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Determining Chamber (Ogive) Length

CrazyJoe

Private
Full Member
Minuteman
Mar 1, 2010
93
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Virginia Beach
Read the introduction to hand loading by Tresmon and meaured my rifle's chamber using his method and a couple others. Asked this question in his Determining OAL post but wanted to get wider circulation. I get consistenly different chamber/ogive length measurements with different bullets. My questions are these:

1. Is ogive length and chamber length the same thing?

2. Is it defined as the distance from the closed bolt face to the lands?

3. Should it be bullet independant?

4. If the answers to 1, 2, and 3 are yes; why do I get one number with 190gr SMKs and another number (+.01) with Berger 185gr LD Target bullets?

5. When it comes to determining this dimension what units are good enough. +/-.001 or +/-.01 etc.

New to loading but already see what the appeal is. Thanks for your input. CJ
 
Re: Determining Chamber (Ojive) Length

Thats a great article. I wonder if I could use Win brass for my tool and load Lapua? Or do I need to use the same brass that I am loading for my tool?
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">Read the introduction to hand loading by Tresmon and meaured my rifle's chamber using his method and a couple others. Asked this question in his Determining OAL post but wanted to get wider circulation. I get consistenly different chamber/ojive length measurements with different bullets. My questions are these:

1. Is ojive length and chamber length the same thing?

2. Is it defined as the distance from the closed bolt face to the lands?

3. Should it be bullet independant?

4. If the answers to 1, 2, and 3 are yes; why do I get one number with 190gr SMKs and another number (+.01) with Berger 185gr LD Target bullets?

5. When it comes to determining this dimension what units are good enough. +/-.001 or +/-.01 etc.

New to loading but already see what the appeal is. Thanks for your input. CJ </div></div>

1. No, the ogive is specific to a bullet.

2. OAL in this case is in reference to how far the ogive sits in relation to the lands.

3. Yes each bullet is different. (168 SMK is different than a 168 VLD)

4. Because those to bullets are very different.

5. To the .001", but is somewhat difficult to get your reloading set up to make bullets + or - .002"ish.

The easiest tool for getting your rifles OAL in my opinion is the Hornaday OAL gauge. You will need a hornday modified case for each caliber you wish to measure.

Gage

Modified case

Hope this helps.

Ty
 
Re: Determining Chamber (Ojive) Length

Alan,

Copy all on the wear issue. I'm still less than a hundred rounds at this point.

Whats your take on this question? If the chamber length is the distance from the closed and locked bolt face to the lands how can it vary with bullet type. If the ojive of the bullet is the point at which the diameter of the bullet is equal to the diameter of the bore then the ojive lenth equals chamber lengh and is constant. The only variables with bullet type (shape) will be COAL and seating depth. I went to public school so I could be all effed up.

My last Caipirinha was at the Shot Show. Developed a tast for Negronis. You have to like Campari though.

Looking forwad to my 6.5. Kevin said the scope was in. CJ
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">Read the introduction to hand loading by Tresmon and meaured my rifle's chamber using his method and a couple others. Asked this question in his Determining OAL post but wanted to get wider circulation. I get consistenly different chamber/ojive length measurements with different bullets. My questions are these:

1. Is ojive length and chamber length the same thing?

2. Is it defined as the distance from the closed bolt face to the lands?

3. Should it be bullet independant?

4. If the answers to 1, 2, and 3 are yes; why do I get one number with 190gr SMKs and another number (+.01) with Berger 185gr LD Target bullets?

5. When it comes to determining this dimension what units are good enough. +/-.001 or +/-.01 etc.

New to loading but already see what the appeal is. Thanks for your input. CJ </div></div>

1. No, the ogive is specific to a bullet.

2. OAL in this case is in reference to how far the ogive sits in relation to the lands.

3. Yes each bullet is different. (168 SMK is different than a 168 VLD)

4. Because those to bullets are very different.

5. To the .001", but is somewhat difficult to get your reloading set up to make bullets + or - .002"ish.

The easiest tool for getting your rifles OAL in my opinion is the Hornaday OAL gauge. You will need a hornday modified case for each caliber you wish to measure.

Gage

Modified case

Hope this helps.

Ty</div></div>

Ty,

Thanks for the tip on the tools. Maybe I need to state this another way.

I agree that the ojive is in different places on different bullets, But if chamber length = ojive length = the point where the ojive just touches the lands then that dimention is constant for a given chamber on a given day (no wear). COAL will vary with the bullet and seating depth will vary with the bullet but the distance to the lands from the bolt face is fixed and that distance will equal the distance from where the bullet just touches the lands at the ojive to the bolt face.

Maybe ojive length isnt the right term. Thoughts?

Thanks

CJ
 
Re: Determining Chamber (Ojive) Length

UK

Great article Thx. I think it supports my premise that the chamber length is the same as the distance from where the ojive just touches the lands to the bolt face. He just doesnt call it ojive length.

CJ
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">
Ty,

Thanks for the tip on the tools. Maybe I need to state this another way.

I agree that the ojive is in different places on different bullets, But if chamber length = ojive length = the point where the ojive just touches the lands then that dimention is constant for a given chamber on a given day (no wear). COAL will vary with the bullet and seating depth will vary with the bullet but the distance to the lands from the bolt face is fixed and that distance will equal the distance from where the bullet just touches the lands at the ojive to the bolt face.

Maybe ojive length isnt the right term. Thoughts?

Thanks

CJ</div></div>


COAL is the length from the head of the brass to the tip of the bullet.

The 'Ojive measurement' is the length from the head of the brass to the ojive of the bullet when it is touching the lands.

So yes, the when you measure to the Ojive, for example, using the hornday OAL gage and 155's, it will give you your chamber length and ojive measure for that specific bullet, simultaneously. Now if you switch out with a different grain bullet, 175, and measure, your chamber length and ojive will be the same, but the bullet seating depth will not be the same as the 155's.

The idea is so you know where to seat your different size bullets so they are touching lands, then you can adjust your seating accordingly.
 
Re: Determining Chamber (Ojive) Length

FFS it's 'OGIVE' not 'OJIVE'.

Sorry. It's just driving me nuts watching this thread.
 
Re: Determining Chamber (Ojive) Length

Lima Charlie. Ogive it is. Besides the limitations of my public school education do you have an opinion on the subject?
wink.gif
CJ
 
Re: Determining Chamber (Ojive) Length

Break, I agree with your observation and so expected to see the same ogive length for both SMK and Berger 185s. Different COALs but the same ogive. In fact the difference was +.01 for the Bergers.

Possible explanantion is the angle of the jacket at the ogive of the Berger is more acute (pointier) than the SMK so tends to seat it self in the lands a little deeper with similar bolt pressure. Anybody buy that? CJ
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">Lima Charlie. Ogive it is. Besides the limitations of my public school education do you have an opinion on the subject?
wink.gif
CJ </div></div>

I have none. I don't bother with all that stuff. I just run an OCW at spec seat (2.800) then once I've got my charge, I adjust seating depth to fine tune. My best groups are currently at 2.815 with .308 178 A-Max. I've got plenty of room with this bullet (2.942 OAL is the average (for my barrel) to just touch the lands with 178 A-Max).
 
Re: Determining Chamber (Ojive) Length

I made one of these before I had a OAL gauge.
http://home.comcast.net/~jesse99/frugaldevice.html
I always shoot 155 grain 155 scenars,and seat them a couple of thou off the lands.
TIP

When you find the best bullet and best seating depth.
Make up a dummy round and color the copper black with magic marker.
Keep this as a reference for future reloading save a lot of time.
 
Re: Determining Chamber (Ojive) Length

the case used to make the oal guage needs to be fired from the rifle it is going to be used in,that way the case will be correct form for the chamber.
 
Re: Determining Chamber (Ojive) Length

Ogive has to do with the shape of the bullet and has absolutely nothing to do with chamber length. The shape of the bullet determines what point on the bullet first makes contact with the lands. Some bullets are still less than bore diameter way back on their length while others are bore diameter nearly at the tip. This is why the measurement is different for each particular bullet type and make. The point at which the bullet touches the lands is determined in various ways and should be done for each type of bullet you're using. So the point of all this is to suggest not using Ogive as a measure of length but rather as an idea of bullet shape. Tangent ogive, secant ogive, elliptical ogive all relate to the type of this shape and how its derived.

Hope that helps

Frank
 
Re: Determining Chamber (Ojive) Length

Frank,

Thanks for the input. I see from the responses that using the term "ogive length" is confusing the issue. What I'm trying to determine is why my efforts to measure chamber length in my new GAP Hospitaller .300WSM result in a difference of .01" when I do it with SMKs and Bergers. I'm using Tresmon's method and it defies explanation. The chamber doesn't change shape with different bullets. I ordered a Hornady tool as suggested above. I'll give that a try.

CJ
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BreakBad</div><div class="ubbcode-body">You'll need a comparator to fit in your calipers, to measure ogive:
http://www.midwayusa.com/product/231904/...-with-6-inserts

http://www.midwayusa.com/product/459683/...m_vc=S015231904

and the oal gage

</div></div>

For the comparator, I like Sinclair's hex: http://www.sinclairintl.com/.aspx/pid=34262/Product/Sinclair-Hex-Style-Bullet-Comparators

And that link was just for the modified case for the Hornady Lock 'n Load OAL gauge. The bolt version only works for bolt, but the semi-auto version works for both. Might as well get the semi-auto version:

http://www.sinclairintl.com/.aspx/pid=35889/Product/Hornady-Lock-N-Load-OAL-Gauge-semi-auto-

Remember to get the modified case with the OAL gauge!
 
Re: Determining Chamber (Ojive) Length

Thanks Carter. I've got the comparator and the calipers. We'll see what the Hornady tool says when it gets here. I'll try it with a variety of bullets. My hypothesis is that dimension from the beginning of the bullet bearing surface (just in contact with the lands) to the locked bolt face should not be bullet dependent. How far the bullet protrudes into the case neck yes, but chamber length no. CJ
 
Re: Determining Chamber (Ojive) Length

The issue is that the comparator is usually a little less than a caliber in diameter, which means it doesn't hit the bullet precisely on the ogive. It also means that different bullets will have different comparator measurements for seating to the lands.

In other words, if you run the bullet in your OAL gauge, that bullet is seated to the lands. Any bullet of that type seated to the lands will have almost the same comparator reading. With another bullet, that comparator reading may be different when seated to the lands... basically, COAL is relative.
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body"> My hypothesis is that dimension from the beginning of the bullet bearing surface (just in contact with the lands) to the locked bolt face should not be bullet dependent. How far the bullet protrudes into the case neck yes, but chamber length no. CJ</div></div>

Not sure if I'm reading what you're saying correctly... but yes, it does generally vary - sometimes quite a bit.

As Carter mentioned, the hole in the comparator is usually something less than nominal bullet caliber. Same thing with the rifling in your gun, actually - the bullet may measure .3084", for instance but the rifling may measure .302 (lands) x .307 (grooves) for an example. Depending on the style and shape of the bullet nose cone i.e. whether its a secant or tangent ogive, or how many calibers the radius of the arc is... that point may be very different from one bullet (say a Berger VLD or Hornady A-Max w/ secant ogive) to the next (e.g. a Sierra MK w/ a more rounded tangent ogive). Remember, think of the throat as a tapered hole - thats why the shape of the bullet nose and its taper/curve has a very marked impact on how one bullet fits into the throat vs. another.

About the only time I've ever seen different bullets have the same base to ogive reading when measuring seating depth is when I'm checking bullets of the same 'family'. For example, I get very similar (almost identical, actually) reads for a Berger 155.5 BT 'Fullbore', Berger 175 LR BT, Berger 185 LR BT 'Juggernaut', and Berger 210 LR BT - they all have pretty much the same nose cone shape, and at the point where they hit the rifling and where they hit my comparator, they give the same readings. But if I take a Berger 155 VLD... same company, but different 'family' i.e. different nose shape, I get a very different read.

The chamber length isn't changing, but where the bullet contacts the lands does.

YMMV,

Monte
 
Re: Determining Chamber (Ojive) Length

Monte, I did'nt realize the throat was a "tapered hole". My understanding was that it is a tube with a constant diameter (either lands or grooves) over the length of the barrel. What you say explains my experieince with SMKs and Bergers in the same chamber. I'll confirm my results when my Hornady COAL gauge gets here.

Thanks to all for your input. CJ
 
Re: Determining Chamber (Ojive) Length

The throat usually has a very slight taper - if memory serves, maybe 3 degrees for factory barrels, while 1 to 1.5 degrees is more common on aftermarket barrels done with a custom reamer. Some reamers can be ordered with no throat at all, with the understanding that the person doing the work will probably use a separate throating reamer to establish whatever desired freebore length and throat angle they desire.

You have several different diameters involved... starting with the neck, ranging (for a .308 Winchester) from .346 (the fat side of SAAMI factory chambers) on down to .340-.342 (common for 'match' chambers) to various levels of tight-neck turn-to-fit setups. Next you have the freebore diameter - again, SAAMI is about .310" as I recall, while 'match' chambers tend to use something much tighter - more like .3085". From there, at the end of the freebore where the rifling starts it tapers from .3085 to whatever the inside diameter of the lands is - .302-304 for 'normal' bores, or .2985-ish for a tight-bore Palma barrel.

This pic shows how some of these relate pretty well...

foto_21.JPG


What they label as 'lead' is what I called 'freebore diameter' earlier, and then you can see the taper from the lead to the lands thru the 'throat'.

foto_01.JPG


Actually, this whole article (from German Salazaar's excellent Rifleman's Journal) is worth reading.

http://riflemansjournal.blogspot.com/2010/07/equipment-throat-maintenance-reamer.html
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">Break, I agree with your observation and so expected to see the same ogive length for both SMK and Berger 185s. Different COALs but the same ogive. In fact the difference was +.01 for the Bergers.

Possible explanantion is the angle of the jacket at the ogive of the Berger is more acute (pointier) than the SMK so tends to seat it self in the lands a little deeper with similar bolt pressure. Anybody buy that? CJ </div></div>
I think you are right.
We are dealing with somewhat compressible materials being gently pushed into a 1.5 degree taper...Not to mention differing jacket thickness/hardness.

I don't think this accounts for all of the 0.01 though.
 
Re: Determining Chamber (Ojive) Length

Memilanuk, That expalains a lot. I was not aware that there is so much going on dimension wise in the chamber. The article is great. The pictures better. I now have an idea WHY measuring the chamber length with different bullets yeilds different results. Along with some info I learned about Bergers liking a jump band I'm ready to advance the art. CJ
 
Re: Determining Chamber (Ojive) Length

X, its always good to know that a least one person thinks you're right. I was thinking about the fact that copper is a malleable metal but I think compressible might be a better description in this context. As stated above there is more going on in the chamber than I knew. Until now... CJ
 
Re: Determining Chamber (Ojive) Length

Ya roger that CJoe...I have a few tests I want to run and measurements to take that require some quality time in front of my measuring gear at the loading bench...Family stuff keeps interning...
I want to make careful measurements then have a one of my machinists check my work...I bet his measure differs slightly.
frankly I suck ballz at that stuff, but I want to see how well I can do
smile.gif
 
Re: Determining Chamber (Ojive) Length

X I want to shoot Bergers and according to some data they published to get the best performance you have to find the "jump" sweet spot. There is a procedure for that but it requires that you know where to start and that is the OAL (front of bullet bearing surface to bolt face) that I now agree is bullet dependent. Waiting on a Hornady modified case to get a measurement. Neither Midway nor Sinclair has them in stock presently.
 
Re: Determining Chamber (Ojive) Length

Remember that those comparators are not the most accurate of measuring tools. There are very slight differences between 2 of the same diameter bushings.

I have the Hornady Comparator and somehow a second 30 cal bushing appeared on my bench, there is around a .003 difference between them.

This is not a problem. It simply means that everything is relative. My OAL is a certain amount with a certain bullet when measured with the same bushing. If I were to lose that bushing, I would have to redo all my measurements. This is why I have dummy cartridges for every different bullet. They have no primer or powder and have a bullet seated to touching the lands. I use these to set seater dies and if needed, to take new measurements using new tools.
 
Re: Determining Chamber (Ojive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CrazyJoe</div><div class="ubbcode-body">X I want to shoot Bergers and according to some data they published to get the best performance you have to find the "jump" sweet spot. There is a procedure for that but it requires that you know where to start and that is the OAL (front of bullet bearing surface to bolt face) that I now agree is bullet dependent. Waiting on a Hornady modified case to get a measurement. Neither Midway nor Sinclair has them in stock presently. </div></div>

I just take a full length sized case and cut a slot in the neck with a jewlers saw or small hack saw. Insert a bullet into the case and leave it as long as possible and chamber the shell. Remove and measure with a comparator. The length to leade is not dependent on the bullet ogive style regardless of the taper b/c the taper is always larger than the bullet body dia. or the bullet would not fit down the barrel. The taper does not under any circumstances engage up on the ogive or the bullet would not make it any further. The comparator just measures the distance from the base to a point on the ogive that is eq. to about 96% of the caliber (0.296 in the case of 308). If you want to set jump then measure the lenght to the leads and use the comparator to set the loads to a point back a certain amount.
344fdde.jpg

ofyskp.jpg
 
Re: Determining Chamber (Ogive) Length

Waste, Going to give it a try once I move into my new digs and unpack. Does your post imply that there should be no change in measured OAL when using different bullets? Thats the position I started with but my measurements did not support that theory. Where do you shoot down here? CJ
 
Re: Determining Chamber (Ogive) Length

There's ABSOLUTELY a change in OAL...
Since the ogive varies on every bullet type, the length from the base of the case, to the ogive seating depth (to load to the lands)varies, and so the overall length must vary, accordingly.

Think about it...

OAL is irrelevant to me, unless I'm considering mag length.
Every caliber, every bullet we load, is measured with the Hornady OAL gauge and bullet comparator to seat the bullet .01-.02 from the lands. When periodically checking during the loading process, I never measure OAL- always the relative measurement obtained with the OAL gauge using the bullet comparator.

Like Rotary said above, it's all about relative- not absolute, measurements.
 
Re: Determining Chamber (Ogive) Length

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wannashootit</div><div class="ubbcode-body">There's ABSOLUTELY a change in OAL...
</div></div>

this. The only sure way to know how long to seat your bullets is to know what the distance to the ogive is supposed to be and go on from there. for example, my TTSX rounds have an OAL of 2.935, distance to the ogive is about 2.445 in my WSM, about .03 from the chamber maximum ogive length. My Berger OTM Tacticals are the same ogive length, but have a OAL of 2.965, the Berger has a longer ogive than the TTSX.
 
Re: Determining Chamber (Ogive) Length

When I referred to OAL I meant the length of the cartridge from the point where the bearing surface of the bullet just touches the lands to the case head. As opposed to COAL which is bullet tip to case head and relevent to mag length. I've seen OAL used in this thread with that definition.

I originally thought that distance between the bullet bearing surface just touching the lands and the case head was called Ogive Length. Somebody corrected me. I don't have a dog in the fight I just want to know the correct terminology and if the dimension varies with bullet type... why. CJ
 
Re: Determining Chamber (Ogive) Length

OAL is base of cartridge, to bullet tip....

This is the measurement you'll see in the reloading manuals.

EDIT:...

I'm gonna edit this to eliminate any confusion...
OAL, is also referred to as COAL, meaning cartridge overall length. Both mean the same thing. Length from base to bullet tip.

Length measured by a bullet comparator device, like the Hornady LNL, is <span style="font-style: italic">meaningless</span>, other than in a <span style="font-weight: bold">relative</span> context for a particular bullet, in the identical rifle.

The device used is nothing but a collar bushing. It will "seat" in a given position on the bullet relative to it's shape. The only thing it does, is that after using it on a cartridge with a loose bullet to determine the length to the lands, it can be used to <span style="font-style: italic">transfer</span> that same seating depth- for only that bullet- to your loads.

 
Re: Determining Chamber (Ogive) Length

Wish I would have read more about coal before doing it for my rifle... Reloaded a box full and realized they none would fit in my box magazine remington 700...

COAL - 2.959 (2.949 sized down to be safe)
Box Max - 2.836 and thats rubbing the metal...

Needless to say, I done a lot of resizing..