Seating depth, are these variations ok? (pic)


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Rmeju
May 18, 2012, 09:06 PM
Hey guys, got another question about some rifle loads.

When seating, I've been getting variations on where the cannelure sits relative to the case mouth. These cases are all freshly trimmed to the exact same length (shorter cases that were too short for trimming are in a different batch), so I think I can rule out variation in the case length.

The bullets themsevles (147gr plinkers) have some tips that may or may not have been a little smushed at some point, so I'm trying to go by the cannelure rather than OAL. On the advice of posters on a different thread, I'm trying no crimp for this lot. The rifle is an M1A.

Most of the finished rounds look like C or D. There's a few that are seated even deeper than A, but only a couple.

Are these variations ok? Too much? These are not going to be precision loads, but I'd like to know if these kinds of differences will effect accuracy for when I do (attempt) to load some precision rounds.

Thanks!

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ole farmerbuck
May 18, 2012, 09:12 PM
I'd say those are ok. When you make your precision rounds, you'll prob use better bullets and wont have the seating problems.

nastynatesfish
May 18, 2012, 09:20 PM
Did you mic them? Could just be ariation in canalure. If your not shooting for money I'd load me up and kill something

rcmodel
May 18, 2012, 09:20 PM
Probably military surplus bullet variation.

Only way to tell is measure OAL using a bullet comparatior, so you are measuring off the ogive of the bullet where the seating die stem acts to seat the bullet, and not the tip of the bullet.
Which really has nothing to do with anything concerning OAL.

http://www.sinclairintl.com/.aspx/pid=34262/Product/Sinclair-Hex-Style-Bullet-Comparators

rc

USSR
May 18, 2012, 09:39 PM
...I'm trying to go by the cannelure rather than OAL.

Ignore the cannelure and ignore the OAL (as long as they fit your mags). Take rcmodel's advice, get a bullet comparator and measure from case base to bullet ogive.

Don

ole farmerbuck
May 18, 2012, 10:50 PM
Ignore the cannelure and ignore the OAL (as long as they fit your mags).

I cant do with one of my Kreiger barreled AR's. The bullets will be into the lands pretty hard.

USSR
May 19, 2012, 09:13 PM
I cant do with one of my Kreiger barreled AR's. The bullets will be into the lands pretty hard.

Well, aren't you the lucky one. With most factory chambered .308's, COAL is restricted by magazine length.

Don

Walkalong
May 19, 2012, 10:07 PM
My cheap bulk Winchester 55 Gr FMJ canellures are all over the place. Cheap is cheap for a reason. They are fine for causal plinking.

http://www.thehighroad.org/attachment.php?attachmentid=120702&stc=1&d=1273145417

rg1
May 19, 2012, 11:06 PM
Seems to me that the cannelure on military style FMJ bullets are applied to these bullets at a distance from the bullet tip and not from the base. Plus the tips on military fmj's often vary with some very sharply pointed and some have a rounded tip. So the cannelure ends up at slightly different positions especially in mixed lots of bullets. If you put them on the tips the cannelures are nearly in the same place but from the bases they vary. No problems if they vary. You can see this in Walkalong's pics above. The bullet with a sharp tip, 2nd from left, has the cannelure higher but if you roughly measure the distance from the tip to the cannelure they all are very close to the same distance from the tip.

gamestalker
May 19, 2012, 11:24 PM
With regard to bottle neck cartridges, I don't even give consideration to the canelure. I seat to what clears the mag, lands, and cycles properly. No need to seat deeper than function dictates, or longer if loading for an auto loading action. Just locate the OAL that functions well, and then either lock your seating die or record the die adjustment to duplicate that depth for future batches using that specific bullet.
GS

noylj
May 20, 2012, 02:55 AM
Surprisingly, not all bullets in a box are made on the same machine and there can be differences in the ogive from different machines. As a very rough rule, one would like to control COL to +/- 0.005". Even a cheap digital caliper can measure better than this.
For this measurement to really have meaning, one needs to measure from a datum line on the bullet's ogive to the case head--as you noted, bullet noses often are "smooshed" in shipping and handling. Hornady and others make case length gages that measure this way.
For pressure increase that could lead to KaBooms, one is looking at bullet set-back of 0.01" or more--generally much more. Do the bench press with each round (although that will "smoosh" those plastic tips) to ensure sufficient bullet grip.
Basically, if your eye can't see the difference in COL, your gun will never know the difference.
One "easy" way to reduce the overall variation is to run each case back through the seating die after several minutes. You'll even feel the bullet being seated deeper in the long COL rounds.

Gtimothy
May 20, 2012, 12:26 PM
Ok, so this may be a stupid question but if you are using your seating die as the guide for OAL and the bullets can vary as much as they aparently do, Where do the bullets contact the seating die? Ogive? Tip? Or does it really matter.....Guess I'm going to have to take one apart and look at it closely!

USSR
May 20, 2012, 06:28 PM
Ok, so this may be a stupid question but if you are using your seating die as the guide for OAL and the bullets can vary as much as they aparently do, Where do the bullets contact the seating die? Ogive? Tip? Or does it really matter.....Guess I'm going to have to take one apart and look at it closely!

Not a stupid question at all. First, the ogive is the entire surface of the bullet from where it leaves being full caliber in diameter, all the way to the meplat (tip). Seating dies for cartridges that normally fire spitzer bullets, contact the bullet somewhere along the ogive relatively near the meplat. As you noted, the ogive varies from one bullet to the next due to coming off more than one machine at the factory. Even with Sierra MatchKing bullets, ogives will vary by as much as .010", so I never seat bullets less than .010" off the lands. Just MHO.

Don

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