Accubond base to ogive discrepancies

[HuntClub]

Opened two new boxes of 7mm 160 accubond boxes... both because of major discrepancies in base to ogive measurments. First box all over the place... second box trying to get enough in one range to work a load with. Had 26 in the 0.8075 range - those all came from the first box. The next closest range was 0.8125 measure.

Did a 9 shot test at 100 yards. The two highest loads with N165 were 67.2 and 67.5 grains. These two loads combined put 5 shots in a 1/2" group with only a increase in speed by roughly 20fps in the higher load. Went to range yesterday with 6 loads - one using the 0.8075 round and one using the 0.8125 round. Both at 67.3 grains.

First load was comparable to first test. Second load opened up to 1.75" group at same seating depth. Now I only have roughly 15 bullets in the 0.8075 measure. What is the best way to get the 0.8125 rounds to perform - reduce powder to reduce pressure? FPS did increase in second load about 25 fps.

This is really a sad thing that Nosler has no more control over base to ogive measure than this. All the other bullets increase in ogive measure as in these first two groups. Think I may not even load the 15 rounds and just call it quits with Nosler.

EDITED TO ADD: Between the two boxes there were also 5 bullets with the tips broken off. There were a few with serious blemishes in the copper as well.

 

[Pres100]

What tool are you using to measure? Assume 2 different lots?

.005 jump or jam delta isn't super excessive but where are you in relation to the lands with the .8075?

 

[C.E.Smith043]

Opened two new boxes of 7mm 160 accubond boxes... both because of major discrepancies in base to ogive measurments. First box all over the place... second box trying to get enough in one range to work a load with. Had 26 in the 0.8075 range - those all came from the first box. The next closest range was 0.8125 measure.

Did a 9 shot test at 100 yards. The two highest loads with N165 were 67.2 and 67.5 grains. These two loads combined put 5 shots in a 1/2" group with only a increase in speed by roughly 20fps in the higher load. Went to range yesterday with 6 loads - one using the 0.8075 round and one using the 0.8125 round. Both at 67.3 grains.

First load was comparable to first test. Second load opened up to 1.75" group at same seating depth. Now I only have roughly 15 bullets in the 0.8075 measure. What is the best way to get the 0.8125 rounds to perform - reduce powder to reduce pressure? FPS did increase in second load about 25 fps.

This is really a sad thing that Nosler has no more control over base to ogive measure than this. All the other bullets increase in ogive measure as in these first two groups. Think I may not even load the 15 rounds and just call it quits with Nosler.

EDITED TO ADD: Between the two boxes there were also 5 bullets with the tips broken off. There were a few with serious blemishes in the copper as well.

Are you absolutely positive you didn't buy factory seconds by chance?

Also 1/2" groups for a hunting bullet is beyond fantastic.

 

[HuntClub]

What tool are you using to measure? Assume 2 different lots?

.005 jump or jam delta isn't super excessive but where are you in relation to the lands with the .8075?

Using Hornady bullet comparator with anvil base. Loaded round is 0.085" from Jam. Tikka will not let me load much longer. Using Hornady overall case length gauge the cartridge length to jam is 2.840" - Brass base to ogive. Loaded round is 2.755" - Brass base to ogive.

The 0.8075 measure is just the bullet base to ogive.

Two differnt bullet lots - Yes. Ordered one box at a time...different dates.

 

[Pres100]

Sorry ... I shouldn't have referred to a "jump or Jam" delta but rather the difference in you Bullet BTO measurements.... that will also influence your cartridge BTO.

If you have 2 boxes of bullets and your BBTO measurements are all over the place, you might want to try sorting by the bullet OAL... I often find that the overall length is easier to measure and be consistent with. You'll likely drive yourself mad trying to sort the impact of all of these measurements and before you now you will be out of bullets and on to another box to start all over agin

 

[Doom]

Since you are dealing with a hunting bullet have you tried seating the bullet to max SAMMI length?

 

[Bill Norris]

Not to argue at all. I have never had a chance to shoot any 7mm A Bs at all but the variances in your bullets does not mirror what I have found with 6mm, .257, 6.5mm, and .308 calibers. The variances I have seen with these calibers have been really small and the accuracy has been and still is very good. You must have been unlucky with those.

 

[HuntClub]

Sorry ... I shouldn't have referred to a "jump or Jam" delta but rather the difference in you Bullet BTO measurements.... that will also influence your cartridge BTO.

If you have 2 boxes of bullets and your BBTO measurements are all over the place, you might want to try sorting by the bullet OAL... I often find that the overall length is easier to measure and be consistent with. You'll likely drive yourself mad trying to sort the impact of all of these measurements and before you now you will be out of bullets and on to another box to start all over agin

I guess I am lost on this... wouldn't loading to a set OAl still create a "jump to lands" variance which would create different impact points at the target range?

I have always loaded based on BBTO and had success with that. Never had two boxes of bullets vary in that measure like this before though.

What are the dynamics of loading to just the OAL? What makes that work if the BBTO is still in play?

 

[Pres100]

BBTO = BULLET BASE to Ogive ... refers to only the bullet.
CBTO = Cartridge Base to Ogive.

BBTO is ONE way to sort bullets. You can sort from the base of the bullet to the Ogive or sort the bullets by OAL. Sorting bullets by OAL is more consistent .... There can be a lot of variance in BBTO if your tools or your method isn't solid.

Any variance in your BBTO will also show up in your CBTO when you seat the bullet.

I find that sorting bullets by overall length is more consistent and basically has similar results on target.

My guess is that you may have received a box with a pretty large variance in shape and quality... After reading your edit in the first post, I'd just just shoot them up and move on to fine tuning a batch of known good bullets

 

[Doom]

I guess I am lost on this... wouldn't loading to a set OAl still create a "jump to lands" variance which would create different impact points at the target range?

I have always loaded based on BBTO and had success with that. Never had two boxes of bullets vary in that measure like this before though.

What are the dynamics of loading to just the OAL? What makes that work if the BBTO is still in play?

I went back and read your original post as I was confused with you description of loads. On the second day you loaded six rounds as I understand it. Three with the 0.8075" BBTO and three with the 0.8125"BBTO with the same CBTO if I aim following your description. If this is correct I would think that one possible issue is the shooter. The other thing I would do is check the 0.8125 bullet in the rifle and use that dimension to set your CBTO to get your 0.085" from jam with that bullet.

 

[HuntClub]

BBTO = BULLET BASE to Ogive ... refers to only the bullet.
CBTO = Cartridge Base to Ogive.

BBTO is ONE way to sort bullets. You can sort from the base of the bullet to the Ogive or sort the bullets by OAL. Sorting bullets by OAL is more consistent .... There can be a lot of variance in BBTO if your tools or your method isn't solid.

Any variance in your BBTO will also show up in your CBTO when you seat the bullet.

I find that sorting bullets by overall length is more consistent and basically has similar results on target.

My guess is that you may have received a box with a pretty large variance in shape and quality... After reading your edit in the first post, I'd just just shoot them up and move on to fine tuning a batch of known good bullets

I am following you on the BBTO and CBTO terms.... maybe I haven't been clear. But, I appreciate your effort to help.

I did a quick measure on three of the bullets sorted by BBTO. They were 0.8085, 0.8080, 0.8080.

I did a quick measure on those for Bullet base to Tip: 1.3880, 1.3890, 1.3910, respectfully.

I did a quick Cartridge base to Ogive: 2.755" all three. The Total cartridge length for them: 3.335, 3.336, ( I forgot to write down #3 lol) . But anyway, I am already loading longer than SAAMI and still shy of the "jam" by 0.085" on the lands.

I have a really good load with a 140 TTSX @3125 fps, but I had these two boxes that I had hoped to find another good load with.

 

[jackieschmidt]

The internal structure of the Accubond might not be conducive to keeping the external measurements as close as some other bullets.

Keep in mind this is a bullet design that stresses terminal ballistics over other features.

 

[TTE]

IMO ... without sorting bullets you will have a hard time seating bullets to the same length (CBTO)

 

[HuntClub]

IMO ... without sorting bullets you will have a hard time seating bullets to the same length (CBTO)

This is where I am at too. Where I measure BBTO and seat bullets for a certian depth I am generally spot on with the others too. But in my test, original post, the 0.8125" BBTO was seated deeper and, I'm certain, it created more pressure - and group opened up to 1.75". Anyway, there are not enough bullets with the same BBTO measure to play around looking for a good seating depth. It will be a waster of powder, primer, and time. (frustration coming out now...) A good piece of change spent on this "quality" bullet and having to deal with this is not a pleasant experience.

I do appreciate all the input from the group. Lots of knowledge and experience in here.

 

[Rsadams]

I mark the cases 1 and 2 when I have those problems that way at least I know there may be a problem when switching and if so what it is....

 

[L1986]

First I definitely wouldn’t be basing my seating depth or any cartridge measurements on OAL especially with plastic tipped bullets. Sounds like you are going at it the correct way though. However going from a 1/2 inch group to a 1.75 inch group with only 5 thou difference in anything seems suspect to me. For hunting bullets and rifles I don’t sort anything because I don’t want to find a load that is that close to going completely crazy with a slight variance in components. When I’m about to pull the trigger on an animal the last thing I want going through my mind is if I grabbed a bullet from the wrong sort pile while loading. If you are using these for serious target work I think you answered your own question and I would just sell them and move on.

 

[Ned Ludd]

I guess I am lost on this... wouldn't loading to a set OAl still create a "jump to lands" variance which would create different impact points at the target range?

I have always loaded based on BBTO and had success with that. Never had two boxes of bullets vary in that measure like this before though.

What are the dynamics of loading to just the OAL? What makes that work if the BBTO is still in play?

As illustrated in the image below, the critical bullet contact points for maintaining consistent seating depth are: 1) the point out near the meplat where the seating die stem contacts and "pushes" the bullet into the neck on the downstroke of the ram, and: 2) the point on the bullet ogive just above the top of the bearing surface where our caliper tool insert seats when we measure cartridge base-to-ogive (CBTO).


Bullet nose length variance in between these two critical contact points will also cause variance in seating depth. The seating die stem pushes on the bullet, and if the contact point at which we measure with calipers varies in its distance from the seating die stem contact, we won't get the same seating depth measurement.

As can also be seen from this image, both of these point lie outside the bullet base-to-ogive (BTO) dimension. Thus, sorting bullets by BTO is not going to do anything to improve seating depth inconsistency caused by length variance in the nose of the bullet. Sorting bullets by BTO will keep the amount of bearing surface and boattail seated down in the neck/case consistent when they are seated at a consistent seating depth. This has an effect on usable case volume and friction between the bullet and case neck wall.

I think the real question here is that you have made the assumption that bullet BTO variance is the major factor causing the difference between the two loads. Based on the measurements you provided, there should be about .005" more shank/boattail sunk down in the case with the longer BTO bullets (.8125" vs .8075"). Is it possible this little extra amount of bullet shank seasted down in the neck raised the pressure enough to increase velocity by 25 fps? Maybe. However, I routinely larger cover seating depth distances than that, moving the bullet by as much as .020" to .030" in the course of a single test with little to no detectable change in velocity. So it's unclear to me whether the difference in bullet BTO was really the culprit in your test. Further testing can probably reveal whether this is really the case, but it might mean larger numbers of loaded rounds than you were hoping for. If the increase in velocity with the slightly longer bullets turns out to be real, perhaps dropping the charge weight enough to bring the velocity back down to the load that shot well would do the trick. You might also consider sorting some bullets by OAL instead of BTO and determine the results.

FWIW - I have tried several of the Nosler .224" RDF bullet weights, mainly for practice/fun loads. What I can tell you is that the meplats are certainly very "pointy", no doubt about it. However, they had to squeeze them down so hard with the pointing die/machine that a significant number of the bullets in every box had an enormous [visible] bulge partway down the ogive. I'm thinking that can't be good for precision LOL. So I switched over to using Hornady ELDMs for these kind of loads, which are very reasonably priced as compared to the Berger and Sierra match bullets I use in competition, and am very pleased with the performance. I am liking the Hornady ELDMs so much in fact, that I may start using them in matches. My point here is that you may want to look for a different bullet manufacturer that does a better job with their quality control.

 

[nksmfamjp]

Shoot those 15 into one group…..then shoot 15 of the remaining into another group. I think you will find your groups are quite similar in Sd and dispersion.

 

[jackieschmidt]

As illustrated in the image below, the critical bullet contact points for maintaining consistent seating depth are: 1) the point out near the meplat where the seating die stem contacts and "pushes" the bullet into the neck on the downstroke of the ram, and: 2) the point on the bullet ogive just above the top of the bearing surface where our caliper tool insert seats when we measure cartridge base-to-ogive (CBTO).

View attachment 1474315
Bullet nose length variance in between these two critical contact points will also cause variance in seating depth. The seating die stem pushes on the bullet, and if the contact point at which we measure with calipers varies in its distance from the seating die stem contact, we won't get the same seating depth measurement.

As can also be seen from this image, both of these point lie outside the bullet base-to-ogive (BTO) dimension. Thus, sorting bullets by BTO is not going to do anything to improve seating depth inconsistency caused by length variance in the nose of the bullet. Sorting bullets by BTO will keep the amount of bearing surface and boattail seated down in the neck/case consistent when they are seated at a consistent seating depth. This has an effect on usable case volume and friction between the bullet and case neck wall.

I think the real question here is that you have made the assumption that bullet BTO variance is the major factor causing the difference between the two loads. Based on the measurements you provided, there should be about .005" more shank/boattail sunk down in the case with the longer BTO bullets (.8125" vs .8075"). Is it possible this little extra amount of bullet shank seasted down in the neck raised the pressure enough to increase velocity by 25 fps? Maybe. However, I routinely larger cover seating depth distances than that, moving the bullet by as much as .020" to .030" in the course of a single test with little to no detectable change in velocity. So it's unclear to me whether the difference in bullet BTO was really the culprit in your test. Further testing can probably reveal whether this is really the case, but it might mean larger numbers of loaded rounds than you were hoping for. If the increase in velocity with the slightly longer bullets turns out to be real, perhaps dropping the charge weight enough to bring the velocity back down to the load that shot well would do the trick. You might also consider sorting some bullets by OAL instead of BTO and determine the results.

FWIW - I have tried several of the Nosler .224" RDF bullet weights, mainly for practice/fun loads. What I can tell you is that the meplats are certainly very "pointy", no doubt about it. However, they had to squeeze them down so hard with the pointing die/machine that a significant number of the bullets in every box had an enormous [visible] bulge partway down the ogive. I'm thinking that can't be good for precision LOL. So I switched over to using Hornady ELDMs for these kind of loads, which are very reasonably priced as compared to the Berger and Sierra match bullets I use in competition, and am very pleased with the performance. I am liking the Hornady ELDMs so much in fact, that I may start using them in matches. My point here is that you may want to look for a different bullet manufacturer that does a better job with their quality control.

Ned, for us that make our own bullets, it is inconceivable to have variations in any of the bullet’s dimensions.
I have never had the opportunity to visit a major manufacturer. Do manufacturers such as Hornady keep bullets out of a single die together as a lot, or do they have banks of dies to make the “same” bullet, all falling into a common area and boxed accordingly?

 

[AlNyhus]

Just because the BBTO (bullet base to ogive) varies, that doesn't always mean the CBTO (cartridge base to ogive) will vary. Even with a production line bullet, the only difference may be how much of the bullet is in the case neck.

Pick two bullets with significant BBTO dimensions. Then seat both bullets and check the CBTO dimension of both.

Good shootin' -Al