223 OAL mystery

jambrdly · April 17, 2010, 11:14 PM

Hello:

I have been loading some 223 for my mini-14 and I noticed something odd.
Using 55 gr fmj bullets (w/cannelure) in Remington cases, RCBS dies, I have been turning out rounds with an OAL of 2.222 inches, which is what I have been aiming for. However, in every batch of 50, I am getting one or two that mike at 2.240 or 2.242. How is this even possible? I ran the long rounds back into the seating die and there was no change in their length. I have triple-checked that the dies are tight in the press (rockchucker). I cannot figure out what could account for this change in OAL? Any ideas?

bullspotter · April 17, 2010, 11:24 PM

Pry the ogive of the bullet to the tip is not the same on every bullet. Your seat stem dosent press the bullet into the case by the tip. This will vary more with the cheaper cost fmj bullets most of the time.

Shoney · April 17, 2010, 11:28 PM

Check the seating die to see if it is dirty.

Also, take a close look at the ogive (Ogive - The curved or tapering section of a bullet’s sides, forward of the bearing surface ( i.e. between the cylindrical section and the nose tip. ) ). That is the most likely reason.

Many reasons for the ogives to be different and travel farther into or less into the seating die. Bullets can be different from one machine to another, or some one threw some bullets out of one bin into another, or it may have been the stock to make the jacket was narrowed in one place.

vladan · April 17, 2010, 11:29 PM

Most likely it is caused by bullet's shape. Your seating die plug seat the bullet not by pushing on the tip, but contact it on ogive of the bullet. If the ogive has slightly different profile, seating plug in the die will contact it slightly lower or higher giving you different OAL because you measure OAL from the base to the tip of the bullet.

http://www.larrywillis.com/bullet-shape.html

mrawesome22 · April 17, 2010, 11:53 PM

Quote:

How is this even possible?

As said before, it's your bullets. Either the tip is varying, or the bearing surface is varying.

RickV · April 18, 2010, 07:08 AM

Are all your cases the same manufacturer? I was having a problem with 380acp where I was seeing .005 differences but only occassionaly. I started checking Headstamps and sure enough that where the problem was there were 2 brands that were causing the problem. So I went thru all my 380 brass and pulled the 2 brands out.

**Unclenick** · April 18, 2010, 09:22 AM

It's .223. Bottleneck rifle cases get trimmed to match. In any event, if the case was long, the bullet should just go in below the cannelure.

Jambrdly,

Since you're asking how it's possible, I assume the cannelures are lining up correctly but you still have the length difference? This pretty much has to be the bullet noses. Even with Sierra match bullets, whose lot numbers are assigned to the production from just one machine and tooling set, I see up to 0.010" difference in length because the edges of the small hollow points don't all draw up exactly even. That's not ballistically significant, but it does make OAL measurements vary. OAL is a fine thing for setting a limit to ensure magazine compatibility, but it's not precise enough for verifying seating depth (how far the bullet is into the case) is consistent. For that you want a comparator head for your calipers.

April 17, 2010, 11:14 PM	#1
jambrdly Senior Member Join Date: January 31, 2010 Posts: 105	223 OAL mystery Hello: I have been loading some 223 for my mini-14 and I noticed something odd. Using 55 gr fmj bullets (w/cannelure) in Remington cases, RCBS dies, I have been turning out rounds with an OAL of 2.222 inches, which is what I have been aiming for. However, in every batch of 50, I am getting one or two that mike at 2.240 or 2.242. How is this even possible? I ran the long rounds back into the seating die and there was no change in their length. I have triple-checked that the dies are tight in the press (rockchucker). I cannot figure out what could account for this change in OAL? Any ideas?

April 18, 2010, 09:22 AM	#7
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,732	It's .223. Bottleneck rifle cases get trimmed to match. In any event, if the case was long, the bullet should just go in below the cannelure. Jambrdly, Since you're asking how it's possible, I assume the cannelures are lining up correctly but you still have the length difference? This pretty much has to be the bullet noses. Even with Sierra match bullets, whose lot numbers are assigned to the production from just one machine and tooling set, I see up to 0.010" difference in length because the edges of the small hollow points don't all draw up exactly even. That's not ballistically significant, but it does make OAL measurements vary. OAL is a fine thing for setting a limit to ensure magazine compatibility, but it's not precise enough for verifying seating depth (how far the bullet is into the case) is consistent. For that you want a comparator head for your calipers. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

April 17, 2010, 11:24 PM	#2
bullspotter Senior Member Join Date: November 2, 2008 Location: Montana Posts: 308	Pry the ogive of the bullet to the tip is not the same on every bullet. Your seat stem dosent press the bullet into the case by the tip. This will vary more with the cheaper cost fmj bullets most of the time.

April 17, 2010, 11:28 PM	#3
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	Check the seating die to see if it is dirty. Also, take a close look at the ogive (Ogive - The curved or tapering section of a bullet’s sides, forward of the bearing surface ( i.e. between the cylindrical section and the nose tip. ) ). That is the most likely reason. Many reasons for the ogives to be different and travel farther into or less into the seating die. Bullets can be different from one machine to another, or some one threw some bullets out of one bin into another, or it may have been the stock to make the jacket was narrowed in one place.

April 17, 2010, 11:29 PM	#4
vladan Senior Member Join Date: March 14, 2010 Location: Central Florida Posts: 813	Most likely it is caused by bullet's shape. Your seating die plug seat the bullet not by pushing on the tip, but contact it on ogive of the bullet. If the ogive has slightly different profile, seating plug in the die will contact it slightly lower or higher giving you different OAL because you measure OAL from the base to the tip of the bullet. http://www.larrywillis.com/bullet-shape.html

April 18, 2010, 07:08 AM	#6
RickV Senior Member Join Date: November 7, 2008 Location: North Florida Posts: 172	Are all your cases the same manufacturer? I was having a problem with 380acp where I was seeing .005 differences but only occassionaly. I started checking Headstamps and sure enough that where the problem was there were 2 brands that were causing the problem. So I went thru all my 380 brass and pulled the 2 brands out.