How to get a new batch of bullets back into an accuracy node?

[jlow]

So trying to rationalize this out so that I know what to do with a new batch of bullets.

Bullet is Nosler CC 77 grains .223 caliber bullets. Rounds with old bullet shooting about ½ MOA.

With the old batch of bullets, I have the following:

Bullet BTO – 0.5897”
Best precision seating depth – round BTO – 1.862”

With the new batch of bullets, I have the following:

Bullet BTO – 0.6024”

So the new bullet is 0.0127” longer.

I figure if I use the same setting in my Wilson seater, assuming the ogive shape is the same (I understand this is an assumption but let’s assume that for the time being so that we can figure out what we can), the round BTO will remain the same with the new bullet i.e. 1.862”

Of course, since the bullet is longer, at round BTO of 1.862”, the base of the new bullet will sit 12.7” thousands deeper into the case? Correct?

So if I assume that the optimal powder weight remains the same (another assumption), I should probably test seating depth of the new bullet first with BOT of 1.862” and then lengthen and test it to reduce the amount it is seating deeper into the case. At 1.862”+0.0127” = 1.8747”, the case volume will now be the same as the old bullet seated into a case. So if case volume is the key to precision, this would get me back into the accuracy node/best seating depth.

Does this make sense? If not, how do you guys work a new batch of bullets into an accuracy node?

 

[3081FTR]

IME - seating depth (TTL) for the new lot is more important than ~13" of case capacity...but that probably depends on how you went about selecting your powder and subsequent charge.

 

[dkhunt14]

Usually if a bullet is longer it is skinnier. Sometimes it takes a different load to get to shoot good again, sometimes you just have to adjust the seating depth. I don't think it is a given thing. That's why I try to buy enough bullets of the same lot to wear out the barrel. Matt

 

[jlow]

Thanks guys!

3081FTR – yea, pretty much trying to do the least to get it back to the node.

Matt – Was hoping to just adjust seating depth but will have to see. I seated a bunch of the old ones and another bunch of the new ones and nope, they did not end up having the same BTO length so definitely slight differences in ogive shape. It turns out the new one seated 6 thousands longer which to me means as you guess correctly that it is skinnier. Guess I will just have to test the waters both ways to see how it goes.

As to buying enough bullets, unfortunately or fortunately it’s a 223 which unlike the 6mm has a much more durable barrel. The Nosler comes in 1,000 count boxes but they still seem to disappear quick!

 

[expiper]

OP,,,if/when I start with and new lot of the same style/type/brand of bullet and find that they are a cupla thou. different (and they usually are) I use the same ammount of jump/jam that worked previously,,,,usually that is the answer,,,,you can change the powder charge up or down a lot and not see any differance ,but the ammount of jump/jam is quite noticable,,,,Roger

 

[bsekf]

One of the articles on the Berger site addresses this. Seat the new bullets so they are the same as the old ones, base to ogive. If the stars are aligned, they will shoot about the same.

 

[jlow]

Thanks guys. I’ve tried the two bullets seated with the same setting with the Wilson seater and they opened up, I guess that is because as per my BTO OAL measurements tells me, the amount of jump has changed by about 6 thousands.... Will try to adjust so the jump is the same and see what happens.

Bsekf – can you tell me where that article is? Is it on their website or the Berger book?

 

[BoydAllen]

You know that the bullets are different, and that the amount that you jump or are into the rifling is important to tune, so what was the point of testing at the old seater setting? I would do what it takes to seat the new bullets so that they have the same relation to the start of the rifling as the old ones did, and then load some test rounds with slight variations in powder charge. I do virtually all of my tuning loading at the range so all of this goes very quickly, but even if you are loading at home, this approach is likely to give you decent results. If you are using an non micrometer Wilson seater, try recording the combined length of the seater stem and cap, and using it as a reference for seating depth changes. That is how I keep my loading records for calibers that I use Wilson seaters to load for.

 

[jlow]

You know that the bullets are different, and that the amount that you jump or are into the rifling is important to tune, so what was the point of testing at the old seater setting? I would do what it takes to seat the new bullets so that they have the same relation to the start of the rifling as the old ones did, and then load some test rounds with slight variations in powder charge. I do virtually all of my tuning loading at the range so all of this goes very quickly, but even if you are loading at home, this approach is likely to give you decent results. If you are using an non micrometer Wilson seater, try recording the combined length of the seater stem and cap, and using it as a reference for seating depth changes. That is how I keep my loading records for calibers that I use Wilson seaters to load for.

Boyd – yes, I knew they were different and likely not going to shoot well without some adjustments. Basically I have come across this situation before but have not done a good job of documenting what it takes to get back to the node. I basically test at the old seating setting as an “anchor point” or control as we would call it in the lab with all new changes relative to that.

Agree that the setting needed is that which gives the same relationship to the rifling but as you know, neither the seater stem or the Hornady tool actually contacts the ogive in the same place as the rifling and what the Hornady tool gives you is a relative and not an absolute number. The change in shape of the ogive of course is always the wild card. So it would be interesting to see how this works out.

I tool plan on doing this with reloading at the range but at least at present, I only feel comfortable changing seating depths and not charge weight so I will be only testing effects of seating depth this time around, but yes being able to do that at the range really helps to speed things up in terms of load development. My Wilson is a micrometer seater (old one thank God…) so I don’t have to resort to the measurements you mentioned.

 

[BoydAllen]

I take it that you do not have a way to come up with the ogive (where the tool makes contact) to head dimension of a round that has its bullet seated to just touch the rifling. If I am wrong about this, all that you have to do is come up with this using both new and old bullets. Of course this will not be possible if you do not have any of the old bullets, and without any information as to where your original seating was in relation to the rifling, you are stuck with doing a load workup holding the powder charge constant, varying the seating depth. One way to do this is to seat all of your bullets long, and then seat them to various shooting lengths at the range.

 

[jlow]

I take it that you do not have a way to come up with the ogive (where the tool makes contact) to head dimension of a round that has its bullet seated to just touch the rifling. If I am wrong about this, all that you have to do is come up with this using both new and old bullets. Of course this will not be possible if you do not have any of the old bullets, and without any information as to where your original seating was in relation to the rifling, you are stuck with doing a load workup holding the powder charge constant, varying the seating depth. One way to do this is to seat all of your bullets long, and then seat them to various shooting lengths at the range.

That is correct, I don’t have any way to do this since this is a tactical rifle and I don’t have the original reamer, so no way to make that tool. The good news is of course I am not in any danger of “using up” the barrel because this is not exactly a barrel burner caliber.

Yes, the old bullets are also pretty much all gone or at least loaded up. Doing a seating depth study at the range is my current plan and what I was looking for with my post is which direction to go as a start. What I have done is weight out a whole bunch of powder in test tubes and with pre-prep cases that has been primed. Basically just pouring the powder in at the range and seating bullets to different depths and testing. I really like this method as I never have to shoot more than 3 rounds for scatter groups as it is pretty obvious after 3 and anything that looks decent I just add more rounds until a good node is confirmed.

 

[ZenArchery]

Ladder load. If you are "certain" of OAL. Then start low load work up to safe hot load. Find the load this is most accurate on the ladder then you are good to go.

 

[BoydAllen]

All you need is the loaded ammo. Set your seater to produce the same ogive to head measurement (measured with a comparator that touches the bullets close to where the rifling will) with the new bullets and play with charge weight changes in very small increments. Once you determine what the best charge is, try very small adjustments (.002 max) in seating depth, going both ways.

 

[jlow]

That's pretty much what I intend to do i.e. use the round OAL from the old bullet as a place to start in terms of where to go next.