Seating issues related to bullet runout

[mtang45]

My latest project is a custom Remington 7mm STW and I have been tweaking the loads for awhile without get the consistent results that I think this rifle is capable of. I have had a concentricity gauge for awhile but have never been able to measure loaded STW rounds for bullet run out because the length was too long for the gauge.

I recently acquired a 21st Century Gauge that will measure the runout of my STW loads and I am shocked at the measurements I am getting. Lets just say its enough to make you say WTF!! I have measured the brass and it is very straight.

I have a Forster micrometer seating die in a RCBS Rock Chucker press and can't imagine what could be going so wrong to shove the bullets into the case at bizarre angles. Does anyone have a suggestion as to what is going on?

 

[BoydAllen]

Your sized brass is straight? I take it hat it is supported near the shoulder and just in front of the head. Where is the indicator tip placed on the loaded rounds?

 

[mtang45]

Your sized brass is straight? I take it hat it is supported near the shoulder and just in front of the head. Where is the indicator tip placed on the loaded rounds?

The brass is straight (within reason at this point) and yes the case is supported just in front of the belt and just below the shoulder. I am placing the indicator approximately halfway between the ogive and meplat.

 

[BoydAllen]

On a given round, what are the readings on the neck just back of the mouth of the case, and say, .2 up from the case neck on the bullet?

 

[steve4102]

You mentioned your seating die and press, you did not mention your sizing die.

IME the majority of runout is caused by the sizing die not the seating die. The best seating die in the world can't fix what the sizing die has screwed up.

 

[holstil]

Just curious, how much neck tension are you using? What are the brass run out readings at the neck before and after sized and loaded? What is the neck wall thickness variance? Can you give actual numbers just so people know how much within reason and WTF is?

Jim

 

[mtang45]

The resizing die is also a Forster and I have been only neck sizing at this point. The loaded case has a variation of .0015 to .002 at the neck. I have some 168 VLD Bergers that vary up to .010 at a point halfway between the ogive and meplat. Some 175 XLD Bergers (my latest load) measured in the same location vary from .008 to .017.

I don't have any measurements on fired cases, or neck wall thickness yet but will tonight when I get home. How do I measure neck tension?

 

[BoydAllen]

For purposes of this discussion, and for most others, neck tension is measured by subtracting the diameter of the sized neck from the diameter with the bullet seated. If a bullet happens to have a slight enlargement at its base, as some custom flat base bullets do, then you take the loaded measurement over that. One other thing that you need to check, while you are at it, is where the seater stem contacts the ogive of the bullet. In some cases, with pointier shaped bullets, the meplat bottoms out inside the cavity, and this is not a desirable situation.

 

[Shynloco]

mtang45,
For the purposes of your consideration, I'll tell you what I found made a difference in runout after I discovered a flaw in what I was doing with my resizing die on my 6.5 X 55 Lapua casings. Everyone else has covered the obvious and most common issues, but "bending necks" (done by the expander ball) in new Lapua brass was my culprit which needed to be corrected via another method of neck sizing.

First I was making the MISTAKE to resize brand new brass before it was fireformed. The darn expander ball was somehow messing up otherwise tight runout which is expected from brand new Lapua brass in the area of .001-.002. But the expander ball was taking that and pushing out to ON SOME BRASS to .004 - .008.

Removing the expander ball from the resizing die and THEN using a mandrel die cured the majority of the brass. Anything over the .002 went into the trash heap. The die itself was checked by the manufacturer and shown to be within tolerance. Since changing my MO and removing the expander ball and using the mandrel die to resize my necks AFTER the body is resized in the same FL die, my runout is unusually under .001 and my neck tension is uniform as well.

Just something to consider as you try and limited the variables with that new custom rig.

Alex

 

[mtang45]

OK to answer some questions.

Fired case neck OD .317", ID .285
Resized case neck OD .308", ID .281
Fired case neck wall thickness .013-.014
Resized case neck wall thickness .014-.015

I have rechecked some of the runout at the case neck on resized brass and loaded brass and am reevaluating what I said earlier. I'm seeing variation from .002 to .0045. When spinning the loaded cartridge on the gauge I can see a wobble in the case neck that gets exaggerated the further out on the bullet you measure. It seems the source is not the bullet being seated cock-eyed but that the neck is tilted. So as some of you have said it does appear that I have induced this in the resizing operation.

Shynloco.... where do I find a "mandrel" die, and can these "crooked cases be remedied by fireforming? I hate to toss all my brass that measures this way, that would be nearly all of it and thats alot

 

[BoydAllen]

One thing that I learned a long time ago, with the aid of my first concentricity gauge, one piece neck dies that use an expander ball produce the absolute worst result as far concentricity is concerned. You really need to stop using that die. It has no provision for keeping the body of the neck in alignment with the case neck, during sizing, and added to that is the probable fact that it sizes necks way too much so that when the expander ball is pulled back through, the shoulder yields asymmetrically, making the situation worse.

If Forster makes a FL die for that caliber, I would suggest that you buy one, and get a caliper attachment to accurately measure shoulder bump. Then after a little head scratching you should be able to send the die back and for the monumental fee of something like $11 have the die's neck honed out so that with the brass that you use the expander ball is only slightly felt in its passage through the neck, expanding the necks only 1-2 thousandths. There is a general feeling that using FL dies is detrimental to accuracy and case life. If properly dimensioned and set up in the press, this is just flat wrong.

 

[mikecr]

http://bulletin.accurateshooter.com/2012/06/neck-expander-mandrels-for-more-uniform-neck-tension/

 

[Shynloco]

Shynloco.... where do I find a "mandrel" die, and can these "crooked cases be remedied by fireforming? I hate to toss all my brass that measures this way, that would be nearly all of it and thats alot

Go to Sinclair's website and you'll find the "Sinclair Generation II Expander Die" (aka: Mandrel Die) as part number 749-011-715SB (Cal 17 - .338) = $24.95. You can get all those caliber mandrels and it's super simply to change mandrels. You will also need the Stainless Steel 7mm Expander Mandrel which is part #749-001-176SB ($8.95). I've had success in "rehabilitating" some brass that is only with .004- .005 out, but beyond that, they are bent at the base to badly to save. But I can tell you since I've gone to using the Mandrel Die method on all my calibers, my runout is terrific in all my calibers and only need to spot check finished cartridges because I shoot strictly to entertain myself, but seek accuracy to the max. Now if you want to compete, check each and everyone and you should find no variance of more than .0015 BTW, I usually run the casings down into the mandrel die two times and hold them in the die/mandrel for a count of 15 or so to allow the casing time to adjust to the expansion and hold it there. And don't worry, the casing will "spring back" which is another test to make sure your brass hasn't lost it's elasticity and time to anneal or toss the brass. BTW, when you FL size BEFORE USING THE MANDREL DIE, remember to pull the expander ball that can become the root of some issues. I also dip the necks of my casings into a small jar of graphite powder so as to lubricate the inside of the necks to allow the mandrel some lubrication for the expansion process. Give a hollar if you need more.

Alex

 

[mtang45]

Alex, thanks for the details; I'll definitely pick those up....going to Brownells/Sinclair right now.

I did still have the question about the ability of the seater die to seat them correctly if the meplat was bottoming out on the stem because of bullet length. I pulled the stem and placed it over the end of one of the XLD's and it fit fine. There was no bottoming out of the nose. So based on that observation there is no way the seater can be pushing these bullets in at an angle.

Some of these cases have been fired 3 times. Is it possible that the necks are already work hardened and when resizing with the expander ball, I am putting extra pressure on the shoulder because of the hardened necks? I was planning on annealing at 4 firings but maybe it should be sooner. Its Remington brass BTW. I have a few cases of Winchester brass that have gone through the same process and they are nearly perfect; .0015 or less at the neck. Also have a small number of Nosler cases that have been fired and resized twice and have neck runout of .0025 or less.

 

[mtang45]

OK a follow up to all the advice. I got the mandrel neck sizer as suggested. I removed the expander ball from my full length sizer and resized all the brass with runout. I then opened up the neck with the mandrel die and checked case neck runout. All brass was .001 or less! I have not reloaded anything yet but with the new brass dimensions I have high expectations of pretty good quality.

Thanks!