Fired brass vs Virgin brass POI shift

[MahtewsSB]

So I just finished up some load development with my 22-250 and did all the development with the same 50 pieces of brass, this was all i had until recently. I purchased another 100 pieces recently and decided to go ahead and load up my final load in most of my brass until i ran out of bullets. While out shooting today, I noticed there was a marginal shift in POI when shooting the virgin brass. I had set my 200 yard zero with the "old" brass and when i started shooting today i was using the virgin brass and the POI was approximately 2.5" right and 2" low at 200 yards. This was a .48" 3 shot 200 yard group, but was not even in the same ballpark as the original brass. I shot a group with 4 of the 7 rounds that were with the original brass to see if something had moved in my scope or if it was due to the brass and this 4 shot group was center bullseye.

Is this normal? Will the POI's match up once the virgin brass has all been shot once and reloaded again? What caused this?

 

[dmoran]

In the forming of the new brass to the chamber walls, robbed small amount of combustion pressure to adhere/iron the cases to the chamber wall. Which as a result would also have robbed a little speed/velocity. The end result being your change in POI and accuracy.
The upshot is, now your new brass is formed to your chamber, and will act like other formed brass near the same cycle/rotation.
Donovan

 

[MahtewsSB]

In the forming of the new brass to the chamber walls, robbed small amount of combustion pressure to adhere/iron the cases to the chamber wall. Which as a result would also have robbed a little speed/velocity. The end result being your change in POI and accuracy.
The upshot is, now your new brass is formed to your chamber, and will act like other formed brass near the same cycle/rotation.
Donovan

That is what i thought was happening but i wanted to make sure as this is the first time this has happened to me. Thank you for the reply and confirming my thought.

 

[jcampbellsmith]

Is all the brass from the same brand? Regards JCS

 

[MahtewsSB]

Is all the brass from the same brand? Regards JCS

Yes all brass is from the same barrel.

 

[swc123]

Ever considered wind and mirage effects?

 

[fguffey]

MathewsSB, I read through your OP, I did not find any mention about sizing as in sizing back to minimum/full length sizing, neck sizing, partial etc.. There are factor changes.

F. Guffey

 

[MahtewsSB]

Ever considered wind and mirage effects?

it was dead still with no wind and no mirage present. I shot the new brass and old brass side by side and there was a difference in poi

 

[MahtewsSB]

MathewsSB, I read through your OP, I did not find any mention about sizing as in sizing back to minimum/full length sizing, neck sizing, partial etc.. There are factor changes.

F. Guffey

The original brass is F/L sized every time and the neck is sized with a bushing And trimmed back to specs if needed. The Virgin brass was only trimmed and the expander ran through the necks to round them all out

 

[dedogs]

Mathew, You didn't say weather this is a factory chamber or custom. If it's a factory chamber you may be shortening the life of your brass by full-length re-sizing each time. I believe this is one of the factors that fguffey is referring to. You might want to consider only bumping the shoulders on your fired brass. Otherwise you and dmoran are correct about fire-forming changing your point of impact. The amount of this change in POI seems to vary with different cartridges. Hope this helps, dedogs.

 

[MahtewsSB]

I guess one way to know for sure would be to keep the old and new brass separated all the way through cleaning and loading one more time and then direct compare them again and see if poi now matches with the cases being fit to the chamber. This will be my first action in finding an answer as I believe that is the problem.

If that does not solve it then I will go from there.

 

[hogan]

Seems like a LOT of shift...

If you have a Wilson Case Gauge or RCBS Precision mic you can measure the oal of virgin and fired cases. Lots of stretch? There is your cause...

Don't want to trim cases before first firing. Don't want to trim them until bolt gets hard to close.

Might want to use Check Weight set everytime you setup your scale. Zero your scale as close to your charge as you can, if not to the closest whole grain value. Might be some variation in your charges if the fired brass was loaded on another day.

Using CCI primers? Might change brands.


Should see very little shift even when fireforming to an AI chamber. Maybe your scope shifted? Had that happen before.
Got a boresighter w/collimator grid? Just one more diagnostic tool to assure proper evaluation of variables.

 

[jcampbellsmith]

Is all the brass from the same brand? Regards JCS

Yes all brass is from the same barrel.

Which barrel would that be? Remington, Lapua, Winchester? Regards JCS

 

[jlow]

Is all the brass from the same brand? Regards JCS

Yes all brass is from the same barrel.

Which barrel would that be? Remington, Lapua, Winchester? Regards JCS

Right, the question were they from the same brand? Frankly the question should be from the same lot. Any difference in average case weight?

 

[savagedasher]

It is all related to case capacity. When fire forming Dasher brass we are increasing the volume of the case around 2 grains more. The impact of un fire formed is always different the a full formed case. Most of the time they shoot well enough to shoot 300 yd matches. 1 /2 '' at 100 . Larry

 

[expiper]

in 2009 I loaded 300 ,,6mm BR (Lapua) that were new and out of the box except for chamfering the case mouths (some were a lil' ruff) ,,,Loaded em with my county fair load of Rx-15 (droped from a Culver powder measure ) and Berger VLD's and went to Folsom for the 600yd Naionals and set a three target NBRSA world record,,,,so "virgin" brass will shoot well if loaded properly,,,Roger...PS..these were not being FF'ed into Dasher,,,just plain ole' BR....

 

[MahtewsSB]

Is all the brass from the same brand? Regards JCS

Yes all brass is from the same barrel.

Which barrel would that be? Remington, Lapua, Winchester? Regards JCS

My mistake I read your post to fast prior to responding, I was in class at the time. Yes all brass is the same brand. It is all lapua brass. I am unsure about it being the same lot or not.