Folks

I just invested in a Forster Case inspector (by mail order) to check out this runout business. I spent the weekend playing with it and most of my loads seem to fall into the 0.001 - 0.002" so I am happy that my loads are acceptable in terms of Forsters frame of reference.

Lets look at the 3 measurements that Forster claim as "critical". I don't have an issue with the first one.

Case neck wall thickness< !--color--> : I neck turn all my cases on the Forster tool, so I get a high quality finish. I actually use the tool in conjunction with the reamer on a fired case, so I am 100% sure I get a concentric neck. The method of measurement with the Case inspector is a tad clumsy, especially for long (H&H and weatherby) cases. I am going to buy a tubing micrometer. 'Nuff said.

Case neck runout (concentricity)< !--color-->:

Here's where I part ways with Forster (in any case their instructions conflict. They say for measurement 2 you need the pilot, then the instructions say use the v block, and the picture shows you use the pilot)

Anyway, using whichever method, you are measuring runout on the neck right next to the point of support, so all you will see is if the neck is oval. My thinking is that the case should be supported at the base in the v block, and supported again in a v block at the shoulder. Then the measurement of the neck would have some relevance because then you would see if the case neck is concentric to the body. I have set it up so that the dial gauge reads on the shoulder of the case. Here any runout is amplified.

Bullet and cartridge runout< !--color-->: Here is exactly the same problem. I believe that runout of the bullet and neck should be measured relative to the Case body. Measuring where shown gives a runout, 'tis true, but the effect is much more amplified at the case shoulder. Support the cartridge at the base and the shoulder, then measure the runout at the bullet tip and you will get a truer idea of what the bullets axis' alignment is relative to the case.

General comments on the Forster tool is that it is not made to the degree of finish of their case trimmer. Disappointing actually. It lacks weight in the base, the dial guage support is too springy and the "v" block set up on the shaft is shoddily made. Long loaded cases such as 300H&H are a tight fit.

I have an idea to make my own, comprising a steel base with two parallel rods with 4 ball bearings mounted as a sliding fit (2 on each rod). You can then place the case on the bearings (base and shoulder), rotate it freely and measure with a instrument stand and a dial guage. Naturally you need a flat reference surface.

Any thoughts or comments?

Pete

I measure the concentricity with my Sinclair gage:


While I believe that the firing pin pushes the cartridge deep into the shoulder and centers there like a collet, I measure with a bearing surface right behind the shoulder and another bearing surface right in front of the extractor groove. The stylus of the dial indicator is then on the neck or the ogive of the bullet.

I believe this compromise works because my chamber is made with a reamer and my sizing die is made with a reamer. The problem is bent necks. So I am assuming the body of the cartridge is concentric with the shoulder, and I am then checking the neck or the bullet with respect to the body, even though it is the neck with respect to shoulder that will determine accuracy. I cannot measure directly with respect to shoulder.

Pete

I'm not familiar with the Forster, but I do agree that it must be on balls or V-blocks at the base and shoulder in order to indicate off the neck and measure the amount of RO respective to the cases axis.

If it uses a pilot in the neck and a V-block at the base, and you indicate off the body below the shoulder, you will see any RO like you said. Measuring the neck with a caliper will indicate if it's round or something else, but is not what you're trying to accomplish here.

I use the RCBS Case Master, it works well, probably not as nice as the Sinclair RO indicator Clark uses, but it does other things that the Sinclair does not, and still works with the same accuracy I'm sure. The base on it is light though, and really would help to be screwed down to something heavy.

However, I'm going to built my own "test station" of sorts here this year sometime, but it will be fully adjustable, indicator stand will slide laterally and lock as well. It'll probably wiegh 10 lbs. when I'm done, but it will be NICE!

If I could figure out how to make an air bearing setup to spin bullets on, I'd attach it to one end as well!! More research on that one though.

Build one, shouldn't be too hard.

Good timing Pete. I was tinkering around with the idea of making one and was looking at the Forster as a guide. I was going to make an adapter set for my Redding trimmer. I also questioned the logic and put the project off today.

Lets say for the sake of arguement that the projectile as well as the area just above the web of the brass is perfect.

So we have the shoulder and the neck. Well I guess we have to settle with the shoulder being good, or at least nothing we can do about it, as our brass was formed in the chamber. That leaves us measuring with 2 V blocks, one at the shoulder and the other at the base. Actually we could use just one long v-block if this makes sense so far.

Next is the measuring tool. I never did like flexable dial indicator holders, many have to be so tight I wonder how long they will last. I just love watching them move all by themselves. So it looks like a magnetic set up deal in my head. Easy enough.

So we take a V-block and weld it to a nice piece of plate, say about 4" by 6" by 1/4" thick. That should be heavy enough. Don't forget to put on a backstop out from the end. You could drill and tap to fasten the block and backstop instead of welding. Clean it all up, Blue it and with 4 little stick-on foot pads its actually presentable.

My thoughts. Yours?

Something I was also thinking about. I was just thinking of milling the long V-Slot down into the base itself, probably 1" thick steel for a good heavy base. The end of the slot would be the stop, but the indicator would move laterally instead, or use a magnetic base with indicator if you like.

I'd like to make a horizontal slide out of square stock to slide the indicator holder across, but be able to move it up and down on a length of square stock.

What I want in one:

1) Heavy base
2) Indicator that adjusts laterally, but "stays" on the case centerline when sliding it to adjust, so it's fast.
3) Indicator adjusts vertically, but does not rotate or move laterally.

Basically, all seperate adjustments, and rotating the indicator on its holder being the only way to adjust the indicator stem perpendicular across the case centerline... if that makes sense.

Brent, Rob, Clark,

I think we are on the same wavelength here, the two reference points should be the base, and the shoulder.

If you take that as your point of departure, your solution is purely an engineering exercise. You could go the whole hog and get yourself a magnetic reference table, magnetic instrument stand and V blocks and that would set you back a few (quite a few) bucks.

Or you could do just a simple steel machined V and do that and that would be quite cheap in comparison.

The idea I got for mine came from a little device that was supplied by the makers of a laser bore sighter that took the form of a cartridge with a laser inside of it. You took the laser and inserted it in the chamber and the laser beam would shoot out the barrel and you could bore sight on the
dot. It was hellish expensive.

Anyway as a demo to show how concentric the thing was made there was this little aid the makers supplied on which you rolled the laser cartridge to show that the dot did not move (ie it was completely concentric to the body). It was constructed like a little jewel.

I am going to see the agent who has this little gizmo and take my cartridges from 222 to 375 and see how it works. If it does, I will try and reverse engineer what he has.

Thank for the comments guys.

Cheers

pete

My benchrest shooting buddy made mine, kind of a Sinclair clone. It uses 4 balls to support the case. With a "V" block, your contact surface is too long. If and dirt/dust gets under the shell it throws readings off. The gauge is adjustable to any lenght of brass.

Thanks AJ300MAG Well guys, we're making progress.
Being the tinkering type, I think I will make a copy of the Sinclair. I'd buy one but hell, I'll spend the money on good brass instead. I already have an unused dial indicator kicking around and the rest is peanuts.

Rob, the bases are made out of 3/4" square CRS (cold rolled steel) and are 3" long. The 1/4" steel balls are locktited into their pockets that were formed by running a ball endmill .1" deep, 3/8" on centers. You can't see at the base of the case is a 3/32" roll bin that you push the brass against. The roll pin is spaced far enough from the balls (3/8") so that a rimmed cartridge rest on the balls in front of the rim. The rod is made out of 3/8" drill rod Nothing elaborate, works like a champ. He had a few guns to have blued, so he also did the gauge for me to repay a favor.

Easy project with that pic for a guide to go by. Thanks AJ300MAG Sorry about the crappy pic

I used 2 guide rods with a thumb tightener on the front right block with a slightly larger hole below that wheel so it glides well. I used a Dremel wheel to cut a small slit in each bearing so the Metal Magic would hold better. As show it is 2.70" from roll pin to stylus. Decent digital camera some day, can't make that though