Just measured 10 155 grain SMK 308 bullets, the 2155 bullet from sierra. These are match grade bullets from Sierra. They varied in length from base to tip by up to .007". And that's only a sample of ten. No wonder when seated consistently by the ogive, they give varying and misleading variances in COAL as measured from the tip.
Why COAL is misleading /match grade bullet variation
- Thread starter Grizzlypeg
- Start date
Yup, drove me nuts until I got a set of bullet comparators. Combine that with a seating die that seats off the ogive and overall length problems are a thing of the past. Nowadays, my reloads that are off by .001" are the exception, not the rule.
I recently measured some test rounds for my 30-06...Measuring the OAL, I had an extreme spread of 0.021", and a standard deviation of 0.0046. Measuring the length to the ogive using a bullet comparator, the ES was 0.005" and the SD was 0.0011....
BTW, that was using teh standard RCBS seating die, not the benchrest micrometer adjust version....
Now, the only time I'm going to worry about OAL is to make sure the round fits in the mag.
BTW, that was using teh standard RCBS seating die, not the benchrest micrometer adjust version....
Now, the only time I'm going to worry about OAL is to make sure the round fits in the mag.
I have slight OCD, so I took this a step further. I measured the bearing surface of about 200 rounds of 168gr SMK:
0.497 on the left, 0.484 on the right.
Interesting results, I grouped them into +/- 0.001" around 0.496, 0.493 and 0.488. Now all I have to do is weigh 'em!
0.497 on the left, 0.484 on the right.
Interesting results, I grouped them into +/- 0.001" around 0.496, 0.493 and 0.488. Now all I have to do is weigh 'em!
Rory McCanuck
CGN Regular
- Location
- Middle of Manitoba
Left to right, we aren't Arabic
I did a similar test with a box of Hornadys that were driving me nuts.
I found three very distinct lengths in the one box of 100.
After seating therm with plain-Jane Lee dies, then measuring them with the plug out of a seating die, there was less than 0.002" variation. Shot really well, too.
Sometimes we really get too wound up worrying about how many angels can dance on the head of a pin.
I have slight OCD, so I took this a step further. I measured the bearing surface of about 200 rounds of 168gr SMK:
0.497 on the left, 0.484 on the right.
Interesting results, I grouped them into +/- 0.001" around 0.496, 0.493 and 0.488. Now all I have to do is weigh 'em!
Ahhh.... An instant graphical representation of a bi-modal distribution. .... The two (maybe even three) "nodes" tell me that the batch / lot you have was made on two or three different machines.
A normal distribution would have one peak, with decreasing quantities of individual bullets on either side of the peak.
To be honest with you, I wouldn't think Sierra would do that. By the looks of the box, those bullets are from a box of 500?
