Load to COAL or Comparator length?

[Majorheadtrauma]

Image link is broken

[BLR81]

TomDW
If your loading for benchrest you use a comparator and forget you ever measured C.O.A,L. to begin with.

The ogives of bullets loaded from a single die vary extremely little.Unfortunately mass produced bullets such as Sierra and Berger are made from a large amount of different dies and they vary as much as 0.020 in a single box.

The Redding seating dies with the hollow stem contact your bullets way up on the ogive probably around 0.218 in diameter.To check this out simply remove the stem and spin a bullet against it with moderate pressure until you see a ring and measure it.

Your bullet will be contacting the barrel at 0.256 diameter assuming a typical Krieger bore is used.So you are seating at 0.218 diameter to make contact at 0.256 diameter with bullets likely to have 0.020 or more variation in a single box.This is why when you measure your seated rounds with a comparator they vary.
Seating depth has the single biggest influence on your group size after you have decided on a powder charge so most competition shooters will try and keep it within 0.002 total variation as measured with a comparator.It sounds like a pain but if your seating with a competition seater with the micrometer top you can seat them all about 0.010 longer than you want them.You can then take all the rounds that were the shortest length and run them through the seater again.You then adjust again and run the next group and so on.

When you see shooters with a pressure gauge on there reloading press to measure seating force they are usually using custom bullets or measured and sorted bullets and the seating force is directly related to the seated length of the rounds.The rounds requiring greater force to seat will be longer as measured with a comparator.
We wil be shooting a 600 yard benchrest mtch this sunday in Ojai and my 6 Dasher rounds all measure 2.510 inches long as measured with a comparator and no rounds measure 2.509 or 2.511.
I will include a picture showing the seating depth measured in 0.001 increments as fired from the bench at 200 yards.You caee the groups tighten then open up again and this is repeatable.
Lynn

Thanks for the info on the Redding seating die. I don't know if my rifle is accurate enough to take advantage of the kind of attention to detail that you take. I know that I certainly don't have the marksmanship skills.

I'm still a beginner when it comes to precision rifle, and I'm only looking for consistency right now while I work to get better. Generally, my loads are seated plus or minus .0015 off of my target seating depth, and I'm fine with that. I can't even take advantage of that precision right now. Still almost 1 flyer with every other 5 shot group at 300 yds.

But, it was enlightening to find out that there was that much difference from one box to another. I makes me think that the purchase of the micrometer seating adjuster was the smartest purchase since I started reloading.

[LynnJr]

Most of your fliers will be seating depth related.The difference between good groups and outstanding groups is a couple thousandths of an inch in seating depth.
It sounds like you have a comparator already so try this the next time you load.
Seat all of your rounds without moving your seating stem at all and measure them into groups of 0.001 increments.Now go to the range and see if one grouping out shoots all the rest.The variation you see with the comparator is neck tension and bullet variation.By segregating your brass so it all has the same number of firings on it you don't have to worry about neck tension unless one feels funny(Loose,Tight) during the seating process.

Don't worry about your skill level either.If you were shooting my rifles you would shoot them very well.I had a 23 year old kid shoot his first match ever with a 6 Dasher back up rifle in 2011 and he finished 7th at 600 yards at the nationals in Sacramento.

On a factory type gun you suffer from a large trigger pull weight which moves the gun backwards in the bags when firing.Our triggers are so light you don't have to control the gun with your hands and the stocks are flat on the bottom or have tracking rails to prevent wobble.I load the same way for my hunting rifles as my bench guns and despite all the horror stories you read about it its not very difficult at all.Most people have too much stuff instead of the right stuff in my opinion.

Sorry about the typing in my earlier post.I am using an IR keyboard and if I don't point it at the tower it drops letters.It killed my last paragraph in the earlier post.
Lynn