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Discussion in 'Reloading' started by Tomcat10, Feb 10, 2017.
what tool do you use to measure oal on pistol cartridges ?
Dial calipers for me.
First thank you for your reply .
That's what I use , but I get a lot of variance in OAL on each cartridge . I'm getting different OAL without adjusting my seating die .
Calipers here also. Technique maybe; shouldn't change if the seating plug is tight.
Seating stem fit to nose profile can affect that. Also those of use that use mixed range brass can experience this too. Some brass has higher seating forces so my theory is that the brass flexes (compresses) a bit while under seating forces. It springs back slightly out to a longer length.
I've noticed with some brass, like worn nickel plated brass, seating forces are lower. Those cartridges are always a hair shorter than other brass with higher seating forces.
Plus there is always the slight production tolerance differences feom bullet to bullet. Narrower bullets seat easier (and therefore less springback) than full diameter bullets. In a box of bullets there can be a half a thousandth or more diameter variance. That makes a little difference in my experience.
Now stack all of those tolerances and you end up with different COLs. Mostly it is something that I don't worry about.
Digital calipers. And you will get some variance in your COL. The way the person measures, bullet, different make cases, just to name a few will cause the difference. If you get around .002 plus or minus in my opinion you are doing good. Set it where you want then maybe measure a couple every hundred rds. or so. Don’t chase your COL Measure a box of factory ammo and you will be all over the place.
THis is normal, especially with mixed brass. The bullet nose can vary 0.005" easily, add in thicker brass, softer bullets will deform that much again. Then there is brass spring back. OAL variation of 0.010" isn't a big deal.
Independent of all the other potential variables, COL is generally measured from the tip of the bullet. But the seater engages the bullet along a circumference at some distance back from the tip. Variations in the shapes of the bullets' noses affect the distance from the tip to that circumference.
I'm getting everything between 1.119 to 1.128 with XTreme 165 gr RNFP for 40 S&W . Dillon XL 650 press , with Lee Dies . BTW I separate all my brass by head stamp .
Mitutoyo digital calipers
Dial calipers and get a very small amount of variance of COAL. Many things can affect the reading and OAL. Have to chase it down one item at a time.
Perfectly acceptable. Even with same headstamps, you get brass variation; number of times fired, diff lots. Dial calipers for me.
Dial caliper or a granite surface plate and dial indicator
Just a wild idea but you might clean your seating die. I had one with a build up of "grime" and was getting OAL variances. Cleaned the ID of the seating die with a bottle brush and the seating stem and got some waxy black stuff. I think it was excess bullet lube from the lead bullets I loaded. OAL settled down after that.
I have both dial and digital. The ONLY time I ever got wild variations in OAL without changing anything was before I realized the importance of lubing my brass. A little One Shot and OAL is the same every time.
I think we are talking OAL of the complete round not the sized case, which doesn't affect OAL of the finished round.
Exactly. Lubed cases or spraying the inside of the seating die. OAL is much more uniform.
Harbor freight digital calipers.
OAL changing without touching the seating die. Hmmm
Does the seater stem match the bullet profile? RN bullet with a WC seater is going to be touchier.
FMJ, Plated or lead? If lead, how do you lube? If you overlube, do you clean out the seating stem from accumumlated lube?
What profile projectile? It's easier to measure OAL on a flat/HP than on a RN projectile.
What's your technique for measuring OAL?
What are you using to measure OAL? I still can't get consistent readings with a vernier!
If using a progressive, do you have all the stations loaded? Having all stations loaded, put a consistent and even pressure on the toolhead.
How are you locking the dies to the press? Lee O ring locknuts, might be convenient; but I find they loosen over time.
Do you sort your brass or is this mixed headstamp?
Are your primers being seated uniformly? A proud primer will throw off OAL measurements.
Lots of issues dealing with OAL.
If you are talking lubing the inside of the case neck prior to seating, a bad idea. It affects neck tension to varying degrees. I have dry lubed, like spray on moly, on the expander of the die, but no wet lubes.
Case wall thickness will effect OAL. If the wall is thicker it will cause the bullet to be squeezed tighter causing it to grow in length. I measure several rounds and find a happy average. I hope this helps.