Help calculate muzzle velocity and drop

[sasquatch]

You should always test drops at least out to the maximum range you're wanting to shoot, or farther. Shooting at 300 and extrapolating to 500 is not the best way to go.

I’m not that far into it yet, it’s for discussion

I can’t even see that far where I hunt.


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[sasquatch]

The only way Im aware of is if a barrel is brand new and its chamber isnt firecracked enough yet to increase pressure and speed up the MV.

So the question is, is the OPs gun brand new?

Close, prob only 60-70 rounds through it


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[Harvey_NW]

The only way Im aware of is if a barrel is brand new and its chamber isnt firecracked enough yet to increase pressure and speed up the MV.

Well now you're aware of another.

 

[Koda_]

Close, prob only 60-70 rounds through it


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In my experience I would run at last another 100rds of cheap ammo thru the gun before working on drops and zero.
My 280ai sped up and leveled off after about 120rds. Yeah, its kinda frustrating, ammo isnt really cheap for this caliber.

 

[hereinaz]

Yes, barrels speed up between 100-120 rounds, but not that much. I don't sweat it that much as long as I have confirmation and don't shoot more than 20 before I hunt again.

If you aren't hunting close to 500 yards, I'd just confirm drop and go kill stuff.

Chalk it up to unknows, like whether Sasquatch is real and aliens exist.

 

[EdP]

New barrels are slow until the bore roughens up some

Taperpin, did your really mean to say that a new barrel roughens up some with shooting?? That wasn't what I was expecting to read. I thought shooting smoothed out the roughness left from machining on a barrel that had not been lapped.

 

[EdP]

Another possibility is that what is printed on the box is wrong because the mfg has changed powders. I read recently that some factory loads are not as fast as in the recent past due to powder shortages resulting from international conflicts. The mfgs are using less optimal powders because the powders they were using are not available. They may have changed powders but not what is printed on the box.

 

[Koda_]

Taperpin, did your really mean to say that a barrel roughens up some with shooting?? That wasn't what I was expecting to read. I thought shooting smoothed out the roughness left from machining on a barrel that had not been lapped.

Its actually the chamber throat that roughens up, increasing pressure and velocity.
The bore smooths out but ive never heard that makes for any practical effect on pressure or velocity.

 

[Harvey_NW]

Its actually the chamber throat that roughens up, increasing pressure and velocity.
The bore smooths out but ive never heard that makes for any practical effect on pressure or velocity.

The firecracking that increases pressure and resistance is in the first couple inches of the grooves in the barrel, not in the throat. If the throat gets carbonized enough to have an effect that would be a "carbon ring".

 

[TaperPin]

Taperpin, did your really mean to say that a new barrel roughens up some with shooting?? That wasn't what I was expecting to read. I thought shooting smoothed out the roughness left from machining on a barrel that had not been lapped.

Yep, the bore from the throat forward a bit, gets so hot it fire cracks the metal surface, which is rougher than the new barrel surface.

Brian Litz has some bore scope pics showing fire cracking and shows his cleaning method in this video (I’m not a Litz fan boy, but it has some useful bits):

 

[TaperPin]

I should have said I’m not going to start cleaning with JB to smooth the bore - simple carbon and copper remover used without scrubbing much is much simpler. I can’t get over the feeling he’s managing velocities with the smoothness of the bore as if it’s commonly done, which while it obviously works for him, seems to add needless complexity, and many of us burn out barrels without an issue JB needs to solve.

 

[GoatPackr]

Where do you live. Maybe someone around you has a chronograph that you can shoot over and see what you get?

 

[sasquatch]

Where do you live. Maybe someone around you has a chronograph that you can shoot over and see what you get?

I have a chronograph stored away that I got for archery. I just have to dig it out, i originally didn’t just due to wanting to see the true proven drop.

Now that it seems very slow I’ll shoot it through one to see what I’m getting. Prob be a week or two

I’ll report back. When I do shoot I’m gonna have a few diff rounds to test out also


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[bpeay4]

He had a chronograph this whole time....

 

[sasquatch]

He had a chronograph this whole time....

Does it really matter? You think 14” low is normal for the caliber?

And if the bullet chronos 2950, should calculate hold overs based on that or the true impact points?

I believe Math is more reliable than a $200 machine I have that is affected by sunlight.

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[Koda_]

Does it really matter?

Yes. Your whole posts subject is about helping you find the velocity of your ammo when you stated you didnt have a chrono. Finding the velocity is literally the subject line, and you have the tool to find it.

I do not have a Chronograph to run calculations, however I have shot a few different yardages and have the measured drops to reference.

I am hoping to figure out from these bullet drops what the muzzle velocity should be to achieve these known drops.

i am wondering what kind of true velocity i may be getting and also from this what should my 400 and 500yd drop be??

No judgement, but now Im at a loss what your trying to accomplish?

 

[sasquatch]

I don’t have one I believe would be as accurate as a mathematic formula, and in the end the number that comes across a screen won’t be as useful as a POI.

I will use what I have to just “see” what I get. When I later have time. I cannot just walk out my door and shoot when I please.

I was looking to see if someone could verify what I was getting with Math, since I’ve not ran these bullet calculations before. It seemed odd to have a known speed caliber come out to be around 2700 fps.

But hell, I suppose I’ll use what the chrono says when I shoot, and ignore what the impact is. After all, the Chrono said so.

Just from archery I’ve seen it be off by 20fps or so. Roughly 10-20% based on what the arrow actually does.


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[GoatPackr]

If the drops aren't close to what they should be using the speed from the chrono then you can start looking at why.

 

[35WhelenAI]

33 posts later, has a chrono. I don't have anything to add with that slightly relevant piece of information revealed... You have everything you need to answer your own question. Let us know what it chronographs and report back.

 

[Koda_]

I don’t have one I believe would be as accurate as a mathematic formula, and in the end the number that comes across a screen won’t be as useful as a POI.

I will use what I have to just “see” what I get. When I later have time. I cannot just walk out my door and shoot when I please.

I was looking to see if someone could verify what I was getting with Math, since I’ve not ran these bullet calculations before. It seemed odd to have a known speed caliber come out to be around 2700 fps.

But hell, I suppose I’ll use what the chrono says when I shoot, and ignore what the impact is. After all, the Chrono said so.

Just from archery I’ve seen it be off by 20fps or so. Roughly 10-20% based on what the arrow actually does.


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So your on the wrong track here, your math formula will never be accurate without chrono data. Everything we have given you is only estimates based on your group locations which isn't conclusive in one string of 3. There's so much off with how your trying to go about this I'm not certain I understand what your trying to accomplish?

If you just want to know how much drop your ammo has at different ranges then just use a tall target like you did. That's not going to be very practical past say 300yds though. If you know your MV then you can accurately do the math to get your drops at any range.

What kind of scope do you have? does it have external turrets to dial for drop?

What kind of chronograph do you have? is it only rated for archery? If not its accurate enough.