Checking o.a.l. with a comparator

[headednorth]

I understand the thinking behind the fact that measuring for oal casehead to bullet tip wont always give you an accurate measurement. Using a comparator wont give you the actual oal either. I assumed if you had a round which measures the same as your target measurement, you would then measure with a comparator, record the comparator measurement and use that. But what if the tip to tip measurement you started with was not accurate?

In other words, how do I convert the length I got with the comparator to the length the book is calling for?

 

[mac1911]

You really don't.
The gauges are to compare your readings.

Let's just say you take your new factory brass and for all purposes it is perfect per industry standards.
You take that case, for example "head space" measurement.
Now you use the factory brass to "calibrate" your tool. Fictional measurements here.
Lets just say factory loads are measured perfectly with a fixed datum point and all is perfect at the factory and they measure 3.000" per specs. NOW your particular tool measure 3.004"
This is your default spec. Measure the case after it is fired and it comes out to 3.014"
You now know your chamber is .010" longer than the case. Now general rule of thumb is shoulder needs to be set back .003-005" for semi auto. So you set your die up until you see a set back measurement of say 3.010" +/- .002" . All but the weakest semi auto actions will "size" the brass a little.
Now for overall case length. I don't have anything that will measure off the datum to case mouth so no input there. I just can't mentally see how after resizing you could have more than say .005" difference in the headspace measurement. If I could video and use my pc well enough I would film myself prepping my 30-06. I don't use a trimmer that references off the shoulder so my over all length doesn't fluctuate much..unless a primer crimp is raised up from deprime or the rim is in rough shape.

I would like to put a 3 or 4 fired case out of a M1 on a run out tester. I'm doubting the case head is true after the first reload?

Now for combined over all length the hornady bullet comparator is only good if your actually trying to seat it at a specific point off the lands or duplicating a factory load.?

To use a over all gauge you need to know what the overall measurement is for your rifle chamber and bullet combo is the right tool helps.
It's my guess the bullet manufactures have a good idea of a safe case head to bullet tip measurement is to remain safe in a specific chamber

 

[headednorth]

What about cartridge overall length?

When I first started reloading (not all that long ago, which is probably pretty obvious) I would be pulling my hair out of my head trying to adjust the seating die so that all the finished cartridges would all be the exact same length. After a while, I had to be happy with them averaging out to be close to where I wanted them to be as long as they were within spec.

After some research, I learned that different types of bullets, different manufacturers, and just variations between one individual bullet and another made it impossible to get consistent measurements from bullet tip to case head. The recommendation was to use a comparator to measure off the ogive to get a more reliable number. Ok, so I can do that, but I havent seen a manual which lists any ogive to casehead length.

So if I have a manual calling for a 3.000" oal which is bullet tip to case head, and I have a comparator measurement of 2.650" which is bullet ogive to casehead, (made up #'s for sake of argument), I need to somehow "convert" the second measurement to what the book is looking for. My thinking is to seat a bullet until the tip to tip is equal to the data in the manual, then measure it with the comparator to come up with the ogive to casehead length. But what if the bullet I got my tip to tip measurement from is funky?

Improbably making this more complicated than it should be...

Now for combined over all length the hornady bullet comparator is only good if your actually trying to seat it at a specific point off the lands or duplicating a factory load.?

Ok, I have an idea about seating off the lands, etc. So maybe Im mistaken regarding finding overall length somehow other than measuring bullet tip to casehead?

 

[EddieCoyle]

You're overthinking things. Unless the bullet tip is noticeably smashed in, how inaccurate could it be?
Seat a bullet to the OAL from the book (measured to the tip). Then measure it with a comparator. Make sure the rest of them measure the same length with the comparator.

 

[headednorth]

You're overthinking things.

I figured as much. Im not shooting out to 1000 yards, but I do want it to go where Im aiming as much as possible. I think a lot of times I make it more complicated than it needs to be.

Unless the bullet tip is noticeably smashed in, how inaccurate could it be?
Seat a bullet to the OAL from the book (measured to the tip). Then measure it with a comparator. Make sure the rest of them measure the same length with the comparator.

Will do, thanks.

 

[EddieCoyle]

Do you have data from your bullet mfg? If not, you're approximating already.

Also, an important part of working up a load is messing with the OAL to see what shoots best with your rifle.

http://www.massreloading.com/rifleCOAL.html

 

[NavelOfficer]

I understand the thinking behind the fact that measuring for oal casehead to bullet tip wont always give you an accurate measurement.

COAL is generally standardized to provide various bullet/powder combinations that have been tested as safe and within specified pressures. Since most rifle manufacturers will build their chambers and magazines to these dimensions, it may not be prudent to exceed (or be too short of) these published COAL dimensions.
A .223 Remington rifle may chamber a 2.300" cartridge that exceeds the listed maximum COAL of 2.260", but it may bind or not fit into your magazine. Some bullet profiles seated too long may also bind into the rifling, even when it is within maximum COAL. Generally, there should be a slight free-bore or jump to the rifling. Bullets seated too deeply could also generate excessive pressures.
As stated above, you may have some latitude within acceptable COALs and may find your rifle's sweet spot.

 

[headednorth]

Do you have data from your bullet mfg? If not, you're approximating already.

Yes, Im using data from the Hornady book and am loading with Hornady bullets.

Also, an important part of working up a load is messing with the OAL to see what shoots best with your rifle.

http://www.massreloading.com/rifleCOAL.html

Very informative, thanks.

- - - Updated - - -

COAL is generally standardized to provide various bullet/powder combinations that have been tested as safe and within specified pressures. Since most rifle manufacturers will build their chambers and magazines to these dimensions, it may not be prudent to exceed (or be too short of) these published COAL dimensions.
A .223 Remington rifle may chamber a 2.300" cartridge that exceeds the listed maximum COAL of 2.260", but it may bind or not fit into your magazine. Some bullet profiles seated too long may also bind into the rifling, even when it is within maximum COAL. Generally, there should be a slight free-bore or jump to the rifling. Bullets seated too deeply could also generate excessive pressures.
As stated above, you may have some latitude within acceptable COALs and may find your rifle's sweet spot.

Thanks

 

[mac1911]

I do not have a bullet comparator, I do have a question though.
If you use the over all length gauge and measure with the comparator will this measurement produce the same "length" if you change bullet profile? For lack of detail , will the distance from the lands be the same if you use the measurement from the comparator from one bullet to another of different weight and profile

 

[akma]

Do you have data from your bullet mfg? If not, you're approximating already.

Also, an important part of working up a load is messing with the OAL to see what shoots best with your rifle.

http://www.massreloading.com/rifleCOAL.html

I was always taught that too. Dan Newberry say's that is not as much a factor as people think. I really want to shoot good groups so I'm going back to square one and relearning everything over. I just need direction and input. Nice web site BTW. I will be reading everything there.

 

[mac1911]

Do you have data from your bullet mfg? If not, you're approximating already.

Also, an important part of working up a load is messing with the OAL to see what shoots best with your rifle.

http://www.massreloading.com/rifleCOAL.html

This does have effect on some rifles/bullets. Although I'm finding Mr. Wylde (Wylde chamber) was correct with the 223.....they like to jump.

 

[EddieCoyle]

If you use the over all length gauge and measure with the comparator will this measurement produce the same "length" if you change bullet profile?

Nope. You've got to do it for each bullet.

Dan Newberry say's that is not as much a factor as people think.

With all due respect to Mr. Newberry, it is a big factor.

This does have effect on some rifles/bullets. Although I'm finding Mr. Wylde (Wylde chamber) was correct with the 223.....they like to jump.

I thought the bullet shape rather than the chamber type determines how much jump is right.

 

[akma]

I was hoping to eliminate one more variable in the pursuit of getting good groups. This kind of stuff can make you crazy.

 

[mac1911]

I was hoping to eliminate one more variable in the pursuit of getting good groups. This kind of stuff can make you crazy.

Yes it can.....Although you need to start with some basic loads and see what happens.
From what I get from Mr. Newberry ( recently revisited his OCW system) You should find a,optimum charge weight for your load/riflle.
I found so,far published data gets you pretty close to a sweet spot on bullet seating depth. YMMV

I can,tell you with my cast loads small changes in the jump show on the target more than FMJ.

What you have to do is only work on one aspect of the load at a time, works for me anyway.

Now for the past few years I have only been shooting service with the AR and M1 so 1moa ammo is,plenty good since once I sling up and go prone im a 4moa shooter on my good days!

 

[Mountain]

To keep it simple, I use a LE Wilson case guage to set up my sizing die. As far as the seating die goes, I use the Hornady bullet seating depth guage and calipers to determine at what OAL the bullet touches the lands. Heavy bullets with a high BC will have a much longer length out of the neck. For example, compare .223 80 gn Berger match to your basic 55gn FMJ.

Once you know the OAL that hits the bore lands, you experiment with jump (set back).

 

[mac1911]

To keep it simple, I use a LE Wilson case guage to set up my sizing die. As far as the seating die goes, I use the Hornady bullet seating depth guage and calipers to determine at what OAL the bullet touches the lands. Heavy bullets with a high BC will have a much longer length out of the neck. For example, compare .223 80 gn Berger match to your basic 55gn FMJ.

Once you know the OAL that hits the bore lands, you experiment with jump (set back).

Now your loading up for service rifle....... load to mag length and have at it. I wouldn't waste 80 grain bullets at 200 yards.....
Have you figured out how far away the lands are in your new rifle. Only bullet I use that is longer than the mag length is the A max.....I got some very nice moa groups at the manuals length.