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OAL Measuring ?

2K views 39 replies 20 participants last post by  fredj338 
#1 ·
what tool do you use to measure oal on pistol cartridges ?
 
#7 ·
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.
 
#4 ·
Calipers here also. Technique maybe; shouldn't change if the seating plug is tight.

wp
 
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#5 ·
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.
 
#6 ·
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.
 
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#8 ·
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.
 
#12 · (Edited)
Perfectly acceptable. Even with same headstamps, you get brass variation; number of times fired, diff lots. Dial calipers for me.
 
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#14 ·
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.
 
#16 ·
I think we are talking OAL of the complete round not the sized case, which doesn't affect OAL of the finished round.
 
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#19 ·
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.
 
#18 ·
Harbor freight digital calipers.

OAL changing without touching the seating die. Hmmm

What caliber?
What press?
What dies?
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.
 
#20 ·
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 .
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.
 
#21 ·
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 .
So essentially you're loading to 1.123 +/- .004. Even when sorting brass by head stamp, I get variations in case length, especially if it's range brass. If you trimmed all your pistol brass to the same length (.845), you'd probably shrink it a bit more, but I don't know anybody that does that. I figure as long as it functions in my pistol (the case gauge is my friend) and is accurate enough to shoot in USPSA, IDPA, Steel Challenge or 3 Gun, I'm good. If you're a bullseye shooter, it might be worth the extra effort.
 
#22 ·
If you're a bullseye shooter, it might be worth the extra effort.
Some BE shooter would have to prove this to me using a Ransom rest. Hmm, sine I just got one, maybe I will run that test.:supergrin:
 
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#23 ·
I think that'd be a great experiment.

My thinking was, like the benchrest guys, they try to take out all the variables (sort cases by length, case run out, weigh/sort their bullets, primer hole consistency, etc.,) so their ammo is as consistent as they can get it. If you sort by headstamp, trim to the same length, I would think, given an accurate powder drop, that it would be more consistent. Any bullseye guys out there?

It's not clear to me, even if it is more accurate, if it's worth the extra time involved. For practical competitive shooting, how much is "good enough?"
 
#24 ·
When I was first reloading, I didn't have a decent dial caliper; only a set of mechanical 'slide rule' verniers. As a result, I kept a dummy 'check load', and used the vernier to check against it, and also to set the bullet seating punch. In some ways, it was probably more accurate than my nice dial unit.
A weird reason for OAL variance; a buddy was having extreme variance (you could pick them out bullet down in the box). Anyway, his resizing die wasn't resizing enough , and the bullets in some cases were falling in to the case. This could cause pressure issues too. In any case, he has new dies on order.
Moon
 
#26 ·
Our late range officer used to cast for all of us with lead he retrieved from the range water tank.
Not unreasonably priced FMJs, Glock rifling and lead issues have kept me away from lead anymore.
Crud in the seating plug can be an issue.
Moon
 
#28 ·
I seat bullets at one station and crimp at the next station. I have found that the semi wad cutter seating stem gives the best consistency in OAL. If you can use the SWC stem, with your bullets started as close to straight in the case as you can, then the bullets should be straight in the case.
 
#29 ·
Best', I've experimented with using flat seating plugs, and even turned one from a bolt, and your suggestion works well with some bullets. The concave seating plugs do have a self centering nature, but any variation in bullet/plug shape can cause variation.
Moon
 
#30 ·
At some point the seater plug is going to grab the bullet and ram it into the case until it stops. My best results start with a bullet that is straight as possible in the case before it is engaged by the seater die. The shape of the plug has to work with the bullet that you plan to use or you just smash things up.
 
#31 ·
+ or - can be different if one round is seated with a slightly different amount of force.
there will always be a deviation. no such thing as perfection.
i am finishing another 1,000 PFP 124 Xtreme run, and my deviation has been + or - .003. minimum is never compromised. most are within .001, but a few are a bit more.
measure some factory rounds and you will note a large variation.
one of the reasons for reloading is more consistent rounds.
 
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