Has anyone tested to see how much the OAL can vary before the POI changes?


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slowr1der
August 10, 2010, 03:05 AM
So this is something I've been wondering ever since I started reloading. I've tested it some, but not a ton. How much can the OAL change between loads before the POI changes? It's not uncommon for my loadings to vary .003-.005 depending on which load I'm loading. So far I've not seen it make a difference, but I was wondering how much it can vary before it does make a difference. Anyone tested this? If say the OAL is a difference of .010 between two rounds but all other factors are the same will it have a different POI or should it not matter?

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Walkalong
August 10, 2010, 07:38 AM
.003 to .005 is nothing. Quit worrying about it. Measure some good shooting factory ammo some time. ;)

slowr1der
August 10, 2010, 12:50 PM
I just wondered when it does start becoming something. Is it at .010 or is it even nothing at that point?

R.W.Dale
August 10, 2010, 01:01 PM
Forget about OAL aside from working in the magazine it doesn't matter


what matters is case head to bullet ogive (you need a comparator to measure this)

While these measure similar things they are NOT one and the same for the purposes of accuracy, POI and repeatability

ranger335v
August 10, 2010, 03:11 PM
"Has anyone tested to see how much the OAL can vary before the POI changes?"

Well, I haven't done as you suggest but my seating ladder tests prove the same point. It does make a difference but it varies too much to try to say. Don't ask us, we don't know your rifle or your load, you'll have to do your own tests.

The "best" seating depth is a range, not a precise point from which bullets will fly all over the paper. Some ranges are fairly narrow, some are as wide as 15 thou. Obviously if we seat on a ragged edge of the good range we'll have a lot of latitude in one direction and virtually none in the other.

kludge
August 10, 2010, 03:51 PM
POI, not so much. But group size, yes, it can matter, but the 0.003" to 0.005" variance you are seeing is probably the variance in the bullet tip, and it's not what matters.

Bullet tips are not very consistent, which is why Walkalong and krochus say not to worry about it, and you will only frustrate yourself. If you vary only 0.003" to 0.005" you are doing great. If you really want to know, as krochus said you need a comparator, which uses the ogive to measure from instead of the tip, which is way more consistent.

When loading rifle rounds especially near max follow the load data for COL (aka COAL) for the bullet you are using as a baseline and never go shorter than that. Now don't drive yourself crazy, measure a handful of bullets and pick one in the middle to use for your "dummy" round, go slowly and get it seated to the listed COL. Then without touching your seater, load the rest of your bullets.

Now if you make any adjustments to your die for a different bullet or whatever, you can always get back to "zero" by placing your "dummy" round in your press, backing out the bullet seater, raising the round up into the die, and then screwing in the seater until it touches the bullet.

What is more important to group size, as ranger355v alluded to is seating depth. The best seating depth for your load/bullet/rifle combination will be unique to your gun. There are a few ways to go about this, but instead of typing, just google it, and pick the method you want to use.

However before I start varying my seating depth, I start by working up a load with the bullet 0.015" to 0.020" off the lands, but never shorter than the listed COL. Once I find the powder charge that gives the best accuracy, then I start adjusting the seating depth to see if I can improve my group size.

If you can't get 0.015" to 0.020" off the lands with the chosen bullet without going under listed COL, then you have to reduce the load and work up cautiously.

I say 0.015" to 0.020" because the variance is going to be less than that and you won't get into trouble by jamming the bullet into the lands, creating an overpressure situation.

Your most accurate load might be less that 0.015" off the lands, but that's not where you want to start. JMO.

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