Truing muzzle velocity

[doctnj]

A month ago I went to our range with my magnitospeed to re check our 3 rifles because I had switched from dry media tumbling to wet. I discovered that for some reason, although I have my own theory, all 3 rifles slowed down around 25 fps.
Also I noticed that my 260 had some pretty bad consistencies. I was asked if I annealed and if I had checked it with tempilaq. I have not ever checked it only gone by the dark room technique.

Robinhood sent me a bottle of tempilaq and I discovered that indeed I had the speed of the machine set pretty close. The main problem with that was I had the flame way to close and wasnt getting even heating over the whole neck and shoulder.

Ill try and make a long story as short as possible.

The High SD's really bothered me so I decided to check and re check every measurement. Good thing I did. Honestly I had been on auto pilot for months and hadnt pulled out calipers to check anything. Well I did and here is what I discovered. I use the Redding type S full lenth sizing die with their piece of crap ring on it. Apparently they all loosened, which they did regularly, and slipped and were no longer bumping the shoulder back at all. I replaced them all with Forester rings. Now as for the slow down with the stainless media. My theory was they were super clean and now the bullet was slightly more loose in the neck. So I dropped all three down one bushing size to counter that effect and all the numbers came right back up. Now that everything is re set and re measured I went to the range to see what the "final" MV was of all this change.

Here is where im getting to my question. Ill use my rifle only as an example.
Magnetospeed average MV 2800 SD 8.3 over 10 rounds fired.
Ok great. I punch all that into my calculator and get set to shoot 300 yrd target. Only Im 3" high. I think I recall Litz saying to true the MV inside the transonic and the BC at the transonic so I measure what the drop should be to be on target and true the MV. It bumped it up to 2900 ish. I reluctantly chose "use this velocity". Now I drop down to shoot 500 yrds at an 8" target. HIGH. So I adjusted to hit center and trued the velocity once again. The actual vs measured and now the mv is like 2974. REALLY?

What is up with that? I confirmed that at that mv I hit dead center at 508 yrds. I had 1.5" group at that distance 1 inch to the right of center. But is the calculator wrong. Is the magnetospeed wrong? I am using the g7 BC that 140 gr berger hybrid says to use.

what is going on? Why are the numbers that far appart?

[Robinhood]

One of the best posts I have seen here in a while Doc. Is the actual BC of your bullet the same as the published BC? Alter the BC in your equation to verify? What variable is off....

[yobuck]

One of the best posts I have seen here in a while Doc. Is the actual BC of your bullet the same as the published BC? Alter the BC in your equation to verify? What variable is off....

Probably not because BC is affected by velocity. Listed BC numbers are best used to sell bullets.
Confirming information by actual shooting has always been necessary.
And the further away the target, the more necessary it becomes.

[doctnj]

Thank you sir. Ive been working on this issue since you and I talked last. In fact the reason I was looking for 243 brass a couple weeks ago was because I didnt have any pristine brass to measure in comparison to what I already had. I am aware of the maximum measurements for all the actions of all my long range guns, but I also like to know what Lapua sends out as standard measurement. Anyhow, I found some on another board. So back to the issue at hand.

One would think, I would think, that if the actual MV is accurately measured, the correct BC is used and current DA known that you should be able to input a distance and get the approximate drop at that distance. I am sure there MUST be error built in to the calculations and conditions do indeed change. This time however, at the time of MV collection, I was careful to collect all conditions on the day of zeroing.

The very next time to the range we shot at 300 yrds. This had the sole purpose of verifying the ballistics and see if the "new accurately loaded" round grouped well at distance. Well they grouped quite well just high. To high to just accept for that. All calculators have a "truing function". So I looked at that. I had the option of truing the MV or the BC. At first I chose the BC. The G7 bc for my bullet is .311 per the manufacturer. I forgot what value is gave me but it was quite low, very different from the published value. The .311 value was supposedly an updated Doppler confirmed value so I went the other way. So I measured what the actual drop should have been and my MV went up.

The next time to the range was now at 500 yrds and current conditions and new MV. I ranged the target, fired 3 rounds at an 8" target, drove down to the target just to see NOTHING. From experience I dialed down .2 mils and was on paper I had to dial back up .1. Ill try to upload a pic in a bit.

Suffice it to say that the mv went up a little more. Teresa's rifle also went up through this whole test period as well. Her's went up substantially more than mine. Granted I shoot 260 and she 6.5 creed. Her barrel has always been fast, real fast.

I just want to know WHY is there sooo much difference between calculated and reality. I use strelok pro and that program gets bashed but Ive compared it to 2 others and it calculates exact numbers as 2 of the other leading programs so Ill stick with it. But that doesnt answer my question. The only thing is the BC. Could the published bc be incorrect? I have asked others in the past 6 months and as far as I know everyone is using the .311. We will go back out tomorrow under MUCH different conditions and run it one more time then re check zero. I wont have time to measure mv again, well I dont think so at this point. But I seriously doubt its actually almost 200 fps faster than last time.


Im still trying to get the pic..... I hate photobucket

[doctnj]

Yobuck, I hear what you are saying about BC's used to sell bullets. But in this case, actual is better than calculated. That means that what I am getting out of my rifle is much faster than using the calculations based on the bc they gave me. Why would they publish a bc that is not as good as it actually seems to be performing?

That is my dilemma.

[doctnj]

2778
This was the final group at 508yrds. The patches below that was the inital OVER adjustment from flying the target on the first shots.

[yobuck]

Yobuck, I hear what you are saying about BC's used to sell bullets. But in this case, actual is better than calculated. That means that what I am getting out of my rifle is much faster than using the calculations based on the bc they gave me. Why would they publish a bc that is not as good as it actually seems to be performing?

That is my dilemma.

We all see and read things differently.
I certainly don't see any (dilemma) with your shooting ability or the accuracy of the gun, and that's about all you have any actual control over to any degree.
The rest is what it is, and tomorrow is a new day.
We are being brainwashed, mainly by people with products to sell that this is or at least can be an exact science.
And your finding it to be otherwise. Thank goodness for old fashioned sighter shots.

[Robinhood]

We all see and read things differently. I certainly don't see any (dilemma) with your shooting ability or the accuracy of the gun, and that's about all you have any actual control over to any degree. The rest is what it is, and tomorrow is a new day. We are being brainwashed, mainly by people with products to sell that this is or at least can be an exact science. And your finding it to be otherwise. Thank goodness for old fashioned sighter shots. A wise man was once overheard saying " I don't always pay attention to what people say but when yobuck utters his wisdom, I listen. Stay thirsty my friend.".

[schnyd112]

Yobuck, I hear what you are saying about BC's used to sell bullets. But in this case, actual is better than calculated. That means that what I am getting out of my rifle is much faster than using the calculations based on the bc they gave me. Why would they publish a bc that is not as good as it actually seems to be performing?

That is my dilemma.

To sell expensive bullets to people who don't test them. Nosler has, for years, been known to inflate their bc numbers. When they came out with the accubond long range, stating .719 g1 bc from a 142g bullet, long range shooters everywhere lost their tops. After being debunked by some of the premiere ballisticians today, nosler still stands by their inflated numbers. I think Litz calculated and confirmed with Doppler that it was closer to .647.

http://www.longrangehunting.com/forums/f17/142gr-6-5-accubond-lr-bc-719-a-154384/

I would be looking at at other factors. A headwind, a tailwind, atmospheric conditions, the position of Venus, something you aren't seeing right would be my suspect. We shot yesterday and had a similiar issue. I had to adjust my dopes on the fly. To true my ballistic calculation with the drops I was seeing my, .260 would have to be shooting 142 smk's at 2950+ when in reality it is still at 2850. A normal 850 yard dope is 20.5. My adjusted yesterday was 18.5 Moa. There was some voodoo in the air and it threw the whole line for a loop.

[yobuck]

A wise man was once overheard saying " I don't always pay attention to what people say but when yobuck utters his wisdom, I listen. Stay thirsty my friend.".

Call it whatever you like, but i wouldnt call it wisdom. Id call it reality, and believing what you see, and not what you'd like to see.

[Robinhood]

Everybody has a chip latey.

[doctnj]

Ok on a different note. I have my rifle trued at distance now (for conversation sake anyhow) I noticed I.E. in the pic that my windage was off. Yesterday I went to 100 yrd target to check windage and sure enough it was off but so was my elevation. Elevation was low by .1 mil. Thats not very much and we dont shoot for x's in our competitions. Im afraid if I bump it up that .1, it will throw off all my long range stuff. I have a competition this coming Sat. and may not have a chance to get to the range but will if I have to.

Should I go ahead and make that adjustment then check at distance and true one last time?

or
Leave well enough alone and realize "thats close enough besides you will almost never shoot anything at 100 yrds"?

[stomp442]

What scope are you using? If all the data is correct and imput into your calculator properly your drops should come out within at least a click or two of your actual shot data. Do you have your scope height set at the correct value and not the assumed 1.5"? What direction are you shooting? Rotation of the earth can and does affect trajectories. Is your temp, altitude and pressure input correctly? Are you using a G1 drag model or a G7 drag model? This alone can make a big difference but if any of these things are off the results can be compounded. I have a hard time thinking the magneto speed is off as they are a very reliable piece of equipment and have been independently tested to be accurate within +- 1fps. Have you performed a tall target test to verify that your scope is level and tracking vertically and the right amount per click?

[doctnj]

Ok Ill run down the list of your questions.

Scope vortex vyper pst ffp 6-24x50
Scope height used calipers from center of vent hole to center of precision vortex rings that are properly torqued on a 20 moa base
Direction of fire NNW 3 degree down angle
drag model G7 of .311 I use kestrel drop for zeroing weather and updated at every shooting event that data is input via blue tooth

So yes that is why Im stumped. Maybe I have a goofed up magneto speed?

[doctnj]

If the magneto speed is accurate and everything else in properly inputted, then the BC is the only thing that could be off.

BUT here is the deal.. the bullet is flying further than calculated!!! performing BETTER than calculated. I routinely have to dial down a couple clicks to get on target.

I had to do the same thing when I finally started shooting at distance last year and again this year. I started off completely fresh this season because I changed my brass prep and measured EVERYTHING again. I also used a tighter bushing in my sizing die. Therefor I did not trust my data from last season. and good thing because it changed.

[wbm]

believing what you see, and not what you'd like to see.

Amen!

[stomp442]

Ok Ill run down the list of your questions.

Scope vortex vyper pst ffp 6-24x50
Scope height used calipers from center of vent hole to center of precision vortex rings that are properly torqued on a 20 moa base
Direction of fire NNW 3 degree down angle
drag model G7 of .311 I use kestrel drop for zeroing weather and updated at every shooting event that data is input via blue tooth

So yes that is why Im stumped. Maybe I have a goofed up magneto speed?



Well I hate to say it, but the weakest link in your set up is probably that Vortex scope. I have had so many issues with vortex scopes, especially with their tracking ability or lack there of. I would seriously perform a tall target test to verify that your scope is moving corectly and vertically. It may turn out that your scope is working fine other than it is moving slightly more each click than it is supposed to so you end up dialing more elevation than you think you are. Possible you have a lemon magneto as well, but the velocity readings seem more in line with typical velocities than your trued one.

[doctnj]

I did a tall target test last spring when I put my custom gun together. If I remember right I went up to 6 or 7 mils only but that encompassed all of the ranges we shoot at. The one thing I noticed doing that test was a slight horizontal shift as I went up. I hung a long level to put my reticle against to try and get it set right. I wound up scratching another line in my bubble level about a mm away from the original.

But to be honest I dont remember anything else about that test that stands out. When I have time Ill do another one with all 3 of my rifles that have the same scope on them. You may be on to something.

If they are not tracking right, I guess I could send them back in to be fixed?

[stomp442]

Yeah, the nice thing about Vortex is they will fix it free of charge and no questions asked. Problem is I started to get to know the Vortex Warranty guys on a first name basis because I was calling them constantly.

[doctnj]

when you sent something in for work, What was average time turn around?