Max OAL decreasing?

MHouser

MHouser

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Some 6 months ago I measured the max OAL for my .308 using Hornady 168gr MATCH BTHP #30501 bullets @ 2.212 measuring on the bullet ogive. Took another measurement tonight as I have fired 300 or 400 rounds since then and got a measurement of 2.204. Used same casing, same bullet and again I measured on the ogive. I tried it 7 or 8 times just to make sure I had it right.

Isn't max. oal supposed to increase and not decrease as erosion occurs or do I have it backwards?

What is eroding exactly to cause it to change?
 
When you say the same bullet do you mean the actual bullet you used originally. Or do you mean the same bullet but from a different box?
 
If it is the same bullet but from a different box it is probably from a different manufacturing lot and therefore the bullet will be slightly different.
 
My guess is a different lot of bullets.

Everytime I change lots I double check the OAL with a dummy round and also check the new lots OAL to lands.
 
Underthegun said:
When you say the same bullet do you mean the actual bullet you used originally. Or do you mean the same bullet but from a different box?
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It wasn't the exact bullet. Same bullet different lot. I thought the same thing so I measured the length of a few bullets from the current lot and they were all pretty much the same. I did not measure the length of the original bullet so nothing to compare to.

Might I have the same problem within the same lot.

Now that I'm typing this and really thinking about it I don't see how the bullet makes any difference. I'm measuring from the base of the cartridge to the point on the ogive where the bullet contacts the lands so the bullet could be 2" long and it would be the same measurement. The length of the bullet doesn't make any difference.
 
MHouser said:
It wasn't the exact bullet. Same bullet different lot. I thought the same thing so I measured the length of a few bullets from the current lot and they were all pretty much the same. I did not measure the length of the original bullet so nothing to compare to.

Might I have the same problem within the same lot.

Now that I'm typing this and really thinking about it I don't see how the bullet makes any difference. I'm measuring from the base of the cartridge to the point on the ogive where the bullet contacts the lands so the bullet could be 2" long and it would be the same measurement. The length of the bullet doesn't make any difference.
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Even though you are measuring to the ogive the measurements can be different from lot to lot.
 
Underthegun said:
Even though you are measuring to the ogive the measurements can be different from lot to lot.
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I guess I need a picture then because in my mind I doesn't matter if the ogive is in a different spot, the bullet is a diff length, etc. I could use anything. A pen for example. Break off the end, jam it in the case, chamber and let the lands push it into the case, then measure from base if cartridge to point on the pen where it contacted the lands. Same measurement.
 
MHouser. I see what you are thinking. But if that was correct it wouldn't matter what bullet you used to measure, as they would all measure the same. But that is not the case. I do understand your thinking though. But the fact is that even the same bullet but from a different lot may not have the exact same shape.
 
Hello again. If you want to double check this. See if you can find 2 same bullets but from different lots and measure them. But make sure that they are from a different lot#. It will be printed on the box somewhere. But make sure you measure them before you load them.
 
When the "dummy" round is used to set the seating die, back the stem out before moving the ram. My Rockchucker press cams over, so when the ram is fully up, and the "dummy" still in the die, the cam over will actually seat the "dummy" a little deaper each time.
Just a thought from my own experience after wondering why my bullets continued to seat deaper.
 
Underthegun said:
MHouser. I see what you are thinking. But if that was correct it wouldn't matter what bullet you used to measure, as they would all measure the same. But that is not the case. I do understand your thinking though. But the fact is that even the same bullet but from a different lot may not have the exact same shape.
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So. If the diameter of the opening on my comparator is the exact same dimension as the diameter of my rifle bore from land to land then my reasoning is correct. The issue is that the two measurements are not the same and variations in bullet profile result in different readings?

Sooooo..... does that mean that I have to check max oal for every bullet before I seat it to ensure consistent jump or just one bullet from each lot?
 
I think what you're saying is that your rifles dimensions are changing not the ammo. This just requires you to seat the bullet to a different length for the rifle. You believe the chamber is getting shorter rather than longer with erosion?
 
hk33ka1 said:
I think what you're saying is that your rifles dimensions are changing not the ammo. This just requires you to seat the bullet to a different length for the rifle. You believe the chamber is getting shorter rather than longer with erosion?
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Either that or I'm simply not understanding the concept completely. If some could confirm or refute my statements in my post just before this one I should have all of the answers I need. Cheers.
 
Huh? I do not understand what you are trying to say.

Tell me if I am wrong here:

A) You loaded some rounds and they are shorter then they were when you loaded them previously. Yes? How did you seat the bullets? Did you seat them using your rifle?

B) You are using the comparator to measure the seating depth directly from the chamber? If so, it is likely that your chamber throat is not as clean as it could be, effectively shortening it.


Or, at others have stated, the ogive is different on this batch of bullets. The comparator is reading the length measuremt off of the bullet ogive, so if the ogive is in a different place, the measurement is different.

And you are using OAL wrong; the OAL is from the base to the bullet tip. What you are using is the base to the point on the ogive that is the same as the comparator bushing. We could call this the "seating depth" if you want.
 
The ogive will differ from lot to lot.

Bullet dies wear out making longer, wider bullets. When new dies are introduced, bullets are now shorter and narrower.

The rounds being shorter has #### all to do with his rifle.
You people make this far more confusing than it needs to be.
 
CyaN1de said:
The ogive will differ from lot to lot.

Bullet dies wear out making longer, wider bullets. When new dies are introduced, bullets are now shorter and narrower.

The rounds being shorter has #### all to do with his rifle.
You people make this far more confusing than it needs to be.
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Thank you. That explains what I'm observing perfectly.
 
My buddy had the same thought as you at one point, and I almost bought his theory until I changed bullet lots and found a difference of .030 in OAL using a comparator IIRC.
 
CyaN1de said:
My buddy had the same thought as you at one point, and I almost bought his theory until I changed bullet lots and found a difference of .030 in OAL using a comparator IIRC.
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Wow. I definitely will be modifying this part of my reloading procedures.
 
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