Seating/Crimping twice?

[Grawfr]

Morning reloaders,

Something I noticed and it makes me wonder. I am using an Hornady L'n'L press, with Hornady dies for loading 9mm. My last die is a seat/crimp die. I lube about half the casings even if it's technically not required.

When I run a batch of reloads through the die, I noticed a marked variance in the COAL of the cartridges produced. For example, with the die set for a final COAL of 1.123" I am getting anywhere from 1.1240" to 1.1305" (avg 1.129" on 10 measurements). Running the cartridges a SECOND time through the die tightened everything very nicely to 1.122"-1.124" (avg 1.123" over 10 measurements).

When actioning the press' lever, I always go with the full range of motion to the mechanical stops, so I know the cartridges are getting inserted as far as the machine is set to go. The die is solidly set, the shell plate is solidly set.

I don't mind running the ammo twice through the seat/crimp die, it only takes a quick minute for 20 rounds and ensures better uniformity in COAL.

My question is: are you experiencing this too, or is there something I set up wrong (loose?) in my press? Why am I not getting the expected COAL on the first seat/taper operation? Casing brass elasticity issue? Bullet/Casing friction limiting the insertion on the first run through? Trapped air pressure in the case? Gnomes?

 

[Spawn-Inc]

How are you measuring th OAL? if you going by the base of the case and tip of the bullet then your variance is from the bullet itself. Measure from the ogive of the bullet to the base and see what happens. That doesn't explain why a second time through it varies less but something to consider.

 

[Grawfr]

Back with another set of numbers. I measure the COAL from the base of the head to the tip of the bullet with a digital caliper: it's the overall length I am after since that's what the seating die should be determining. The caliper's smallest increment is 0.0005", so I round any figures to 0.001"±0.0005". Practically, I suspect the accuracy is more ±0.001" anyhow.

Geco brass (it's a tad shorter than the IMI brass I used on the first post), Win 124gr FMJ bullets, sample of 10 out of 20 cartridges made.

1st seating pass: COAL 1.121" to 1.130", avg 1.127"
2nd seating pass: COAL 1.120" to 1.122", avg 1.121"

 

[Spawn-Inc]

Your bullet seater typically seats using the ogive not the tip of the bullet depending on the bullet shape. But if it was using the tip of the bullet then it should be seating and measuring at the same or close to it.

 

[luckey]

This is perfectly normal on progressive and happens on my Dillon 550 as well simply due to the different physical resistance from other stations, mostly the decapping/resizing station.
Usually for me, the OAL is about 5/1000 of an inch difference with and without a brass on station 1. If without anything on station 1, OAL is within 1/1000 or 2/1000 inch for me.
I am using mixed stamped range brass(some are nickel plated as well) and my dies are all LEE carbine dies.
Since I am doing pistol only up to 25 meters, I don't even bother to go through the 2nd round like you are doing. I did do it for the sake of experimenting to make sure my setup is correct.

Morning reloaders,

Something I noticed and it makes me wonder. I am using an Hornady L'n'L press, with Hornady dies for loading 9mm. My last die is a seat/crimp die. I lube about half the casings even if it's technically not required.

When I run a batch of reloads through the die, I noticed a marked variance in the COAL of the cartridges produced. For example, with the die set for a final COAL of 1.123" I am getting anywhere from 1.1240" to 1.1305" (avg 1.129" on 10 measurements). Running the cartridges a SECOND time through the die tightened everything very nicely to 1.122"-1.124" (avg 1.123" over 10 measurements).

When actioning the press' lever, I always go with the full range of motion to the mechanical stops, so I know the cartridges are getting inserted as far as the machine is set to go. The die is solidly set, the shell plate is solidly set.

I don't mind running the ammo twice through the seat/crimp die, it only takes a quick minute for 20 rounds and ensures better uniformity in COAL.

My question is: are you experiencing this too, or is there something I set up wrong (loose?) in my press? Why am I not getting the expected COAL on the first seat/taper operation? Casing brass elasticity issue? Bullet/Casing friction limiting the insertion on the first run through? Trapped air pressure in the case? Gnomes?

 

[Blastattack]

Back with another set of numbers. I measure the COAL from the base of the head to the tip of the bullet with a digital caliper: it's the overall length I am after since that's what the seating die should be determining. The caliper's smallest increment is 0.0005", so I round any figures to 0.001"±0.0005". Practically, I suspect the accuracy is more ±0.001" anyhow.

Geco brass (it's a tad shorter than the IMI brass I used on the first post), Win 124gr FMJ bullets, sample of 10 out of 20 cartridges made.

1st seating pass: COAL 1.121" to 1.130", avg 1.127"
2nd seating pass: COAL 1.120" to 1.122", avg 1.121"

Good lord. Stop wasting your time and go out shooting. You're reloading 9mm mate, not 6br for a rail gun. A difference of .005 is less than negligible for what you'e doing.

 

[Grawfr]

I know what you mean Blastattack, but my pet project is to see how accurate I can MAKE 9mm Luger. Could I reach sub-MOA at 50m? I think so, since I've done 2MOA with good ammo (Geco) already.

So I'm just back from shooting those reloads, as it happens. Beretta Cx4, from a front rest and sand bag under the rear, shot 4 groups of 5 rounds with the scope at 3x.

All data using CCI 550 primers and Winchester 124gr FMJ bullets, average of groups:

IMI 9mm 124gr FMJ COAL 1.162" (control group): 5.5 MOA
IMI brass, 5.1gr CFE Pistol, COAL 1.123": 5.5 MOA (best 3.5 MOA)
Geco brass, 5.1gr CFE Pistol, COAL 1.121": 3.5 MOA (best 1.5 MOA)
IMI brass, 5.3gr CFE Pistol, COAL 1.123": 2.7 MOA (best 2.0 MOA)
Geco brass, 5.3gr CFE Pistol, COAL 1.121": 3.2 MOA (best 3.0 MOA)

Not one bit conclusive, going to have to shoot a lot more to figure what the Cx4 likes (WEEEEEE!!! ). I need to try at least one 5.5gr charge and I need to try 115gr bullets. And I need a slower powder, too, something like Accurate No7 or VV 3N38.

One thing I noticed is that the Cx4 is a "dirty" gun. This is how the IMI factory brass came out:

And this is how the 5.3gr load in the same brass came out:

I don't have a gauge to make sure, but I suspect the chamber is slightly oversized. It's a straight blowback design after all, there's no delaying mechanism to it apart from the inertia of the breech AFAIK.