Tolerance for OAL?

[twarr1]

What is the tolerance for cartridge Overall Length?
The reason I ask is my Lee .223 bullet seating die seems erratic. Length varies up to 0.010". Is this a consequence of bullet length differences or am I doing something wrong?

 

[Steve C]

Most likely cause of your variation is the fit of your seating stem to the bullet. When the seating stem fits well there is little variation in seating depths and OAL. If the bullet doesn't fit so it either deforms at the tip (mashing it down) depending upon your operation of the press handle and variation in pressure applied OR the bullets are not uniform from one to another a greater variation will be seen. To get the best uniformity in OAL you need a good quality bullet and an exacting fit to the seating stem.

If you have a particular brand or bullet make and type that you will be loading most of the loading tool manufacturers will custom make a seating stem that fits your bullet for a reasonable price. They generally want you to send them a bullet to take their measurements from.

 

[twarr1]

Steve C - Thanks for the reply. I wondered about the seating stem. I've been using 55 grain V-Max bullets, but I see the variation in other bullets as well.
I may try a different brand seating die.

 

[bush3755]

Yes, it's due to bullet dimensions.

If you're measuring from the case head to the bullet tip, a few to several thousandths spread is normal. All bullets of a given lot don't have their tips at exactly the same place relative to some point on the bullet ogive that the seating stem contacts. The bullet's tip doesn't touch anything except the target after it's fired. Commercial match ammo with such normal tolerances will shoot 1/4 MOA at 100 yards from good barrels in good rifles.

The seater's contact point on the bullet ogive is typically not at the point on the bullet that first touches the rifling anyway. That point's typically a couple thousandths inch smaller than bullet diameter. On 22 caliber bullets its at about the .221" diameter point because the barrel's bore diameter is about .218" and groove diameter about .224. Seater plugs usually touch the bullet ogive at a smaller diameter closer to its tip. I only know of one person who ground a 1 caliber larger bullet seater plug down to the diameter of the seater's bullet chamber then opened up the plug so it contacted the bullet only at mid point between the barrel's bore and groove diameter on its ogive.

Few people will be able to tell the difference on target with such cartridge OAL spreads. Same thing with .010" spread in bullet jump distance to the rifling. Besides, it gets more with barrel wear at the rate of .001" more for every few dozen rounds shot for a given cartridge OAL. As the case headspaces on it shoulder, it's the distance from shoulder to some point on the bullet that causes the spread. The case head will be clear of the bolt face in a few thousandths spread when the round fires because the firing pin drives the case hard into the chamber shoulder before the round fires.

While OAL is easy to measure to 4 decimal places, it's a waste of time in my opinion. Whatever the seater die makes it with the normal spread the individual bullet ogive tolerances have is good enough for one-hole groups if all else is top quality.

 

[spitballer]

Most of my OAL variances have been caused by hard brass with inconsistent neck tension. New, soft brass never gave me trouble. Making use of older brass may mean neck turning and neck sizing.

 

[mdi]

In my "black and white" thinking, the seating die goes down the same distance every time and the distance from the seating stem to the shell holder should be pretty close to the same every time; mechanically limited. Variations can occur in the cases (variations in the rim thickness, burrs on the case head/primer pocket, slightly bent rims), and in the bullets (manufacturing tolerances, deformed in shipping tips, and factory seconds). I would clean the seating die and check how the bullet fits the stem. Measure the bullet's length, and closely inspect the case heads (I once had an OAL variation due to slightly "high" primers). But I believe yer right, .010" is a bit much...

 

[Schwing]

Depending on your press, some OAL variation can be simply due to the shell plate flexing slightly.

Not to make light of it (because I know a lot of reloaders are nearly OCD about OAL) but, for me, +- .005 is no big deal. If you are a competition shooter or you ARE noticing swings in accuracy or having cycling issues, then I would worry about it.