CRTO?

Haven't heard of this one before. Might be on to something...chamber rifling to ogive of .20 is usually the recommended starting point. Would go with CBTO...cartridge base to ogive.

.40

forty_caliber said:

CBTO...cartridge base to ogive.

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This is the correct term. I suspect It was merely a typographical error.

On second thought, it could be referring to the bullet jump to the rifling. Defined as 'off' or 'in' the lands. That measurement could be twenty thousandths 'off the lands'. But I don't know what the abbreviation could mean. Neither the cartridge or the chamber have rifling, the barrel does.
Strange.

I see the term CBTO ( Case Base To Ogive ) is correct , I think of to as Closed Bolt To Ogive is probably the same thing . I found my measurement by using a stripped bolt ( Rem.700 ) with a Go Gauge and shimming up the back of the gauge until I felt a slight resistance . Worked well for me , the gauge measurement is 1.630 my true chamber measurement is 1.632

CBTO is differentiated against BTO. Cartridge Base to Ogive rather than Base to Ogive - the latter being a measurement from the bullet base, not the cartridge base.

Note - Cartridge Base to Ogive should not be the same as “closed bolt to Ogive.” That’s like saying a foot is the same thing as a shoe.

Varmint
When measuring your chamber for headspace you need to know from bolt face to shoulder or datum line , knowing the cartridge base to datum doesn't help do anything for sizing headspace for your rifle .
PS: I just realised what you were saying , cartridge meaning bullet base to ogive. The post was for CRTO , I'm sure it was a type o

I would be leery of any cartridge dimension of .200" that's almost 1/4 inch. Rifling to ogive? That's a lot as far as I know...

mdi said:

That's a lot as far as I know...

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Two Hundredths

Of course, maybe it's a Weatherby.
Then a quarter of an inch to the rifling would be normal. But twenty thousandths off (-.020) is normal-ish.
I have one that works best at "in three thousandths" (+.003).

cw308 said:

Varmint
When measuring your chamber for headspace you need to know from bolt face to shoulder or datum line , knowing the cartridge base to datum doesn't help do anything for sizing headspace for your rifle .
PS: I just realised what you were saying , cartridge meaning bullet base to ogive. The post was for CRTO , I'm sure it was a type o

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No confusion on my part here. CRTO is a clear typo for CBTO.

But your confusion of “closed bolt to Ogive” instead of “cartridge base to Ogive” remains to be that - confusion.

You can’t ever actually measure actual “closed bolt to Ogive.” We can measure reference lengths using a tool - for example, seating a bullet to kiss the lands, the measure the cartridge base to the ogive of that particular round. Inherently, as I said above, to pretend these are the same thing is like saying a foot is the same as a shoe. There’s always a clearance necessary for a cartridge to fit within the chamber, short of an interference fit. Headspace is another metric - we can’t measure actual headspace, but can only measure a reference dimension on a tool, like a headspace gauge. We know our tool bushings don’t perfectly match the chamber shoulder nor the chamber/bore leade, so all we’re capturing here are reference dimensions.

So what we measure is a reference dimension from the “cartridge base to the ogive” of the bullet, NOT the bolt face to the ogive, or bolt face to the leade.

Humm
.20 CRTO ?
I would not assume a typo
What possible cartridge would or could be .20 in length from CBTO?
It doesn’t make sense therefore I would ask the author for clarification rather than assuming.
Just me of course
J

Well guys going with Close Bolt To Ogive , I first start with finding my zero measurement in Closed Bolt To Datum . Using that zero headspace case with a stripped bolt , seating a bullet long and slightly lowering in the seating die until you get a bolt lift without any resistance is your Closed Bolt To Ogive . I find no confusion there . It just works for me for a repeatable measurement in both CBTD & CBTO . Finding the Datum is with a stripped bolt only on with a bolt closure , both with a Full Length sizing die along with the Redding Competition Shellholders you can size your case with a zero on up headspace. Ogive setting is really from datum to ogive , if you have wiggle room in your case how can you adjust a accurate jump or jam , you have to know how .much room you have between your case base and bolt face. That's why I like my Closed Bolt in CBTO , Sorry it's just me .

Chris
Is that you in there?
J

cw308 said:

I see the term CBTO ( Case Base To Ogive ) is correct , I think of to as Closed Bolt To Ogive is probably the same thing . I found my measurement by using a stripped bolt ( Rem.700 ) with a Go Gauge and shimming up the back of the gauge until I felt a slight resistance . Worked well for me , the gauge measurement is 1.630 my true chamber measurement is 1.632

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Are you seating or headspacing

Jim
I feel is important first to size the case and know what headspace your working with before seating for a jump or jam . People that neck size only are dealing with fired cases with different headspace , only when it comes to a hard bolt lift or chamber can you size down the case to a perfect chamber fit.
Hope things are going well. Be Safe

Chris

cw308 said:

Jim
I feel is important first to size the case and know what headspace your working with before seating for a jump or jam . People that neck size only are dealing with fired cases with different headspace , only when it comes to a hard bolt lift or chamber can you size down the case to a perfect chamber fit.
Hope things are going well. Be Safe

Chris

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Thx Chris

I know what CBTO is , I use that for seating,but the op was asking about CRTO .20 , and while everyone seems to be speculating or assuming I chose clarification of an unknown reference from the author.

I agree.

South Prairie Jim said:

Thx Chris

I know what CBTO is , I use that for seating,but the op was asking about CRTO .20 , and while everyone seems to be speculating or assuming I chose clarification of an unknown reference from the author.

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Unfortunately, OP seems to have abandoned his own thread. He logged in as recently as yesterday. Hopefully, he'll see fit to rejoin the thread.

I can assure you I meant only the original author may have made an error, not you, for there are no wrong questions.
Have heart, we're not like that around here...

Good , I always try to answer every person . We are here to sort out problems or find some answer to what question is posted . When someone takes the time in answering a post and the OP finishes with " I'm done here . foxmeadow is a name to remember , it's been a good talk with the rest of you .

Chris

cw308 said:

Good , I always try to answer every person . We are here to sort out problems or find some answer to what question is posted . When someone takes the time in answering a post and the OP finishes with " I'm done here . foxmeadow is a name to remember , it's been a good talk with the rest of you .

Chris

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foxmeadow said:

It was not a typo on my part. .......
What's been fun is watching y'all read what I wrote wrong, assume it refers to cartridge length to ogive (.020")? and generally chew it up and spit it out.

I'm done here...

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So-o-o, you left us hanging for your own amusement. Not very highroad, but let's just move on, nothing to see here.

Hate to say it BUT....,

J