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OAL fluctuations


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Using 9mm  RCBS dies in my 550B Dillon unit, I'm having a problem with maintaining correct OAL. Loading Extreme 115 gr HP plated bullets to 1.130 ", the 1st couple will be OK then start varying by .003 - .010". Same thing happens after reset the seater die. I'm also using a Lee factory crimp die in station 4 but I don't think that would have any affect on the length. Just wondering cause I also load for 38 super, 38 special and .357, and .454 with no problem. Anyone out there experience this problem. Could it be I'm expecting to much, just a 74 yr old nitpicker. 

thanks for any help...captn-tin   Same headstamp in batches.

Edited by h110
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I use mix brass and am shooting for 1.13 but seem to fluctuate between 1.124 all the way to 1.139 and I haven't noticed a difference at the range yet or any problems.

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I'm also running into the same issue , I have 3 Dillon 550's the oldest one is at least 25 years old. When I run one single case through the press to set dies it holds at 1.125 every time on a mix of head stamps. When  its full it will run all the way up to 1.132 this press has run a bit long when full but its getting worse. I will switch to my newer press and see if it fixes the issue and may send my old press back to Dillon for a refurbish.

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Also when my shell plate  has one round in it will bell the case as set, but when the shell plate is full it will hardly bell the case and my ram seems to twist at the top of the up stroke. See if yours is also doing the same.

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We give you tons of the same reasons every time this topic comes up. For very good reasons - they’re likely.

 

And in 9mm most of us get ..005” to .010” variation, so it comes up often. This is is normal. 
 

But here’s the thing: the press is seating off the ogive of the bullet, not it’s tip. And various brands of brass will accept it slightly differently.

 

I’ve seen variations of .008 to .010 with every brand of plated, coated, and FMJ I’ve ever loaded. And I’ve used over a dozen.

 

Then recently... I worked up a batch of 124 XTP hollowpoints. I measured thirty of them because I couldn’t believe they held .002”. Every single bullet was 1.130 to 1.132 which is fascinating since swapping in a coated 124 got me .010 again.

 

The coated ones vary slightly in shape and the JHPs don’t. But what matters is consistent case volume, not consistent distance from base to tip.

 

Aparently you’re still seeing that, because the coated bullets only shot a group 0.5” bigger at 20yds than the high end JHPs. And the standard deviations across a chronograph were identical.

 

So don’t worry about it! Go shoot your ammo. If It groups well, why would you care if it varies in length? ;) 

 

Edited by MemphisMechanic
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2 hours ago, MemphisMechanic said:

We give you tons of the same reasons every time this topic comes up. For very good reasons - they’re likely.

 

And in 9mm most of us get ..005” to .010” variation, so it comes up often. This is is normal. 
 

But here’s the thing: the press is seating off the ogive of the bullet, not it’s tip. And various brands of brass will accept it slightly differently.

 

I’ve seen variations of .008 to .010 with every brand of plated, coated, and FMJ I’ve ever loaded. And I’ve used over a dozen.

 

Then recently... I worked up a batch of 124 XTP hollowpoints. I measured thirty of them because I couldn’t believe they held .002”. Every single bullet was 1.130 to 1.132 which is fascinating since swapping in a coated 124 got me .010 again.

 

The coated ones vary slightly in shape and the JHPs don’t. But what matters is consistent case volume, not consistent distance from base to tip.

 

Aparently you’re still seeing that, because the coated bullets only shot a group 0.5” bigger at 20yds than the high end JHPs. And the standard deviations across a chronograph were identical.

 

So don’t worry about it! Go shoot your ammo. If It groups well, why would you care if it varies in length? ;) 

 

Yeah, I like the JHPs.  My last major they Chrono'd 905 and 905.  Done......

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Ok I switched from my old Dillon 550 which is at least 25 years old to my brand new one it dropped from .010 to .004. I then I started lubing every 5th to 8th piece of brass and it knock it down to .001 and she runs really smooth like I'm not even resizing brass. I have never lubed pistol brass before except for my 10mm and .40 I do a full push through resize on. I'm getting the occasional one that runs long but I'm using powder coated 124 gr bullets from Brazzos. I believe my issue is resolved good luck to every one else.

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