Sleeping bag fill question

[Powder River]

I ordered a Western Mountaineering Antelope MF from an online store, then immediately canceled it because I saw it somewhere else with free overfill. As it turns out, the first store shipped it anyways and now I have two identical sleeping bags, except one is 2 ounces overweight (the non overfill) and the other is 6 ounces overweight. (it was only supposed to be 3 ounces overfill)

So my question is, assuming the weight difference between the two (and also compared to the specs on the web page) can be attributed to additional fill, what is the temp rating on these bags? The Antelope is supposed to be a 5 degree bag.

And here is another variable. WM has a -10 degree bag called the Lynx, which is supposed to have 32 ounces of fill. That happens to be the same amount of fill that I calculate is in the heavier of the two bags I received. However, the Lynx has 5 ounces more fabric than the Antelope, while their measurements are almost identical.

At first I was thinking that the 6 ounce overfilled Antelope would be around -10, because that's how much fill is in the Lynx. But now I'm wondering if that extra material the Lynx has is necessary to allow the fill to expand, etc. In other words, the extra 6 ounces might be useless weight because it would not add to the warmth of the bag. What do you think?

[Snowleopard]

There can be variations in weight of fabrics and of sewn goods. The weight differences could be different batches of the fabrics used or different seam allowances used, or more down. The overfill adds some warmth, but my guess is that it doesn't take it down to the temps of the warmer rated bag.

I have a Feathered Friends 20F bag with several ounces of overfill and my guess is that it's good for 10F to 15F.

You could call the maker and ask how much warmth the 3 oz overfill adds.

You would be better off believing that it's a lot warmer, then by the placebo effect you'll feel warmer. Enjoy your new bag.

[The Will]

A friend ordered a Feathered Friends bag with overfill. During the course of their discussion the FF rep mentioned that if a person were considering 6 oz or more of overfill that it would be better to just get next warmest model.

My take on that is this: while there is a positive correlation between overfill and warmth there is a point where you get diminishing returns. The warmer bag would have deeper baffles to allow the down to loft higher, creating a thicker insulating layer.

This is just from vague memory but recall hearing something about every 2 oz of overfill adds 5 degrees. That's just a statement, a rough guide. I wouldn't put anymore stock into that than I do about liners adding a SPECIFIC amount of warmth.

[Franco]

An extra 6 oz of fill is about an extra 23% total fill, so that would be very noticeable. Like Snowleopard has explained fabric can and does change in weight. Some years ago I weighed 4 or 5 tents ( BD Lighthouse or Firstlight) at a local shop. There was a variation of 4-5 oz between the lightest and the heaviest. No two were the same.
My guess is that you did get about 3 oz extra fill the rest is fabric in that one , and possibly fabric in the other
Franco