interesting results!

[johnmventers398]

so earlier this year i had my 22" 243 win shortend down to 16" fulley embracing the idea i was going to be having velocity losses.

however, this would apear not to be the case.

i was predicting velocities of around 2700 or 2800 at a push.

today i was out accuracy and drop testing at distance. only 360m but that is about my max hunting range.

my predicted drops did not match up with my actual drops. not by a fair bit...

the calculated velocity from "0" is 3200FPS with 105's..

i am all kinds of confused but actuly really pleased. i have litrally given nothing up by loosing the length.

has anyone els ever had such unexspected results?

 

[Crow]

has anyone else ever had such unexpected results?

As a matter of fact...

http://forum.accurateshooter.com/threads/affect-of-freebore-on-velocity.3964287/

Not exactly the same scenario as yours, but perhaps some similarities. Trying to back into drop charts to arrive at velocity can produce imprecise results, particularly if the barrel was altered significantly. Best to go to a chronograph for accurate numbers was my takeaway from the experience.

 

[tomswede]

Can be related to scope height and the actual zero distance. Can get confusing at relatively short distances.

 

[Rodney]

I agree with tomswede, especially scope height and weather. 3200 with 105’s from a 16” barrel is fascinating. What’s your load, if you don’t mind sharing.

 

[tomswede]

I agree with tomswede, especially scope height and weather. 3200 with 105’s from a 16” barrel is fascinating. What’s your load, if you don’t mind sharing.

A hefty charge of Bullseye to get that speed out of a 16in barrel

 

[Zero333]

You're velocity is between 2,800 and 2,900 fps at the most. For a 16" bbl to reach 3,200 fps with 105's you'll need over 90,000 psi of chamber pressure. ( 90,000 psi is 50% above MAX safe pressure )

Sorry to burst your bubble.

Chances are you miscalculated something or your scope doesn't have true mil or moa adjustments.

3,200 fps with 105's in the 243win is a challenge in a 26" bbl let alone a 16".
I could reach 3,400 fps with a 26" bbl but the brass would be toast after one or 2 firings.

 

[Ledd Slinger]

I remember when I was young, my father always handloaded for his 300 Win Mag (back when nobody had a clue what a 300 WM was). He did not own a chronograph. He only estimated speeds by his powder charges and elevation drops. His guess was his 180gr Nosler Ballistic tip bullets were leaving the muzzle at 3250 fps (which is possible with the 300 WM) so thats what he always told people when he talked about it.

Many years later, I was getting serious about hand loading and taking the art to a much higher level of precision than my father. Of course I had my own chronograph for testing loads. So one day shooting with my father he wanted to see what speed his bullets were doing. He fired 5 of his rounds across the chronograph. To his surprise, the average speed was 3060 fps. Nowhere close to what he had always thought.

Now I'm not saying the OP's 105s are going slow in a 16" barrel because I have been able to achieve good velocities in short barrels by using faster burning powders, but I don't think 3200 fps is a realistic estimate. Need to shoot it across a chronograph.

 

[johnmventers398]

I agree with tomswede, especially scope height and weather. 3200 with 105’s from a 16” barrel is fascinating. What’s your load, if you don’t mind sharing.

I use 50.0 gr of ramshot mag over federal champion primers.

my "0" is bang on at 182m.

 

[johnmventers398]

You're velocity is between 2,800 and 2,900 fps at the most. For a 16" bbl to reach 3,200 fps with 105's you'll need over 90,000 psi of chamber pressure. ( 90,000 psi is 50% above MAX safe pressure )

Sorry to burst your bubble.

Chances are you miscalculated something or your scope doesn't have true mil or moa adjustments.

3,200 fps with 105's in the 243win is a challenge in a 26" bbl let alone a 16".
I could reach 3,400 fps with a 26" bbl but the brass would be toast after one or 2 firings.

no bubble burst. im baffled by it. i was estamating velocities of around 2800 and thats what the balistic calc was set too.

i used the velocity trueing program on the gunwerks G7 program by inputing my estamated velotity and then inputting the deviation from exspected results. the program then spits out the true number.

my bras is showing no sign of stress. primers are good. my bolt always leaves a donut around the firing pin even with factory and mild loads. always has.

i was looking at a magneto speed today but couldnt quite add to cart.

 

[johnmventers398]

Can be related to scope height and the actual zero distance. Can get confusing at relatively short distances.

my scope is set at 1.75" and my "0" is 182m checked and spot on.
how would scope hight affect velocity predictions?
i know it changes how the arc interescts the line of sight but beyond that i dont understand how it would effect velocity calculations.

 

[Ledd Slinger]

Get a chronograph. Don't need anything expensive. Magnetospeed will screw up your point of impact on the target anyhow.

 

[johnmventers398]

Get a chronograph. Don't need anything expensive. Magnetospeed will screw up your point of impact on the target anyhow.

i would just use it for velocities. the problem with a trad chrono is i do not use a dedicated range and often have to hike into the hills to get a safe place to do load work. a magneto would be most practical.

 

[Ledd Slinger]

i would just use it for velocities. the problem with a trad chrono is i do not use a dedicated range and often have to hike into the hills to get a safe place to do load work. a magneto would be most practical.

Yeah that makes sense. A lot easier to set up for sure. Just as long as you are aware of the known issues with POI when using them.

 

[Milo 2.0]

Did you by chance rezero your scope, or reinstall it the exact same way?

 

[johnmventers398]

Did you by chance rezero your scope, or reinstall it the exact same way?

i checked my zero before shooting at longer range. i hadnt alterd the zero at all.

 

[johnmventers398]

Yeah that makes sense. A lot easier to set up for sure. Just as long as you are aware of the known issues with POI when using them.

yeah i am aware of the potential for poi shift.

i guess the only way to really find out what is going on is to head out again and get a chrono.

if i am getting that speed i would need write a whole article spouting about how evryone who ever said you lose velocity might be wrong...

 

[tomswede]

my scope is set at 1.75" and my "0" is 182m checked and spot on.
how would scope hight affect velocity predictions?
i know it changes how the arc interescts the line of sight but beyond that i dont understand how it would effect velocity calculations.

With high mounts you could run into zero at the “up” part of the trajectory this can confuse things. With your height it should not be an issue. Still there is an error somewhere since there is no way you are getting 3200 ft/s out of a 16in barrel.

 

[Zero333]

What you need to do is zero the rifle at 100 meters. Then find your dope for 350 meters and back calculate the velocity.

If you zero'ed at 182 meters and then proceeded to find your dope at 360, that's not enough distance between the 2 zeros to estimate velocity.