Precision reloading problem: Accuracy vs. Headspace ?

[DG Photography]

Hi DG,

I wouldn't call them my "expectations" of accuracy. In calm conditions from bags, this rifle has shot tight groupings like i mentioned, regularly with this load. When the wind picks up I will get the lateral dispersion, but the vertical is still very tight in windy conditions. Extreme spreads in velocity are typically single digits or low teens.
I have fully bedded the rifle action to the stock ( which was a vast improvement over the accu-stock ) the floating bolt that savage uses, I machined the face to within a tenth or two square to the back faces of the lock up lugs (may not have been completely necessary but I believe did not hurt) and the stock rails have been removed and a 20MOA steel pic rail bedded to the action. Scope rings are beefy leupold Mk 4 steel rings, that I fully lapped before installing the scope. Al screws are still properly torqued, and have not come loose. I am a machinist by trade and although the Lapua cases were very good from new, I am confident that my neck turned cases are more consistent, although you may be right about not making a difference in the looses chamber. I still have a small batch of the last round of reloads that I am using for comparison. They still shoot how they should, but it is this new batch that is giving me trouble. You've obviously been shooting this caliber a while, and have some ample experience. I am interested in your resizing technique to get 40 loads out of your brass. I will PM you about this. Thanks again.

Okay this is the info I wanted this is not a bone stock rifle
And your expectations are reasonable as you stated in calm conditions
On a regular basis.

The one thing I have witnessed too often is dirty oily bedding and
Under the scope rail migration of oil and loctite I do not think wet
Application loctite is appropriate for scope rails.

 

[Mystic Precision]

Hi Jerry,

You have read and understood everything correctly, The rifle has been fully bedded to achieve the results I was getting earlier, and the steel 20MOA rail is glued to the action as you suggest. All things (except headspace? ) being equal to the dummy round, this problem has started. Just to confirm, the bolt DOES close on a loaded round with the same apparent resistance it closes with on an empty chamber. The case neck thicknesses have grown slightly from the start, maybe .0005-.0008", but the fired cases seem to accept a bullet without resistance. Perhaps my necks need to be turned again ? I have not measured the chamber in this rifle yet, what method do you use to measure chamber dimensions accurately ?

The best and really only way to measure a chamber is using CERROSAFE - low temp alloy that you pour into the chamber after melting. Makes a cast of your chamber. However, if a bullet will drop into a fired case that usually indicates you have enough clearance.

I would keep to outside neck turning. Moderate the neck tension - maybe you are getting some bullet distortion during seating? Definitely look at annealing on a reg bases. Lapua brass is hard enough and work hardening more is not going to help anything.

Watch your case length. maybe cut to min spec just in case you have a shallow chamber????

Check the fired case for concentricity. maybe you have a chamber that is not true or round and the fired case is forced to come out wonky????

Try another batch of brass or brand of brass and see if the problem persists.

Simple stuff but a pain as it is trial and error.

Good luck.

Jerry

 

[Mystic Precision]

In my T-Wolf the lapua neck thickness of 15 thou works fine
And does not stick. Neck turning has given me a slight benefit in calm
Conditions. I will try again at 12 thou I only tried 14 thou learn something
Everyday. Okay I have some things to try out thanks for the info

Neck thickness onto itself is not the end all. Ductility IS. lapua is a very hard alloy and the cases almost always are on the thick side. That makes the flexibility of the neck even harder. That can lead to inconsistent bullet release which affects pressures and accuracy. Why annealing the necks is such a good idea.

Thinning the necks will reduce that tension somewhat but the biggest gains here is helping the INSIDE of the sized neck to stay concentric. Except for the Lee collet neck die, all sizing dies squish from the outside in. If a neck is not even in thickness, when sized, the outside becomes even but the inside takes on whatever irregular shape is formed due to the extra brass. Now you are forcing a bullet into this wonky shape and it has to iron out the defects (or not) towards the outside. High runout is a by product as well as damaged bullet jackets if neck tension is high enough.

Anytime you use a bushing die, I would outside neck turn and keep cleaning things up as the brass flows. You may have a no turn chamber but the cases need constant TLC for peak performance.

If something helps in calm air, it helps in all air.

Jerry

 

[!Peter!]

Anytime you use a bushing die, I would outside neck turn and keep cleaning things up as the brass flows.

Jerry, just to confirm, are you saying that you should outside neck turn before sizing with a bushing die?

Also thanks for your input on this thread.

Peter

 

[Mystic Precision]

yes, turn before sizing.

This is the complication with bushing dies - chicken and egg. you need to ensure the "bore" of the case neck is true and of the right diameter to put on the mandrel BUT you need to get to the right thickness inorder to size.

So, the proper solution is quite complicated. First you OVERSIZE, then expand on a properly sized mandrel, then you outside neck turn, then you resize and hopefully all is well.

Why I just use a Lee collet neck die.

Simple.

Jerry