Modifying cartridge OAL - Which seating die is best?

[rquack]

I'm loading for two 7mm-08's now and will be going through a load development process for each of them again after starting a new powder container. In the past i've just altered my powder charge and generally used saami oal or used an arbitrary .015 off of the lands as a standard. So I've little experience with serious oal adjustments in search of better accuracy. I've been using only the standard RCBS dies in the past.

I'm looking for a product to assist in making accurate, subtle adjustments during load development and afterwards doing "production work" as I may need to shift between the two rifles.

After a bit of research it seems that the Forster ultra micrometer seating die with the micrometer adjustment seems to be a preferred piece of equipment for producing repeatable results between two different rifles that may require differences in powder charge and OAL. Is this a good product? Should I be looking at other products that may do a better job?

I appreciate the willingness of the many members of this forum in sharing their experiences. Many thanks to you all.

 

[SJB358]

I’d grab a Hornady Comparator tool with the 7mm insert. It attaches to your calipers and measures off the ogive of the Bullet and will allow you to repeatedly get exact numbers and to set your seating does up correct.

Nosler bullets have been the worst for me in varying between lots so since I shoot Noslers in the majority of my rifles a comparator was the tool for me to get consistent numbers.

 

[ShadeTree]

Hate to say it Scotty, but I concur. I don't want to paint with a broad brush because I don't have Nosler bullets for all calibers, but the ones I do I've run across substantial ogive differences in some boxes. That and the fact there's only 50 per box so you can soon run out makes it important to check each new box if you want to keep your favorite load clicking.

Nosler makes some darn good bullets but being aware of a few things makes life go easier.

 

[joelkdouglas]

Scotty already covered the gauge. I don’t even measure OAL any more (unless trying to determine something like magazine length), just Cartridge Base to Ogive (CBTO).

As for your dies question, the best three are the Wilson inline seater with micrometer top, the Redding Competition and the Forster Ultra Micrometer.

You need an arbor press for the Wilson. As an added benefit you can seat bullets at the range with this setup. But it’s not a traditional die.

The Redding and Forster both fit into a regular press. The Redding has a bit better finish, functionally they are equal. The Forster is cheaper, I think about $50 cheaper. Both have sliding sleeves that support the body of the case while seating, and both produce rounds with excellent runout.

I have and use all three types of dies, and I rarely have loaded rounds with runout more than 0.003. I reject loaded rounds at 0.005 for sighters.

 

[ElmerThud]

Without doubt the Wilson seating die yields least run out when bullet seating, but requires an arbor press. Not too expensive, but does work.
You have to be sure your case neck/case body run out is low too for consistently low run out on the finished cartridge, so your sizing die needs to be set up correctly as well.
Other seating dies can work well too, but a lot depends on the alignment of the prepared case.
Good luck.

 

[magothy1]

Another vote for the Hornady comparator tool. Ogive is the number that seems to matter.

Use it to check the Nosler bullets from Shooters Pro Shop sometime and you may have an unpleasant surprise.

I bought a used RCBS competition seating die with the open window and adjustment knob. It works very well for me, eliminates guess work.

 

[slickrem]

if the ogive is different then you have to check each bullet for consistency

 

[Darkhorse]

I know this is an old post, but I did a lot of testing of this subject some time back and perhaps my comments are relative. At least for those who are just thinking of using seating depth to improve accuracy.
I never measure OAL, it is not relative to what I do. I only measure to the ogive and I use the Hornady bullet comparator and a set of Starret dial calipers for this.
When a round is fired the barrel will oscillate, meaning the end moves around. If your bullet exits when the end is to the right that round will impact the target to the right. If your next bullet exits to the left that round will impact the target to the left. And so on to end in a spread out group.
However if you can find a node, a spot where your barrel end is motionless, and you can manage to get your shots off in this spot then group will tighten up. There is more than one node and by changing seating depth you move where the bullet exits the barrel. So the whole thing about seating depth is you are searching for a node.
This same thing applies to the powder charge. By varying the powder charge you vary the speed of the projectile and it will exit the barrel at different points also. One of these targets were shot with one seating depth but varying powder charges.
Notice how the group moves to different points with changes to the seating depth or powder charge.
I do extensive case prep to insure there is as little runout as possible to include partial neck turning, to give the load it's best chance.
I seat my bullets with a Hornady inline bullet seater. I also use standard loading dies. This combo gives me groups hovering around 1/2" consistently.

 

[rquack]

Thanks for the pics, Darkhorse. That's some great data that you've shared. It clearly illustrates the effect of any change that's made. The trick is isolating changes and insuring that I'm only altering one spec at a time so as not to confuse the results.

I've been unable to get out and do any shooting for quite a bit this summer. So I'll be reloading some ammo and shooting some ladders and then beginning to fine tune the load. I'm thinking that I'll pick up a Forster micro adjust seating die and the Hornady comparator when I get ready to shoot again. Right now, I need to focus on shutting down the cottage for the season. And address another family issue that is complicating things a bit right now.