Your issue could be several things. One or more of these may apply....
► Large fluctuations in OAL are a common issue when the operator is new to the machine or reloading. It has to do with the smoothness of machine operation.
Concentrate on your arm motion being slow, smooth, and consistent. Make a conscious effort to think about your arm motion on every swing. This usually goes away after ~1000 rounds after your arm develops the "muscle memory" on its own.
b) Dillon suggests that the top of the op lever be close to the same height as your shoulder. Change your chair, stool or machine height to accommodate this height.
c) If you learned to reload from watching YouTube videos, then most of those people are doing it exactly WRONG. Reloading is "
careful, thoughtful manufacturing". It's
not a "
race".
Slow down !!
► Lubricate your cases !! I know what the die maker's Marketing Dept said, but I'm asking
YOU to think of something that doesn't feel better with lubrication.
You can't do it. Everything is smoother with lubrications. Remember too, on a progressive you're Sizing and Seating at the same time. It's the Sizing operation that 's most likely messing up the Seating operation results.
Case lubrication doesn't need to take a long time, be a thick coating, or cost a lot. In fact I'm a fan of the homebrewed alcohol and lanolin solution you can find on THR. Lay 50 cases on their side and give a single spritz from a spray bottle and they are ready to load immediately.
► Imagine trying to put on a glove without holding the opening toward the hand. That's a good mental image to have for my last suggestion.... While RCBS dies are very nice, I believe you would be better served by using a Seating Die that accommodates a wide variety of seating stems, or what I call "anvils".
Dillon and
Hornady are 2 names that come to mind. Then, you can make or modify existing anvils to
straighten and
center the bullet BEFORE the seating action starts. How the anvil "supports" the bullet is really important to the final cartridge dimensions and accuracy.
This graphic shows how the red anvil centers and guides the bullet
much better by supporting the ogive rather than simply pushing on the meplat.
Additionally, I would also suggest that you would be better served with an OAL of 1.150" when loading the Berry 147gr RN. The action inside the magazine will be improved and the retention of the bullet within the case mouth will be much better.
Hope this helps.