Firearm & Gun Forum - FireArmsTalk.com > Gear & Accessories > Ammunition & Reloading > Caliper Accuracy Issues

Reply
 
LinkBack Thread Tools Display Modes
Old 02-21-2011, 01:55 AM   #1
Feedback Score: 0 reviews
 
Join Date: Jan 2011
Location: Sumter,SC
Posts: 29
Default Caliper Accuracy Issues

Need some help…

I’ve decided to get into reloading, so I bought a few things yesterday including a dial caliper and a Sierra reloading manual. I’ve been wanting to start reloading for a few years now, and I’m finally taking the plunge.

So anyway, I’m reviewing some of the data in the manual at the same time I’m measuring some of my ammo here at home, but the numbers don’t match?! My problem is that I’m concerned that my caliper isn’t accurate, but I don’t really have a way to verify without getting a second caliper.

Here are a few examples: When I measure the bottom (rim?) of the .45 ACP case, I come up with .476”, but the book says it should be .480”. The same holds true when I measure the rim of a .357 magnum case, I measure .434”, but the book says .440”

Now, if the readings were always consistent (say .005 off), I could conclude that my caliper has issues, but sometimes the reading is spot on. For example, when I measure the bullet for a 7.62x39 cartridge, I get a value of .311, which is exactly what I would expect.

So what do you folks think? Is this normal, or do I need to replace this caliper? If it’s normal, do the values in the book represent the max allowable?

Thanks in advance for any help.

__________________
Richz99 is offline  
 
Reply With Quote

Join FirearmsTalk.com Today - It's Free!

Are you a firearms enthusiast? Then we hope you will join the community. You will gain access to post, create threads, private message, upload images, join groups and more.

Firearms Talk is owned and operated by fellow firearms enthusiasts. We strive to offer a non-commercial community to learn and share information.

Join FirearmsTalk.com Today! - Click Here


Old 02-21-2011, 02:13 AM   #2
Moderator
FTF_MODERATOR.png
Feedback Score: 0 reviews
 
JonM's Avatar
 
Join Date: Nov 2009
Location: Rochester WI,Rochester WI
Posts: 17,176
Liked 5302 Times on 2768 Posts
Likes Given: 334

Default

not all brass is the same. outside dimensions may vary slightly from brand to brand. measure the diameter of a known bullet. your caliper should be ok. just zero it out and get after it.

__________________

"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith

The problem with being stupid is you cannot simply decide to stop doing dumb things...

JonM is offline  
 
Reply With Quote
Old 02-21-2011, 03:54 AM   #3
FTF_SUPPORTER.png
Feedback Score: 0 reviews
 
aandabooks's Avatar
 
Join Date: Sep 2010
Location: Central Illinois
Posts: 1,454
Liked 303 Times on 177 Posts
Likes Given: 58

Default

What brand caliper did you buy? Calipers generally are not the most accurate choice for measuring round items. If you want to get the most accuracy you need to buy a good 0-1" micrometer. Calipers rely too much on the operator being square to the part and using a consistant pressure time after time.

That being said, calipers are faster to use than micrometers and if you purchased a digital set, they are easier to read at a glance.

__________________
aandabooks is offline  
 
Reply With Quote
Old 02-21-2011, 04:52 AM   #4
Feedback Score: 0 reviews
 
Join Date: Jan 2011
Location: Sumter,SC
Posts: 29
Default

It's a Lyman dial caliper; analog. I usually prefer analog over digital when it comes to precision measuring. Call me old school...

__________________
Richz99 is offline  
 
Reply With Quote
Old 02-21-2011, 07:22 PM   #5
Feedback Score: 0 reviews
 
Join Date: Jul 2010
Location: Tucson,AZ, for now
Posts: 211
Liked 7 Times on 7 Posts

Default

Consider manufacturing tolerances and then look at the case diagram. Do you see min/max tolerances? Do all you cases measure exactly the same?
Measure case length. You will find that all your pistol cases measure less than the case drawing shows.
Per SAAMI, the body diameter is x.xxx +0/-0.006.
Go to http://www.saami.org/PubResources/CC_Drawings/Pistol/45%20Automatic.pdf
and
http://www.saami.org/PubResources/CC_Drawings/Pistol/357%20Magnum.pdf
and study the drawings. There is no +/-, everything is +0/-x.xxx.
We do not live in a perfect world, so dimensions do vary.

__________________
noylj is offline  
 
Reply With Quote
Old 02-21-2011, 10:10 PM   #6
Moderator
FTF_MODERATOR.png
Feedback Score: 0 reviews
 
c3shooter's Avatar
 
Join Date: Feb 2008
Location: Third bunker on the right,Central Virginia
Posts: 16,360
Liked 8409 Times on 3644 Posts
Likes Given: 1299

Default

Flashback- the day I came back from TDY, and found my bride had glued and clamped a broken widget using my Starret 0-1 mike.

If you doubt accuract of a caliper or mike, use a known object, such as a feeler guage. Brass WILL vary.

__________________

<--- Your Moderators at our weekly Troll Hunt

c3shooter is online now  
 
Reply With Quote
Old 02-21-2011, 10:55 PM   #7
FTF_SUPPORTER.png
Feedback Score: 0 reviews
 
aandabooks's Avatar
 
Join Date: Sep 2010
Location: Central Illinois
Posts: 1,454
Liked 303 Times on 177 Posts
Likes Given: 58

Default

Have never heard of Lyman. Calipers are generally sold with a +/- of accuracy stated. Get a gauge block so that you can periodically check your calipers for accuracy.

__________________
aandabooks is offline  
 
Reply With Quote
Old 02-22-2011, 02:11 AM   #8
Feedback Score: 0 reviews
 
Join Date: Dec 2010
Posts: 266
Liked 2 Times on 2 Posts

Default

As mentioned before brass case dimensions will vary from what's listed and from one brand to another. They may even vary from one lot to another of the same brand. If it's any help, I just measured the rim (yes it is the rim you measured) on four pieces of Remington 357 brass and four Federal in 45ACP, the 357 has the same number you measured, the 45 measured .475". I get the same numbers with three different calipers, Fowler, some China knock-offs and my Browne & Sharpe. They all read the same measurements.

Your caliper sounds like it's fine and you shouldn't have any trouble measuring round objects down to a .001" accuracy as most calipers are designed, including your Lyman.

Quote:
Originally Posted by aandabooks View Post
Have never heard of Lyman.
Never heard of Lyman?? They produce reloading and shooting accessories, and equipment.

Lyman Products Your Primary Source for Reloading Equipment
__________________
Eric0424 is offline  
 
Reply With Quote
Old 02-22-2011, 03:26 AM   #9
Feedback Score: 0 reviews
 
Join Date: Jan 2011
Location: Sumter,SC
Posts: 29
Default

Eric,

Thanks for the help; I really appreciate it!

Now it looks like I have a lot of reading ahead of me to ensure my first reloads don't blow anything up

__________________
Richz99 is offline  
 
Reply With Quote
Old 02-22-2011, 06:00 AM   #10
Feedback Score: 0 reviews
 
Join Date: Dec 2010
Location: Lima,Ohio
Posts: 2,715
Liked 2222 Times on 1001 Posts
Likes Given: 2154

Default

Quote:
Originally Posted by c3shooter View Post
Flashback- the day I came back from TDY, and found my bride had glued and clamped a broken widget using my Starret 0-1 mike.

If you doubt accuract of a caliper or mike, use a known object, such as a feeler guage. Brass WILL vary.

I know that is sad but still a little funny.
__________________
rjd3282 is offline  
 
Reply With Quote
Reply

Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Firearms Forum Replies Last Post
RIA 1911A1 Issues CA357 1911 Forum 28 02-25-2011 10:24 PM
Springer GI issues Scratchammo 1911 Forum 14 12-02-2010 05:37 PM
New AR issues TheDaggle AR-15 Discussion 16 07-10-2010 03:02 PM
CZ issues DAMMIT General Shotgun Discussion 0 01-12-2010 12:52 AM