Dumb neck sizing question - Lapua brass

[justpete]

New to reloading and this may be a non-problem but it's leaving me confused at this point.

Using new Lapua 308 brass, Forster dies, and a Co-Ax press I'm getting up to five mils TIR runout on seated bullets, 175gr SMKs.

The neck runout is less than five tenths TIR, one mil TIR rarely. Outside chamfer is done with a Forster tool, inside with a Sinclair carbide VLD cutter in their handle applied while the case turns in a Lee trimmer lock stud mounted shellholder in a power screwdriver. Trimming is done with the Lee trimmer tool and the case lengths are very uniform and square, both within five tenths typically.

The Forster Benchrest Seater is properly adjusted, cleaned with Hoppe's #9, lightly lubed with machine oil, bullets are seated by hand as straight in the case mouth as possible, and the press is carefully operated using the optional short handle to improve feel.

Some rounds come out with very little runout but the bulk are at two to three mils with the occasional one at four or five mils, all TIR readings from a Forster Cartridge Inspector correctly set up.

I've discovered the Lapua brass, as new, has a wire edge around the outside of the case mouth, a smaller case mouth ID than neck ID, and the former can cause some scoring on the outside of the neck while the latter is exacerbated by passing the case through either the Forster full length or neck sizer.

Using a small hole gage and a micrometer that reads to one tenth the case mouth as sized is about 0.306" while the ID just a bit farther in can be as high as 0.308" or a bit more. This doesn't seem like a lot of bearing area for the bullet and removal with a kinetic puller is actually pretty easy.

Got a Lee Collet die yesterday, used some 400 grit wet and dry to deburr all the parts, re-oiled, re-assembled with NECO Moly-Slide on the collet bearing areas, verified the mandrel diameter at 0.305", and sized some already sized Lapua brass.

The step down in the case mouth diameter was mostly ironed out, the neck ID dropped to close to 0.3075", and there aren't any strongly visible collet marks on the OD of the neck. It seems like the bearing area is now larger and more uniform and bullets seated are harder to pull. The runout is pretty uniform at two mils or so TIR. The neck runout was still less than five tenths TIR after this reforming.

I'm still wondering if the bullet runout is indicative of a problem I'm not seeing or if all this is beside the point until the brass has been fireformed to the chamber. The rifle, fwiw, is a Rem700 that's been squared and trued with a Rock 5R barrel fitted and cut with an Obermeyer Match chamber.

Any help in understanding the characteristics of new Lapua brass and whether I'm just chasing a non-existent problem would be greatly appreciated.

TIA,
Pete

 

[billmo]

Pete, That much runout is pretty much a norm for new brass. I would check the brass once it is fired in your rifle. The brass at that point should be straight. If the brass neck wall thickness is good then you should see almost no runout thus letting you know your chamber is straight. Hope this helps. Bill

 

[Forum Boss]

What Billmo says is right.

If you're not doing it already, I would also suggest running an expander mandrel down the neck pretty much before any other operation. Neck tension is excessive on brand new Lapua brass. This fixes that, and the mandrel will also straighten out the necks a bit.

I would also be careful with the power screwdriver when doing the inside neck chamfer. I might try doing that process by hand and see if it makes a difference on run-out. Also you really don't need much of an inside chamfer on boat-tail bullets. As long as you get rid of the sharp edge and smoothed the entry, if you've used the expander, you should be OK.

 

[justpete]

Billmo, Good to know this runout is normal at this stage. Thanks very much.

 

[billmo]

Sure thing man. Next time around loading those cases it should look a whole lot better to you. Probably will not see much over .0005 with that brass. Good shooting. Bill

 

[justpete]

Moderator, I've used both the neck and full length sizer dies,Forster Benchrest 308NM) as the new brass measures about 0.305" neck ID. The expander balls measure about 0.3075" on both dies but the neck ID ends up larger than this and the neck mouth constriction is minimally opened up. Neck runout is five tenths TIR, typical.

The bearing surface for the bullets being a concern to me I ran these full sized cases through the Lee Collet die,another twenty beyond the sample of five previously mentioned) ironing out the constriction and uniforming the neck ID to about 0.307" or a bit less. Neck runout is less than one mil TIR across the lot at this point with about half at five tenths. Resizing through the Collet die with a 90deg rotation made no difference in runout as far as I can tell.

I'm about to order a Mitutoyo 2776S indicator from Long Island Indicator to replace the one on the Forster gage. The indicator support could use some rework to be more rigid, too. I'd feel better about the measurements that way. As it is the TIR numbers can vary as much as nearly a mil with little stress applied to the assembly so it takes an awful lot of care to get what I consider 'real' numbers. Well, within the differential error of the indicator anyway.

Using a Starrett half-ball small hole gage the major diameter of the inner chamfer appears to be 9.4mils nominal larger than the neck ID. The 28deg included angle of the cutter would indicate a chamfer depth of approximately 19mils which appears to be correct by inspection under magnification in comparison with a 0.019" Starret feeler gage.

The outside chamfer combines to reduce the flat end of the case mouth to a bit less than 10mils. Original thickness is about 15mils. A Sierra 175gr SMK sits in the case mouth with the boattail completely inside the case.

The internal chamfer isn't as symmetrical as I'd like. I'd hoped the cutter would act as a center and any wobble would create a uniform, if inaccurate, chamfer but this appears to be unattainable. My attempts to manually use the cutter in the handle were less successful. Using the Sinclair power adaptor and running the cutter in the power screwdriver didn't fare much better either.

Clearly I need a lot more practice at this. That or I'll need to build some kind of jig to maintain centers. Failing that I may have to convert to a Wilson case trimmer and use their internal chamfer cutter to guarantee concentricity.

I'm about to order a Barcor chamfer gage from Long Island Indicator,pricey suckers these things) but it only measures the major diameter of the chamfer, I'm not sure what can be used to measure any angular error. I'm also not entirely convinced chamfer major diameter uniformity, and thus chamfer depth uniformity, is critical enough to justify the expense.

This latest batch of twenty processed cases are going to get loaded with Re15 a grain or so below the max load given in the Sierra manual, using BR2 primers, in order to get a better handle on bullet runout with assembled rounds. The cases in the previous lot of five were not loaded, only bullets seated for a quick test. Hopefully bullet runout will not exceed a couple of mils TIR.

Thanks very much for all the help, it's much appreciated belive me.

 

[justpete]

I loaded the twenty rounds mentioned in the previous post with 39gr of Re15, fwiw, and carefully set each bullet on the case mouth as straight as possible prior to working the press.

Thinking the bullet might be seated straighter if the lever was worked slowly and tapped slightly to align the nose with the seater force was then applied slowly and evenly until reaching the end of the press stroke.

Earlier I'd noticed if there wasn't a dwell time the round would 'stick' a bit on removal from the die so I dwelled for a few seconds this time and there wasn't any 'sticking'. Only one pass through the seater was made and all rounds but one out of the twenty measured at two or less mils TIR runout. One round was at five mils for no apparent reason. And no amount of hand-applied force would change that.

A Hornady LNL seating depth tool reported uniform seating depth within a mil, even for the one with the excessive runout. So if two mils TIR runout is typical for new brass Lapua needs two steps to get there. One is to expand the neck and the other to iron out the case mouth and uniform the neck ID as prior to doing this getting runout less than three or four mils TIR was a rarity.

Thanks you guys for all the help and the sanity check, I know I'm not out in the weeds now. It'll be interesting to see how runout progresses with each fireforming pass.

Cheers,
Pete

 

[hayseed]

Wow Pete -

You may be new to reloading, but you do take it pretty seriously. You've got a great systematic approach to things.

I've been considering one of those Forester cart inspectors. Would it be reasonable to guess that you're less than thrilled with it's performance? I don't suppose you've had a chance to get the new gauge mounted yet, and I'm not sure what would be involved with beefing up the support, but I would be interested in your review. It is a tool that a person would like to have confidence in...

Thanks,
hayseed

 

[justpete]

hayseed,

Thanks for the kind words. The good folks at Forster have helped out with some more steps to take that'll improve the overall results with Lapua brass. I've sent in the dies for polishing and should have them back this week, maybe.

The Forster Cartridge Inspector is a lot of quality for the money, IMHO. The support for the dial indicator and the indicator itself present a number of problems some of which can't be eliminated entirely but can be reduced to negligible levels in practice, depending on your definition of negligible.

Do I trust any gage on the market for five tenths readings that are actually meaningful? No. This would require substantially more stable jigs and the use of much higher quality indicators, preferably low force test indicators such as those from BestTest.

The Mit dial indicator has a travel of 1" while the one on the Forster gage is 0.5" but it typically operates at or above 0.4" of compression on the stem. This means its absolute accuracy is undoubtedly very poor given the quality of the dial indicator. Its incremental accuracy at this compression is probably on the order of the error created by the flex in the support rod in response to the force exerted by compressing the stem, but that's just a guess.

If you're looking for one mil numbers I think the Forster gage is as good as anything else and in some cases better. If you want to know absolute concentricity of case neck to case body you'll have to indicate on each and determine the relative runout to get the number you want. My opinion is that it's immaterial in the context of the case/chamber fit but I'm no expert long range shooter by any stretch of the imagination so I could easily be quite wrong.

Judging from results given in the Rifle Accuracy Facts book and measurements of Federal Gold Medal Match ammo from lots separated by a decade it would appear that a centerline runout of two mils or so is most likely to generate a POA error in the noise compared to the shooter's own error. I figure the benchrest guys shooting bugholes have entirely different concerns given their specific chamber designs.

Now that I'm getting five tenths to two mil TIR runout,+/- indicator error) on most of the rounds I've been loading, with factory new brass, I've ceased to worry about it as much. And especially in light of the FGMM measurements.

However, I might have the base of the Inspector bored to 3/8" where the dial indicator rod mounts so a test indicator adaptor can be installed. With the right setup it'll be much easier to move a test indicator axially for different runout measurements.

HTH,
Pete