Acceptable Variation in Bullet Base to Ogive and OAL

[just_jon]

I received a couple of boxes of my favorite 6.5 bullets and found a 0.017" variance in bullet base to ogive measurement. Bullet maker lists .665. Average of 20 bullets selected from multiple boxes came to .682. I took these measurements because I've been experiencing a similar variation in CBTO using these bullets. In loading for a seating depth test, I found it necessary to start long and incrementally seat each bullet to obtain desired CBTO with my Hornady match grade seating die. I experienced the same issue during OCW, but attributed to my RCBS seating die, thus the new seating die. Now I'm not so sure the die was the problem.

So I ask, how much is too much? I'm happy with performance from this bullet in my creedmoor (2856 fps, ES 8, SD 3 and sub 1/2 MOA) and don't want to blow things up by changing bullets. Also don't want to have to adjust seating stem for each round. Appreciate your input.

 

[Rardoin]

You may be best served, depending on precision you desire, by sorting the bullets base to ogive and placing them into lots of at most 0.004" variation. I sort most factory produced match bullets and group them to lots with 0.003" spread for 600/1000yd matches. What you are seeing is not uncommon. It is why, if I have a favored bullet I know I will shoot out a barrel with, I buy enough in the same lot # to last that barrel's remaining lifespan. Otherwise one has to deal with inter-lot variation as you are seeing. Even some of Berger's most popular match bullets, the 105 hybrid, 108 vld, and 140 hybrid, has shown me inter lot variance of over 0.015" at times.

PS- One anomaly I have found is the Hornady 190 A-tip. I have three different lot numbers and nearly all of the ones I measured, which is a couple of hundred, fall within 0.001" BTO with a couple 0.0015" BTO...which is in the margin of error of my caliper/insert/technique. Sure shocked me to say the least.

 

[just_jon]

Thanks Rardoin. i just looked at the data from my seating depth test and found I had no need for concern as seating +/- .010" of my load's CBTO still gave me single digit SD and the same level of accuracy.

 

[Rardoin]

Sounds like you found a good seating depth then.