Seating depth experiments

[joelkdouglas]

Hey gents

The family's all moved to Louisiana (new duty station), and I found a rifle range. Time to start messing with seating depth to see if I can get my rifle to group under 1/2 inch.

The rifle is a Rem 700 .30-06 (my only other thread has a picture of her), with a long throat. I got a Hornady OAL bullet comparator and then was disappointed to figure out I couldn't seat to 0.03 inches off the lands anyway, because the bullet is only about 0.22 inches into the case. My Nosler manual says to have at least a bullet diameter seated into the case for proper bullet alignment / tension.

I think I can start seating about 0.1 inches from the lands, unless one of you experienced fellas has some other idea.

Is that where you would start, and then slowly push into the case, like 0.1 inches at a time? Does having a shorter seating depth raise case pressure?

Also another question: I've shot about 1/2 of my Lapua brass 6 times, and I usually neck size afterwards. The brass isn't splitting or anything. I just wondered if I will start to see reduced accuracy the more the brass is shot?

Thanks gents.
Joel

 

[DrMike]

Work with what you have. It sounds as if you will of necessity have a long jump to the lands. It is not uncommon that a load will have multiple nodes (accuracy depths). At the extreme, I've had a couple of rifles that had to have as much as 0.25 inches to the lands. One, in particular, was exceptionally accurate. The greater the case volume (i.e., the less the bullet intrudes into the powder column), the greater the allowance for pressure. Nevertheless, it is wise to consider SAAMI pressure standards as maximum when working up a load.

 

[Guest]

You're on the right track, Joel, in thinking about seating depth as a tuning mechanism for your rifle. Half inch groups are tough to get (consistently) with many factory rifles, but you can likely get under 1" pretty handily with that rifle.

I think you should reconsider your seating depth change increments, though. With your rifle, if you've got .220" of bullet base in the neck at .030" off the lands, you could then have .310" of bullet in the neck and be about .118" off the lands. That jibes with what you posted, so it's all good so far. When you start making changes, I'd set it up at .120" (just because I like round numbers) and then back off either .005 or .010" at a time, rather than .1". Other than that, you're on the right track.

Don't worry about not being able to seat close to the lands. My most accurate rifle is my 270Wby Mark V, and I can't even touch the lands with the bullet ogive and it still be in the case at all. I am generally seating very far off the lands (something on the order of .2+) and yet the gun will print groups smaller than the .277 bullet diameter (center to center) on occasion, and consistently print .5-.75" groups with several different loads.

 

[1Shot]

One little tip I will pass on to you that I have found with rifles that have loooooog throats. Use a Lee Factory Crimp Die. It improves accuracy for me greatly. My theory is that it holds the bullet in the case for a moment to allow the powder to get a good burn going and build pressure properly just like when a bullet in a shorter throat rifle does when the bullet hits the lands and retards it's movement for a moment will do the same thing. All I know is that it works. The Lee Factory Crimp Die can be used with any bullet. The bullet does not have to have a crimping groove. Just leave your cases 5 thousands longer than the trim to length so that you will have enough case to get a good bite on.

 

[baltz526]

My rifles with a long throat have all shot long bullets better. You can track group size by bullet weight in the vangard 300 win mag. 150gr-2 1/2". 165gr-2". Standard 180gr-1 1/2". Long 180gr etip 1 1/4". 200gr-1". 220gr under 1". Magazine limits my oal to 3.495". I also lee crimp them all.

 

[Guy Miner]

Doug Arnold - who owned Arnold Arms, a Pacific Northwest shop that built several thousand Very Accurate custom rifles over about ten years - is a firm believer that getting the seating depth right is one of the most important things a handloader can do for accuracy. I got the impression that he's worked most extensively with Hornady bullets, but I think his experience applies to other bullets as well. Doug puts seating depth well ahead of powder charge as a factor in accuracy... Contrary to the belief of many. I attended one of his reloading classes a while back, and he got me thinking. Scary stuff that thinking...

So yes, play with that seating depth - it may lead to great things!

Also - if that long throat is really messing with you and your loads, consider having a smith remove the barrel, cut off a thread or two, and re-install it, perhaps even cutting a new chamber. This is similar to what many target shooters do part-way through the life of a barrel, to get another thousand rounds or more of accurate barrel life. In your case it would be to eliminate that excessively long throat, which could improve accuracy.

Or - just set reasonable accuracy goals and run it the way it is - most game will never know the difference. How accurate is your .30-06 now - and how accurate do you need it to be for your hunting? My .30-06 barely manages MOA with the well worn barrel, but it's fine for poking game at 300 yards.

Regards, Guy