Accuracy testing of "cheap" calipers and digital scales

[LiveLife]

For those curious about how accurate "cheaper" calipers and digital scales perform, I did some testing with Lyman shooters check weights and a new feeler gauge.

Products tested:

- New Frankford Arsenal 6" dial calipers
- ~ 20 year old Frankford Arsenal (MidwayUSA) 6" dial calipers
- ~ 3 year old Harbor Freight 6" digital calipers
- New Frankford Arsenal DS-750 digital scale
- ~ 20 year old Frankford Arsenal (MidwayUSA) digital scale

Check weight range: 0.5, 1, 2, 5, 10, 20 grains

Feeler gauge range: .0015", .0020", .0025", .003", .004", .005"


Here are the results (To factor in effects of fluorescent lighting, two CFL clamp lights were used over the bench during the duration of testing with ambient temperature of 68F):

- Harbor Freight 6" digital calipers bought about 3 years ago measured .0015", .002", .0025", .003", .004", .005".

- New Frankford Arsenal 6" dial calipers measured .002", .003", .004", .005" (needle tip was between lines for .0015" and .0025").

- Frankford Arsenal (MidwayUSA) 6" dial calipers about 20 years old measured .002", .003", .004", .005" (needle tip was between lines for .0015" and .0025").


- The check weights were weighed on two Ohaus 10-10 scales and they weighed 0.5, 1, 2, 5, 10, 20 grains on both 10-10 scales. The 10 grain check weight was weighed using both the large poise or the micrometer poise set to 10 grains and both methods gave the same weight.

- New Frankford Arsenal DS-750 digital scale with 2 AAA batteries read 0.5, 1, 2, 4.9 briefly then read 5, 10, 20 grains. After the scale was calibrated (first calibration out of the box), it read exactly 0.5, 1, 2, 5, 10, 20 grains.

- Frankford Arsenal (MidwayUSA) digital scale about 20 years old with 2 new CR2032 batteries read 0.4, 1, 2, 4.9, 10, 20 grains. After the scale was calibrated (it was last calibrated several months ago), it read 0.4, 1, 2, Flickered between 4.9/5.0, 10, 20 grains.


Summary - Although Harbor Freight digital calipers were accurate, I would suggest you check their dial calipers with feeler gauges as I found over the years, many to be off by .001"+ and felt gritty without smooth action so I never bought any. The digital calipers I checked were accurate and I would endorse them. If you are looking for dial calipers, I would not hesitate to recommend Frankford Arsenal dial calipers.

I have always used the old Frankford Arsenal digital scale knowing that it had 0.1 gr variance but it was fast for weighing bullets and military .308 cases for sorting. The new DS-750 model is certainly accurate enough for me and both digital scales never showed any effects of florescent (CFL) lighting I used directly over the bench.

Suggestion for digital scale use - The old FA digital scale came with specified operating temperature range of 59F - 95F and the new FA digital scale came with specificed operating temperature range of 50F - 86F. I found that using the old FA digital scale outside of the temperature range and/or with weak batteries resulted in inconsistent scale readings.

 

[Blue68f100]

Will add the accuracy test you did is for that range ONLY.

As things slide down the scale more and more error can accour. My Sterrett's that were off where ok in the range you tested but get in the .060- 0.080" is were things were off as much as 0.003".

 

[Rule3]

Thanks for the review. It appears that us 'frugal" reloaders ar OK with the less expensive calipers. I still prefer my beam balance for long term use, But that's just me.

Did you try any test (for scales)with slight air movement like a ceiling fan or air vents??

 

[GaryL]

I'll add my results to this, for a Hornady GS-1500 digital scale (~$35 a couple years ago)

I took a couple plastic chips, a metal knockout slug, and an NRA chip to work to weigh on one of the R&D scales. I asked the guys in the lab how good the scale was and they said it will weigh fingerprints easily. I think it's an Oehler - not positive, and it doesn't really matter. Accurate to 0.0001 gram, and it's calibration certified every year.

Anyway, I just now put them on the scale, in the powder pan, and this is what I got:

Cal, GS-1500
Chip 1 - 6.71gr, 6.6gr
Chip 2 - 8.13gr, 8.0gr
Chip 1+2 - 14.84gr, 14.7gr
Slug - 66.25gr, 66.0gr
NRA Chip - 200.9gr, 200.5gr

I seem to recall the first time I did it, the numbers were a bit closer. It's possible, it's still on the original battery.

 

[LiveLife]

As things slide down the scale more and more error can accour. My Sterrett's that were off where ok in the range you tested but get in the .060- 0.080" is were things were off as much as 0.003".

Good point.

I measured the largest feeler gauges in the range of .025", .026", .028", .030", .032", .035" and the readings on the Harbor Freight were spot on. Readings on the dial calipers were also repeatable for the ranges measured.

I do not have a gauge block but measured some Montana Gold and Remington Golden Saber jacketed bullets and they were measured at .355" and .400" using all three calipers.

Did you try any test (for scales) with slight air movement like a ceiling fan or air vents??

I always turn off the central heating/air conditioning and close the door to the reloading room as air movement (ceiling fan/vent air) will be detected by the Ohaus 10-10 scales. But I just ran the following tests:

- I turned on the central heating and the Ohaus 10-10 moved when the air came out of the vent while DS-750 did not register the air movement.

- I placed the DS-750 in different locations under the ceiling fan on medium/high and it would fluctuate but would show a constant reading shortly like 1.5 gr. Ohaus 10-10 went crazy under the ceiling fan.

- Gentle fanning of air with a piece of cardboard about 6 inches away moved the 10-10 scale but not the DS-750.

- Gently blowing with mouth moved the 10-10 and the DS-750 registered fluctuating readings but it quickly returned to zero.

 

[RandyP]

The test that convince me that my Harbor Freight calipers and $30 digital scale were mighty ' good enuff' for MY needs?

Measuring a box of factory ammo for OAL of each round and then pulling 10 and weighing the powder charge.

The variances I found were educational and since then I fret much less over the microscopic accuracy level of my equipment and my reloads.

 

[Rule3]

Good point.

I measured the largest feeler gauges in the range of .025", .026", .028", .030", .032", .035" and the readings on the Harbor Freight were spot on. Readings on the dial calipers were also repeatable for the ranges measured.

I do not have a gauge block but measured some Montana Gold and Remington Golden Saber jacketed bullets and they were measured at .355" and .400" using all three calipers.



I always turn off the central heating/air conditioning and close the door to the reloading room as air movement (ceiling fan/vent air) will be detected by the Ohaus 10-10 scales. But I just ran the following tests:

- I turned on the central heating and the Ohaus 10-10 moved when the air came out of the vent while DS-750 did not register the air movement.

- I placed the DS-750 in different locations under the ceiling fan on medium/high and it would fluctuate but would show a constant reading shortly like 1.5 gr. Ohaus 10-10 went crazy under the ceiling fan.

- Gentle fanning of air with a piece of cardboard about 6 inches away moved the 10-10 scale but not the DS-750.

- Gently blowing with mouth moved the 10-10 and the DS-750 registered fluctuating readings but it quickly returned to zero.

Thanks. Good info to know. I have a My Weigh 101electronic scale I bought a while ago. It is a little better than a cheapo one and it has a plastic wind screen around it to use or not. It's very accurate but I never seem to use it. 30 yr warranty.

http://www.oldwillknottscales.com/my-weigh-ibalance-101.html

 

[Potatohead]

Thanks BDS

 

[PJSprog]

It's a nice test, but if you're going to test the calibration and accuracy of calipers, it should be done through the entire range of motion - in this case six inches. As already mentioned, a barely noticeable deviation at the thousandths-of-an-inch level can translate into a very noticeable deviation at four to six inches.

Same goes for the scales.

(I'm a Quality Manager = kind of anal about calibration stuff.)

 

[ironworkerwill]

The variances I found were educational and since then I fret much less over the microscopic accuracy level of my equipment and my reloads.

Right on Randy! A while back, reloading the wssm family, I noticed fairly tight tolerances on factory stuff. I guess they had to push the edge of performance and wanted to insure safety. But, pull some average '06 factory ammo! It will make you feel better about what you do at the reloading bench.

 

[LiveLife]

Someone more knowledgeable/experienced correct me if I am wrong.

For me, it's the reloading powder range, especially near max/max charges that I am concerned with. So I want to verify my scales are accurate at 4.0 - 5.0 grains with 4.0/5.0 gr check weights, especially with fast burning powders I am working with (Bullseye/Titegroups/W231/HP-30/etc.). I am less concerned about the accuracy at 300 grains. While I do sort bullets/cases by weight but that's done with less than 1.0 grain consistency, not 0.1 grain.

As to calipers, I am using mostly .355"-.474" range to measure bullet diameters and loaded rounds for taper crimp. If the calipers are consistent at these ranges to .001", how will 6" measurement consistency help me with my taper crimp measurements?

Am I missing something?

 

[jaguarxk120]

You did not use any calibrated standard in any of your tests.

Checking weights against two scale that are accurate to 1/10 of a grain just means that the weights are plus/minus 1/10 grain.
You need laboratory weight standards for measuring mass.

The calipers and the feeler gauges are in the same ball park as the weights you used, generally useless.
Did you ever hear of Johansson Gauge Blocks?

Or Gauge blocks in general. Every tool shop has a set of "Jo Blocks" that all gauges or measuring instruments are calibrated to.

 

[LiveLife]

You did not use any calibrated standard in any of your tests.

So check weights and feeler gages don't count for accuracy to .1 gr and .001"?

You mean like this Mitutoyo gauge block? What size block would you suggest? - http://www.amazon.com/Mitutoyo-Stee..._5?s=industrial&ie=UTF8&qid=1388192135&sr=1-5

Every tool shop has a set of "Jo Blocks" that all gauges or measuring instruments are calibrated to.

I may make a trip to local machine shops and see how the calipers fare against the gage blocks (I may even have the machinist do the measuring to remove "me" factor out).

So if all three calipers measure .355"/.400" jacketed bullets consistently, they are useless, even though one digital calipers also measured the feeler gauges to .0005"?


I do understand the notion of 0.1 grain variance being +/- so there's a potential range of .2 grains. Since most of my pistol loads are mid-to-high-range load data, I feel I have some buffer there.

I was trying to illustrate that some of the "cheaper" reloading equipment can be accurate/consistent enough to be used for reloading. So I guess even if we are using Ohaus/RCBS 10-10 beam scale, we must be careful that the powder charges may be off by .1 grain.

I am curious though. So, how did many bench rest shooters (like for Palma match) load their precision rifle loads many decades ago? Did they use beam scales like Ohaus 10-10 or something more precise?

 

[Peter M. Eick]

I have to comment on one point. I bought an RCBS 10/10 scale because I succumbed to the concept that my RCBS digital was not accurate enough. You know, you read online all the time how bad the digitals are it eventually gets under your skin.

Dumbest investment of my reloading career, ok, second dumbest, first was buying a lee safety scale in the first place.

I have found that every time I compare my digital to the 10/10, I get the same value on both. I still check occasionally but drop a bullet in one and then the other, same number. Put a check weight in one then the other, same number. They just seem to work.

Now regarding the cheaper tools like Harbor freight calipers, I have tended to buy the more expensive Starrett's or similar quality level. I like the nice feel of the quality instrument and enjoy the precision it gives. Since reloading is my hobby, I don't like doing it on marginal hardware. I would prefer to do it quality tools.

 

[GaryL]

I have to say, I've seen quite a few discussions about calibration, accuracy, etc, get way off track over details that really don't matter. While there is a very small amount of rocket science in reloading (the same laws of physics apply), we don't need to adhere to the same requirements as NASA scientists and engineers. bds is correct about the importance of knowing how accurate and repeatable your equipment is in the ranges that matter. Especially the repeatability thing.

I have been in the business of non contact measurements for over 20 yrs now. On a recent project, I spent $4k on a lens, because accuracy and repeatability of measurement across the entire field of view is very important, and there are people on this board who will benefit directly or indirectly (that is all I can say about it). I have had plenty of projects where accuracy and repeatability was important, and a $250 lens with a lot of distortion was more than adequate. The reason it was adequate was that the lens only needed to work across a small range, and it was easy to calibrate the range that mattered. No measurements were being made in the parts of the image that were highly distorted. This is equivalent to having a caliper that is off by an inch at 6", and 0.010" at 0.250", but accurate to .001" from 0.750"-1.125". A worthless caliper to be sure, but if I only use it to measure 1.00" blocks that need to be 1.00" blocks, plus or minus 0.005", it will work for that task. As long as the caliper repeats, I could use it to compare 5" blocks to 5" blocks, but I'll have no idea how close to 5" they are, unless I have a 5" reference block to calibrate to. Then I'll know what readings from the caliper indicate 5".

So in reloading, there are a lot of factors that go way beyond the accuracy of our scales and gauges. We start low and work up for a reason. So if I follow good reloading practices, it doesn't matter if my scale is off by .3gr, so long as it repeats to better than .1gr, and I always use the same load I worked up and the same scale and range to verify that load. I may not be happy about the inaccuracy of the scale, but if it repeats, I'll get the same results every time. Now if I want to switch to a more accurate scale, I need to use the old scale for a starting reference to find out how much that charge I liked really weighs.

IMHO, the best thing about check weights is the ability to check repeatability. Otherwise you have no idea if the 5.0gr you measured last week is the same 5.0gr you want to measure today. Doesn't matter if the check weight is off by 0.1gr, unless you need to match 5.0gr from one scale to another, with no way of using the same check weight to verify both scales - in that case, a reference standard is required.

 

[celem]

Today, I was reloading and noticed that my Chinese eBay digital calipers turned on when it got within less than afoot of the tubes in my florescent light fixture. I normally store it on a shelf that is close to the lights - no wonder the battery just had to be replaced.