New chronograph showing high velocity

[willy]

Just got a Caldwell chrono and tested my old stand by 44 spl reload of 7.5 gr of unique with a 240 gr, SWC,,Was expecting 950 FPS,,but I got average of 1050 out of a 7 1/2” barrel colt SAA,,and 1038 FPS from 6” S&W ,,So is it my chrono,,or is Unique powder the culprit for the 100 FPS increase over the reloading manuals?

[dannyd]

Definitely go with your chronograph before the manual because you don't know all the parameters that the writer of reloading manual used. weather, distance, screen position, barometric pressure.

[Winger Ed.]

I'd double check what the test barrel or firearm the book used for their data.

If both chronos are right, other things can cause differences in your results over theirs-
range temp., primers, seating depth, the size of the vent to duplicate the cylinder/barrel gap used in the test gun.
Maybe a few other things too.

[Silvercreek Farmer]

Are you the recommended distance back from the chrono?

[willy]

I set up 15 feet from the chrono,,I also was shooting on a incline,,but I pulled a line from the backstop to my shooting position and the line was the same height from the chrono on the front and rear sensors . Also used the LED lights that came with the chrono,,

[Silvercreek Farmer]

Have you checked your scale with a calibration weight?

[Silvercreek Farmer]

Does your 240 SWC seat a little deeper in the case than some others? What brass and primer are you using?

[willy]

Have you checked your scale with a calibration weight?



No I haven’t,,After reloading for over 45 years I have never checked the scale! If it is the scale then,,,YIKES! God has been watching over me.

[willy]

Does your 240 SWC seat a little deeper in the case than some others? What brass and primer are you using?


star line brass,,cci 300 large pistol primer

[willy]

Just tested a 45acp load same gun as in the manual shows 900fps and my average for three shots was 1015fps

[Silvercreek Farmer]

Starline brass is said to be a bit thicker which would result in more pressure and velocity, not sure if it would account for 100 fps or not.

Try 10 shot strings for a good average.

Got a friend with a chronograph you could test against?

[willy]

Starline brass is said to be a bit thicker which would result in more pressure and velocity, not sure if it would account for 100 fps or not.

Try 10 shot strings for a good average.

Got a friend with a chronograph you could test against?

Good idea but don’t know anyone with chrono,,My friends will be wanting to use mine,,,Mpst my friends are more hunters than shooters,,And most only use factory loads

[kingrj]

One way to checki your chrono is to fire a standard .22 LR round from a rifle through it. They are very consistent with what the manufacturer specs are for that specific cartridge. If the set up distance between for the screens is correct then I would "trust" the crystal controlled oscillator in the chrono. I have heard of some "re-triggering" issues when the muzzle is placed to close to the start screen but 10 to 15 feet you should be good.

[country gent]

I used a rws side cocker pellet gun with a select lot of pellets ( nothing special but that lot number was set back to use for this to verify chronographs set up and accuracy. 5 rounds at the start and used the average. A 22 will work also but here I would definitly set a brick or 2 back for this use.

When I got the lab radar I verified it by shooting each round thru 3 chronographs a pact professional with sky screens and one of the Mag???? and the lab radar. each round was read by all three. They were all very close. Looked really interesting with the rifle and Mag???? adapter on it the sky screens and the lab radar all set up together.

You might try a second chronograph and see ow the numbers compare.

[farmbif]

maybe try testing it with some standardized ammo like 22lr and see what the chrono says. ive found most lr 22's are pretty consistent at 1240 to 1280, was in mini mags, Winchester , 555's, 333's dynapoints, rem golden, and even armscor 36 gr plated.

[Larry Gibson]

Besides checking the barrel length used in the manuals/data you refer to check the bullet weight. The 7.5 gr Unique "Skeeter Skelton" load was usually with a 250 - 260 gr 429421 bullet. The use of many 240 gr bullets will result in higher velocity.

[willy]

Besides checking the barrel length used in the manuals/data you refer to check the bullet weight. The 7.5 gr Unique "Skeeter Skelton" load was usually with a 250 - 260 gr 429421 bullet. The use of many 240 gr bullets will result in higher velocity.

That makes sense,,But I also fired 230 gr, 45acp load with the same gun as in the manual which was listed as 900fps but I was getting an average of 1015fps

[willy]

Just tested some 22lr rated at 1260fps,,A enrage of ten shots was 1268,,high was 1280 and low was 1238,,So it looks like the chrono is ok. I have a balance beam scale,,amd I check the powder dispenser every ten rounds,,Does anyone else shoot the same 7.5 grains of unique with 240 gr,hard cast SWC ,,and chrono the FPS?

[megasupermagnum]

I just put the load into Quickloads. They predict right at 1000 fps with plus or minus 10% burn rate bringing 955 fps to 1022 fps. I'd say you are close.

[willy]

I just put the load into Quickloads. They predict right at 1000 fps with plus or minus 10% burn rate bringing 955 fps to 1022 fps. I'd say you are close.

Well that makes me feel better about my chrono,,,,,Thanks or that info,,,,

[Mal Paso]

I had a Caldwell read 1456 fps on a load that was about 1100 fps under low angle Winter light with some tree cover. Overcast seems to work better than low angle sun.

[rockshooter]

As has been pointed out, lots of factors involved in chronographing loads. I use the .22-shooting method myself, just to make sure the chronograph (Labradar in my case) is awake and set to the right ranges, then I trust it. This is akin to the question of why a particular mold doesn't cast the "correct" weight.
Loren