What Is Acceptable OAL Variance?

[alamogunr]

I am loading 9mm for grandsons guns and in the interest of safety I've been checking everything that can possibly vary. From powder(Bullseye) charge to Cartridge Overall Length. The bullet I'm using was purchased from a local commercial caster/coater. The bullet is a 135 gr round nose(it has an almost unnoticeable meplat). I don't know anything about the coating except it is black and he uses the "shake & bake" method in a cement mixer and bakes the coating in a continuous oven. The charge i
s 3.4 gr of Bullseye.

As I said I'm checking all sorts of things and COL is varying +or- .003. The only thing I can imagine would be causing this is a variation in the nose that would cause the bullet to be seated more or less. The variation could also be the thickness of the coating although I don't know enough about that to say any more about it.

My first question: Is +or- .003 in an overall length of 1.134" enough to worry about. My first reaction is to not worry since the powder charge is on the low side. Out of 40 or 50 I've checked, most center around the 1.134 and only 2 or 3 touch on the upper and lower limit.

[fcvan]

Overall length it largely a matter of what feeds and chambers in your weapon. When i first started loading 9mm, it was for a S&W 459. I made a dummy load with which to reset my dies. That setup has fed in many weapons including carbines.

Rule of thumb is use a factory round to set your dies and try that. Other rounds like cast SWC took some tweaking, round-ish boolits always worked well. 9mm is my fun plinker, easy to load and cheap shooting.

[reddog81]

A human hair measures .003 in diameter. That small of variation is fine.

[alamogunr]

A human hair measures .003 in diameter. That small of variation is fine.

Thanks! I never thought of it like that. Loading for others is something I have shied away from until the grandsons wanted to shoot. Between their father and I we bought them handguns. I've always taken to heart the warnings about seating too deep causing increases in pressure. The small amount of variation that I was getting would not worry me for my own use. Just theirs.

[ryanmattes]

For plinking ammo +/- .003 is fine. Unless it was all loaded waaaay short, 3 thousandths isn't enough to cause a major pressure issue, especially in a moderate load like that. It's not match grade ammo, but it'll do a minute of soda can.

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[tazman]

Small differences in nose shape that are unnoticeable to the eye can cause even greater differences than what you are getting.
Given the powder charge you are using, the small differences in COL are of no consequence.

[kevin c]

I was told by a commercial reloader that a range of 0.005" was normal with the pistol cartridges I was asking about. I thin that's with mixed head stamps, since I get less variance with sorted brass. I haven't bought factory new pistol cartridges in years so I don't know how consistent those are.

[onelight]

Some bullet shapes cause OAL to vary more than others as can the brass as has been pointed out but + or - .003 I see as acceptable with cast and plated like taz that is acceptable to me . I have fought to get them exact on single stage , turret and progressive and I lost and could see no difference on paper or performance so I have learned to ignore it .

[charlie b]

Good for you to ask about it. Too many folks just slam loads together and shoot, thinking they have OK loads.

The 9mm can be a finicky little devil. Small case, high pressures means there is not as much leeway as there is on something like a .45Colt or .38spl. If yours shoot well, keep dong the same thing.

[onelight]

Another thing to consider is when adjusting your seating die you may cycle the same bullet several times while getting it where you want it , the next one that is cycled once will probably be longer so may need another minor adjustment to get it back to the OAL you are wanting.

[LinotypeIngot]

+/-.003 is pretty normal if you're using mixed headstamp brass.

[Jniedbalski]

.003 is not much. A piece of typing paper is .004 thick. Your load is a low target load . I shoot 3.5 to 4.0 of bullseye. I have in the past checked each bullet and the ones a little long I re ran through the seating die. Now I don’t ,found out it don’t make any difference on target. That low of a charge of bullseye won’t increase pressure on only .003.