bullet length differences batch to batch impacting accuracy?

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I found a good load using sierra 180r SBT for my 300 win mag, consistently shooting about .75 MOA at 300 yards. OAL using the hornady bullet comparator is 2.850. Wouldn't you know it, ran out of bullets right as i found the load. So I bought another package. Not changing the seating die the OAL with the new batch is 2.856.

I've been to the range twice and the new bullets look to group about 1.5 MOA at 300. I would never discount operator error, but looks to me like the difference in length from batch to batch is impacting my accuracy as all other components are the same.

Could a .006 change in OAL cause my groups to double?
Assuming, the operator is not the error, what is your suggestion from here? Should I just seat the bullet .006 deeper or start messing with charge weights? Other ideas?
 
Don't seat the bullets the same as the first batch. Seat .006 further from the lands. That's what I do for varying length batch numbers of the same bullet.
 
what's the difference in OAL of the Bullet it self?
Actually do you have any of the older loads left?
what's the OAL of the case and bullet not to ogive much difference?
check the catalogue # might be a different bullet.
 
Did you by any chance measure the diameter of those bullets?
I have seen a difference of .0006" between two batches of the same bullets.
This always affects the way they shoot in my experience. Dave.
 
Different lot of ANY component.. work up again.

Yes, buy your stuff in bulk to save this headache.

Yes, changing the ogive location vs the lands WILL affect the effective charge and tuning of a load. You may be lucky and just have to seat the bullet in a bit deeper but I would suspect you will need to change BOTH seating depth and powder charge.

Jerry
 
Measure and sort all your bullets by base to ojive length using your comparator.

Load using only one length at a time.

If you find that using a different length makes drastic changes, your load tuning is not optimal.
 
I've seen changes in groups on different range days, with the same batch of bullets. Remember there are many variables when it comes to shooting good groups. Wind direction and consistancy, temperature, how clean or dirty the barrel is, amount of copper build up, the shooter, even the angle of the sun can make a target clearer on some days I find.
 
Varmit said:
I've seen changes in groups on different range days, with the same batch of bullets. Remember there are many variables when it comes to shooting good groups. Wind direction and consistancy, temperature, how clean or dirty the barrel is, amount of copper build up, the shooter, even the angle of the sun can make a target clearer on some days I find.
Click to expand...

Also, don't disregard neck tension / hardness and neck cleanliness. We just had a discussion surrounding cold soldering (may not specifically apply to this case but still worth considering). Many times I have experienced the same lot of bullets resulting in different CBTO length measurements due to neck inconsistencies.

http://www.canadiangunnutz.com/forum/showthread.php/1443660-Interesting-experience-at-the-range

Rooster
 
If you find a bullet you like, buy a big supply of them. I sometimes buy 5 thousand at a time.

Make sure you get all of them of the same lot number. The bullet forming dies get changed from time to time, so each lot can be different in shape. Also, the lead hardness inside the bullet is a variable.

Solution - several cases of the same bullet, so your load data is correct. (Buy several cases of primers of the same lot #, too.)
 
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