Ladder Test failed--- what happened?

[audredger]

The gun is a Remington 700 Tactical XCR in 308 win. I'm trying to find that "perfect" load so I can win a bird or two at our local turkey shoots. Might like to try F-TR also.

Did two ladder tests at 200 yard; Using new Lapua Brass, CCI BR-2 primers & Lapua D-46 185 gr FMJBT slug set at magazine length of 2.82"
First test was with AR-Comp powder. 4 fowler's at 37.5 grains then 16 loads starting at 37.5 grains to 40.5 grains in .2 grain steps. Results were anything but a ladder! I got a shotgun pattern where all shot fit within 3 1/4" circle? no apparent rime or reason to the pattern. MV from 2284 to 2521.

Cleaned the bore well and went on to the Second test using Varget. 4 fowler's using 41 gr. then 16 shots starting at 41gr. to 44 gr. in .2 gr steps. Similar results! No ladder! A shotgun pattern but 4 1/2" this time. MV from 2422 to 2614

Just to know that things hadn't gone totally south, I shot a different load that had shown some promice and shot a 1.74" 5 shot then a .97" group both @ 200 yd. Load was 42 & 42.5 varget with 175 Berger vld's set to jump .002". ( Way over mag length 2.986")

You guys have any clues for me other than perhaps the D-46 does not like to jump?

 

[BoydAllen]

What you have found out is that you probably need to spend some time evaluating various amounts of bullet jump. Assuming that the combination of throat length and magazine length mean that you can't touch the rifling with rounds that fit in the magazine. Now, if you think that reasonable, let me make a couple of suggestions. Put some things out between you and the target so that you can see what the wind is doing. Shoot each test on a separate aiming point, at 100 yards, on a day when the wind is light and steady. Do your initial testing with two shot groups. After you have an idea about what seems to look promising, you can always go to more shots per group. If it looks ugly after two, what's the point is more shots? What short of bench and rest setup are you using? What is the pull weight of your trigger? Have you checked your rifle's bedding, and action screw tightness? What scope do you have?

 

[queen_stick]

there are a number of things going on here...

1) ladder tests work best when shot at long range (300+ yards). I have a hard time with the ladder tests at 300 yards... 600 yards would work better, and 1K yards would be ideal.

2) Before you try the ladder test, find what your bullet likes (jumped or jammed). Find a basic load that produces the smallest group consistently, then do the ladder test based on the most accurate node you found. The D-46's are great bullets, but maybe your barrel doesn't like them. Play with bullet seating!

3) shoot at different targets. Use load #1 to shoot at target #1, load #2 for target #2, and etc... alternate the shots through the string, so the same variables effect each group (in theory). For example, you're using 3 different loads for the ladder test.... shot #1 is the first load shot at target #1, shot #2 is the second load shot at target #2, shot #3 is the third load shot at target #3, the fourth shot is the first load shot at target #1 again, and the cycle continues. Some prefer that method, as each load is on its own target, and variables like barrel heat and fouling are distributed amongst all three loads.

4) try a ladder test where bullet seating is the only variable, instead of changing powder charges. It might mean more than changing powder charge weight. A word of caution though... if you're jumping your bullets with a hot load, then do not use that same hot load with jammed bullets - pressure will increase when jammed, and might go above safe limits if your not careful.

Ladder tests can create an 'information overload,' which is frustrating, because when you're done with the test, you have no idea what to take from it. I think in your case, simply redoing the same ladder test, but shooting at different targets with each load, will produce much more informative results.

EDIT:

Boyd responded while I was typing my post. Boyd and I agree that bullet seating depth should be top on your list of things to try. Boyd also pointed out the use of wind flags, and I couldn't agree more, even if it's an old arrow with a piece of plastic bag tied to the end of it!

 

[audredger]

Thank you both for your responce...
At the 200 yd range the bench is a very solid concrete & steel bench with a plywood cover; at my 100 yd range the bench is an old wire spool, solid but not as solid as at the 200 yd range.
Pull weight is lite... no trigger scale but lighter than my 2 1/2 lb bullseye pistol.
Stock has an aluminum bedding block & screws are good & snug. Guess I need to break out the torque wrench!
Scope is a Vortex 6.5-20 Mill dot.
Front rest is a Caldwell adjustable rest, rear is a sand bag.

I don't believe that the bedding , scope or rests are the issue. But I could be wrong.
As I said after the ladder test I shot a sub inch 200yd group with another test load.

Your point on the jump must be the answer... I thought the D-46 would be tolerant of jump... perhaps not!

Long ranges are a problem here... I have 100 at the house, 200 in town 35 miles away. anything longer is 100+ miles away & 1000 is 400 miles away. May have to shoot from mountain top to mountain top.

 

[joejo]

shooting a ladder test is a waste of ammo at 200 yds. like others have said 600+ is where you will find they work out.
i get a good bit of overlap at 450 yards. also with a .2 grn increment overlap is even more prevelant.

are there any pipelines around you? those make great place to shoot long range. thats what i use anyway.

 

[XTR]

After working up loads for 3 different bullets in two different barrels on my F-TR gun I'm a believer in the OCW over ladders.

I do my OCW workups at 200 yards and if you do it right you will be able to tell where the node falls, after that you can dial in the seatig for group size.

 

[Keith Glasscock]

I've never had any luck with ladders even at 300 yards with my 308. While I can find adjacent loads that have the same impact point, those do not mean that the most accurate load is there.

I've gone to 3 shot group "ladders". I am looking for 2 (perferably 3) groups that look pretty good and have the same point of impact. With that information, I can better predict where I am going to have some luck finding a good node (not all nodes are equal).

What I have found with 200 yard ladders is a 1/2" group for 5 shots in .1 grain intervals - (yes it was at the node by luck not design). With larger intervals and more shots (2.2 grain spread) at 300 yards, I get 2-3" groups that are as wide as high. I can't explain why, but I know that my rifle likes to shoot right at the top of the pressure. It is darn hard to get a ladder to work when the last 2 shots (1 of which is hotter than you are willing to shoot repeatedly) are where you need to be.

I have developed loads for quite a few bullets in 308 now. I haven't played with the D46. The Berger LRBT likes the top of the load spectrum with Varget. Likewise, it seems to like a significantly more mild load with H4895 (try 2600 fps or so in a 26" barrel - shorter barrels will be slower).

Since you have a home range, I would do most of my development at 100 yards. If it'll shoot consistently there, It will do fine at even 400. Past that, velocity variation comes into play. If you want to shoot 600 to 1000 yards, you need to either become quite good at chronographing loads, or shoot those ranges for testing. I just had what looked like a great load blow up when I went to 20 shot string fire at 600. I found that the load got the barrel too hot at 15 shots (1 minute intervals) and started shooting all over the place ( I had 9's every direction possible). That one is down the tubes, and my old standby came out tonight to make certain that the barrel is OK. With a good group at 300, I'm certain that the rifle is fine.

Every time I go shoot I learn something. Tonight I learned a little bit about my setup, and some problems I've been fighting in prone. Funny thing is, the problem was actually 3 problems creating the same symptoms. I had ruled each one out as the symptom didn't go away when I addressed each one. Needless to say, I've found that shooting is very dynamic, and I've got more to learn.

Good luck with your development,
Keith

 

[BoydAllen]

One little piece of anecdotal information that I have run across in my own unscientific testing is that when I added weight to the muzzle the amount of powder required to hit a given node decreased. Testing this does not take any fancy equipment, just some sort of compact weight and a way to secure it to the muzzle that does not allow movement. I am not talking about a tuner, just some weight, accompanied by normal load work up. If you find that your best accuracy happens at a velocity that is paired with too much pressure, adding weight to the muzzle will slow the barrels swing, allowing a bullet at a slightly lower velocity ( and pressure) to exit at the same point in the cycle as the higher velocity without the weight.

 

[Keith Glasscock]

Boyd,

That's brilliant! I've been wondering why my heavier profile barrel seemed to like a slightly lighter charge. It is about .2 grains lower than the lighter profile one. It is the first 308 barrel that I've had any head room with at the node.

If true, it would be one more reason to convert to all heavier profile barrels on my F-TR rifle.

 

[BoydAllen]

You want to lower the frequency, not raise it. At a given length, a thicker barrel will vibrate faster than a thinner one. You would be going the wrong way. Fellows are often influence too much by the desire for rifles to look good, and not appear different than anything that they commonly see. This is why more shooters do not use mirage shields on the barrels of their varmint rifles, that are shot enough to warm up their barrels. They buy good scopes, only to lose their optical performance to barrel mirage, that could easily be prevented by a inexpensive, or free, barrel mounted mirage shield. On the weight, put a strip of electrical tape on bottom of the barrel, running back from the muzzle about 3" , and then tape a piece of 1/2" diameter steel rod, cut about 2 1/2" long to the bottom of the barrel, flush with the muzzle, with 2-3 tight (fully stretched) wraps of the same tape. Then retune your load. It should take a little less powder to get to the same node.

 

[dannyjbiggs]

Be different, at 200 yards, try a "horizontal" ladder, using an offset aimpoint (so you don't shoot your aimpoint away!), clicking 1-2 minutes of angle between each shot group. Don't play the wind/mirage by holding off for it; rather, time your shots around them, and hold hard on the aimpoint with each shot. Later, when you look at the shot groups, you can easily make excuse for those wide shots from wind/mirage...after all, you are MOST interested in how ELEVATION is held! (If conditions are just too bad, you need to pick another day...you should have only come out on a still morning anyway for group-size testing!) If you don't have QL, use an "exploratory process" with a wide base, starting with a very low powder charge and shooting 3-round shot groups at .5 grain intervals, over a 2 to 3 grain span, even wider, depending on what you know. Talk to Sierra for safe loads associated with their similiar weight bullets, and EXPLORE if you are using another brand. (If you are using Sierras, FINE TUNE, see next sentence.) If you have QL, or have a pretty good idea of a safe(?) load, use a "fine tune process" with a more narrow base; say, starting at least a full grain below the load you heard from a trusted friend (and researched a little further), and shoot 3-round shot groups at .2 grain intervals, over a 1 to 1 1/2 grain spread. Then, pick your 2 best shot groups (hopefully next to each other!!), come back and shoot 3 each 5-round shot groups, minimum; 10 rounds best...one on each and one in the middle. This evolves to a confirmation group using at least 10 rounds...sometimes 20...down on the ground. That generally works for me. As an aside, on a wide base "exploratory process", you may notice shot groups opening up, coming together, and opening up again over the regime...those coming together reflect the "accuracy nodes" reloaders talk about.

Since you are using a .308, suggesting a vent for F-TR, and have not mentioned using my favorite powder (and I'm just not shooting much competitive F-TR anymore), you might cut-to-the-chase and try 48.00 grains of H4350 with a Berger 185 grain Boat Tail. Don't worry, it's safe...the ultra conservative Sierra loading manual indicates so: 48.2 grains IMR 4350 w/190 grain SMK, 47.9 grains IMR 4350 with 200 grain SMK...little pressure difference--lotta accuracy difference--between IMR and Hodgden...provided that you have a weapon in great condition. (Back in the 1990's, my NRA HP load for the 600 yard line using a Model 70 SA outfitted for Match Rifle was 48.00 grains of IMR/H4350 using a 200 grain SMK.) I entered this paragraph by providing you my F-TR load, bullet soft-seated into the lans, out of the Remington BR case primarily and the Win case secondarily, which has fared me well. After a little experience with this load, you might want to try "horizontal ladder shot grouping" with the other Berger 185 grain family, on up to 200, 210, etc (to keep up with the Jones)...mind you, FINE TUNING with the 48.0 grain load up thru the 210 grain bullet (maybe start 2 grains lower with this bullet and stick to non-high temperature days)...do your research for anything higher!! You will need to THROAT OUT 0.130 inch for the Berger 185's, and more as you increase bullet length with the heavier bullets. Use the most sturdy bench you have, and use as a minimum the 200 yard line, my personable preferrable distance. A single-shot action and at least a 30-inch barrel (Bartlien or Krieger) will serve you best...don't be afraid of putting powder burns on the target with even a longer barrel. It's possible to make F-TR weight with a 32-inch heavy palma contour barrel. And, if you can't achieve at least...at least...a 1/2 MOA 10-shot group with the recommended load...first, FINE TUNE it; if still not after that, better check ALL of your equipment closely and your loading techniques; otherwise, without a 1/2-minute gun, or prayerfully less, you can only expect to be an observer at the award ceremonies.

Danny Biggs

 

[dannyjbiggs]

Michael...as I read my above piece after posting, I see that while I was in the "preview" mode, I deleted considerable text to rearrange, and I carelessly did not get back in the integration of the "exploratory process" with the "fine tune process", here goes:

I EXPLOR to find the pressure point; thereafter, I back off a grain and 1/2 and commence the FINE TUNE process. Sorry for any confusion.

Danny Biggs

 

[audredger]

Thank you all... this has all has been very helpfull and I am trying to absorb.

Thank you Danny for the load info.

Boyd.."You want to lower the frequency, not raise it. At a given length, a thicker barrel will vibrate faster than a thinner one." Would a barrel with a higher frequency not have a lower amplitude and more node's?

 

[BoydAllen]

The higher the frequency the narrower the nodes, an the harder they are to stay within. You are trying to have bullets exit on a particular part of the barrel's swing, and the spread of velocities within a group is such that as the frequency increases this "target" portion of the swing plot becomes smaller and harder to stay within. If you want to do a lot of interesting reading and see some great work on the subject, you should Google Varmint Al and look at the sections pertaining to tuners, and how they work. When a barrel swings too rapidly for the velocity of the bullets, they cannot exit the muzzle in the most advantageous part of the barrels swing, and when they do not, the effects of variations in velocity are exaggerated in terms of the vertical within the group.
Boyd

 

[nosualc]

Boyd, et. al,

So if a thicker barrel equates to higher frequencies and narrower nodes, one would conclude that thicker barrels are harder to tune, and that thinner barrel is easier to tune? This seems counter intuitive.

Intuition would suggest that amplitude would be an equally if not more important factor?

What am I missing?

-nosualc

 

[BoydAllen]

Thicker and thinner are relative terms. You may also go back to where I mentioned adding weight to the end of your barrel. I did this on a rather short stout short range benchrest barrel, and it did what I thought it might. Also, intuition is not a reliable standard. There has been some engineering and testing on this. Did you go to Varmint Al's web site and do the reading that I suggested? His screen name is not an indication of his sophistication, and background. He is very smart, and has done a lot both with computer simulation and testing that is wholly original, and which has been very important to my developing a better understanding of what is taking place as a rifle is fired. From time to time I share something that I have tested, and know works, and get a response from someone who has not, along the lines of "well I think...". Thinking and imagining are only the first step. Reading to find out what others have done, designing experiments to verify theories, and actual testing, in an organized manner, are farther along the line. There is a whole world of shooters out there that simply want to ignore many important variables in their pursuit of accuracy, and that is there perfect right, but it can limit their outcomes. Good luck with your rifle. I wish you every success.
Boyd