Questions about measuring OAL and crimp

[Watarski]

I just spent way too long adjusting my Lee seat and crimp dies in my RCBS Pro2000. I found that having my seating die adjusted down like the Pro manual says, it was actually crimping a little too much and shaving some off the lead.

I purchased a digital caliper and a micrometer (not sure why I bought the micrometer now) to measure OAL and crimp. I am basing my target measurements off Wilson's recommendations - 1.25" OAL and .469 crimp.

When I measure OAL with the calipers, I get varying results. If I apply slight pressure on the caliper, I get a smaller reading. If I measure at the center point of the round vs measuring across the entire width of the round, I get slightly different readings. My best readings bounced between 1.247 and 1.254 - is this close enough?

When I measure crimp, I'm not sure where I'm supposed to be measuring, and if I should keep using the calipers or the micrometer. The micrometer is wider which makes measuring a taper crimp more difficult. Also, am I supposed to measure the taper crimp at the case mouth, or a little further back when it starts to flatten out? Again, trying to nail down an absolute measurement of .469" was giving me heartburn...

Any help for a newb is much appreciated

[herd48]

I wouldn't worry about .007 difference on oal. Set your micrometer at .007 and you will see it isn't much. I doubt .007 will make a difference in terms of reliable feeding. Which is always my #1 priority. If you're just starting out. I would not load too many until you can actually fire them and check function and reliablity. Do not hand cycle them to test function. This will tell you nothing. But it can cause a little set back if done repeatedly.
You never did say what your crimp measured. Yes measure at case mouth. If it's too much, back off a quarter turn. Crimp another round and measure. Do this until you get the crimp you desire. Anything from .471-.469 is ok for me. You can use the barrel of your gun as a case gauge to see if they will chamber. Don't forget to reset oal. I guess you know that many folks taper crimp as a seperate step. But a 3 die set can be used successfully. Good luck.

[TheGerk]

I just spent way too long adjusting my Lee seat and crimp dies in my RCBS Pro2000. I found that having my seating die adjusted down like the Pro manual says, it was actually crimping a little too much and shaving some off the lead.

Having the dies setup correctly for your press is important to you, take the time to get them dialed in right. It will save you grief down the road.
(A photo would help here)
One of the rules in Handloading is NEVER be in a hurry to get anything done.
Load, setup, anything.
You’ll just break or blowup your gun and or hurt yourself, hence the NEVER part.

Once dies are set per caliber they should be good to go for the duration.
Remember the press is a basic practical machine, chances are if it doesn’t look and or seem right it’s probably not.
It’s ok to use your sound mechanical senses. When you’re starting out it’s ok to second-guess yourself a bit. It’s almost part of the process.
On your crimp settings just back up the die or crimp die adjuster and retry for effect.

I purchased a digital caliper and a micrometer (not sure why I bought the micrometer now) to measure OAL and crimp. I am basing my target measurements off Wilson's recommendations - 1.25" OAL and .469 crimp.

This is reasonable and a sound measurement datum point to start with to see if your gun likes it.
The micrometer is an excellent measuring device but the dial caliper is better suited for the rounded surfaces of a cartridge (i.e., crimp measurement) the thin sharp blades of the caliper may provide a more precise measurement when mated to the cartridge’s rounded surface.
And it's a lot faster!

When I measure OAL with the calipers, I get varying results. If I apply slight pressure on the caliper, I get a smaller reading. If I measure at the center point of the round vs measuring across the entire width of the round, I get slightly different readings. My best readings bounced between 1.247 and 1.254 - is this close enough?

I would have recommended a Mechanical dial caliper to start with, unless you purchased a top quality unit costing several hundred dollars most of the cheaper ones I see for Handloading are not very user friendly on repeating consistent measurments.
If your digital caliper has no numerical graduations on it you have to rely on the digital readout.
One of the reasons you are seeing the variance in measurements is these digital calipers use a sensor with light or a laser source to measure the distance when making a scale measurement.
The distance is then calculated and converted in the little chip in the unit.
When you press down on the cartridge to measure OAL if you don’t apply the same exact pressure you will see changes in your read out
The digital caliper will interpret the difference in force applied and any flex in the unit and convert this to the measurement.
Go back to your high school science class books; Light and metal both can be bent.
Or a better term might be “altered”

This is one of the reasons you are getting the inconsistent readings on the digital calipers
Buy a mechanical one.
I like the mechanical one from Dillon. It’s probably made in the same shop in China as all the rest but the numerical readout is larger than most I find and this is a plus for my older aging eyes.
A reliable mechanical dial caliper would be a positive assist to you if you were just starting out.
Getting reliable repeatable measurements builds the confidence in your work that you need to move forward.
This opinion would apply to powder scales as well.

When I measure crimp, I'm not sure where I'm supposed to be measuring, and if I should keep using the calipers or the micrometer. The micrometer is wider which makes measuring a taper crimp more difficult. Also, am I supposed to measure the taper crimp at the case mouth, or a little further back when it starts to flatten out? Again, trying to nail down an absolute measurement of .469" was giving me heartburn...

You can measure between .010” to .040” below the cases mouth and be good
The ACP cases taper runs out well below that and with the bullet in the case it won’t matter.
When you crimp to measurement (this example .45ACP is at .470”) also look at the case mouth rim, you only want just a “hint” of a shiny edge on the case mouth rim from the taper crimp die, if this edge is broad or real shiny you are probably over crimping.

You crimp measurement shouldn’t need to be to NASA spec on every damn cartridge although it can’t hurt in the accuracy department.
The SAAMI chamber measurement specification at the case mouth for the cartridge is .473” MAX
(.476” MAX at the case web)
The chamber measurements are .479” web section and .474” at the case mouth.
As long as your getting most of them sized between .468” and .472” at the case mouth they should work in most guns. (Or there is some other problem)
(Most of my guns like .470” to .471”)
Then you can dial in up or down for enhanced accuracy once you get the cycling and reliability worked out. .

Good Luck