OAL question

[dickn52]

Ok, I take my Hornady OAL to the local range and meet up with a guy. He has three bullets, the case for the gauge etc...He has the book for that particular round manufacturer.

1. The book says the min OAL is 2.80 (These numbers are for point of reference and not actual) Using the OAL gauge I get a reading of 2.78. Minus the .02 for an OAL for that rifle of 2.76. He keeps going back to the book numbers at a min 2.80 figure. This was a 6.5 Creedmoor Savage. I keep telling him the book is a guide only and we should be concerned about the oal readings instead. So, the question is do we load to the OAL gauge or go by his book? I'm leaning towards the gauge findings. **** He had some of his reloads at 2.80 and I found them to be a 'tight' fit when chambering them.

 

[T-shooter]

Ok, I take my Hornady OAL to the local range and meet up with a guy. He has three bullets, the case for the gauge etc...He has the book for that particular round manufacturer.

1. The book says the min OAL is 2.80 (These numbers are for point of reference and not actual) Using the OAL gauge I get a reading of 2.78. Minus the .02 for an OAL for that rifle of 2.76. He keeps going back to the book numbers at a min 2.80 figure. This was a 6.5 Creedmoor Savage. I keep telling him the book is a guide only and we should be concerned about the oal readings instead. So, the question is do we load to the OAL gauge or go by his book? I'm leaning towards the gauge findings. **** He had some of his reloads at 2.80 and I found them to be a 'tight' fit when chambering them.

You can't always go by the book. Like you said, it's a point of reference. Bullets vary by brand, type and even different lots. Example, 2 different lots of the same Hornady bullet. If you are measuring from the tip, you could be as far as .021" or more in the distance to the lands depending upon how you load them. These measurements were taken with the tool pictured below. The inside bore is .010" smaller than the bullet diameter.

Are you using this tool to measure? A friend of mine has the exact same tool and it measures several thousandths difference. It is useful for a reference measurement.

 

[Shynloco]

Make up a DUMMIE round with each measurement if you wish. Put the dummie in the chamber and close the bolt. Then extract and re-measure each of the dummies and see what you have. Personally, I'd go with what the reading is on the extracted dummie. The book is ONLY a guideline (and SAMMI spec in general) for the rifle they used in their testing. Your rifle may well be different and it is the only measurement that matters. Besides, being that close, did you measure and separate the bullets as I'm willing to bet those bullets you are using come in a variety of Ojive and OAL measurements, unless you trimmed them to all be the same. And even then (if you trimmed them) bet the Ojive varies.

Alex

 

[T-shooter]

Make up a DUMMIE round with each measurement if you wish. Put the dummie in the chamber and close the bolt. Then extract and re-measure each of the dummies and see what you have. Personally, I'd go with what the reading is on the extracted dummie. The book is ONLY a guideline (and SAMMI spec in general) for the rifle they used in their testing. Your rifle may well be different and it is the only measurement that matters. Besides, being that close, did you measure and separate the bullets as I'm willing to bet those bullets you are using come in a variety of Ojive and OAL measurements, unless you trimmed them to all be the same. And even then (if you trimmed them) bet the Ojive varies.

Alex

The dummy round works well and I've done that for years. I took a case and made 2 tiny slits in the sides of the neck to relieve tension. The bullet is snug but moves easily and isn't forced into the rifling. And close the bolt gently too. A bit of case lube may help on the tip. Check your measurements several times because sometimes the bullet will tend to stick in the rifling and get pulled out a little.

 

[Shynloco]

The dummy round works well and I've done that for years. I took a case and made 2 tiny slits in the sides of the neck to relieve tension. The bullet is snug but moves easily and isn't forced into the rifling. And close the bolt gently too. A bit of case lube may help on the tip. Check your measurements several times because sometimes the bullet will tend to stick in the rifling and get pulled out a little.

T...Just as a consideration, I LESSEN the neck tension to avoid that issue of the rifling you spoke about. I do so by using an Bushing Die (with a bushing a few thou larger than I would normally use) so I don't have a bullet hanging up in the rifle as I'm looking the contact point (with the rifle) and not so much how deep I can get into the rifling. But I can see you are in tune with my thoughts, just use a different method. I try not to render a casing useless after conducting my test.

Alex

 

[spife7980]

For finding your length to the lands I find it hard to go wrong with the wheeler method

 

[jepp2]

Make up a DUMMIE round with each measurement if you wish. Put the dummie in the chamber and close the bolt.

My suggestions are:

1. Don't follow the book. In one case it resulted it a jam into the lands of around 0.050"

2. If you seat the bullet into the lands using your bolt, it can be as much as 0.030" to 0.050" jam, depending on neck tension.

3. I measure from the bullet tip, using a special rod (photo below), and using "light" finger pressure on a 1/8" dowel rod to seat the bullet in the lands I can EASILY get 0.030" difference to "touch" OAL length. After using my system for years, I am repeatable withing a few 0.001"s. (And yes, I pick my measuring bullet lengths carefully.) I realize I "might" be giving up a few thousandth's in precision by not measuring on the ogive, but I accept that.

Other methods (blackening the bullet tip with carbon, using a Magic Marker and looking for land marks can also work).

 

[Shynloco]

My suggestions are:


2. If you seat the bullet into the lands using your bolt, it can be as much as 0.030" to 0.050" jam, depending on neck tension.

Other methods (blackening the bullet tip with carbon, using a Magic Marker and looking for land marks can also work).

I DO NOT measure anything based upon "jam." I base my bullet seating on touching the rifling for the very reason you stated of the variance you noted. And the magic marker thing is a given.

Alex

 

[noylj]

Unless the book used YOUR exact bullet and your exact gun, IGNORE the book.
Personally, I think too many are over-complicating the whole COL (Cartridge Overall Length) issue and making problems where they don't exist.
For me (not you), ALL my rifles shoot best at the longest COL that fits the magazine and feeds and chambers. For single-shots, I start with the bullet just touching the lede/rifling and work up the load and, so far after more than 40 years, I have never found moving the bullet back (making the COL shorter) improved accuracy--but that is just me with a limited number of rifles.

 

[dickn52]

You can't always go by the book. Like you said, it's a point of reference. Bullets vary by brand, type and even different lots. Example, 2 different lots of the same Hornady bullet. If you are measuring from the tip, you could be as far as .021" or more in the distance to the lands depending upon how you load them. These measurements were taken with the tool pictured below. The inside bore is .010" smaller than the bullet diameter.

Are you using this tool to measure? A friend of mine has the exact same tool and it measures several thousandths difference. It is useful for a reference measurement.

Yes we are. And yes they were all different even with the same bullet. We did find same huge swings in case length as well. So the SAMMI specs call for 1.920 on the case length and we were getting anything from 2.015 to 1.990. So I'm going to suggest he clean them up with a trim to spec first.

 

[T-shooter]

My suggestions are:

1. Don't follow the book. In one case it resulted it a jam into the lands of around 0.050"

2. If you seat the bullet into the lands using your bolt, it can be as much as 0.030" to 0.050" jam, depending on neck tension.

3. I measure from the bullet tip, using a special rod (photo below), and using "light" finger pressure on a 1/8" dowel rod to seat the bullet in the lands I can EASILY get 0.030" difference to "touch" OAL length. After using my system for years, I am repeatable withing a few 0.001"s. (And yes, I pick my measuring bullet lengths carefully.) I realize I "might" be giving up a few thousandth's in precision by not measuring on the ogive, but I accept that.

Other methods (blackening the bullet tip with carbon, using a Magic Marker and looking for land marks can also work).

I use a similar method. I bought some drill depth stops and use them on a cleaning rod that is close to the bore diameter. I also got a kit several year ago that had some flat tip screw in plugs for the cleaning rod but they also had some flimsy plastic stops that I don't like to use. On a bolt gun, I sometimes use a rubber band just strong enough to keep the bolt against the case and the case in the chamber.

Close the bolt and run the rod in until it touches and make sure it's not on the ejector pin. Run the (#1) stop up against the muzzle and lock it. You need to make a dummy bullet that is seated too long to chamber. Lightly run it into the chamber until you feel it touch. Now add the second drill stop on the cleaning rod, then insert and lock it in place when it lightly touches the bullet tip. The headspace/COL is the distance is from outside to outside the drill stops minus the thickness of the last one (#2 here). By being careful, I can repeat measurements to .001". This will work on one exact bullet and sometimes only with one lot number. You can now seat the bullet to the same overall length you measured and take your measurements from there. Maybe use the Hornady bullet insert/comparator to get a reading and then subtract what ever jump you want to have. Keep in mind, the overall length of the bullets can vary several thousandths even in the same lot. It takes a light touch not to jam the bullet into the rifling or to move the bolt backwards when the dummy round is in the chamber. Sometimes I use my finger instead of the bolt so I can feel when the rod makes contact. If you use another rod (aluminum would probably be best) instead of a cleaning rod, you won't need to plug the threaded end.

 

[hrlincoln]

Yes we are. And yes they were all different even with the same bullet. We did find same huge swings in case length as well. So the SAMMI specs call for 1.920 on the case length and we were getting anything from 2.015 to 1.990. So I'm going to suggest he clean them up with a trim to spec first.

Trimming brass to consistent length is important for a number of reasons and is one more step to producing accurate ammunition....many good articles in the 'Tech' section regarding case preparation.

Here are a few more for you to check out...the first article has a good explanation of COAL (COL) vs CBTO which you may not have seen. COAL (COL) can be important for a number of reasons as noylj alluded to in post #9. Your Hornady OAL Gauge, when used in conjunction with a bullet comparator on your calipers (T-Shooters picture, post #2), yields a measurement more closely referred to as CBTO.

http://www.bergerbullets.com/wp-content/uploads/2013/03/COAL.pdf
http://www.bergerbullets.com/setting-loads-optimum-accuracy/
http://www.accurateshooter.com/gear-reviews/hornady-oal-gauge-and-comparator/