disappointing chronograph results?

[coosbaycreep]

I recently got a chronograph because I wanted to see what kind of velocities my .500S&W handi rifle was getting. I've always read that you generally gain 50fps of velocity for each extra inch of barrel length, and since this gun has a 22" barrel, and most .500mag ammo testing results is usually done with a 9"< revolver, I was really hoping that this gun would be real close to .458winmag velocities with some of the heavier bullets. Turns out, it's not.

On most of the factory ammo I tried, some of them are only gaining about 100fps over what the published velocity is. Some of my handloads were significantly faster than the velocities in the reloading manual, which makes me wonder why there's not much improvement over the factory ammo.

My hottest load was a 350gr JHP at 2,385fps, which equates to 4,422 ft. lbs of knockdown. 700gr hard cast bullets were 1,373fps. The .500mag ammo that BVAC (cheap stuff from the gun shows) sells was only 1,470fps, and I think it's only 300 or 350gr. The good thing is that round has absolutely no recoil. The bad thing is I didn't buy this gun to shoot mild loads. I bought it because I was too cheap and poor to buy an honest to god elephant gun like a .458win/lott, and while it's still fun to shoot and does impressive damage to whatever you hit with it, I still think I'm eventually going to have to put out the cash for something bigger.

So, does the 50fps for every 1" not apply to pistol calibers or something? Is it the burn rate of the powder that makes the difference? I tried some .44 mag through a 5" 629 and a ruger carbine yesterday, and while a few of the loads gained little velocity in the rifle, most of them had significant improvements over the revolver. I also shot my keltec .32 through the chronograph (763fps with a 71gr fmj), and that did very little to inspire confidence in my carry gun.

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[NoAim]

does the 50fps for every 1" not apply to pistol calibers or something? Is it the burn rate of the powder that makes the difference? I tried some .44 mag through a 5" 629 and a ruger carbine yesterday, and while a few of the loads gained little velocity in the rifle, most of them had significant improvements over the revolver. I also shot my keltec .32 through the chronograph (763fps with a 71gr fmj), and that did very little to inspire confidence in my carry gun.

Generally. Most .500S&W factory loads are setup to be shot out of a revolver with a 8-10" barrel. So you want a faster burning powder.

Likely you are using a slow burning powder that can take advantage of the barrel length.

As an example, .45ACP from a 5" barrel is 850fps or so. From a 16", you'd expect a huge increase. The total increase is 100fps only, or about the same from a 9" barrel.

 

[BillM]

If you are shooting loads from pistol data, you are pretty much burning
up all the powder in the first 8-10 inches.

You need to develop a load with a slower powder for rifle use if you want
to see higher velocities.

After you do that, go back and shoot some of your rifle loads in the
pistol. You will probably have a fireball the size of a VW bug.

 

[johnboy]

I think BillM is right....slower powder if you can find data for it in that caliber. I would only used published data. Sounds like it is pretty potent already....but you are the ultimate judge of that. Be sure the chronograph is FULLY opened up or you will get false readings but you probably have checked that....

 

[orygun]

I had a 5" Smith 500. (actually 4" plus comp) It had 95&#37;+ of the velocity rated for an 8 3/8 barrel. I think what you are running into is the amount of "push" (or time of "pushing") compared to the amount of drag created by that length of barrel. If you can find some data for this cartridge in a rifle barrel you would find significantly different powders compared to pistol data. Similar, but inverse, of what the first guys to shoot rifle loads out of 10, 12 and 14" Contenders found and much like what I'm having to deal with a 7mm-08 in a 16". I'd look for any data that includes slower powders.

As far as the chrono being fully open, if it was slightly closed, he'd be more than happy. It would read optimistic that way. You' would have to over open it to get it to read slow. But, that's a great line of thinking. "Out of the box" has solved many problems.

 

[orygun]

Congrats on the chronograph. Now you ain't guessing anymore! What kind did you get?

 

[coosbaycreep]

prochrono is the brand, it was about the cheapest one from midwayusa

What do you mean by having the chrono "opened up"? I didn't do anything other than stick a battery in it, put the little antennae looking thingies on it (diffuser?), and shoot rounds through it. I've tried a pellet gun, .32acp, 2 different .44mags, and the .500, and while some of the readings have been slower than I hoped/expected, a lot of them sounded about right.

I haven't found any rifle specific data for the .500 yet. In fact, even the pistol data is fairly limited, but I expect that to change as the round gets more popular....hopefully.

There's not much variance in powders in all the reloading data I've read either, and I haven't found any with a powder slower than AA 1680, which I plan to eventually try out. Almost every load I've tried so far has been with lil gun or H110, as those have the highest velocities published in the books I have.

thanks for all the info

 

[Randini]

I could run your data using my ballistics software if you like, it will take into account the barrel lenght, just need all the data cartridge OL for how deep bullet was seated, bullet GR. and who makes it, powder and GR. used.