.308 Comparator mystery...

[fla9-40]

Got a question to ask:

Was checking the lands on a new box of .308 Sierra 168gr HPBT MATCH
bullets mfg # 2200.
Was using the "start the bullet in the brass and closing the bolt on it method"

I was using brass fired from my rifle, Cleaned, checked length trimmed if needed,
and Neck sized.
I random picked 7 pieces of brass and 8 bullets.

This is the first 8 measurements with the Hornady Bullet Comparator:

2.299
2.296
2.294
2.295
2.298
2.298
2.294
2.295

Now the next 10 measurements:

NOTE: After the first measurement from this batch I Neck sized the brass before
each test. Again random brass matched up to random bullets:


2.313
2.314
2.308
2.310
2.295
2.301
2.304
2.314
2.296
2.312


Checked to see if calipers were zeroed each time.

Can someone shed some light on this, are the bullets from the last 10 being pulled from the brass
when I gingerly extract the round to measure???

Thanks for help on this!

[acemisser]

maybe with the full sized brass you pushed the shoulder back .oo3 or whatever ....I do not think this is the
best way to determind the bullet into the rifleing test....

[82boy]

Several things going on here. To start you need to measure the ogive of the bullet right out of the box, and seperate then buy this length. (Your Comparator should measure the bullet at the ogive.) I have found in a box of 100 Sierria Match kings 2 and 3 diferent ogive lengths on bullets. Second thing is you may have some problems with your seating die, it may be pushing the bullets by the tip, or not fitting the bullets properly. Last you will have inconstant seating depth by neck sizing brass, the brass will be diferent lengths, and therfore contacting the shoulder at diferent lengths, and inturn alowing the bullet to seat deaper or shalower each time. (Another reason why a PROPERLY seat up FL dies is king.)

I would also get away from using the "start the bullet in the brass and closing the bolt on it method," most guns preform better with a small amount of jump. (Usualy .005) Second reason is if you ever have to remove the case from the gun (Cease fire) you may stick the bullet, and dump powder down into the chamber. The best method is find a light jamb, and then adjust you bullet in out out from there to find where it shoot best, and then seat all you bullets there. Actulay what you doing is called a hard jamb. Yes you better beileve that when you extract a round that is hard jambed into the lands that it will pull out.

[John_M]

fla9-40, It is my opinion that "...Was using the "start the bullet in the brass and closing the bolt on it method..." is NOT the most accurate method of measuring the OAL of the cartridge from the base of the brass to the ogive on the bullet. I would expect those inconsistent measurements using the method you describe.
I would recommend using the Hornady OAL length Gauge (http://www.midwayusa.com/product/570611/hornady-lock-n-load-overall-length-gage-bolt-action) in conjunction with their OAL Bullet Comparator to get the most precise measurements. Follow Hornady's enclosed instructions for using both tools.

I use both of these inexpensive and well-made tools. They make the process of determining this measurement easy and the results, accurate.

Others on this site have had success using measuring methods similar to what you describe but they used home made tools and slightly different techniques than what you used.

Good luck.

Edit: I strongly endorse the above comments by 82boy

[fla9-40]

maybe with the full sized brass you pushed the shoulder back .oo3 or whatever ....I do not think this is the
best way to determind the bullet into the rifleing test....

These were not FL sized only neck sized....

[fla9-40]

I never do live rounds like this, this is only to determine where my lands are so I can start my testing on what this gun likes as far as bullet jump with this bullet.
I'm beginning to see what you say about different ogive on the same box of bullets. I think I will separate them.
I am going to look into the tool that John_M suggested and see how much this does change things.

This is the first time I have run into this using my method so it was just strange it happened.
Thanks for your input on this!


Several things going on here. To start you need to measure the ogive of the bullet right out of the box, and seperate then buy this length. (Your Comparator should measure the bullet at the ogive.) I have found in a box of 100 Sierria Match kings 2 and 3 diferent ogive lengths on bullets. Second thing is you may have some problems with your seating die, it may be pushing the bullets by the tip, or not fitting the bullets properly. Last you will have inconstant seating depth by neck sizing brass, the brass will be diferent lengths, and therfore contacting the shoulder at diferent lengths, and inturn alowing the bullet to seat deaper or shalower each time. (Another reason why a PROPERLY seat up FL dies is king.)

I would also get away from using the "start the bullet in the brass and closing the bolt on it method," most guns preform better with a small amount of jump. (Usualy .005) Second reason is if you ever have to remove the case from the gun (Cease fire) you may stick the bullet, and dump powder down into the chamber. The best method is find a light jamb, and then adjust you bullet in out out from there to find where it shoot best, and then seat all you bullets there. Actulay what you doing is called a hard jamb. Yes you better beileve that when you extract a round that is hard jambed into the lands that it will pull out.

[82boy]

I personaly would not get the Hornady OAL length Gauge, IMO it is a waste of time. To start you have to buy cartridges made by them, with brass that is not fit for your chamber. Second from my experince the tool is far from accurate. A better tool would be the Sinclair Bullet Seating Depth Tool. http://www.sinclairintl.com/.aspx/pid=35491/Product/Sinclair-Bullet-Seating-Depth-Tool This tool doesn't use costom made brass and other stuff, it is far more accurate than the Hornaday model, but even it I have found to lie.

The way I use is lightly seating a bullet and closing the bolt, I then extract the round, and taking 0000 steel wool I clean the marks off the bullet, and then adjust my seater die in, and then close the bolt on the chamber again, I repeate procedure several times untill I get a light square mark on the bullet. (If you watch the shape a hard jamb will be retangular, touching will be square, and lightly touching will have a disaperaring mark going back to a retangular shape.) When this happens I call this light jamb, and adjust my depth off from that measurement.

[thomae]

I would invest in purchasing (or making your own tool similar to) the Hornady Lock-N-Load Overall Length Gage tool.
Use that on the breech end and a wooden dowel down the muzzle and you should be able to get repeatable and accurate measurements with your Comparator.

[fla9-40]

82boy Just tonight I measured the ogive of each bullet. It ranged from .627 to .636!
I would have never believed it if I had not measured myself!

[Deerhunter 28]

175 SMK will vary .011
I assume 168's will do the same?
178 AMAX will vary .002-.003




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