Bullet Variances between lots

[Rustystud]

Both my customers and I shoot a fair bit. We have noticed variances between Same bullet manufactures lots of bullets. Recently Had customer who purchased several thousand 105 grain 6 mm bullets from company "B". the bullets over all length and weight were with in a +/-.001" and +/-.1grain. But the bearing surfaces varied as much as .030". There was a significant extreme spread +/- 60 fps between the long and short bearing surface lengths where the like bullets extreme spread was less then 9 fps. This cause both seating depth issues and vertical issues at 600-1000 yards.

I have been shooting my .308 hunting rifle with company "S" 150 gr bullets. Last years load worked up to .5" moa load. Shot the same bullets this year and they were all over the place. Thought it might have been a scope issue and changed scopes still shot all over the place. Changed triggers and stocks and no improvement. I tried some other bullets company "C" and powder Company "I" and the groups tighten up to sub .5" again.

It amazes me how a bullet can be loaded exactly the same same bullets, primers, powders, brass, clean or fouled barrel and not shoot the same from year to year in the same rifle.

I am convinced that some of the large bullet manufactures quality of materials and quality control have taken a hit with the rush to get products out to a component starved shooting community.
Nat Lambeth

 

[Mikecr]

I don't understand why you would have seen any MV spread between them. Those long bearing bullets are obturating to groove the same & 30thou of initial engravement is nothing. I never could produce an affect from bearing & discontinued the measure of it.

But there is also method to measurement to consider. Isolating bearing variance alone is not an easy task. You have to remove boat tail angle variance and ogive radius variance to qualify datums.

Everything varies by lot.
With this, I buy enough in lot for the life of each barrel.