so i am doing further load development on my Gap-10. it has a very tight match chamber. I know that "fire formed brass" is supposedly more consistent/accurate. however the shoulder is only set back .005 from my chamber. will it really effect my load development if i choose to use the virgin brass?
not that it matters but my data is as follows
gap-10 20"
.308
new win brass
178 amax
42-44 gr of varget
CCI LR

It may change it up some. Just keep the head stamps the same. If you do a partial sizing, make sure they will chamber. I'd recommend a FL sizing for a gas gun.

it is all Winchester. all FL sized. i guess i suck at asking my question correctly, but what i mean is virgin Winchester brass has shoulders sized.005-.007 deeper than my chamber. when i full length size i usually only bump back about .004" therefor these will have an extra .002-.003 to expand, will that aspect effect load development or accuracy?

It can. I'll verify my load again from virgin brass to once fired brass. I normally don't see much difference. I did see some differences in my 6.5x47 Lapua from virgin brass to once fired. I sized it with a slight bump of .003", and picked up about 50 fps and had some sticky bolt lift. So, I may need to reduce my load a touch. It also didn't put them in the same hole like they did with the virgin brass.

So it's Actually NEW brass? If so there may be a slight change in pressure thus velocity once you resize but not enough to fret over and there is nothing you can do but fire and resize to suit yourself.

so load develope with the virgin, then fine tune with once fired... i guess it sounds like i was being too OCD about the extra .002-.003 of setback

Exactly what I do. Most of the time your load with new brass will be very close to what you get with fire formed brass. Sometimes exactly works or sometimes a tenth or two more or less gets you there.