bullet seating and COL

[gspn]

I was loading some Sierra Gamekings tonight and had a terrible time getting consistent Overall Length measurements. After a few rounds I took out a few bullets and measured them...I got readings form 1.18 to 1.19 on the bullets themselves. That's a pretty big range...enough to put my overall lengths anywhere from 3.28 to 3.30 inches (it could be even more as I only measured 4 bullets for length)...my target is 3.29...and I like to be exact.

For comparison the Nosler accubonds I have on hand have significantly tighter variances in length. I can generally get all of my overall lengths very close to each other by setting the die once and leaving it.

Ultimately this caused me to have to back out the bullet seater on every round and slowly tighten it down until I got each round right on 3.29. If I go below that I have to pull the bullet and start again. This got me thinking about bullet seaters...are there any that are indexed such that I can turn the knob to change the seating depth by a set amount? For example, if I know that I need to seat deeper by .003 is there a die with lines or index marks on it that lets me change the depth by exactly .003 just by lining up the index marks?

 

[Ridgerunner665]

If your measuring from the tip of the bullet...thats your problem.

The die seats the bullet with pressure on the ogive...not the tip.

I'm sure your ogive measurements are far more exact than the OAL...and the ogive measurement is the one thats important. The OAL only tells you if it will fit in the magazine....

 

[bullseye308]

Yep, the bullets themselves can have that much variance in them.

 

[twofifty]

understanding tolerances

After awhile, you'll figure out what dimensions are mission critical, which ones are important to +/-, and which do not matter that much. You'll also develop a sense of what your tolerance errors +/- are, for each gun and each chambering/load.

At the beginning, I got bogged down chasing thousandth's where it didn't matter to the end results. I then put my worries aside by measuring chamber and round dimensions with a Stoney Point gauge and bullet comparator,
so now:

- brass is cut to length when it falls outside my +/- parameters;
- brass is sized to an optimal base-to-shoulder length +/-;
- bullets are seated to a +/- base-to-ogive length that I want;
- given an OK base-to-ogive length, the COAL takes care of itself.

The results are consistently under 1MOA out to 300yds.

 

[gspn]

Thanks to all for the very helpful replies. It looks like Hornady bought Stoney Point so I'll order a comparator from them.

 

[flashhole]

You can save some money and make a simple tool from a hex nut. Drill a hole in one side of the nut that is smaller than the OD of the bullet such that it contacts the ogive on the bullet. It will always contact the bullet at the same place. Use a seated bullet/brass assembly that is correct for your guns chamber and use that measurement as the master datum. All subsequent seating measurements using the hex nut will provide a consistent data point not affected by bullet tip variance. I usually drag the side of the hex nut opposite the hole on some fine emery paper to ensure it is flat and the caliper readings are not skewed by a slight imperfection on the nut. It's a simple thing to do and is quite handy at the loading bench.