Comparator Accuracy (or not)

[Miseryguts]

Hi, always used my Hornady comparator for determining CBTO, CBTL etc for my 223. Recently got into 308 win. reloading and could not get an Hornady 308 insert x stock, so went for a Sinclair.

Worked out all the figures for two or three bullet options. Today my Hornady comparator 308 win insert arrived, so I remeasured my parameters.

I expected some difference, but not of the magnitude that I got!

Sierra 155gn HPBT loaded to 2.800 COAL, Hornady CBTO - 2.224; Sinclair CBTO - 2.087 (= 0.137 difference)

Hornady 155gn ELD loaded to 2.810 COAL, Hornady CBTO - 2.183; Sinclair CBTO - 2.066 (= 0.0.117 difference)

That seems a big difference to my mind, or is that what one should expect??

M (amazed in sunny monmouthshire)

[Popsbengo]

The comparator is exactly that - a comparator.  The readings are non-transferable and not relevant to other gauging systems - even another of the same make.

The two inserts will measure off different datums on the ogive (a very small diameter variance will be magnified in length measurements).

It's irrelevant to compare one to the other, the comparison is between a correctly sized case/bullet in your chamber and then a sized assembled round with the desired offset of jam or jump (obviously with the same gauge set up)

[GT3_richy]

What he said ^^

Comparator (inserts) are not...comparable, nor are they intended to be. You're as likely to get fractionally different CBTOs using two of the 'same' Hornady 30cal inserts.

 

[Miseryguts]

OK, that's what I thought, just that the differences were bigger than I thought they would be.

Just not used to these funny bottleneck thingies

M

[Popsbengo]

Just don't get them mixed up!!  I'd sell one insert (the Hornady, stainless-steel is better than aluminium).

In fact I've ordered a Sinclair SS insert for .338 - the Hornady one is too tight really to gauge the .338 bullet without introducing possible errors.

 

[No i deer]

I'm not sure this is a silly question but did you rezero your calipers when you changed comparator parts,the oal should be the same measurement give or take a thousanth.

[Popsbengo]

Just now, No i deer said:

I'm not sure this is a silly question but did you rezero your calipers when you changed comparator parts,the oal should be the same measurement give or take a thousanth.

Disagree.  The Sinclair insert is not identical to the Hornady insert.  The profile of the respective bore is different.

[No i deer]

Not familiar with the Sinclair.

Its was just a thought.

Gotta picture handy....

[Popsbengo]

No, but I can see the difference between the ones I have.  Anyhow it's not relevant - the same gauge should be used to measure the lands position and set ogive to head length - the gauge isn't a measuring tool - it's a comparator.

[No i deer]

It is.

When checking with the hornaday comparator I always check the oal aswell as the comparator measurement as it's zeroed when in its closed position does both....

That's why i asked if it had been rezeroed as that's how I record both of my measurements.

[Miseryguts]

Don't fall out boys - you have to zero the gauge to use either comparator!

M (wishing he'd kept his mouth shut in sunny monmouthshire)

[No i deer]

No falling outs just trying to help 👍😁.

It's been wall to wall sunshine here in Bath too 🌞🌞

Out of curiosity why have 2 different types of comparator gadgets.....?

[Miseryguts]

as per original post, hornady out of stock so got a sinclair to get some measurements before crashing in. On Hornady arriving today, redid measurements and found what I considered to be a big difference and just wondered if such a difference  was normal - obviously it is

M ( still learning in dark mommouthshire)

[Popsbengo]

😁

 

[Popsbengo]

1 hour ago, Gluv said:

Pops will fall out over anything ! 

He even wants to ignore the democratic vote of 17 million people and stay in the Eu with the traitors in parliament 😂😘

Gluv 😎🇬🇧🇬🇧

What a dick 🤣

[Popsbengo]

4 hours ago, No i deer said:

No falling outs just trying to help 👍😁.

It's been wall to wall sunshine here in Bath too 🌞🌞

Out of curiosity why have 2 different types of comparator gadgets.....?

I'm not arguing or falling out with anybody:  I think you may not realise the Sinclair and the Hornady inserts are almost the same thing.  They both fit the Hornady system carrier that clamps to the calliper. The Sinclair is in stainless and has a very slightly different profile to it's bore and the bullet will sit a tiny amount different to the aluminium Hornady insert.  Both would need to be zeroed before taking a reading.  The point is that the calliper is just to compare the bullet seating to the throat so no absolute measurement against any external reference is required.

[Popsbengo]

1 hour ago, Gluv said:

😘🙂

 

Ah, that's nice

[gruntus]

On a similar vein when using the shoulder bump gauges they don't necessarily measure to the same datum point on the shoulder as used for headspace. As above they are just for comparing a given known (in this instance a fired case/chamber size at a particular measuring point and the amount that you want this reduced by.

Note:* Its a given that a few things need to be taken into consideration such as spring back, the case should be fired three times to ensure it has fully formed to the chamber etc. etc.

Just give up now! 😋😀

Cheers

G🙂

[No i deer]

I double stroke the ram when I'm bumping the shoulder back 2 to 3 thousanths because some don't bump back that much on 1 stroke of the ram and I notice it chambering the bolt,i guess the brass springs back...

The double stroke ensures it's actually bumped it back the desired amount.

[gruntus]

I anneal each time, use the isopropyl/lanolin DIY lube and leave the case for 2 - 3 seconds before taking back out of the die and get good consistent bump each time.

Cheers

G

[No i deer]

I will try that then.

The second stroke is another pump/bump,I don't take another full stroke, just make sure the case holder bottoms out twice.