Regarding those plastic calipers.........

[3006guns]

I spent a frustrating day yesterday, forming 8mm Mauser brass from 30-06. Normally, this is an easy job that I've done many times before using a Redding form and trim die. This time however, I decided to use my Lee hand press and standard dies instead of my 310 tool. That's when the problems surfaced.

I set the Redding die up in my Rock Chucker, making sure that the linkage barely "cammed over" at the top of the stroke. A little Imperial wax on each case and away we go. I was careful to file each case flush with the die top, remove outside burrs and deburr the inside of each case mouth. I set up the RCBS F/L die and ran them all through again, both to deprime and make sure they would all be to spec.

Long story short, after priming and charging I started to seat my .325 boolits. I found it took more pressure than normal to seat the boolits and upon chambering them in my rifle none of them would go in without hammering the bolt handle down. What the....??? I suffered through ten of these before I stopped loading and started examining things. First of all, the RCBS expander measured .321. Okay, too small for my boolits but why the difficult chambering? Turns out that each time I seated the boolit, the end of the case neck would "bottom out" and further pressure caused a bump at the case mouth of about .005......grossly oversize for decent chambering. And yet the next case would chamber fairly easily.

But why? All of them were carefully filed to the same length, or so I thought. I measured the overall lengths with my Lyman plastic calipers and found differences of up to .012". Trouble was, a repeated measurement on the same case always came out different! I ran out to the shop and grabbed my good pair of Japanese stainless calipers. Measurements now revealed differences of over .025" and were all different. All of the cases were run through my trimmer and measured again......this time the maximum variation was .003".......a lot better. The ammunition now chambers perfectly.

So, here's what happened.

First of all, even though I was careful to set the trim die up so that the press cammed over, there's evidently some slop in the linkage causing different lengths. Simply lopping them off does NOT guarantee correct lengths. It's a "rough" forming tool at best.

The longer cases were shoved up against the crimp portion of the die, causing the necks (which were already oversize because of the lead boolit) to swell. I should have suspected this after the first cartridge.

My 30 year old Lyman calipers, made of "glass filled nylon" aren't trustworthy anymore. I noticed that, in addition to any wear, just putting a bit of force on the thumb wheel can change the reading up to .010 or more.

So, half my problems were from inattention and the other half from a piece of equipment (the calipers) that were plain worn out. Another learning experience!

[lightman]

Well, I'm happy that you discovered the problem. I have a set of plastic calipers that I have had for a long time. I use them as a go/no go gauge. I prefer to trust a quality steel dial caliper for important measurements.

[3006guns]

Agreed. I'm going to bend/break and donate those Lymans to the trash can. Don't get me wrong, they've served me well for many years but wear can creep in without you noticing. As for the rest of the problems, that was plain old overconfidence coupled with a desire to "get 'er done"....an attitude that doesn't go well in hand loading. It's doubly embarrassing because I'm usually very anal, double and triple checking everything to get the best ammunition I can!

Oh, I had another thought. Some of the "slop" I mentioned when forming the cases may have been due to the shell holder, combined with a mixture of different cases.......some military, some foreign, some commercial. All of them should have worked beautifully if I'd have caught the OAL issue.

All in all, I ended up with 47 out of 50 usable cases so not too bad for simple jackrabbit loads........

[DougGuy]

Find you a nicely cared for vintage set of USA made calipers on ebay..

[EDG]

You might want to reconsider the cause of the length variations.

When forming cases it sometimes takes more pressure to push the shoulder back.
In addition variations in the amount of case lube makes the case vary in how far it is pushed into the die.

The speed you size the case can also cause variations as well as the dwell time at the top of the press stroke. To make all your cases come out the same size each case slowly with about a 4 second dwell at the top of the stroke. After the stroke lower the case and rotate it 1/3 turn and size again slowly with the dwell.
Then lower and turn 1/3 of a turn and size a 3rd time with dwell. This redundant amount of sizing gives the formed brass time and enough force to creep to the same finished dimension.

[rbuck351]

I don't like cam over. I make sure the dies is low enough that it won't cam over and then push the shell holder hard against the die, pull the case out, rotate and repeat 3 or 4 times with some delay at the top. Then trim with a good case trimmer and measure with good calipers.

[3006guns]

EDG and rbuck351.........thank you. I hadn't thought about a delay at the top of the stroke, although I have rotated the cases a might to make sure the setback is even. Not delaying at the top of the stroke might very well have caused the issue though. Sometimes we forget that it takes metal time to move! This would also explain why even the finished cases seem to have the shoulder a bit too far out, and only shooting a forming load puts them in the right place. I never thought about that before, but I will adopt that technique in the future.

Again, many thanks!

[RED BEAR]

I bought a pair of those years ago because they were cheap were no good the day i got them. A little pressure on thumb wheel would change reading from get go.

[retread]

A good set of calipers will last a lifetime. Buy good ones, ie Starrett. Mitutoya, Brown and sharp, etc. Like said earlier, shop ebay for a deal.

[Bookworm]

I have a set of the plastic calipers. It never gets within 50 feet of the reloading bench.
I use it to measure things like -
-the length of a bolt,,
- the size of a large nut that needs loosened, so I can make one trip to the toolbox.

In short, only non-critical measurements. If +/- .001 is going to be a problem, I have real measuring tools.

[RED BEAR]

+1 on a good set i still have all my measuring tools from when i worked. All still work as good as the day i bought them. If you want some advice i have used starrett and Mitutoya they are both good quality but can't touch brown and sharpe.

[Drew P]

Find you a nicely cared for vintage set of USA made calipers on ebay..

Mitutoyo, tesa, B&S = good
Hornady, rcbs, Fowler, starret, any digital = meh
Plastic = no.

[6bg6ga]

I find that in the right hands plastic will measure correctly. That is plastic calipers without a dial. I've found them to be every bit as accurate as steel calipers with a dial read out. Want real accuracy then ditch the dial or digital read out. One needs to remember the correct way to use calipers. Most people use too much tension which is incorrect. As a former inspector my opinion is they are ok in the hands of someone that is properly trained and knows how to handle calipers. You would be surprised how many operators I had that would screw up a brand new pair of dial calipers. After all they are not a set of pliers.

[EDG]

I spent 50 years in manufacturing and never saw a single company try to use plastic calipers for acceptance of product. Plastic expands much faster than steel when subjected to the heat of your hands.
Yes I have seen dial calipers screwed up, usually by dropping them or a machinist getting aluminum debris in the rack.
Vernier calipers have their own problems.
1. Most young folks have probably never been taught to read a vernier
2. Most old folks that know how to read them cannot see well enough to read the vernier.
3. The vernier should be read while in contact with larger items so you get the true reading. When you try to get them closer to your eyes or into better light they often move from the measured size of the part.

I find that in the right hands plastic will measure correctly. That is plastic calipers without a dial. I've found them to be every bit as accurate as steel calipers with a dial read out. Want real accuracy then ditch the dial or digital read out. One needs to remember the correct way to use calipers. Most people use too much tension which is incorrect. As a former inspector my opinion is they are ok in the hands of someone that is properly trained and knows how to handle calipers. You would be surprised how many operators I had that would screw up a brand new pair of dial calipers. After all they are not a set of pliers.

[SSGOldfart]

You had enough people tell you about your calipers so I guess "if it isn't broken,don't fix it" you made a change in how you formed your brass and had to trouble shoot the sizing operation. Tumbs up to you.let us know how it shoots.

[Conditor22]

Glad you figured it out.

When I form brass, I always finish trimming to length on my case trimmer. No Surprises there.

[Petander]

I actually use those green calipers in my "Room B".

They came with some other Ebay stuff long time ago,I was going to throw that plastic thing away... But I developed a touch for it instead. Comparing to proper calipers with known things like NOE expander plugs, it's not hard to learn a feel for them. Better steel calipers have a " feel" as well.

I guess mine haven't worn out yet. I keep checking my touch whenever I use them.

[skeettx]

I used them when I was younger to measure case length and cartridge length, that was all.
A 0-1.00 Starrett Digital Micrometer 216FL was used for fine work

[Winger Ed.]

I had some that did OK for awhile. I tried to be real easy with them.

I finally got a nice steel set and put the plastic ones up on a shelf.

I'm saving them to loan out to someone who never brings stuff back.

[one-eyed fat man]

...Vernier calipers have their own problems.
1. Most young folks have probably never been taught to read a vernier
2. Most old folks that know how to read them cannot see well enough to read the vernier...

I am in firmly in group 2, but I keep a set of verniers in the tool box. The young'uns never ask to borrow them again.