6.5CM resized brass Comparator 0.400 measurement ?

[Zatoichi66]

I purchased a Hornady Lock n Load Comparator to check my FL resized 1x Lapua 6.5CM brass as the OAL is exactly the same on once-fired resized brass as virgin Lapua brass. The datum diameter is 0.400” because that measurement can be found on the SAAMI spec. Hornady’s website recommended 0.375” comparator, but that didn’t seem to make sense since that datum measurement isn’t on the SAAMI sheet spec i have on 6.5 Creedmoor, so….here’s my data:

Per SAAMI spec, this measurement at 0.400” diameter on the shoulder datum/case base to the shoulder datum at 0.400” diameter (i‘m not sure i’m using proper terms) should be 1.5438-0.007, which i assume is a tolerance meaning 1.5368“ is minimum? I’m not sure, which is part if my question. My virgin Lapua brass doesn’t meet this measurement since it measures 1.5360“ with the same comparator, same measuring session. I spent an hour doing these measurements for consistency sake. The Mitutoyo digital calipers with an add-on comparator are likely not as accurate as SAAMI measuring equipment, i guess? It is snug/secured and there‘s no movement. My measuring technique included rotating the brass 90 degrees to get a second measurement to confirm the measurement, and i was consistent.

My Redding full length resizing die has my datum measurement at 1.5305” for 10 cases. Virgin Lapua brass is 1.5360” for 10 cases. I am quite impressed by the datum & OAL of Lapua brass—very consistent. And, my Redding dies resizing is quite consistent, too.

But in full disclosure, I resized with Lee dies & never measured Lake City 5.56 this obsessively.

My questions:

1) why the difference between virgin brass and SAAMI spec? Am i interpreting the 0.007 as a lower tolerance spec?
2) Did i over-resize these cases? The OAL is the same as virgin. Unfortunately, I don’t have the Redding competition shell holder to adjust the resizing; or, am I over-thinking this?
3) can i just back off the resizing die a partial turn to make the resized brass a few thou longer, or am I “chasing thou’s” as my former boss used to tell me in the machine shop back in the 1980s?

Thank you for the help.

 

[OREGUN]

I wish @F.Guffey was here to handle this.

 

[Zatoichi66]

I don’t know Guffy….but i am concerned i’m over-thinking & measuring stuff that doesn’t matter. When my resized 1x brass was the same OAL, it was suggested i do a datum measurement on the shoulder—which i did & it’s confusing, since virgin brass is smaller than SAAMI spec, unless i subtract the tolerance,

i’ve seen consistency is key with my first target loads and am trying for sub-0.5MOA. I posted my handloads & 0.6“ - 0.7”-ish 5 shot group. I don’t want my loads to limit me.

 

[OREGUN]

I’ll read it all and think about it and give you a real answer once I’m not at work. Guffy was a dude that used to haunt these kinds of forums and would always have a lot of really esoteric things to say about measuring in particular.

 

[whatsupdoc]

It is a comparator not a measuring tool it does not provide a case datum measurement.
It measures the shoulder and gives you a reference measurement, you then use that reference measurement
to adjust your die to bump your shoulder back.

You take you fired brass and remove the primer, then you measure with the comparator
and get your reference measurement.

You then adjust your resizing die to push back the shoulder say .003
So if your fired brass measures 1.539 on the comparator then after sizing it should measure 1.536 measured on the same comparator.

Use the .400 comparator even though using the .375 one will not make any difference because in reality its just
subtracting one number from another.

 

[FLIGHT762]

First thing, your Hornady tool is a "Comparator", not a SAAMI spec gauge. You're NOT going to get SAAMI spec drawing numbers off of that comparator. Proper use of the comparator is to measure your fired cases in your rifle and use the comparator to set your F/L die to bump the case shoulder back .002" or so.
On all of the comparator inserts, there is a bevel on the the of the insert.

If you are curious as to the SAAMI minimum on your comparator insert, you could take a 6.5 CM GO gauge and get a measurement off of that to see what the comparator number is, but it really isn't necessary.

As an example, I have a friend who let me borrow his 1.630" GO gauge for 308 Winchester. I have two .400" Hornady comparator inserts. One is a very old insert, the other is a newer insert. When I measured the old insert, I got a measurement of 1.611". On the newer insert, I got a measurement of 1.621".

What this showed me is the old insert has a .019" bevel / chamfer and the newer one has a .009" bevel / chamfer.

So, on the old insert, 1.611" is 1.630" SAAMI minimum. On the newer insert 1.621" is 1.630" SAAMI minimum.

I only did this for curiosity since it it didn't cost me anything.

For a gauge type measurement on SAAMI minimum there are tools like the RCBS Precision Mic and the Whidden case gauge. Both of these tool are set to a "0" SAAMI minimum on their micrometer dial. You drop you cases in the gauge and see if your cases are plus or minus or "0" on the micrometer.

Your Comparator is working and will give you the numbers you actually need to properly set your F/L die off of your fired cases. Don't get caught up on SAAMI numbers with a comparator.

**EDIT** I see whatsupdoc got his post in as I was typing my response. He's giving you the same advice.

When I first got my comparator, I went through the same head scratching as you did off of using SAAMI numbers until the light bulb went off above my head and I said "Duh".

 

[lariat]

Your fired brass is your golden number because that is your chamber. Everything should measure in relation to that. In that regard and for purposes of this conversation SAAMI is not relevant.

 

[Zatoichi66]

Got it. Thank you.
Can i just back out the die 0.006” and not perform full-length resize? The competition shell holders aren’t available & i don’t want a ring of unresizd case that could prevent chambering.
or is 0.006” probably not going to matter? i think this will be a “shoot & evaluate” moment given differences between rifles, chambers, etc.

 

[lariat]

A number of people just bump the shoulder. Some like it, others hate it. Eventually you may need to F/L resize. Read up on it and see if its what you want to do.

 

[spife7980]

Just set your die to turn your sized brass shoulders .002 less than fired. That’s as complicated as this needs to be.

 

[Doom]

I don’t know where you get the .375” recommendation. It should be the .400” insert.

 

[lariat]

I don’t know where you get the .375” recommendation. It should be the .400” insert.

It doesn't matter if it is used to compare a resized case to a fireformed one - it is only a reference measurement on the bearing surface of the case that has a consistent shoulder angle. Any insert that falls within 0.295 - 0.460" will supply the same information if a comparator is used correctly. If you are comparing to the actual SAAMI print then you would be best served by using an insert that matches what they are calling out as the datum. Either the fireformed case or the print is your standard you are measuring to.

 

[FLIGHT762]

Got it. Thank you.
Can i just back out the die 0.006” and not perform full-length resize? The competition shell holders aren’t available & i don’t want a ring of unresizd case that could prevent chambering.
or is 0.006” probably not going to matter? i think this will be a “shoot & evaluate” moment given differences between rifles, chambers, etc.

Just set your die to bump fired cases .002". Most chambers are cut to be no more than .002"-.003" from a SAAMI minimum GO Gauge.

You are F/L sizing. When you bump .002". F/L sizing doesn't mean setting your die so the shell holder smashes into the die as far as it will go.

Setting the die to bump your shoulders .002" is NOT going to cause your case web not to be sized. You're way overthinking this.

 

[FLIGHT762]

I don’t know where you get the .375” recommendation. It should be the .400” insert.

The recommendation for the .375" insert for the 6.5 CM is on Hornady's web page recommending it.

Lock-N-Load® Headspace Comparator & Anvil Base Kit - Hornady Manufacturing, Inc

Lock-N-Load® Headspace Comparator & Anvil Base Kit Lock-N-Load® Headspace Comparator The Lock-N-Load® Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures...

www.hornady.com

 

[Baron23]

Whidden case gauge.

I have one and like it very much. Seems a bit easier and quicker to check my bump back that putting the Hndy comparator on a caliper.

 

[918v]

I use a .40 S&W case to compare fired to sized. You people are making this way too complicated. Second, it is silly to try to gauge a difference that falls within the error range of your measuring tool.

 

[Baron23]

Second, it is silly to try to gauge a difference that falls within the error range of your measuring tool.

And....you .40 S&W case is what....calibrated to NIST standards???

 

[918v]

Mechan

And....you .40 S&W case is what....calibrated to NIST standards???

You didn’t think that through, did you?

 

[Baron23]

Mechan


You didn’t think that through, did you?

Ok, perhaps not. Can you share with me exactly how you use this case

 

[Zatoichi66]

And....you .40 S&W case is what....calibrated to NIST standards???

Easy gentlemen….

It took me 4 years to decide on the Tikka & 6.5CM—I realize I am cautious & over-think things I am unfamiliar with—hence my posts.

I have never reloaded precision reloads—I HAVE loaded a few thousand 5.56, 9mm, etc on my Dillon 550B. If my Giraud trimmer didn’t trim a case—it seemed it didn’t need it—but every case went through the trimmer—I never measured.

seems PRS can be as lax or intensive as the shooter makes it—I’m going for 0.5 MOA as my next goal!

who’s with me?!?

 

[918v]

Ok, perhaps not. Can you share with me exactly how you use this case

Use a new or sized .40S&W case in good condition with no burrs and perfectly round. The case mouth will act as a blade to index against the shoulder of the bottleneck case you intend to measure. Place the two cases inside the jaws of your caliper and rotate them inside the jaws to square them up while applying pressure with the jaws.

This alignment is much more precise than anything you can get from a comparator bolted to the jaws. Couple that with a certified dial caliper that gives you accurate information and you will know exactly how much you’re bumping.

vs

misaligment in the bolt-on comparator tool exasperated by the plus/minus .001” accuracy of your typical caliper. People swear up and down they bumped the shoulder but haven’t or bumped it too much.

All these trinkets are no better than a case gauge.

 

[Zatoichi66]

I sold my .40 cal—but that’s a cool trick! I agree the comparator are a bit suspect—my 0.0000” digital caliper is going to be screwed by 1/4 or even an 1/8 screw turn.

but I thought I was looking at SAAMI spec—not comparison

 

[lariat]

Calipers are certified to +/-0.002. Depending on the pressure you use while measuring you can flex way more than that out of them. They are notoriously the measuring tool beginning machinists misuse because they do not know the proper amount of finger pressure to use. And I never trust anything a digit caliper says after three decimal places.

while we are here on this, the use of a straight walled case is pretty cool. However, I have taken the time to feed my OCD and measure the the deformation the stamping puts in on the case head. If your looking for 0.002 you can be thrown off by this. I say can because it is extremely inconsistent. Since all the the length measurements are coming from this common point I put it out here as some thing to consider.

 

[Zatoichi66]

The calipers might be that accurate, but the comparator is a Gerry-rigged gizmo—it absolutely requires consistent technique for meaningful data. I know this because I had to invent a technique to square the case head centered on one jaw. A few thou error are easily made without consistent technique

 

[spife7980]

It’s not hard.

Make this fired case reading

Do this when it comes out of the die

Now for the short kids in the back row.
This

To this

And if they dont all come out perfect, well... welcome to reloading. Do the best you can and itll be just fine.

 

[OREGUN]

It’s not hard.

Make this fired case reading
View attachment 7689902
Do this when it comes out of the die
View attachment 7689904

Now for the short kids in the back row.
This
View attachment 7689905
To this
View attachment 7689906

That Gerry-rigged gizmo could never be right.

 

[Doom]

The recommendation for the .375" insert for the 6.5 CM is on Hornady's web page recommending it.

Lock-N-Load® Headspace Comparator & Anvil Base Kit - Hornady Manufacturing, Inc

Lock-N-Load® Headspace Comparator & Anvil Base Kit Lock-N-Load® Headspace Comparator The Lock-N-Load® Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures...

www.hornady.com

The 6.5 CM is a 0.4” headspace but with the 30 degree angle and the longer shoulder than the 30TC, the .375” insert catches further down the shoulder.

Either should work and the .375 is a good reference point.

 

[Zatoichi66]

That Gerry-rigged gizmo could never be right.

I bet it’ll read a few thou different when removed & replaced.

but what would i know—CNC didn’t exist in the 1980s when i worked in a machine shop.

i had resized almost 400 spent cases after a PRS course & was surprised when they all were the same OAL as virgin brass in a prior thread. That led to this thread when the comparator didn’t show SAAMI datum reads.

asshats—they’re not just on the internet anymore

 

[Baron23]

It’s not hard.

Make this fired case reading
View attachment 7689902
Do this when it comes out of the die
View attachment 7689904

Now for the short kids in the back row.
This
View attachment 7689905
To this
View attachment 7689906


And if they dont all come out perfect, well... welcome to reloading. Do the best you can and itll be just fine.

Yeah, I have the Hndy comparator and also use one of the...whatever they call them...anvils??...bases???...on the other leg of the caliper to give me a nice wide, flat surface. When I put them on, I then close the caliper with some tension on it, loosen the locking screws on both to get them even/flat, and tighten again while continuing to keep tension on the caliper. Seems to give me fairly repeatable results and, as you have pointed out, we are just looking for a relative figure showing the bump back, right? Start at x and end at x - .002"

I do like the Whidden gauge, however, as its quick and easy to grab and once again I'm just looking for relative numbers.....if fired is "this mark here", then I want resized to be "this mark here - .002".

As you know, I'm very new to metallic reloading but this doesn't seem to be one of the harder parts and I don't see using a .40 SW case as being any better.

 

[spife7980]

we are just looking for a relative figure showing the bump back, right? Start at x and end at x - .002"

Exactly.

 

[OREGUN]

Perfect quote from another thread:

You'll need to start to understand the process before blaming your tools.

 

[Holliday]

And if they dont all come out perfect, well... welcome to reloading. Do the best you can and itll be just fine.

Yep. Sage advise. Welcome to reloading.......

 

[B y r o n]

The recommendation for the .375" insert for the 6.5 CM is on Hornady's web page recommending it.

Lock-N-Load® Headspace Comparator & Anvil Base Kit - Hornady Manufacturing, Inc

Lock-N-Load® Headspace Comparator & Anvil Base Kit Lock-N-Load® Headspace Comparator The Lock-N-Load® Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures...

www.hornady.com

Here is how they came up with the number: "Determining the proper bushing diameter: If you add the neck diameter and the shoulder diameter and divide that number by two, use the bushing closest to that number."

As previously stated, either will work.

 

[rottenruger]

I purchased a Hornady Lock n Load Comparator to check my FL resized 1x Lapua 6.5CM brass as the OAL is exactly the same on once-fired resized brass as virgin Lapua brass. The datum diameter is 0.400” because that measurement can be found on the SAAMI spec. Hornady’s website recommended 0.375” comparator, but that didn’t seem to make sense since that datum measurement isn’t on the SAAMI sheet spec i have on 6.5 Creedmoor, so….here’s my data:

Per SAAMI spec, this measurement at 0.400” diameter on the shoulder datum/case base to the shoulder datum at 0.400” diameter (i‘m not sure i’m using proper terms) should be 1.5438-0.007, which i assume is a tolerance meaning 1.5368“ is minimum? I’m not sure, which is part if my question. My virgin Lapua brass doesn’t meet this measurement since it measures 1.5360“ with the same comparator, same measuring session. I spent an hour doing these measurements for consistency sake. The Mitutoyo digital calipers with an add-on comparator are likely not as accurate as SAAMI measuring equipment, i guess? It is snug/secured and there‘s no movement. My measuring technique included rotating the brass 90 degrees to get a second measurement to confirm the measurement, and i was consistent.

My Redding full length resizing die has my datum measurement at 1.5305” for 10 cases. Virgin Lapua brass is 1.5360” for 10 cases. I am quite impressed by the datum & OAL of Lapua brass—very consistent. And, my Redding dies resizing is quite consistent, too.

But in full disclosure, I resized with Lee dies & never measured Lake City 5.56 this obsessively.

My questions:

1) why the difference between virgin brass and SAAMI spec? Am i interpreting the 0.007 as a lower tolerance spec?
2) Did i over-resize these cases? The OAL is the same as virgin. Unfortunately, I don’t have the Redding competition shell holder to adjust the resizing; or, am I over-thinking this?
3) can i just back off the resizing die a partial turn to make the resized brass a few thou longer, or am I “chasing thou’s” as my former boss used to tell me in the machine shop back in the 1980s?

Thank you for the help.

I would certainly expect Mitutoyo to be adequate to this task. Just upped to one recently and am sure going to be disappointed to find it's anything less than top of the line for this homeshop reloading boy.

 

[lariat]

I would certainly expect Mitutoyo to be adequate to this task. Just upped to one recently and am sure going to be disappointed to find it's anything less than top of the line for this homeshop reloading boy.

Miti’s are great, but you can still throw bad reading is you don’t use them correctly and understand the accuracy limitations of calipers.

 

[Mike Casselton]

I use a .40 S&W case to compare fired to sized. You people are making this way too complicated. Second, it is silly to try to gauge a difference that falls within the error range of your measuring tool.

I also use the 40 S&W case.
It's unfired and deprimed.
It saved $40 and measures just as accurately.
That case stays in the die box.
Sometimes old school shit still works.

 

[Mike Casselton]

The calipers might be that accurate, but the comparator is a Gerry-rigged gizmo—it absolutely requires consistent technique for meaningful data. I know this because I had to invent a technique to square the case head centered on one jaw. A few thou error are easily made without consistent technique

There's a guy on Accurate Shooter .com that sells another gizmo that squares up your cartridge on the caliper.
It's designed to work with the Horndaddy tool.