1/4-1/2MOA but then very poor accuracy at 300

[jmd]

I'm shooting a 7mmWSM. I'm getting good grouping using RE19 and 120gr Vmax at 100 yards & 200 yards. It will shoot 1/4 to 1/2 MOA up to 200 yards. I finally got out to check it at 300 and found that I can't hit the broad side of a barn at this range. Most of it was vertical but it was huge. I understand that I should try bumping up and down on the powder charge to cure vertical stringing, but I do not understand how it could go from no more than 1/2 MOA at 200 yards to 4 MOA at 300. Maybe 4 MOA at 300 is even underestimating it. Has anyone come across this problem? Any possible thoughts on solutions? I don't want to cook this barrel just trying to get it shooting better at longer ranges.

 

[FURMAN]

What are your extreme velocity spreads?

 

[Nomad47]

Were you shooting the 200 yard groups at the same location? If so, what is between the 200 and 300 yard point?

 

[jmd]

I haven't shot it through a chronograph yet so I don't know the ES or SD which could be useful for ranges past 200. Shot at the same range with nothing special in between the 200 & 300 yard marks. What were you thinking of when you asked what was in between? Natural features that form wind tunnels? This whole thing is baffling me. I guess it is possible for a given load to shoot well at 200 with a large ES, but I wouldn't think accuracy would go south that quick

 

[wwbrown]

After the poor 300 yard results did you verify that the accuracy was still good at 100 and 200 yards? Maybe the barrel needs to be cleaned more often, did the ring or base screws loosen, same for action screws, etc.

My first step would be to verify that the accuracy is still good at 100 and/or 200 yards.

Good Luck,

 

[jmd]

Since I started at 300 that day I checked everything and then shot at 100 & 200. It shot fine at 1 & 200 but poor at 3

 

[AlNyhus]

For vertical stringing, the things to try (one at a time) are:
- Change powder charge by .5gr. Try going up first, then back it down if you run into pressure issues before fixing the vertical.
-Seating depth.
-Neck tension (very overlooked)

If none of these bring it around at 300, then you're going to have to look at another powder.

All of this asssumes you're using wind flags of some sort, right???......

Good shooting. -Al

 

[jmd]

Yes wind flags were used & there wasn't a cross wind. It was a slight tail wind and the stringing was vertical. I just didn't expect to see it open up so much. My only thought was to try your suggestion of bumping up & down on the charge to see if it settles. .The problem is that I've basically gone through the powder charge ladder study & a separate one using seating depth, but both of these were at 1 &200. Neck tension could very well be an issue. I honestly don't know how to test this other than to change the die I'm using. Any suggestions?

 

[BoydAllen]

You have not mentioned this, but I think that whatever you are planning in the way of tests, that you will get through it much more efficiently if you take a loading setup to the range, and do all of your testing over a chronograph, continuing with wind flags, spread throughout the entire distance. Let us know what you find on this. A friend has done a lot of hunting with your caliber with Sierra 175 MKs and H1000 at about 2,950, with excellent long range results. What kind of die are you using? What is the difference in diameters between the neck of a sized case, and the same case with a bullet in place? Are you weighing charges?

 

[jmd]

My initial dies were Lee which I had to opt for since nothing was available. I essentially used them for initial load development until I could get a set of Redding dies. I didn't see any change in accuracy between the two sets. I did measure neck diameter on a handful & didn't see any notable differences as it was less than .001" in most cases & I attributed variation to neck thickness . I did not measure any after seating bullets though. I'll give that a try since I do not have a way to check run out. All charges are weighed. I'm thinking about trying a load I had with 140gr TTSX. It shot around 1/2 MOA at 1 &200. Maybe it will settle in better than the 120Vmax at longer range. I guess in reality I should try to run a heavier bullet with a higher BC for longer range shooting anyways. I was more curious if anyone else has come across issues like this. I also slightly wonder if I'm just pushing those thin jacketed Vmax bullets too fast & tearing up the jacket, but if that was the case I wouldn't think it would shoot well at 1 &200.

 

[Turbulent Turtle]

It would have been interesting for you to go back to 300 after seeing that 200 and 100 was not showing a problem.

However, what you are relating sounds like a possible dynamic instability issue. This is when the bullet may be damaged and this induces a gyrating motion on the bullet that causes it to start deviating from its path. The thing is that at closer ranges this may not be apparent as it takes time (distance) to show up.

 

[jmd]

Bayou shooter,
I probably didn't explain it, but I did go back to 300. I initially started there for the day & then checked grouping at 1 & 2 to verify it was shooting well there. After that I did try at 300 again & I wasn't even on paper. Could you elaborate on the instability you speak of? I was concerned I was shooting a thin jacketed vmax at too high of a velocity, but I didn't think that was really a valid concern. I guess I've heard of over stabilizing a bullet, but I know it isn't common. I'm shooting a 1:9 fast twist barrel & the vmax were probably doing around 3300+fps. thoughts?

 

[bozo699]

jmd,
I mean this as no disrespect so don't take it for more then its intended purpose of helping you figure out your problem. I don't see you have a load issue or a rifle issue or a bullet choice issue. can you shoot past 200 yards? have you successfully shot at extended ranges before? what kind of bench, bag setup , and is your three hundred setup the same as the 100-200 yard setup? #! question is your scope properly adjusted? are you paralax free? was it cloudy, sunny, or was it a mixture of both? Boyd Allen is one of the smartest load developing guy's I know and I have learned a lot from him so listen to whatever he tells you, however when you go from 1/4 moa to 4moa in just a added 100 yards something much more then reading wind flags are involved unless you were shooting in extreme switchy winds and if you were then re think the whole thing! I am pretty sure you will find your problem in your scope, scope setup, or shooting ability in the conditions you had.
Wayne.

 

[Turbulent Turtle]

Bayou shooter,
I probably didn't explain it, but I did go back to 300. I initially started there for the day & then checked grouping at 1 & 2 to verify it was shooting well there. After that I did try at 300 again & I wasn't even on paper. Could you elaborate on the instability you speak of? I was concerned I was shooting a thin jacketed vmax at too high of a velocity, but I didn't think that was really a valid concern. I guess I've heard of over stabilizing a bullet, but I know it isn't common. I'm shooting a 1:9 fast twist barrel & the vmax were probably doing around 3300+fps. thoughts?

I'm assuming that all other issues have been eliminated. There are two kinds of bullet instability; static and dynamic. Static instability is simply that the bullet is not stabilized in flight and it tumbles. This occurs when a bullet is not spinning fast enough for the gyroscopic effect to counteract the overturning forces acting on the bullet by the resistance of the air and the bullet tumbles and keyholes are apparent on the target at short range. If the bullet is staticaly stable at 100 and 200 yards, it will most certainly be statically at 300 yards and further out. In fact the longer the bullet flies, the more stable it becomes, staticaly speaking.

The other kind of instability is the dynamic kind. This can occur with a danaged bullet or with a bullet that has an air buble in it or some other imperfection. You can picture this by looking at a football that is badly thrown of if you have ever seen a spinning top in action, just stick something on one side of it and see what happens. The bullets could be damaged in the barrel and when they exit the bore, they fly correctly at first and then as the instability builds up, they start drifting from their intended course. My concern is that now you say they do not even show up on paper at 300 yards when you went back to that distance. Are the bullets blowing up at this point because it's warmer? It's very difficult to troubleshoot something like that on an Internet board. I have seen bullets blow up in flight but that usually occurs inside of the first 100 yards; it looks like a little white puffy cylinder. 1:9 is not very fast and I just don't think it could, by itself, do that. But if the bullets are damaged, anything goes.

 

[Nomad47]

I think there is a very good chance Denys is on the right track. And I think the OP REALLY needs to chronograph the load. 120 VMax, 7mmWSM, 9 twist, stout load. . . . Hornady says their 105 AMax can fly apart at 3333 MV out of a 8 twist. I don't know about the 120 VMax, but I would guess it is no better, maybe worse.
Without a chrony, I think the OP should stick with at least 150 grain bullets.

 

[jmd]

Wow. Are you serious? I was leaning towards an issue with Vmax's but I hadn't come across any max velocity recommendations. I will shoot it through a chronograph at some point just to check (assuming I can get my buddy to bring it), but for now I'm going to the heavier higher BC bullets & I will check them at longer ranges. I can't see what else would be causing the problem. It is too big of a problem to be caused by reloading or shooting errors but that is my opinion. I appreciate everyone's feedback on this. I'll let you know how it goes after I run some heavier bullets through it.
Thanks,

 

[Nomad47]

What I was getting at was too much velocity for the spin rate/jacket material. Like mentioned earlier, normally when you over spin the bullets, they go 'poof' before they even get to the 100 yard point. But in your case, maybe something else is going on that is related to the spin rate/velocity.
Did your 300 yard target have nice clean round holes? With no other 'splatter' on the paper?

 

[KevinThomas]

jmd,

I'm a bit surprised that no one has mentioned this yet, but you may have simply run into a combination that shoots bug holes at short range, but is a very poor performer at longer ranges. This is actually quite common, and why you'll never see an experienced long range shooter developing loads at short range and just assuming they'll shoot at the long line. Many of them won't, despite being superb performers at shorter distances.

I'd take it out to the distances you're wanting to use the load at, and see what it does there. If it's not working at distance, don't get too focused on how great the short range groups may appear.

 

[FroggyOne2]

Kevin is very correct in what he is saying, I personally do my load testing @ 600 yards for elevation.

 

[Erik Cortina]

jmd,

I'm a bit surprised that no one has mentioned this yet, but you may have simply run into a combination that shoots bug holes at short range, but is a very poor performer at longer ranges. This is actually quite common, and why you'll never see an experienced long range shooter developing loads at short range and just assuming they'll shoot at the long line. Many of them won't, despite being superb performers at shorter distances.

I'd take it out to the distances you're wanting to use the load at, and see what it does there. If it's not working at distance, don't get too focused on how great the short range groups may appear.

Kevin, actually I now do my testing at 100 yards even though I have a 1000 yard range. 100 yard accuracy will carry all the way out to 1000 yards, but you need a good chronograph and also need to know how to "read" the groups. It took me some time to learn what to look for, but now I can evaluate a 100 yard group and know if it will shoot or not at longer ranges.

Having said all that, it is true that some loads shoot at close range and not at long range. The bullets just happen to "cross" paths at the shorter ranges but at longer ranges they show vertical, lots of it!