Trimming new Win 308 brass... FYI inconsistent lengths


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Franco
October 16, 2010, 03:58 PM
I recently purchased 100 new cases and resized with small base die to shoot in my 7.62x51 FNAR. I loaded the first bullet to where the cannelure was 85% covered by brass (the way I like it and end up with exact COAL) and then set my die. However, as I was loading more shells, I found that the cannelures would range from being covered 50% to almost 100%! I stopped loading and measured the cases. They varied by as much as +/- .006. I then measured my Win 147gr FMJ bullets and found that the distance from the tip of the bullet to the top of the cannelure varied by about half that much (not awful). But when you combined the two, you end up with inconsistently placed bullets. Has anyone else seen what appears to be a lack of quality control in Win products? I've never experienced such deviation in new brass so I'm now trimming all of my new Win 308 brass after it's resized to be exactly 2" (untrimmed range was about 2.002 to 2.008). Can't fix the bullets though. Just an FYI.

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Offfhand
October 16, 2010, 04:04 PM
Next time measure before resizing, there may be a lesson there.

ReloaderFred
October 16, 2010, 04:21 PM
If you've ever toured a manufacturing company making brass or bullets, you'd be amazed that they come out as consistent as they do. The .308 Winchester is a very popular caliber, and they probably have several production lines making the brass. The final case trimmers are probably not set exactly the same on each line, but within manufacturing parameters.

It's a good practice to prep all new brass before loading for this reason.

As for the cannelure location on your bullets, when bullets are run through a cannelure machine, the location of the cannelure is set from the base of the bullet, not the nose. Most bullets vary in length by a couple thousandths, and the base never varies, but the nose does. They are also probably run through different machines. After all, the 147 gr. FMJ bullet is designed to be accurate to minute of enemy soldier......

Hope this helps.

Fred

243winxb
October 16, 2010, 06:20 PM
From link belowSeating depth variations

There are a number of possible causes for overall length variation. One is the way it is measured. If you measure overall length from the tip of the bullet to the base of the case, remember to subtract the variation due to bullet length tolerance. The bullets will vary in length due to manufacturing tolerances (bullets with exposed lead noses are the worst in this regard) and this will add to the overall cartridge length variation. Remember that the bullet seater plug does not (or shouldn't) contact the tip of the bullet when seating, but contacts farther down the ogive. For a more accurate seating depth measurement, take the seater plug out of the bullet seating die, place it on top of the cartridge and measure from the base of the case to the top of the seater plug.

Another possible cause for bullet seating depth variation is seating and crimping at the same time when trying to apply a firm crimp to untrimmed cases. Variation in case length also causes variation in the amount of crimp applied. Long cases get a heavier crimp than short ones. When seating and crimping at the same time, the crimp is formed as the bullet is seated into the case. The crimp will form sooner on a long case, and therefore the bullet will not be seated as deeply. The solution is to seat and crimp in a separate step (the Lee Factory Crimp die is good for this) and/or trim cases to a uniform length.

The amount of force required to cycle a progressive press varies with the number of cases in the shell plate. When the shell plate is full, it is harder to lower the lever than when there are one or two cases present. This can lead to variation in cartridge overall length because there are different loads placed on the working parts of the press. When the shell plate is full, seating depth will be slightly long, because the load is higher and all of the clearances are taken up. With the shell plate nearly empty, the load is not great enough to squeeze out these clearances, and the seating depth is short.

jr_roosa
October 17, 2010, 01:37 AM
For new brass (I prefer Winchester too) I always prep them almost the same as fired brass:

-Full length resize mainly for fixing dings in the case mouth. My die barely touches new brass since it is set a little long and they are all a little short.

-Trim everybody to minimum. I use a RCBS trim pro and it's faster to trim them all than to measure and sort.

-Debur flash holes.

-Load as practice ammo with FMJ or whatever is cheap.

Until it's been fired once in my rifle I don't use them for accuracy loads. It probably doesn't matter, but I need the offhand and rapid fire practice anyway.

-J.

ranger335v
October 17, 2010, 07:35 PM
"
... measured the cases. They varied by as much as +/- .006.
"

Typical. And it means nothing unless you're shooting groups in the sub 1/4" range.

USSR
October 17, 2010, 08:54 PM
Sierra MatchKing bullets will vary as much as 0.010" in the bullet base to ogive measurement.

Don

MEHavey
October 18, 2010, 02:55 AM
Always measure/trim cases AFTER you resize them (especially using SB).
Think toothpaste.

Franco
October 18, 2010, 08:46 AM
Thanks all. Lesson learned. I did resize all of the new cases but didn't think to trim given that they were new brass. I will now do that going forward.

243Win: Thanks for your comment but I don't have a COAL problem. The COAL has been exactly the same for each loaded cartridge. The problem I was having was the location of the end of the brass neck on the cannelure as the brass length was inconsistent. However, your comments are definitely good advice for COAL issues.

velocette
October 18, 2010, 09:47 AM
147 grain Win. FMJ bullets are not known for consistency or accuracy. They usually do go downrange when fired but if you can squeeze out 2 ~ 3 moa, you're doing (very) well with them.

Roger

SlamFire1
October 18, 2010, 10:25 AM
Modern 150's FMJBT's may be better than old. At least if you hit a sweet spot.

This 100 yard ten group is with 150 FMJBT Horndays and 41.0 grs IMR 3031. For cheap bullets it is outstanding. Same load does not shoot nearly as well in other rifles, but it works in my Ruger M77
http://img.photobucket.com/albums/v479/SlamFire/Targets/150Hornday410grsIMR3031-1.jpg

Now these groups are with IMI 148 FMJ's. Not so good

148 IMR 40.0 grs IMR 3031

http://img.photobucket.com/albums/v479/SlamFire/Targets/148IMIFMJIMR3031.jpg

148 IMI 41.0 grs IMR 3010
http://img.photobucket.com/albums/v479/SlamFire/Targets/148grIMI410grsIMR3031.jpg

1968 WRA ball really sucked!

http://img.photobucket.com/albums/v479/SlamFire/Targets/150gr1968WRABall.jpg

USSR
October 18, 2010, 12:55 PM
The problem I was having was the location of the end of the brass neck on the cannelure as the brass length was inconsistent.

You are liable to have this problem even with brass trimmed to the same length. The problem with cannelured bullets is, the location of the cannelure relative to the bullet ogive varies (specifically, the part of the ogive where your bullet seater contacts it).

Don

Franco
October 19, 2010, 09:46 AM
Thanks USSR. The reason it threw me was because I've loaded tons of 45-70, 460 mag and 44 mag (all having cannelures) and when I set my seating die the first time, they all come out perfectly. With the .308 147gr fmjs, I experienced significant (at least to me) differences in cannelure location relative to case neck without adjusting the die. I'll just have to go on a cartridge-by-cartridge basis from now on. I think that case trimming will help somewhat too.

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