbag resting a pistol affect point of impact?

First topic message reminder :

Hi all, I have a question. I am bench rest testing a Nelson conversion on a 1911 frame. I think I have it sighted in while shooting offhand. But then when I rest it on a sandbag to test fire it, the group moves up to the top of the target frame, in the 5-ring. Is that normal? I know it's not free floated like a national match rifle is, but I wasn't expecting that.

Also, the best group size I got was 3.5" wide at 50 yards with a 10 shot group. The worst group was 4.5". I don't think that is very good accuracy from a sandbag. This is all with iron sights since I don't have a scope or dot. Isn't that poor accuracy?

I think I went to a 16 or 17 lb spring on my Marvel to fix it. Left it full length. Don’t remember the original main spring weight.

I remember doing that to my old unit. I should do the same with this one. I went with a lighter 7# spring and I may have even trimmed that spring also.

I think the 9# spring is the "standard" spring that comes with the unit. However, 9# is not "standard" for me.

I have a spare spring kit for this, and the 8# spring is painted red. There is another spring and it is painted orange. Does anyone know what weight that one is? Is it 7#?

Is the barrel free floating or bedded?

I don't think it's either.