Case Trimming & Measuring Questions...

[copperking81]

I'm new to reloading. One observation I have made while trimming and measuring my brass casings is that I can never seem to get consistent measurements with my calipers. We're not talking about significant differences but none the less...inconsistent and poor repeatability between measurements.

In example, I've been trimming .220 Swift brass with an LE Wilson case trimmer with micrometer and using a set of Hornady dial calipers. The case trim length is 2.195 inches. If I take a piece of brass that I've trimmed and measure it multiple times...I don't get repeatability in the measurements. I'll measure once and get 2.197 then 2.193 and then 2.195 and so on. I'm guessing these inconsistencies are so small that it doesn't really matter but given my lack of experience, I'm not sure if that is true. This also makes it difficult to truly dial in and lock down the case trimmer knowing that it will repeatedly produce the same 2.195 desired results.

Am I doing something wrong here or is this fairly normal and I shouldn't worry too much about it? I've calibrated the calipers, they're brand new and I don't think there is an issue with them. I suspect the problem is with my measuring technique or that being inconsistent by a few thousandths isn't that abnormal.

It also seems like the micrometer on the LE Wilson isn't that precise either. I zero it out with a piece of brass. I then measure the brass and find the difference between that measurement and the trim to length and apply that to the micrometer. In example, if the brass prior to trimming measures 2.210 I subtract 2.195 (case trim length) to find the difference of 0.015 and add that to the micrometer. Then trim the brass but it seems like I always end up with something other than 2.195. Again, is that normal? It doesn't help that I'm not confident in my measuring practices either....

Any help would be appreciated!

 

[dkhunt14]

I think it is all your measuring. Maybe the calipers are no good or you are not getting them straight or square in line with the jaws. Different pressures on the calipers will change measurement. I can easily hold .001 with my Wilson trimmer. If you are trimming a lot you have to keep turning till you feel no resistance. Matt

 

[copperking81]

Thanks dkhunt. I think you're right in that I'm probably not getting them straight or squared up with the jaws consistently. I pay particular attention to that but seems like that is pretty easy to miss on when we're talking about thousandths numbers. Did it take you awhile to master that technique? In other words, is that something I should expect to get better with practice or should it be straightforward right out of the gate? If not...it may be the calipers.

 

[SS427]

I have to slightly rotate the case in the jaws of the caliper to get an accurate measurement. If I don't I can get a longer measurement. I don't use the sharp edge of the caliper but the flat section behind the blade that flattens out. It does take a little practice. (I'm assuming you are popping out your primers before you try to measure.)

 

[dkhunt14]

Sometimes trimming lets a burr, especially if you are taking a bunch off. The burr could effect your measuring. Take something that is flat and practice taking measurements. Then you can see if you repeating your measurements. Matt

 

[copperking81]

Yep, primers have been removed.

 

[Jet]

Is the spent primer removed? If not it can keep your calipers from contacting the base of the case.

Rich

 

[lightman]

There is a little bit of a learning curve with calipers and micrometers. As mentioned, you may have a burr on the case mouth. You may also be having trouble with your calipers.

 

[copperking81]

There is a little bit of a learning curve with calipers and micrometers. As mentioned, you may have a burr on the case mouth. You may also be having trouble with your calipers.

Ok cool. That's what I figured but having no real previous experience with these tools, I wasn't sure. I guess I just need to keep practicing. May need to pick up some of those aluminum blocks with known measurements and just practice with them. I think I'll get better with the micrometer once I'm confident in my actual measurements and technique.

 

[7887mm08]

Yes all measuring tools have a learning curve, the problem is you need to have a standard that you could practice with so you could learn what feel you need to use.
It will come be patient. You can easily get .002-.003" variation using dial calipers just by using different pressure. The better the tool, usually the more accurate they are.

 

[TimP]

Copperking81
If you are relatively new to using a dial caliber and or a micrometer your problem more than likely is just inexperience/lack of practice/technique. Do yourself a favor and purchase a gauge block. Use this gauge of know dimension to practice your "feel". Mitutoyo makes a .050 gauge block. You can purchase this tool at MSC Industrial Supply or similar suppliers.

 

[savagedasher]

Copperking81
If you are relatively new to using a dial caliber and or a micrometer your problem more than likely is just inexperience/lack of practice/technique. Do yourself a favor and purchase a gauge block. Use this gauge of know dimension to practice your "feel". Mitutoyo makes a .050 gauge block. You can purchase this tool at MSC Industrial Supply or similar suppliers.

Many of times from trying to go to fast you haven't finished the trim. Dull cutter or hard brass will give you numbers like you have.
Larry

 

[TimP]

Many of times from trying to go to fast you haven't finished the trim. Dull cutter or hard brass will give you numbers like you have.
Larry

"It doesn't help that I'm not confident in my measuring practices either".... that's why I recommended a tool that will help build confidence in his measuring technique .

 

[savagedasher]

"It doesn't help that I'm not confident in my measuring practices either".... that's why I recommended a tool that will help build confidence in his measuring technique .

Practice and and go slow is the best . Like.
2.193 or 2.197 is that critical on triming.
Larry

 

[LHSmith]

IMHO after using several sets of calipers from vernier to dial to digital, I have found that for best repeatable measurements the higher end instruments are needed and I much prefer digital. The Midway, RCBS, Hornady are good for general use, but when you must hold to 0.001" consistently they are lacking. When measuring hold the calipers up to the light and make sure the jaws are square to the case head.
I have (2) Wilson trimmers, one with the micrometer and clamp. I believe the clamp helps with consistency vs. holding the case. However on both trimmers I have found that it works best by letting the cutter do the work vs. pushing the cutter into the work. FWIW, I tried the carbide cutter, but went back to the standard steel cutter.
For PPC and 30 BR I maintain my case lengths to within 0.002" for competition use. I can trim them to 0.001" consistently.
Make sure you are not measuring with the primer in.

 

[savagedasher]

IMHO after using several sets of calipers from vernier to dial to digital, I have found that for best repeatable measurements the higher end instruments are needed and I much prefer digital. The Midway, RCBS, Hornady are good for general use, but when you must hold to 0.001" consistently they are lacking. When measuring hold the calipers up to the light and make sure the jaws are square to the case head.
I have (2) Wilson trimmers, one with the micrometer and clamp. I believe the clamp helps with consistency vs. holding the case. However on both trimmers I have found that it works best by letting the cutter do the work vs. pushing the cutter into the work. FWIW, I tried the carbide cutter, but went back to the standard steel cutter.
For PPC and 30 BR I maintain my case lengths to within 0.002" for competition use. I can trim them to 0.001" consistently.
Make sure you are not measuring with the primer in.

I feel trimming cases to .001 is the same as setting chamber head space to the same tolerance . A total waste of time. Till someone can show me on paper . Larry

 

[LHSmith]

I feel trimming cases to .001 is the same as setting chamber head space to the same tolerance . A total waste of time. Till someone can show me on paper . Larry

I like to eliminate as many variables as possible when prepping for Shortrange BR. If Jack Neary claims maintaining a uniform case length matters - then I listen.

 

[amlevin]

A nice little item that makes it easier to measure cases/cartridges more uniformly is the anvil offered by Hornady. Attach it to one blade on your caliper and it holds the case nice and straight when measuring.

$16 at Midway.

http://www.midwayusa.com/product/584824/hornady-lock-n-load-bullet-comparator-anvil-base-kit

Also great when measuring CBTO.

 

[Paddyd]

I had the same issue till I started doing two things. First, get the jaws squared to the case. Second, use the 'same' pressure on the slide for each measurement. You'll notice if you just run the jaws up to the case mouth you get one reading, but apply a bit more pressure and you get another. I use a firm repeatable pressure on the caliper when measuring my cases.

 

[savagedasher]

I like to eliminate as many variables as possible when prepping for Shortrange BR. If Jack Neary claims maintaining a uniform case length matters - then I listen.

Like I said before if you believe it is better then do it. I haven't been able to see on paper. I have a dasher I chambered deep and just guessed on the head space that shoot. The neck is short . I just don't let the Carbon ring to start. The only answer it paper .
Larry