Help with getting a consistent OAL measurement (9mm)

[jrdavidson]

First post by newbie reloader here. I could really use some advice on how to get consistent OAL measurements.

Here's my setup:

Redding T7 turret press

RCBS 9mm decapper/sizing die
RCBS expander die
Redding Competition Seating die
Redding taper crimp die

Rainier 115 gr RN plated bullets

I have segregated 1-time fired cases by headstamp, trying to rule out variations there.

Here's the problem:

I'm making up some trial rounds last night (no primer, no powder, just cases and bullets), taking them all the way through the press: decapper/sizer, adding slight bell flare (just enough to let the bullet start to seat), seating, and taper crimp.

I get a good seat and crimp - just enough to remove the flare and the slight wasp waist in 9mm that everyone says is fine. Everything *looks* great - but I want to confirm my OAL is what I'm looking for.

Here's my problem - using calipers on my assembled test round, I can't get a consistent measurement because the round keeps moving around in the caliper differently everytime I measure. The variance can be as much as +-.005 thousandths on the caliper. The guilty party is the RN nose.

On rifle rounds I see some people use the Hornady comparator setup with a case cage mounted to the caliper jaw to measure off the ogive of the bullet as opposed to the bullet tip - but these comparators are used only for rifle rounds for some reason. No 9mm setups.

So what's the secret to measuring OAL on a 9mm RN round using a caliper? I just can't get it to be consistent. Any tricks?

Thanks!

 

[Bmac1949]

If your rounds are coming out within .005" you're good to go. Make sure you keep them within specs ie. below max OAL and above minimum OAL anf .005" and it shouldn't matter. Some of the more experienced hands might have some advice on using the calipers. I've been reloading now for the better part of a year and over time I have less and less problems with alignment on the calipers even with rn bullets. By the way how do you like your T-7. I've had mine for less than a month and couldn't be happier with it.

 

[jrdavidson]

T7

The T7 is a tank. I bought the primer tube accessory too and that really helps you get into a rhythm. I emailed Redding and they sent me the base schematics for the bolt hole locations which I gave to a local machine shop for a metal mounting plate for the bench. The result is that I will torque the bench before I do the press(!). Its a real confidence builder.

I guess getting a consistent measurement is a matter of practice. I am a bit gun-shy (pun intended) of loading too short in 9mm. I set up the redding competition seating die to give me 1.150 OAL, which it does every time (again, to the degree I can measure it accurately). But I don't want to be actually loading at 1.146 just because I can't handle a caliper well. Maybe I'll extend my target to 1.155 to start with - that way even if I'm actually shorter by .005 I'll be safe.

 

[Walkalong]

As posted, a spread of .005 in O.A.L. for 9MM is fairly normal. Some bullet/seater stem combo's can do a little better. No worries.

Welcome to THR

 

[gamestalker]

Indeed .005" variance is acceptable. However, if your having trouble using the caliper try seating the head on the flat portion of the caliper so it doesn't teater. This will enable you to get an exact measurement all the time. But if it wants to teater your primer's may not be setaed deep enough. Also on that same note, if the variance your getting is a constant your primers may be above the head by several thousandths. In other words, you may be measuring from the primer rather than form the case head.

 

[918v]

Use a case mouth expanded die to final seat the last .010" of the OAL.

 

[LiveLife]

Unless you are seating flat point bullets using flat bullet seating stems, most bullet seating stems in bullet seating dies for RN bullets don't use the tip of the bullet to seat the bullet, but rather a little down from the bullet tip.

If there is variations in the height of bullet tip/ogive of the bullet nose, this is going to reflect in your OAL that you measure to the tip of the bullet nose.

Measure some bullet lengths and you'll see variations in lengths.

As many posted, .005" variation is normal.

 

[ThumperACC]

I have some real troubles with consistent COAL until I discovered that I had too much crimp going on. My RCBS seating die crimps as well. I bought a bullet puller, pulled some heads and was appalled at how much the case was digging into the FMJ of the bullet. Once I got my crimp under control, my 9mm COAL varies by +/- 0.001 with the occasional +/- 0.002.

Check you crimps.

ThumperACC