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Help Reading Nodes - 7mm Rem Mag

F

feetfats

Private
Full Member
Minuteman
Jul 12, 2013
16
0
#1
I could really use some help here with my load development. I've been chasing the white rabbit for months on end. I just get a good load, take it back to the range and it turns into a crap load. I've decided to try and work on finding 'nodes' instead of groups. I downloaded this target here on snipershide and ran some tests. Please tell me what you think. Also note that I don't know if I can trust this cheapo chronograph so take the fps with a grain of salt. The velocity is pretty high on some of these but I see no cause for concern on the brass.

Specs.

Tikka t3 lite 7mm rem mag
9.5" twist
24 3/8"

168 Berger VLD
Retumbo
.120" off lands, best I've found that fits mag
0.002" neck tension
Fed 215M

These groups were shot Round Robin style with cool down between each shot. Horizontal line next to hole means shot one, vertical line means shot two and no line means shot 3.

I think that 71.5 to 72.0 looks great but maybe I am being tricked by that sweet group.

OCW Retumbo003.jpg

I really appreciate any help. And I wonder if I should be concerned about these velocities and look for a node lower down?
 
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#2
Its too scattered for me to read anything into it.

Your group at 71.5 is good but both lower and higher suck. So if you get outside that "node" your in trouble.

I like to see a group with the same POI before and after the charge weight I choose.

The rifle can produce a good group, you proved that. I ask this respectfully, do you think its possible some of the poor groups were you ? Going back to the basics, shooting it another day might bring more fruitful results.

If you havent read this

OCW Overview - Dan Newberry's OCW Load Development System
 
#3
Node testing can be tricky. The real key is a stable setup. What sort of bags were you using and was it bench or prone, if bench was it concrete or wood?
As far as looking for the node after shooting. I've found the only unbiased way to do it is to plot all the holes on a grid in excel. I note the location from bullzeye in x and y coordinates for each hole, then measure group size, vertical group size, velocity, SD for velocity, and average group center location. That way I can find places where multiple different measurements give the same evidence of the node. Good luck!

--- aim small miss small ---
 
#4
Velocity will tell you more about an accuracy node than the group a charge produces. 70-71 appears to be a node the way velocity is flattened out between the three charges.

I would try a different bullet if it was me. Your groups are a classic example of what happens when Berger VLD's don't like the jump you're giving it. All of my experience has shown that the VLD's don't like much jump and you have a very long jump. Berger recommends starting in the lands and loading out .010 at a time out to .040 and see where your rule like them best and then commence loading. Kissing the lands or that close probably isn't going to happen in that rifle at mag length. Try the classic hunter if you want to stick with Berger, it is a hybrid and is much more tolerant of long jumps.
 
#5
redneckbmxer24 said:
Velocity will tell you more about an accuracy node than the group a charge produces. 70-71 appears to be a node the way velocity is flattened out between the three charges.

I would try a different bullet if it was me. Your groups are a classic example of what happens when Berger VLD's don't like the jump you're giving it. All of my experience has shown that the VLD's don't like much jump and you have a very long jump. Berger recommends starting in the lands and loading out .010 at a time out to .040 and see where your rule like them best and then commence loading. Kissing the lands or that close probably isn't going to happen in that rifle at mag length. Try the classic hunter if you want to stick with Berger, it is a hybrid and is much more tolerant of long jumps.
Click to expand...

What he said and I believe that you should be increasing your powder charge in .2 or .3 increments, not .5
 
#6
Rprecision said:
The rifle can produce a good group, you proved that. I ask this respectfully, do you think its possible some of the poor groups were you ? Going back to the basics, shooting it another day might bring more fruitful results.

System[/url]
Click to expand...

This is a fair question that I even ask myself from time to time. I am using a lead sled for development and I shoot a lot. I've put about 580 rnds through this particular rifle since august. I don't flinch very often and I know it when I do.
 
#8
redneckbmxer24 said:
I would try a different bullet if it was me. Your groups are a classic example of what happens when Berger VLD's don't like the jump you're giving it. All of my experience has shown that the VLD's don't like much jump and you have a very long jump. Berger recommends starting in the lands and loading out .010 at a time out to .040 and see where your rule like them best and then commence loading. Kissing the lands or that close probably isn't going to happen in that rifle at mag length. Try the classic hunter if you want to stick with Berger, it is a hybrid and is much more tolerant of long jumps.
Click to expand...

The only reason I am still fighting with these bullets is because a friend's Tikka T3 7mag is shooting these same bullets from the magazine with amazing results. But at the end of the day no two guns are alike. I suppose maybe I should finally put these VLD's to bed but I really want to be sure.
 
#9
feetfats said:
This is a fair question that I even ask myself from time to time. I am using a lead sled for development and I shoot a lot. I've put about 580 rnds through this particular rifle since august. I don't flinch very often and I know it when I do.
Click to expand...

That is interesting. Could be that you're actually between nodes. A velocity plot would be interesting to see. Then a retest. I've taken immense amount of data for about 7 different OCW tests now over the past few years for my 6mmAI. The most consistent effect that I see is the level off in velocity data as you go up in powder. That region seems to be where my smallest groups hover around, and the tightest SD. That being said when I've done the same test twice I don't necessarily get the same node, but its always close...

--- aim small miss small ---
 
#11
No1 said:
Ditch the lead sled. If you're worried you will flinch, then get 1 of these Reactar Pad G2,, Browning Outdoor Clothing Product
and a vest that will hold it.
Click to expand...

I'm not so concerned about flinching. I just find it very stable on the sled. I have a bipod but I need to get a bag or something for the rear. I find I just cant hold it as still on a bipod, which is fine for practice but I hate having human error in load developing.

You are not the first person to mention ditching the sled so maybe I should try it though.
 
#14
I really really don't trust this chrono.

I did a drop test with the 71.5 load. Bipod, bag and hand for rear.

101 yards 0.47" group
295 yards 3.20" group :( Pretty sure I flinched a little bit.

12.25 inches drop.

Temp 32F
28.6 inhg
No wind

This works out to 2736 fps, not 3100 the chrono reads??

WTF?
Something is wrong. Should be a lot faster at 71.5 shouldn't it?
 
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#15
feetfats said:
I really really don't trust this chrono.

I did a drop test with the 71.5 load. Bipod, bag and hand for rear.

101 yards 0.47" group
295 yards 3.20" group :( Pretty sure I flinched a little bit.

12.25 inches drop.

Temp 32F
28.6 inhg
No wind

This works out to 2736 fps, not 3100 the chrono reads??

WTF?
Something is wrong. Should be a lot faster at 71.5 shouldn't it?
Click to expand...

how did you measure the drop, did you hold same point of aim with no scope correction and measure the actual drop or are you basing it on the scope corrections? If you measured and your zero was correct then "believe the bullet" and check your inputs on the ballistics program you are using to calculate the velocity. If you are basing it on the scope corrections then do a box text and be 100% positive your optic is tracking (i don't care if it is a budget or a bender, check it).
 
#17
[MENTION=61632]Tiger[/MENTION]fan

Same point of aim. No turret correction.
I used a large piece of paper. Shot at 101, walked out and moved same paper to 295.

I also used two different calculators, and checked my numbers many times.

I guess 2700 it is
I will retest to be sure though.
Makes me wonder how much Retumbo I can possibly feed to this thing. Getting kinda crazy. I need to find another chrono. Christmas is coming.

[MENTION=59700]280nosler[/MENTION]
I use this much powder because I seem to have a slow barrel. Normal book charges are very very slow in this rifle. This is my 2nd 7mag and its a totally different animal than the last one. The last one I had would show pressure before book max. This one goes way over max and shows nothing. I stopped at 73.5 grains and still no issues.

So far during my testing of this gun I've found reading primers to be very unreliable. Low charges make very flat primers and the flatness decreases into the higher charges. Loads like 73.5 Retumbo show a tiny bit of crater. This gun makes top hat primers all day long on min or max doesn't matter so I've stopped looking at them so much.

My last 7mag made no flat primers but would crater at almost any charge (rem700) go figure.
The data out there varies wildly. Look at the hodgdon site and it will show a 170grain bullet with 75 grains retumbo for 2899 fps. Once again, go figure.
 
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#18
feetfats said:
Same point of aim. No turret correction.
I used a large piece of paper. Shot at 101, walked out and moved same paper to 295.

I also used two different calculators

I guess 2700 it is
Click to expand...

For the velocity calculators to back calculate you really need to shoot a lot farther than 300 yards. The longer the distance the more accurate they will be, try stretching it out and see what you get.
 
#19
"For the velocity calculators to back calculate you really need to shoot a lot farther than 300 yards. The longer the distance the more accurate they will be, try stretching it out and see what you get."

That's where it gets hard. Ranges past 300 are a PITA around here. Think dense forest and a lot of swamp.
I can believe error happening at 300 but I see it highly unlikely that I will find this to be a 3000fps load when I shoot it at long distance? Maybe I am wrong, could the error be that large?

I've been trying my damdest to find a load around 3000fps that is decent accurate and fits my magazine. I have put my name on 4 boxes of 168 classic hunters and I will pick them up next time I go out of town in a couple weeks. By then it will be cold as hell here so I will probably stop shooting until spring or the odd day that isn't too cold.
 
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#20
feetfats said:
"For the velocity calculators to back calculate you really need to shoot a lot farther than 300 yards. The longer the distance the more accurate they will be, try stretching it out and see what you get."

That's where it gets hard. Ranges past 300 are a PITA around here. Think dense forest and a lot of swamp.
I can believe error happening at 300 but I see it highly unlikely that I will find this to be a 3000fps load when I shoot it at long distance?
Click to expand...

I'd agree with that. While the 2736 might not give you a great dope at long range I would says it should be within 100 fps of what you got and not the 3000 fps you are hoping for. Maybe you could try H1000 (if you can find any).
 
#21
"I'd agree with that. While the 2736 might not give you a great dope at long range I would says it should be within 100 fps of what you got and not the 3000 fps you are hoping for. Maybe you could try H1000 (if you can find any)."

Respectfully, I don't think powder is my problem. This gun has burnt R-22, R25, IMR 7828, and Retumbo behind the 168 VLD's. All were slow. I've been looking at H-1000 because it's great in 7mag but so are the other 4 powders I've used.

61.0 R-22 dropped in at 2686fps (1000yd). (using clicks on my huskemaw blue diamond 5-20) I didn't have a barometer then so I can't compare it directly to this latest Retumbo load.

I think my gun shoots very very slow, is this even possible?
 
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#22
My brother had a 7mag that we reloaded for and never got anywhere near published velocities until we upped the powder quite a bit. He even had the barrel scoped to see how bad the throat erosion was (used gun). It was eroded bad and after a barrel replacement it shot more similar to published data. We figured a combination of having a chamber towards the larger end of "standard" plus throat erosion caused the "slow barrel" effect.


--- aim small miss small ---
 
#23
feetfats said:
"I'd agree with that. While the 2736 might not give you a great dope at long range I would says it should be within 100 fps of what you got and not the 3000 fps you are hoping for. Maybe you could try H1000 (if you can find any)."

Respectfully, I don't think powder is my problem. This gun has burnt R-22, R25, IMR 7828, and Retumbo behind the 168 VLD's. All were slow. I've been looking at H-1000 because it's great in 7mag but so are the other 4 powders I've used.

61.0 R-22 dropped in at 2686fps (1000yd). (using clicks on my huskemaw blue diamond 5-20) I didn't have a barometer then so I can't compare it directly to this latest Retumbo load.

I think my gun shoots very very slow, is this even possible?
Click to expand...

I'd keep uping the charge until you find pressure (0.5 grain increments or smaller). I've read the published maxes for the 7mm rem mag are pretty light (as with many of the older chamberings). Once you find pressure start backwards looking for an accurate load.
 
#24
"I'd keep uping the charge until you find pressure (0.5 grain increments or smaller). I've read the published maxes for the 7mm rem mag are pretty light (as with many of the older chamberings). Once you find pressure start backwards looking for an accurate load."

It makes me feel like a dangerous Fudd to do this but I am starting to think that max loads make a good start charge in this rifle. The real thing I've learned is no two rifles are the same and book values are to be safe for all rifles.

I'm pretty sure if I had put a load like this in my m700 7mag I would be in for some serious trouble.
 
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