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Canuck
07-15-2014, 02:10 PM
I've always wondered how much difference there is in various reloading operations that affect case neck runout. Had some time on my hands so I tried a little experiment. I took 10 new cases. They were Hornady Match cases in .308 calibre. They were brand new, unused. I measured the concentricity at a point half way between the shoulder and case mouth.
Although they were match cases I assumed the most runout would be here. That was the case (no pun intended).
The lowest runout was .0025. The highest was .003. The average runout for these cases was .0172.

Moving on to the next operation I sized the cases using RCBS Competition dies. The lowest runout after sizing was .0004. The highest was .001. The average for the same 10 cases was .0064. Sizing trued them up substantially. Average difference between sized and unsized was 0.0108".

Then I primed them and loaded them up with some VV 540 and Berger Big Bore .308 match bullets. I actually expected the runout to be somewhere between the sized and unsized cases assuming the bullet seating process might affect the runout. Interestingly, this wasn't the case. The lowest runout with the same cases and the Berger bullets was .0001. The highest was .0018. The average was .00086. I can only assume that the Berger bullets, that are very consistent, helped smooth out inconsistencies when seated in the case neck. Average difference between unsized and seated bullets was .016634"; between sized and seated was .00554".

My data seems to confirm that sizing new cases is beneficial. I have some confidence that the match dies are doing their job and that the seating process is consistent with these RCBS dies. I may have missed some other conclusions, or I may have missed some considerations while doing this experiment. I welcome any comments or questions.

Coincidentally or otherwise, the rounds have proven to be very accurate.

Dmay
07-16-2014, 06:33 AM
My thoughts are that the brass must have fairly consistent neck-wall thickness, as pushing a bullet in will show differences in thickness as run-out. I bet if you had turned the necks, numbers might be even tighter...

Canuck
07-16-2014, 09:33 AM
My thoughts are that the brass must have fairly consistent neck-wall thickness, as pushing a bullet in will show differences in thickness as run-out. I bet if you had turned the necks, numbers might be even tighter...

I think you're right. I don't have a neck turner but am considering one. Although the groups have been good as is, the turner might tighten things up further. This was shot from a DPMS based build I did in .308 with Shaw barrel: 5 shots = .857" @ 200 m. Bullets were seated to fit mag, next batch will be seated longer and fed singly.


http://i75.photobucket.com/albums/i293/picsalot_2006/100_2690_zpsc8cf0a67.jpg

Rory McCanuck
07-16-2014, 10:43 AM
I have to ask what you are using to measure all this as you are getting some incredibly precise readings.
Just for comparison's sake, do you have another set of dies? Everyone raves about the quality of Redding dies, but could you get similar numbers with say, RCBS?
Another run with some cheapy once fired non-custom Hornady brass? How much bigger do the groups get?
It's hard to argue with success, but I sometimes wonder if we don't have much wider margins to play with than we think?

Canuck
07-16-2014, 11:34 AM
It's just one of your run of the grade NASA laser devices. Just kidding. I am using a Teclock dial gauge, made in Japan. Have had it forever. I measured each case twice before recording the runout.
Rory, I am a little confused about your question about getting similar numbers with, say, RCBS dies. Did you miss the part where I said the dies were RCBS Competition dies? The only other dies in .308 that I have are RCBS Small Base dies. Have a ton of FC .308 brass I could do a run of for comparison if that is what you meant. I can tell you right now that the Hornady cases will produce better groups- just from my own personal experience however it might be interesting just to see what the difference is. At the cost of Berger Big Bore bullets, I won't be doing more than 10, LOL. If you are going for precision loads you aren't going to scrimp on any components. It's all or nothing!

Thanks for the ideas. I will check out the FC brass for comparison and I might have some WW as well. Will post the results.

Rory McCanuck
07-16-2014, 11:52 AM
Rory, I am a little confused about your question about getting similar numbers with, say, RCBS dies. Did you miss the part where I said the dies were RCBS Competition dies? .

:red: I read it last night and replied today. Somehow my pea brain transposed it into Redding.
Good thing I'm so handsome, I doubt I could get by on just my brains...

I guess what I meant was just trying a set of less expensive dies, just to see if they are anywhere as close to "true."

Canuck
07-16-2014, 12:06 PM
:red: I read it last night and replied today. Somehow my pea brain transposed it into Redding.
Good thing I'm so handsome, I doubt I could get by on just my brains...

I guess what I meant was just trying a set of less expensive dies, just to see if they are anywhere as close to "true."

Yes, I did understand that part. The SB dies I use in semi autos for Service rifle, CQB, etc., where function is paramount with potential sacrifices to accuracy. But it would be a good exercise. I am going to give it a try.
In the same vein, I have often wondered about how long dies keep their precision. Can you wear out dies? Do they lose their precision over time? I have some .45 ACP RCBS carbide dies that have reloaded in the neighborhood of 10, 000 rounds. Have often wondered if they are as tight as they were originally. Hear anything about that?

bearhunter
07-19-2014, 11:02 AM
Canuck, your assumption that sizing new cases is beneficial is correct, for the fist shot.

Now, you need to check how true to center your sizing die is as well as your seating die.

Then, you need to make a casting of your chamber and part of your barrel together and check how true to center that is.

If all of these things are consistent with being true to center, your rifle will be accurate. Even if your necks have a bit of run out the rifle should shoot well.

Most hand loaders do not full length resize. Even when they do more than neck resize, it is usually only enough to set the shoulder back a few thou. This means that as long as your bolt face is at a perfect right angle to the center of the chamber and bore that the cartridge case is still being held true to center in the chamber.

Now, here is where the conundrum comes in for off the shelf rifles. They are much better now than they used to be but they still have generous dimensions for the most part. The reason for this is obvious. Hand loaders don't make up a huge portion of the shooting community. I don't know what the ratio is but it's low in comparison to those that shoot factory ammo only.

Of course, we all know that there are slight dimensional changes in every lot of ammunition produced as well as chambers.

The sizing and seating dies made during mass production need to take all of these factors into account. For the most part, they do a pretty good job.

Concentricity is the biggest issue when it comes to accuracy. You are definitely on the right track in your experiments and good for you for keeping records. Such records are great to fall back on so that you can compare them to different rifles. This saves a lot of time and trouble on occasion. Every thing you can eliminate will help solve or at least pinpoint the problem.

There is a very good reason why match chambers are usually tight. Sometimes so tight a special set of sizing dies needs to be cut with the same finishing reamer as the bbl was cut with. The less slop in the chamber the less any off square bolt face will cause canting of the cartridge off center in the chamber and to the center of the bore.

I have seen several very serious bench rest shooters mark the cartridge rim in some permanent manner to keep the cartridge in precisely the same position against the bolt face and in the chamber so that each firing if the cartridge is as consistent and all angles are as consistent as possible from shot to shot. Many swear this pays off for them. I was never that anal but maybe I would have been a more consistent winner if I had done similar things.???????