Head scratcher, Seater Die issue

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bbqreloader

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Facts: 40 Cal, RMR RNFP 165 gr plated. LNL AP (spare me the Red jokes), using RCBS Seater Die, RN. stem. Seating depth 1.130 -/+ .005. Using Hornady Bullet feeder Die.
Seater die is the number 5 station.
Issue: Ran 300 rounds, about number 350, 12 rounds went to 1.113 -/+ .005.
Had the same issue on friday, about the 300 round mark.
Now am using a Lee bullet feeder tubes with Bully Adapter. The bullets kept either hanging up or dropping more than one, so tinkered with die and got it set.
Was using it today, same issue, thought maybe I touched the seater die on Friday when I adjusted it, so made sure I was no where near touching it today. Same issue, all of a sudden the rounds were seating well below what I had been reloading. I had been measuring a couple of rounds every 25 or so just to make sure and all seemed within my spec until about round 350
Pulled the rounds, resized and reloaded, normal range, +/-.005.
The cases all measured in the .640 range. Bullets weighed between 164 and 166.
I did look inside seating die to see if something got jammed up in there to cause issue and nothing or than some residual bullet plating.

So any thoughts as to why all of a sudden my seating depth would have drastically changed, never had this problem before??
Thanks.
 
Basically what you are saying is that you have your seating die set at 1.130 and some of your bullets are measuring deep 1.113

Since you have eliminated the seating die as being out of adjustment or dirty, the next logical place to look is:

1. skinny bullets
2. not enough case mouth tension

I'm sure others will chime in with other possibilities
 
The RN seating die seats off of the Ogive and inconsistent OAL can be expected especially with plated bullets where thickness can vary from bullet to bullet or lot to lot. The fact that they managed to fall back into the average you expected and set for is the part is more of a mystery to me. Either way some have noted as much as .030" swing where yours was .017".

Edit to add:If you measured from the Ogive you would see a more consistent OAL. Just like rifle rounds are measured.
 
The RN seating die seats off of the Ogive and inconsistent OAL can be expected especially with plated bullets where thickness can vary from bullet to bullet or lot to lot. The fact that they managed to fall back into the average you expected and set for is the part is more of a mystery to me. Either way some have noted as much as .030" swing where yours was .017".
Edit to add:If you measured from the Ogive you would see a more consistent OAL. Just like rifle rounds are measured.

I just cannot figure out why it did it. Might not have worried to much, but seeing as OAL (i know it's subjective) is 1.125 for 40, don't want to swing to far down and run my pressures up.
 
I just cannot figure out why it did it. Might not have worried to much, but seeing as OAL (i know it's subjective) is 1.125 for 40, don't want to swing to far down and run my pressures up.
I get that and a lot of people rely on the OAL to calm fears but the bullet seats the same depth to a safe degree. Go measure some factory ammo and you will sleep like a baby ( I know you have heard that before in some way or fashion). ;)

Man it's times like this when I miss RCmodel. The man had a way with words!
 
Does it seat them short when there is also a case being sized at the same time? My Pro 2000 will seat bullets a few thou shorter if there is no case being sized at the same time, i.e., the last 4 rounds of a run. Wondering if an LNL AP does the same.
 
hig, no, I was running 10 rounds then 20 the first couple of hundred to make sure things were running smooth. Never saw a variance the last few rounds that went thru. Like I posted, a real head scratcher as to why it did it around 300 or so.
 
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