? on length of sierra 39 bk .204

[josebd2006]

the shortest is .738,longest .747 with .738 at 2.250 on the .747 do i seat it at 2.241?im going for accuracy here so im just wondering about it.what caught my eye was the plastic tips,some were not seated all the way down?i measured some sierra 53 hp match,they all were within .001

[WrzWaldo]

You will want to seat them all to the same length (from the ogive). If you seat them based on base to tip measurement you will destroy accuracy as the bullet ogive will be different distances from the lands. Do yourself a huge favor and get a comparator for measuring OAL.

[KIM204]

Wrzwaldo, what reading do you get with your stoney point,if you put it at 2.320 col ?

[skipper]

I made this drawing a while back but it would seem to illustrate what WrzWaldo is saying. It really doesn't matter that two bullets have different base to tip measurements. (within reason) The seater doesn't push on the tip of the bullet, it pushes near the ogive. That means that the seating die is seating all your bullets to the same depth at the ogive. Since the ogive is where the bullet makes first contact with the leade to the lands, all your bullets will have the same ogive to leade measurement.

Since your bullets have tips that aren't all seated the same way, your loaded cartridges will have varying lengths if you measure with a bare set of calipers, from base to tip. That is why you need to use a comparator attached to your calipers. Then you will be measuring the loaded rounds from base to ogive.



When you get your comparator, use it to measure one of your loaded rounds, that measures 2.250 from base to tip, and then you will have a comparator measurement to use as a reference. Write that measurement down in a safe place and use it to measure your loaded cartridges instead of the 2.250 base to tip measurement. You'll get much more consistent rounds that way.

Don't use someone else's comparator measurement. Their comparator may be a different size than yours. Even comparators made by the same manufacturer may be different enough to make a difference.

[KIM204]

Shipper, I was asking Wrzwaldo because He said on a post that he seeded the 39 bks at 2.320 COL . So if you use a comparator it may read 2.990 or so?

[josebd2006]

so i can just leave the setting on the bullet seater alone and it should seat the bullets the same everytime?i use the forster micrometer

[jo191145]

wrzwaldo and Skipper are right on the money.

Simply speaking. Let your seating die seat the bullets. I've never noticed any seated bullets from the same lot off by more than .002 to the ogive. Thats close enough for a varmint gun with a freebore as long as the 204. You do need a comparator for accurate and repeatable measurements.
Thats another reason I never seat bullets "kissing" the lands in other calibers. Some might kiss, others might tease and some may French A good way to get fliers IMO. .005 off the lands or .005 into the lands is as close to kissing as I get.

Now your Sierras seem to have a pretty large variation. For accuracy you could segregate by bearing length but you would need two comparators for that. You could separate by overall length but its no guarantee they'll be right. Should be pretty darn close though.
Sierra sure makes you guys work hard don't they.

[WrzWaldo]

Shipper, I was asking Wrzwaldo because He said on a post that he seeded the 39 bks at 2.320 COL . So if you use a comparator it may read 2.990 or so?

Dang I gotta learn the difference between the edit and quote button...


Do you mean 1.99 or so?

As for comparator I use the magic nut method. Then I create a magic round (dummy of course) and use that to set the seating die for that particular bullet/brass combo.

WW

[KIM204]

Wrzwaldo, I'm talking about using the stoney point comparator.

[skipper]

Shipper, I was asking Wrzwaldo because He said on a post that he seeded the 39 bks at 2.320 COL . So if you use a comparator it may read 2.990 or so?

That is correct. That's why I said you should use a set of bare calipers to make sure that your round is seated at 2.250 from base to tip. Then attach the comparator to your calipers and measure the same round. It may read 2.990, it really doesn't matter what it reads. Write that measurement down and use it, with your comparator, to measure your cartridges when seating in the future. That way all your bullets will be seated the same length from base to ogive, where it counts the most.

A lot of people use bare calipers when seating and measure from base to tip. They set the die so that the first round is right on the money 2.250 measured from base to tip. Then they seat another and take a measurement only to find out that the measurement is now 2.253 or something like that. Then they adjust the die again until it seats the bullet at 2.250 again. You could do that all night and think you are creating identically seated ammo. The truth is that all those rounds may be the same measurement from base to tip but, they are probably all different lengths from base to ogive. If they would have left the die alone and seated all the bullets they would have had more consistent ammo.

The tip of the bullet doesn't make contact with the lands at all so trying to get all your bullets seated the same length from base to tip isn't helping accuracy. If you are using a comparator you should see a lot less variation in your loaded rounds because you are measuring closer to where the seating stem is contacting the bullet. If your comparator was the exact same dimensions as your seating stem, you wouldn't see any variation at all.

Remember that the term "COL" is sometimes used to describe different measurements. COL could mean Cartridge Overall Length, Case Overall Length or Comparator Overall Length. IF in doubt about the use of the term, ask what they mean.

[WHISTLEPIG]

Excellent advice from all. I just might add that unless you are using a premium seater you should make sure that the die is seating off the ogive and not the tip of the bullet. My RCBS window die had to be modified to seat on the ogive. I only used that die for a week before I realized it was a piece of junk and got a Redding. It now sits on a prominent shelf in my reloading room to remind me to buy the best the first time.

[skipper]

Excellent advice from all. I just might add that unless you are using a premium seater you should make sure that the die is seating off the ogive and not the tip of the bullet. My RCBS window die had to be modified to seat on the ogive. I only used that die for a week before I realized it was a piece of junk and got a Redding. It now sits on a prominent shelf in my reloading room to remind me to buy the best the first time.

Amen to that.

[josebd2006]

ok,that makes sense,thanks guys!

[josebd2006]

Sinclair Bullet Comparators 2 will this be allright to use?

[WrzWaldo]

Sinclair Bullet Comparators 2 will this be allright to use?

That's the magic nut I use, model 09-700. Sorry, I should have been a bit more specific in my other post.