Bimodal Bullet Ogives in the 175 gr smk

S

Stats Shooter

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This morning I began reloading some AR-10 match loads using 4064, LC-12 brass, CCI BR2's, and 175 gr smk's. The details of which are in an older thread but it is a great load.


Well, as I measured the first few coming off the line of my Dillon, I had CBTO's of 2.235 (which is what I want) and some at 2.224".... consistently two different CBTO'S.

The Bullets were a 500 count bulk pack of 175 gr smks. With only about 15 rounds loaded, I went and measured the base to Ogive of all the remaining 485 bullets.

I found about 300 had a base to Ogive of 0.660" and about 200 had a base to ogive of 0.650"...(with about 6 oddballs having base to Ogives of 0.665-0.670").

I will also add that the bullet lengths were the same on average regardless of the ogive measurements. Also the weights had no observable correlation to if it had a "short" or "long " ogive.

I am going to finish this batch of 200 with the long ogive bullets getting me the 2.235" CBTO I want, but I will shoot the short CBTO loaded cartridges along side them and note the difference.

Then, I will adjust my seating die to seat the short ogive bullets to a CBTO of 2.235" also once I run out of the longer ones.

I believe the "longer" base to Ogive bullets are standard because my tool head was already setup with a different batch and they gave the desired measurements.

I think the short ogive bullets will shoot just as well, provided they are kept amongst themselves, and seating die adjusted accordingly.

But I did find this strange.... almost like two lots of bullets were thrown together to make this bulk pack. Normally some ogive variation is expected, but not two distinctly uniform groups.
 
Two different tooling sets. I made the same measurement for some .308 150 grain SMK's made circa 1990. I got a 0.008" spread. The sample was just 15, though, so I didn't identify the number of tool sets, as I've done with brass before, but there were signs it would be 4. Mine had more length variation than ogive variation though (about 0.013" ES).
 
Check to see if the bullet tip is hitting the top of the cavity in the seating tool. If it is you can either contact your die maker and ask for a seater that fits your bullets or do like I do and drill the hole deeper.
 
Check to see if the bullet tip is hitting the top of the cavity in the seating tool. If it is you can either contact your die maker and ask for a seater that fits your bullets or do like I do and drill the hole deeper.
Click to expand...

Good thought, but that wasn't the issue. As I said I measured each of the remaining 485 bullets and found d the two different ogive groups.....and my measuring tool is designed to handle VLD bullets so no way a tangent ogive bullet bottoms out. Also, I have been using 175 gr smks and this load with this die for a while now.

This also isn't the first time I have had to adjust a seating die with the same bullet from different lots.....but I was surprised that it happened from bullets in the same box of 500.
 
Wow , I consider that unacceptable . Did you contact sierra ? It's one thing for the base to tip being off but a .010 swing on base to ogive is ridicules for a match bullet .

If this was two different tooling lots being mixed . Would be safe to assume that there were only a few boxes that had both lots of bullets in them . Thinking as bullet lot A in bin x gets low they refill the bin with bullet lot B causing some boxes to have both bullet lots A & B in them ? But on the whole you should have all the bullets in the box coming from one tooling lot ???
 
Called Sierra today. They want me to send in 5 from each group and inspect them. Whichever are out of spec will be replaced. I suspect it is the short Ogive bullets .

Sierra said that even if they are from two different lots, they should not be that far apart in ogive to boat tail measurement.
 
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