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Old December 27, 2012, 02:14 PM   #1
TheDutchman19
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OAL sanity check please!

Question:

I have determind my bolt face to lands measurement for a specific rifle. I also know that distance as it relates to my bullet comparator. I have check various bullets with the comparator as well as varifing them in the chamber. They are all equal in the comparator but vary in their OAL.

Other than the bullets fitting in the magazine, do I need to pay attention to OAL or can I verify length with he comparator only?

Thanks for all of the past input. It's been a big help.
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Old December 27, 2012, 02:17 PM   #2
Jimro
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Pay attention to? Only if you really care about that. My experience is that any bullet that fits into the magazine will be nowhere near the lands. Unless you have a custom chamber cut for your rifle I would simply make note of the distance to the lands for your records, and maybe try a few seating depth variations to see if you can spot a more accurate load.

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Old December 27, 2012, 05:29 PM   #3
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Dutchman.

The illustration below is an extreme example of why COL (OAL, COAL, OL, etc.) isn't the same with different bullets. What you've discovered is normal. If you look at the SAAMI standards they usually give a fairly generous range for COL, but the purpose for that range is to guarantee fit into and feeding from magazines, and that is all. If your gun is a single shot or if you use your gun as a single shot, the measurements of fit you get are all that matter.

A second point to make, though, is that seating bullets closer to the lands is a strategy for accuracy that each bullet shape seems to like a little different. Read this procedure from Berger for VLD's (secant ogive bullet shapes). The more common tangent ogive shapes seem to be more forgiving. What's interesting to note, though, is that some bullets in some rifles shoot best when jammed a short way into the lands. Some shoot better a hundredth back of the lands; some three, some five, some eight, some all the way back half a caliber or so. There's no way to know what your bullet will like best in your chamber until you seek it out. Very often you will discover more than one seating depth sweet spot, in which case at least one of them falls inside the SAAMI COL range most of the time, and that's the more versatile one since it lets you use the magazine or not, as you choose for the occasion.

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Old December 28, 2012, 10:16 AM   #4
TheDutchman19
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Unclenick

Is there a SAAMI standard that specifies a "norm" or a "range" for the bolt face to lands measurements for any giving caliber?

Is there a name for that measurement?

Is it common practice for bullets to be placed in the lands?

Now that I am armed with this info, I have been able to go back and measure factory ammo I have tried in the past. Some of the product that didn't work well in my rifle seem to have the bullet setting in the lands. I had wrote it off as bullets my rifle didn't like. Other ammo that worked better weren't quite to the lands. Turns out it could be a depth issue.
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Old December 28, 2012, 12:43 PM   #5
RC20
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What kind of a gun do you have and caliber?

Its become relevant as all factory ammo should fit in your gun well before contacting the lands.

Bad chamber job or custom rifle?
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Old December 28, 2012, 01:35 PM   #6
TheDutchman19
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I have a Savage 11/111 in a 30/06. I had been loading two different rounds my self and was having good results. I bought some cheap factory loads from Brand-F and they were similar to my own. I bought some Trophy Grade from Brand-N and it was not as good. Months later or last week I put one of the Brand-N cartridges in my comparator and it was in the lands by 0.020. Brand-N OAL was 3.330

As I continue to read up and develop my own loading skills, I am trying to fully understand all of the "cause and effect". Now instead of checking my loads OAL, I am check them with my comparator. I am guessing that is the measurement that is most critical for consistency?
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Old December 28, 2012, 02:09 PM   #7
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Loading into the lands used to be a common bench rest technique. You have to be aware it can cause pressure to increase about 20%, so you need to work your load up with the bullet out there and watching for pressure signs. Many have found some bullet/chamber combinations work still better seated deeper, so that's not as common as it used to be.

.30-06, .308, and .223 have all got a variety of match chamber reamers out there, so it is certainly possible to get a chamber intentionally made with a short throat, but I doubt Savage did that. It seems more likely that, since Savage headspace can be set by how far you screw the barrel in, that your's is just slightly tight. Any gunsmith should be able to check with a headspace gauge.

The SAAMI standard chamber geometry is in the lower drawing, here. It shows that rather than a freebore, the standard .30-06 chamber has what's sometimes called a ball throat, which is just a 22 minute angle down into the rifling that begins 2.5228" forward of the breech and is down to bore diameter by 2.7442" from the breech. Those are minimum numbers with a +0.015" tolerance. I don't know a special name for that particular measurement.
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Old December 28, 2012, 03:47 PM   #8
TheDutchman19
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Thanks for the feedback. Have a great New Year.
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Old December 28, 2012, 09:39 PM   #9
tobnpr
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Quote:
do I need to pay attention to OAL or can I verify length with he comparator only?
Comparator only is fine- PROVIDING you're talking about the one bullet...as every bullet type, even of the same weight, has an ogive that's going to hit the lands at a different point.

I determine my loaded bullet length with an OAL gauge, and then set the loaded bullets to length- using the comparator for adjustments- with the seating die to correspond to the jump I'm seeking.

I could not even tell you, the "overall length", of ANY of the bullets I load for the seven calibers I handload for. It is irrelevant unless there is a restriction related to magazine length.
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