developing a load - start with col or powder weight?

[Milligan]

M, Once per bullet type/make/weight surely?

ft

Perhaps we're talking at cross purposes.
OAL gauge is this thing. which I use once per rifle.
Comparator is this thing. which I use all the time for loading pretty much everything and ensuring the same length to Ogive.

 

[gitano]

Good point to illustrate the differences, Milligan. It is certainly true that one could choose to use the OAL once on a chamber, note the length with a specific bullet and then using the Comparator, only measure other bullets and calculate the actual chamber length with all other bullets. I prefer to measure chamber lengths with the OAL for every bullet I intend to use. I would not suggest that the method I choose is the "only" NOR the "right" way to do it. For the most part, results are what matter, not processes.

Regards,
Paul

 

[Milligan]

Good point to illustrate the differences, Milligan. It is certainly true that one could choose to use the OAL once on a chamber, note the length with a specific bullet and then using the Comparator, only measure other bullets and calculate the actual chamber length with all other bullets. I prefer to measure chamber lengths with the OAL for every bullet I intend to use. I would not suggest that the method I choose is the "only" NOR the "right" way to do it. For the most part, results are what matter, not processes.

Regards,
Paul

Fair enough, but I should point out I borrow the OAL gauge when I get a new rifle

 

[gitano]

Regards,
Paul

 

[204 Ruger]

Good point to illustrate the differences, Milligan. It is certainly true that one could choose to use the OAL once on a chamber, note the length with a specific bullet and then using the Comparator, only measure other bullets and calculate the actual chamber length with all other bullets. I prefer to measure chamber lengths with the OAL for every bullet I intend to use. I would not suggest that the method I choose is the "only" NOR the "right" way to do it. For the most part, results are what matter, not processes.

Regards,
Paul

I do the same, I did borrow my mates OAL guage until recently when I got a used one for £20 (£35 new here)

 

[Brithunter]

Hmmm let me get this straight the comparitor is made to a nominal size for the bore........... yes?

But how many barrels are actually of nominal size in the bore , i.e land diameter, or at the leade?

Unless the comparitor is the exact same diameter as YOUR barrel and the leade matches then any measurements you take with it are only for comparison and do not actually relate to the position of the bullets ogive to the leade in YOUR barrel.

So exactly what is achieved here by using one?

 

[c18rch]

Even if a bullet comparitor isn't the same diameter as the bore it will give you a more accurate reading than just measuring the OAL as most of the variation in bullet (by which I mean bullet heads) length is in the tip.

A better way if you fave the facilities is to make one yourself on a lathe to the same diameter as your bore.

 

[Milligan]

Hmmm let me get this straight the comparitor is made to a nominal size for the bore........... yes?

But how many barrels are actually of nominal size in the bore , i.e land diameter, or at the leade?

Unless the comparitor is the exact same diameter as YOUR barrel and the leade matches then any measurements you take with it are only for comparison and do not actually relate to the position of the bullets ogive to the leade in YOUR barrel.

So exactly what is achieved here by using one?

What is being acheived is that you can swap bullets and maintain the same jump to the lands. As you point out, it's only for comparison.

I take your point about the comparator and land diameter not being the same, but in this case it doesn't matter, as long as it's consistent.

 

[gitano]

Consistency is the goal. Taking into consideration BH's comments about 'comparison', we can get a better idea about what's going on by 'sidestepping' to something that is much easier to see.

Imagine a rifle with open sights that shoots nice tight groups, but they are always 2" high and 3" left of point-of-aim (POA). Because we KNOW that the center of our groups (the point-of-impact (POI)) is always 2" high and 3" left, (the "bias"), we can compensate (correct) for the bias by aiming 2" low and 3" right of where we want the POI to be.

In the case of cartridge lengths, assuming the Comparator is the exact same diameter as the bore (when it isn't), introduces some unknown level of bias into the settings that we use for seating depth. Our settings will be consistent, but they MAY be biased (and likely are). Without measuring we can't know what that bias is. If our settings, with their bias, "work", then measuring every bullet isn't necessary, and having the inside diameter of the Comparator be exactly equal to the bore diameter isn't necessary. This is precisely why I said, process isn't as important as results. However, if we eliminate the bias in our chamber measurements, we are doing the equivalent of adding a 'scope to the rifle in the above example, and we can 'adjust' the sights so that the center of our groups are coincident with the POA.

It isn't difficult to make the ID of one's Comparator equal to the bore of your rifle. It only requires slugging your breech, and using a little emery paper and a dowel on the ID of your Comparator. (In my experience, most Comparators are "small" relative to the true bore.)

BH is a machinist. His life is precision and accuracy. He has "issues" with "bias".

Regards,
Paul