AOL error in manual?

hoochie

hoochie

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Trying to load 140gr BTHP for my .270WSM, and found that the length in the manual is far too long and cant be chambered.
With the precision mic, I measured the chamber and wrote down all the numbers with the 130gr SBT, which is a tad bit longer than what the manual says. With the 130's I get good groups, 1moa or better.

Back to the 140's:
the manual says OAL 2.765, with the mic checking the chamber, and comparing other known accurate rounds, the actual length comes out to only 2.722

So, from the same manufacturer, and using their software, why would I have one bullet type be longer than given, and another far shorter?

I know that seating to deep will cause an increase in pressure, but the mic wont lie. After checking over and over again today, I am convinced its a typo in the manual.
Thoughts?
 
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You are overlooking the simple fact that generally, the COL listed in a loading manual, is the COL that they used in their test gun. The same goes for the maximum load,most accurate load, and the velocity produced with a given load. It is very common for throat lengths to vary from rifle to rifle, so that COL may have worked fine in their test gun. Loading manuals are a guide based on their test gun, and their lots of components, I wouldn't expect the results to be exact with your rifle, or with your lots of components.
 
I justed checked the test rifle info, for both rounds it says winchester model 70, 24" barrel 1X10 twist.
Understanding that rifles vary, this was my initial point.
How can I be longer than suggested with one round, but I cannot even get my mic to close, nor chamber the 140gr. If I am longer than the manual with my 130gr SBT's, then there is no way in hell they got the 140gr bullet to chamber in their test rifle.

At the suggested length, I cannot get my mic to even start threading closed to get a measurement.
 
I justed checked the test rifle info, for both rounds it says winchester model 70, 24" barrel 1X10 twist.
Understanding that rifles vary, this was my initial point.
How can I be longer than suggested with one round, but I cannot even get my mic to close, nor chamber the 140gr. If I am longer than the manual with my 130gr SBT's, then there is no way in hell they got the 140gr bullet to chamber in their test rifle.

At the suggested length, I cannot get my mic to even start threading closed to get a measurement.
Click to expand...

You are only talking about a difference of .043" from the COL in the manual, to the number that you determined for your rifle. It's quite common for the throat lengths between rifles to vary more than that. It's also quite common to have to vary the COL by more than that to obtain the proper distance to the lands, with different bullet types and weights. You are worrying far too much about something that isn't worth worrying about. Just seat your bullets until they are .010" to .015" from the lands in your rifle and be done with it. Start with the suggested minimum load, and work up while watching for pressure signs.
 
ok, never mind.
I know what my gun reads, but dont understand how there can be a variance in the same test gun. Both my dummy rounds have the same ogive measurement in the mic, so I dont know how they came up with the number for the 140gr. thanks for your input
 
I know what my gun reads, but dont understand how there can be a variance in the same test gun. Both my dummy rounds have the same ogive measurement in the mic, so I dont know how they came up with the number for the 140gr. thanks for your input
Click to expand...

I am looking at the Sierra manual, that I assume you are referring to, and I see no issues at all. So the 130gr SBT can be loaded longer in the same rifle, it has a pointed tip, so the distance from the ogive to the tip is likely longer than the same distance with the 140grHPBT. Your RCBS Precision Mic measures the overall length to the ogive, not to the tip. The COL listed in the manual is the overall length including the bullet tip.
 
here is the length with calipers
PB180095.jpg


here is what my mic reads:
PB180094.jpg


both rounds have been measured to my chamber using the mic.
The COL ( as per the calipers) have changed from the manuals' suggested length.

I thought I would either be adding length to my bullets, or shortening them.

I understand that bullets of different shapes will have different lengths, but what I am saying is that the ogive distance as per my mic remains the same with both bullets.

Then why is my bullet .045 shorter with one, and +.010 longer with another when reading it with a caliper? wouldnt/shouldnt both be either a +.010 or a -.045?
 
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The calipers are indicating the actual OAL of the loaded cartridge. The RCBS Precision Mic seating die does not measure OAL. The scale on the die indicates contact of the seater with the bullet, which is something else entirely. It is used to be able to seat the bullet precisely to a previously known seating depth of the same bullet.

The ogive profile of the bullet determines where it contacts the seater, not the length of the bullet.

Ted
 
Yes, I fully and completely understand the difference in the 2 tools.
I would have thought that if my bullets are the exact same in the mic (which they are), then they both would be either + or - the same according to the calipers.

For example, if I am adding .020 to a round, then I would be adding .020 to all the rounds sierra make.

Maybe I am over thinking it.

Yes, Ted...
I use the freebore tool, inserting it in the chamber and closing the bolt. removing it from the rifle and placing it in the mic. Taking that reading, I adjust my die to seat the bullet just under what the freebore tool measurement was. I check head space with the other part of the mic tool. building a dummy round, then test chambering it.
For some friggin reason I grabbed my calipers and measured that length...
thats what has gotten us this far in my "bang head here" situation.

the part of the mic on the right is called the "land nut" that measurement tell a guy where his lands are. my lands dont move, but the numbers of COL dont jive. my COL is longer with one bullet and much shorter with another. The suggested length in the manual is too long for me to close my bolt. And knowing I can add length with the 130gr bullet; I simply assumed I would be able to add the same length with the 140gr HPBT, not subtract .045
 
both rounds have been measured to my chamber using the mic.
The COL ( as per the calipers) have changed from the manuals' suggested length.

I thought I would either be adding length to my bullets, or shortening them.

I understand that bullets of different shapes will have different lengths, but what I am saying is that the ogive distance as per my mic remains the same with both bullets.

Then why is my bullet .045 shorter with one, and +.010 longer with another when reading it with a caliper? wouldnt/shouldnt both be either a +.010 or a -.045?
Click to expand...

Those COLs listed in the manual do not necessarily have both bullets the same distance off of the lands, as you seem to be assuming. They may have adjusted one COL to provide more bullet shank in the case, or one bullet just may have been more consistent with a different distance to the lands.

Ignore the COL in the manual, it wasn't derived with your rifle, so it means nothing where your rifle is concerned.. Even if the make and model of your rifle is the same as the one in the manual, the throat length can be different. Find the COL to the lands in your rifle with each bullet, and start loading each .010" to .015" from the lands. Fine tune from there for accuracy, or if you find that you don't have enough bullet in the shank due to the boattail, or if the loaded round won't function in the magazine.

You are over thinking this, it really isn't that complicated.Remember that the loading manual is intended to be used as a guide, not as gospel. What are you going to do if your velocity with a given load is 100fps less than the velocity listed in the manual, with the same load? What if the so called accuracy load listed in a manual shoots poorly in your rifle? If you worry every time that your results don't match those in a loading manual, you will drive yourself off of the deep end, in short order.
 
I recommend getting a hornady overall length guage, I find this to be one of the most consistent methods for finding the max oal for your specific rifle and bullet of choice. I use this tool every time I try a different bullet, I usually subtract .030 from the max length measured as a starting point and then tweak the load from there . I also take the measurements from the ogive of the bullet as the melplate/tips of some bullets can be distorted and cause inconsistent measurements. Having said this some chambers will have different amounts of freebore depending on the reamer used to chamber the barrel, on some barrels it may be impossible to to touch the lands and still have the shank of the bullet in the case neck because of the amount of free bore cut. In this case I usually seat the bullet so that the shank of the bullet is seated equal to the diameter of the bullet ie; if you are loading 30 cal bullets I would seat them so a least .300 thou of the shank would be in the case neck. As others have stated the manuals are a guide, but usually the recommended oal they publish should work in factory firearms, as the chambers of these rifles should be within sammi specs. Most factory rifles I have owned will take a longer oal than stated in the reloading manuals. Hope this helps.
 
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