7-08 / Big Game

[Brian in Montana]

I cooked off a ladder test yesterday using Big Game and 139gn Hornady Interbonds. Flat spots were not super flat, but looks like there could be a couple of promising loads in the data. I started at 45.3gns and worked my way up in .2 increments to 47.5. MV was pretty impressive. Maxed at 2936 fps, but most charges were near or above 2900 fps. Its just a matter of seeing what will group.

I did some thing a little different on this project in terms of seating depth. Usually I just look at the manual and use the recommended COL, but on this one I seated the bullets as long as they would fit in the magazine - this gave me a COL of 2.83 whereas the Hornady manual recommends 2.755. I'm going to follow this project to completion, but I was wanting to ask: of you guys that have loaded Interbonds before, does this bullet tend to like being closer to the lands or does it prefer a little jump. Accubonds seem to like a little jump in this rifle I've noticed, but there are some significant differences between ABs and Interbonds.

???

 

[std7mag]

The higher BC will help you out downrange.
Less wind drift, little higher velocity & energy retention.
If you get a 140gr with BC in the 0.489 range at a little over 2,800 fps, i've found BDC scopes line up nicely too.

 

[blueridge]

I started testing this combo today (BG & 140g Etip) and had some very confusing results. Could not get consistent or predictable velocities (i.e. 100 fps variance for the same powder weight, and same velocity for powder charges 3g difference.)

The only thing I can think is incomplete burn. Is that what is sounds like to you all? Are you all putting a crimp on etips?

 

[std7mag]

Some will disagree with me, but...
Mono's usually like a jump to the lands. Barnes, Hornady, Nosler recommend 0.050" off the lands.
Crimp does seem to help.
I think the theory is it allows some pressure to build up before the bullet starts moving, helping it's running start to the lands.

 

[N2TRKYS]

Some will disagree with me, but...
Mono's usually like a jump to the lands. Barnes, Hornady, Nosler recommend 0.050" off the lands.
Crimp does seem to help.
I think the theory is it allows some pressure to build up before the bullet starts moving, helping it's running start to the lands.

Everybody I know that shoots Barnes says that they like a jump, but none of them crimp. Heck, all my Partitions and Accubonds jump. I never chase the lands.

 

[blueridge]

How do you explain this craziness, and where would you start? You’ll see why I asked about crimping. Only thing I can think of is the powder is still burning and the bullet is gone.

5 each at 43.5g, 45.5g, and 47g. Shot 3 shots of each weight, then final 2. Chrono’d velocities:
43.5g: 2487, 2506, 2424, 2760, ER
45.5g: 2645, 2624, 2682, 2777, 2677
47g: 2506, 2604, 2732, 2760, 2666

Other details:
Tikka T3 7-08
Once fired (in my rifle) Rem brass
Federal 210 primers
140g etip
Case trimmed to 2.035
OACL 2.77
Confirmed powder weight with second scale. POI’s consistent with chrono velocities.

What would you try first: crimp, different brass, other?

 

[std7mag]

I gotta ask....
How far away is your chrono?
Is there fresh batteries in it?

 

[blueridge]

ProChrono, fresh batteries, 1’ from barrel end. 4:30-5pm with sun at 10 o’clock to the target. Sun glare was noticeable in scope. Shooting lane is cut through the woods. Good thought. Maybe it was the light throwing it off? Maybe I’m not crazy. (3:05am, can’t sleep from thinking about it. No, I’m crazy.)

 

[std7mag]

The instructions for the Pro Chrono say 10-15 ft from end of barrel.
There is your problem.

Page 6....

 

[sbhooper]

ProChrono, fresh batteries, 1’ from barrel end. 4:30-5pm with sun at 10 o’clock to the target. Sun glare was noticeable in scope. Shooting lane is cut through the woods. Good thought. Maybe it was the light throwing it off? Maybe I’m not crazy. (3:05am, can’t sleep from thinking about it. No, I’m crazy.)

The chrono should be at least nine feet, unless you are using the magneto speed.

 

[MThuntr]

I think I agree with the others. Your chrono may be getting messed up with the muzzle blast. You may not be getting a complete burn although I could be talking out of hindend with that one.

I have that new StaBall 6.5 that looks promising on this one. I'll test when the weather decides it's done being winter, spring, & hurricane in the same day

 

[ImBillT]

Ladder tests are only meaningful shot to shot. The final group is largely meaningless. Your groups is over 1 MOA tall(even ignoring a couple fliers). If it was totally random, then your gun is grouping 1MOA, and not only was your ladder test fairly meaningless, but any future ones probably will be also. On the other hand, if it would print 3-5 shots with the same elevation within .3-.5 inches, and then 2-3 shots would impact noticeable high or low, and then 3-5 shots would go right back where the previous 3-5 shots did, then you learned something. As your barrel vibrates, if the muzzle is low and moving upward as the bullet leaves, then it will compensate for velocity dispersion. Bullets leaving early due to higher velocity will print in the same place as bullets leaving late due to low velocity, because the ones experiencing less drop, left the barrel while it was pointing lower, and the ones experiencing more drop left the barrel while it was pointing higher. The effect is most dramatic around 100yds to 200yds, and often times, a 100yd accuracy node will not quite work out at 200yds. A 200yd accuracy node will almost always work out 100yds. At 200yds however, it takes a VERY accurate gun(sub .3MOA) to pick up the nodes easily do to all the other reasons for a bullet to hit somewhere else being compounded. I tend to perform a ladder test at 100yds to identify 1-3 nodes, and then just shoot some groups at 200yds to see if it holds up. When you remove your magnetospeed, the velocity window of your accuracy nodes will change. OCW is based on the idea that there is a range of powder charges that will produce consistent velocities. I’m not convinced that it’s reliable, and even if it is, it has nothing to do what velocity your accuracy nodes will land on. Beyond 200-300yds depending on velocity and BC, the window within which your accuracy nodes can compensate for velocity variation becomes very narrow, and the most important thing for reducing vertical dispersion is to reduce your velocity dispersion, but because we cannot reduce it to zero, it is still ideal to be on an accuracy node. Minimizing velocity dispersion in your load is useful at all ranges and on and off nodes. If OCW type testing helps you get a load that does that, the thaw a good thing. Still, in the end, the target tells the story. None of this really matters if your gun won’t shoot around .5MOA or better. Although I do try to squeeze what I can out if a hunting gun, it’s also not terribly important to get a hunting gun under 1MOA. It would certainly be nice to be under 1MOA once you get into the 500yd range, but out to 400yds I don’t know that 1MOA vs .5MOA is going to be meaningful very often.

The group you posted with your .308 showed clear vertical dispersion suggesting that you were about as far from an accuracy node as you could be. I would definitely try a different load in that gun, and possibly conduct a ladder test if you’re bored. A 50-100fps shift in muzzle velocity would probably clear up a lot of that vertical. It is possible that your vertical dispersion was gun handling, bedding, scope, bases etc. but I would adjust the load first it it was me.

 

[Tjay]

I agree with moving the chrono and I would add that trying a mag primer could help.

 

[std7mag]

One thing at a time people.... Lol

Try moving your chrono first.
My 7mm-08 out of a 22" barrel needed 15 ft.

 

[Firemedic92]

I found the same thing. Any load over 45 grains i got diminishing returns. I am shooting etips out of mine and saw the best groups with 44.5. At 45 it starts to open up and after that the velocity starts to go down. I am also using WLRM primers. Using Fed 210's didn't make any difference. In my Win Mod 70 super grade I am averaging 2730 15ft from the muzzle.

 

[FLS]

If you enjoy it it’s not a waste of time
OP If you’re shooting your ladder test at 100 yds it’s not a very useful ladder test. You’ll need to back up to 300 to get any meaningful results. IMO, You’re trying to do too many things at one time there. Shoot a velocity test to look for nodes, then test those nodes at 200 for accuracy. Then find tune your most accurate group with seating depth.
Consistent neck tension and good brass and prep is where you will get you’re low ES/ SD. An extruded powder will give usually better results as well.

 

[ImBillT]

100yds is probably the best distance to perform a ladder test.

.2gr increments is too small.

 

[FLS]

I don’t think we’re talking about the same thing. There will be almost no vertical dispersion at 100 yds.
This is a ladder test:

Long Range Load Development

Written by Sierra Bullets Product Development Manager Mark Walker Since I just put a new barrel on my F-class rifle this spring, I figured it might be a good time to discuss load tuning for long ra…

sierrabulletsblog.com

 

[ImBillT]

I don’t think we’re talking about the same thing. There will be almost no vertical dispersion at 100 yds.
This is a ladder test:

Long Range Load Development

Written by Sierra Bullets Product Development Manager Mark Walker Since I just put a new barrel on my F-class rifle this spring, I figured it might be a good time to discuss load tuning for long ra…

sierrabulletsblog.com

There’s all the dispersion needed from an accurate rifle at 100yds. A rifle that isn’t accurate enough to show you all you need to know from a ladder test at 100yds isn’t accurate enough to benefit from a ladder test.

A ladder test at 100yds may be 1” tall or less. If your gun won’t shoot 5-shot groups under .5” center to center almost every time, then a ladder test isn’t going to help you. It doesn’t turn a 2MOA gun into a .5MOA gun. I helps you sort between .1MOA-.2MOA loads and .7MOA-.8MOA loads very quickly. A .2MOA load through a .5MOA gun is going to give you .5MOA groups most of the time. Really bad loads are better than a lot of guns out there.

If you’ll look at Mr Walker’s target chrono data you’ll see that he has fairly inconsistent velocity increases with each powder charge increase. This is because even if all eight shots had been the exact same powder charge he’d likely have had 9-18fps between his high and low. That’s at .3gr. By using .4-.5gr increases in powder charge, you’ll still catch your nodes, but by making your gaps larger between shots, the velocity variation due to powder charge becomes larger compared to the velocity variation that you just can’t get out of a load. Too small of load increments muddies the waters. It takes an extremely accurate rifle to shoot small load intervals on a ladder test and not end up with a confusing mess. It also takes both an accurate rifle AND a very experienced long range shooter shooter from a competition quality rest or bipod to prevent other things from muddying the waters.

The ability of barrel vibrations to compensate for velocity variation is not linear, and the farther from the muzzle you get, the smaller the window of velocity variation you can get away with. Eventually velocity variation is almost all that matters, and getting a lid with a very low ES/SD has nothing to do with barrel vibrations(which is the only thing that “nodes” are related to). Low ES/SD is related to ignition quality. Different powders/charges/primers/seating depths can improve your ES/SD.

The last ladder test I shot is below. It was extremely windy...that doesn’t hurt a ladder test. There are two nodes. If a ladder test shows more than 1MOA I’d vertical, there is more than powder charge that needs to be tweaked.

 

[Brian in Montana]

Been a while since I have this thread much of a look. I just thought I'd follow up a little since it was a little over a year ago when I started it. I consider myself still relatively new to handloading, but I have learned a lot in the past few years and put together some darn ammo, if I do say so.

What I referred to is a "ladder test" is really more of a "flat spot" test using a Magnetospeed. Most of you guys seem to get that and k ow the process. I can say it was very new to me at the time. I've since experimented with the process a great deal and refined the way I do it. The flat spot test has its detractors and one complaint I've heard is that the "flat spot" in the velocity data doesn't necessarily mean that charge will be accurate. In my experience, that's true, but USUALLY it is accurate, or at least enough to tighten up groups with tweak or 2. I've found this to be a valuable and efficient step in load development - when I shoot a velocity flat spot test I come away with a good idea of what to work on next or it it seems the project is even worth pursuing. There are several in my notes (I keep meticulous notes) where I just looked at the velocity data I wrote down at the the range and for one reason or another, just decided it was a no-go.

On this load, the one I was on when I started this thread, it turned out to be one of my best. But I did largely the same process using Hndy Interbonds instead of Nosler Accubonds, and that one has basically become my standard. It consistently group about .8", averages 2920fps which is pretty screaming for a 7-08.