What makes a bullet shoot BAD!

[RonAKA]

I've been testing 4 different bullets in my new Savage LRPV 6BR (1 in 12 twist). Overall I have been very impressed with the accuracy of this factory gun. Best accuracy so far has been with a Berger Match Target 68 grain with three 3 shot groups averaging under 0.2" at 100 meters. Virtually all bullet/powder combinations have averaged under 0.5".

However, one is a real problem child. The Berger Match Target 62 grain has shot groups that average 10 times the size of the Berger 68 grain Match Targets - close to 2". The spread is mostly horizontal.

I see lots of things to do that make a load accurate, but asking it the other way around what makes it bad? I really don't think it is the gun, or even the shooter as we are common to all the other good groups. About all I know that is different about it is that I am short of neck to seat the thing to a jam and am putting it less than 0.050" into the neck. However, I am doing that with a High BC 69 grain as well, and more or less getting away with it. It however is the second poorest bullet, but still averages just under 0.5" for groups.

I will try some loads with a 0.020" jump and see what happens, but if that does not work, I guess they will be just used up as fouling shots...

Your thoughts?

 

[bozo699]

RonAka,
For what its worth, and that isn't much, That is my usuall findings with berger bullets.I am not saying bergers are bad bullets,heck there are lots of guy's winning with them. It's just to get bergers to shoot for me I have to really fool around,burn half my barrel life up getting them to shoot. With SMKs I size a case slop some powder into the hull slam it through the seating die and the darn things shoot
Wayne.

P.S I never learn though, I just got my 7mmk-08 hunting rifle shooting real good yesterday with nosler accubonds, couldn't stand it stopped by today on my way to work and picked up a box of 168 gr berger's ???

 

[RonAKA]

I probably did not make it clear in my OP, but all four of the bullets tested so far are Berger, so that is a common element as well, along with the gun and the shooter. The 62 and 68 are both Berger's Match Target standard profile bullets (no low drag or high BC).

I never considered actual issues with the bullet. I don't have much for measuring tools beside a 1/10 thou micrometer and scale to 0.5 grains accuracy. Should I be checking the bullets? I suppose that the lighter the bullet the shorter the bearing surface and errors could become more significant. However, it seems to be something much more serious than that...

 

[Steve Blair]

RonAka,
For what its worth, and that isn't much, That is my usuall findings with berger bullets.I am not saying bergers are bad bullets,heck there are lots of guy's winning with them. It's just to get bergers to shoot for me I have to really fool around,burn half my barrel life up getting them to shoot. With SMKs I size a case slop some powder into the hull slam it through the seating die and the darn things shoot
Wayne.

Wayne,

It is generally true that Berger VLD bullets require a bit more fiddling than other types but shoot well once tuned. Berger also makes several other bullet profiles that are as easy as Sierras to tune. Attached is an image of three 7mm Bergers that I shoot in my .284. The VLD and XLD are fairly touchy but the Hybrid shoots very well with a jump from .02-.04. The second image shows that I do like Bergers but also shoot Sierra and other manufacturers. In my 6BRs, I shoot nothing but Sierra 107 MK.

As far as the 62 MT Bergers: The throat diameter in factory barrels can be a problem for very short bullets. If it is too large, the bullet can "ballot" or tip as it leaves the case and enter the rifling poorly. A very tight throat can prevent this from happening but is rarely seen in factory barrels.

 

[whiskey08]

i kinda subcribe to the fact that once you do your preparation, then where youre bullet ogive is seated in relation to the lands is the single most important factor in accuracy. So two different bullets, two different ogives, two different group sizes.


I ve tried laupuas, and bergers and agree that you'll use half your barrel life trying to find the sweet spot. Sierras are simple 2 -5 thousandths off the lands and bingo

 

[bozo699]

Steve,
I did try to state I know bergers are good bullets I just have had trouble tuning them, so no offence to people that like there bergers You did make a point though Steve, I wonder if the mouths are not square or the chanfering is uneven.
I recently read a post on 6br on somthing about that. I will do some resurch.
Wayne

 

[bozo699]

RonAKA,
Ron I know you are only shooting 100meters and this pertains to 1000 yards but I found this post I was reading earlier. I don't know if I am allowed to copy other post from other threads or not. If not pardon me I won't do it again.

George:

You clearly stated your friends' problems. A 20 ES is not good at 1000 yards and will take you out of where you want to be on the 1000 yd BR target, the 1000 F-Class target, and even the 1000 NRA prone target.

The very first key in getting your ES down in the single digit area (especially the low single digits) is accuracy in your power charge. I can't express this enough. I use a Charge master to dispense the desired charge (which is almost always a little low) then I take the pan from the Charge Master and pour the charge in the the pan sitting on my Acculab digital scale which measures to .02 grains (or so they say). At any rate, I try to charge my cases exactly correct, down to one kernnel of powder, as best I can.

After you have the fundamental element of an exact powder charge taken care of, you need to make sure your ignition is very consistent. As an aside, all Lapua brass is not made the same! I have had 6BR brass where the flash hole was so uniform that I did not want to touch it. However, most of the time, I uniform the flash hole. I do not uniform the primer pockets until after the first fireing. The most uniform ignition will come with mild primers like the Wolf/Russian -- the term Magnum with those primers is more a reference to a thick cup which helps you find higher nodes without primer problems.

Part of the low ES formula is uniform bullet pull, also called bullet release. You CANNOT get that with necks that are not uniform, and the best way to get neck uniformity is to neck turn.

Pay attention to your neck chamfer. This is the last place the bullet lives before entering the barrel. You want it to enter exactly the same without any deviation in how the bullet marries up with the groves and lands. Perfect chamfers are what you are looking for. Treat your neck chamfers with the same respect and protection you give your crowns.

Bullets that are uniform base to ogive helps keep the prerssures the same as the bullet engages the lands -- even when you shoot off the lands. That is part of the low ES package. There are many more items in prep that can enhance your low ES package, but these are just a few.

Does all this matter? As I write, I am looking at a perserved letter written to me on December 16, 2002. It says "Dear Jim, In my over 60 years in the bench rest game, I have found the following to be true. Accuracy is the result of a multitude of tremendous trifles. Sincerely, Ferris Pindell." Nuff said.

I hope this helps a little,
Jim Hardy

 

[Steve Blair]

Wayne,

Your post was clear on that point. I was trying to state that Berger makes several bullet types, some of which are easier than others to tune. The 30 cal 210 Grain Match Target BT Long Range that I shoot in .308 is a very easy bullet to develop if you have the twist for it.

 

[bozo699]

I gotcha, thanks. And yes the 210 must be easy to tune I was using them in a .300wm with a short throat and I was having to seat them way past the neck/shoulder junction and they shot awesome You will find I am very opinionated but I am not a ford,dodge,chevy man I like what ever works! If I do it one way and you can show me a better way or logically show me I was incorrect,well..... I am always striving to do better so I am allways open to suguestion and possible change That is why I like this site so much, great people and no four letter words flying everytime you ask a question someone deams stupid!! Like some of the other forums do, you know the one's I am talking about. Thanks again Steve.
Wayne.

 

[RonAKA]

I'm using the same lot of Lapua brass for each load. It is weight sorted. All cases got a light chamfer on the ID. Essentially case preparation was identical for the best (68 grain) and worst (62 grain). I've shot the same powder in each (Varget) from the same container, and the same primers from the same box (BR-4). Standard deviation for velocity of the worst groups was 11. Standard Deviation for the best groups was 22.

The cases are within 1/2 thou of each other for length, at about 1.556. I will do some bullet measuring today to see if I can detect a difference in tolerance. I believe both the best and the worst bullets have the same ogive profile.

 

[MarkS]

RonAKA,

Vertical spread is normally a seating thing. Not being able the jam into lands or come close, may be your problem with the the smaller bullets. Do you know how far you are from the lands with the 68 gr. ? One bullet you need to try, is the 80 Gr. Berger, they will give more room in seating depth, and they shoot great in a 12 tw. see shttp://www.6mmbr.com/Schronce600.html
Berger's are my standard for accuracy. If the 68gr shoot the 80gr. should work to.

Mark Schronce

 

[RonAKA]

Vertical spread is normally a seating thing. Not being able the jam into lands or come close, may be your problem with the the smaller bullets. Do you know how far you are from the lands with the 68 gr. ? One bullet you need to try, is the 80 Gr. Berger, they will give more room in seating depth, and they shoot great in a 12 tw. see shttp://www.6mmbr.com/Schronce600.html
Berger's are my standard for accuracy. If the 68gr shoot the 80gr. should work to.

Both the 62 and 68 grain bullets were jammed 0.010". I have tried the 80 grain Berger as well. It has given the second best groups after the 68 grain. Around 0.3-.4" at 100 meters.

I measured 10 of each of the 62 and 68 grain bullets today. Results:

Variable Measured - 62 Grain - 68 Grain

Avg Press ring Dia. - 0.24325 - 0.24316
Standard Dev - 0.00005270 - 0.00005164

Avg Body Dia. - 0.24283 - 0.24269
Standard Dev - 0.00009487 - 0.00003162

Avg Weight - 61.995 - 67.965
Standard Dev - 0.02838 - 0.02415

Overall, the 68 grain seems a little smaller in both the pressure ring and body. Other than that I don't seem much difference in them for size variation. Perhaps a bit more consistency in the 68 grain body diameter.

I'm still puzzled...

 

[jo191145]

Typically

The less bearing length in the case and jumping usually requires more powder to settle em down.
Might not be able to get enough Varget in the case to achieve that.
You may have reached the point where Varget (slow burn rate) is just not gonna work with that light of a pill.
I've seen quite a few Sav factory tubes shoot very nicely at normal velocities. Reach a certain higher velocity and copper accumulates FAST.

Benchmark or X-Terminator have given me best results in a 6BR with light pills.

 

[RonAKA]

Typically The less bearing length in the case and jumping usually requires more powder to settle em down.
Might not be able to get enough Varget in the case to achieve that.
You may have reached the point where Varget (slow burn rate) is just not gonna work with that light of a pill.
I've seen quite a few Sav factory tubes shoot very nicely at normal velocities. Reach a certain higher velocity and copper accumulates FAST.
Benchmark or X-Terminator have given me best results in a 6BR with light pills.

Have not tried Benchmark or X-Terminator yet, but I have used both Varget and H322 with the 62 grain. I got about 3460 fps with H322 and a 1.8" average group size. With Varget I got 3255 and an average group size of 1.4". I was trying to hit 3400 with them both but did a bit of a mis calculation, especially on the Varget. However especially for the H322 the 3460 should have been good. The 68 grain at essentially the same velocity was under 0.3".

The case seems to hold about 35 grains of Varget right to the start of the neck. Have not run out of room yet, but some of the ladder test loads were slightly compressed.

While I got some copper in the first 15 rounds I don't see much indication now after 200 rounds through the gun. When the carbon and powder residue come clean in 2-3 patches there is no hint of blue.

 

[clowdis]

Just a thought, but have you checked the diameter of the of the bullets that won't shoot and compared them to the ones that will shoot? I have been surprised by what I've found there.

 

[RonAKA]

Just a thought, but have you checked the diameter of the of the bullets that won't shoot and compared them to the ones that will shoot? I have been surprised by what I've found there.

Yes, check a few posts up to see the numbers. Your comments on the differences? I wasn't sure they were significant.

 

[clowdis]

Sorry Ron, went to sleep there! I don't think there is enough difference to matter in your case. I have seen .3075 bullets not shoot well in a well used .308 barrel while .3080 bullets shot very well. I had no way of measuring the barrel to get an accurate reading on the groove diameter of it, so I don't know what the actual clearance was.

 

[GerryM]

It could be over stabilization, with the 12 twist.
The rate is 1.825 with the 12 twist,
With the 68 gr it more like 1.485 or close to.
Spin rate has a lot to do with accuaracy,
Maybe you should try some 80 gr pills.

 

[RonAKA]

It could be over stabilization, with the 12 twist.
The rate is 1.825 with the 12 twist,
With the 68 gr it more like 1.485 or close to.
Spin rate has a lot to do with accuaracy,
Maybe you should try some 80 gr pills.

Good point, and I never considered that. I ran the spreadsheet calculation I got from Don Miller. It generated the following for the 62 grain (0.768" long) bad actor, and the 68 grain (0.841") and star performer to date. Both velocities were 3400. I have shot the 80 grain Berger as well. It is second to the 68 grain for group size at about 3100 fps. It measures 0.919"

62 grain - 1.63
68 grain - 1.38
80 grain - 1.23

The 68 grain according to the Miller Rule is just stable. The 80 grain is questionable, but Berger says it is OK for 12 twist. Miller says if the stability factor is over 2.0 you may lose accuracy. Considering the group size for the 62 grain is almost 10 times that of the 68, I'm not sure excess spin can account for that much of a difference?

 

[jo191145]

I've shot 55gn Noslers out of an 8 twist. With an arbitrary powder charge and good amount of jump they were well under 1 moa at 200yds. Just sayin.

Theres no doubt excessive twist can create problems tho. IMO thats not a concern with a 12 twist.