Variance in FPS in my .45acp loads

[JimGun]

I recently purchased a ProChrono chronograph. In testing 50 rounds of .45 ACP loaded with 5.1 grains of Win231, Ranier RN 230 bullet, the FPS varied from a low of 715 to a high of 804.

I load a block at a time and drop powder from a RCBS powder thingamajig (I know there must be a name for it).

Any suggestions on what could cause the variance or is such variance normal?
thanks

 

[rcmodel]

Your load sounds on the ragged edge of a starting load with plated bullets.
It may not be getting enough pressure for a clean burn.

Try bumping it up a bit (say .5 grain more) and see if you get better results.

Also, have you checked several thrown charges on a powder scale for consistency?

Also, try throwing 5 or 10 charges with the measure, then weigh the result and divide by 5 or 10 to see if you are really getting an average weight of 5.1 grains.
You may be surprised!

rcmodel

 

[MutinousDoug]

I don't know how you are set up but if the screens are too close to your gun, the shock wave or muzzle blast can affect the reading.

 

[jfh]

If you are convinced your weights are accurate, and / or that your charge is not too low for plated bullets, then you can try tweaking the round by 1) adjusting the crimp slightly, or 2) adjusting the LOA.

However, my personal guess is that you simply haven't found the "sweet spot" for your recipe with this particular pistol.

Finally, keep in mind that accuracy, or a power factor, doesn't always correlate with low ESs / SDs--so if the round does what you want it to, then put the chrono away after you try some of the proposed changes and simply enjoy shooting it.

Jim H.

 

[Walkalong]

If it is accurate and meets whatever other expectations you have for it, just shoot it, but you can do better than that.

Reasonable crimp differences are not going to fix it. Powder choice and amount will make a huge difference in ES and SD.

Try 5.5 Grs W-231 with that Ranier bullet, as already suggested. The Berry's 230 Gr RN does much better for me, by the way. The Ranier 200 Gr SWC is serious accurate if you want to stick with Raniers.

AA #2 is a powder that will give good accuracy, a clean burn, and great ES & SD numbers in the .45 ACP. If you are looking for the lowest ES & SD numbers, AA #2 is hard to beat in the .45.

 

[rcmodel]

Reasonable crimp differences are not going to fix it.

Unlike a revolver roll-crimp, an auto-pistol taper crimp has next to nothing at all to do with increasing chamber pressure, or bullet pull.

Fogetaboutit!


Unlike a revolver bullet, an auto-pistol bullet has no crimping groove to roll the case into.

If you squeeze the case down with a taper crimp, you are also squeezing the bullet down with it.

Before long, the bullet is less then bore size, and doesn't fit the barrel anymore.
Then you get gas blow-by, and serious accuracy problems!

Come to think of it JimGun, too much taper crimp can seriously effect your standard deviation, due to the reason just mentioned above.

rcmodel

 

[Wildfire]

RC has it.

Hey There:
I agree with Rcmodel. Leave the crimp alone. Some varyation in velocity is normal. Yours sounds like a lot . But , Chronos can lie. And we do not know how you are doing this. 15' is about right for the distance. Just dont shoot the gadet. That sucks. Too close and you will get false readings.

 

[jfh]

Guys, in self-defense here, I must say that I did say to "...(adjust) the crimp slightly...."

It seems to me that you are operating from the assumption that he currently has the crimp adjusted correctly. I was operating under the assumption he may not, and that he could at least try seeing if that was the problem.

This nit-picking on my part aside, I whole-heartedly agree that he needs to work with charge weight and possibly powders (but still can consider his assembly settings).

Jim H.

 

[Car Knocker]

Were they all the same brand of brass?

 

[strat81]

Have you weighed those Rainiers to see how consistent they are? When I think consistent, I think Sierra, not Rainier.

 

[JimGun]

I appreciate the comments. I didn't have any idea about how far away to put my chronogragh - I had it approx. five feet away.
I did weigh ten of the Ranier bullets. the weight varied from 230.1 to 229.2.
I was using starline brass.
I'm unsure of the crimp. I have followed the procedure defined in the brochure that came with the dies. Is there anyway to measure to see if there is to much?

 

[rcmodel]

.45 ACP case in front of the rim is .476" and the mouth is .473".
That's only .003" taper from front to back.

Measure your loads and see if you are crimping the case mouth way more then that.

You just need enough taper crimp to iron out the belled mouth back straight again after the bullet is seated.

If you don't have a dial caliper, lay a straight-edge against the case and hold it up to the light.

If you can see the taper at the mouth, it is probably too much.

rcmodel

 

[Ridgerunner665]

This is usually caused by varying bullet weights...but other things can cause it.

I recommend weighing every charge if you want consistency...it works for me.

I have the ProChrono Digital chrono too...I tested mine against the one they have at the range...theirs was 6 times the price of mine...and the ProChrono was just as accurate and much simpler to operate.

 

[cpttango30]

Yoru chrono should be 10 to 15' infront of the gun. You might be able to get away with 6 to 8' out of a pistol. But watch it, when I first bought mine I was getting SD well over 100fes some bordering on 200fps out of my rifle.

Then I figured out that I had it way to close it was about 4' from the muzzle. moved it out and bang SD shot down. still not where I want them but I am getting closer.

 

[Walkalong]

After you master the crimp, and get the chrono situated it's powder and charge weight. The Raniers obviously are not Sierras, but they are good enough to give better numbers than you were getting.

The Pro Chrono is the same unit I use. I walk 5 paces and set it up there.

 

[345 DeSoto]

...uh, what is ES and SD?...

 

[rcmodel]

ES = Extreme Spread = Highest & lowest velocity of the shot string.

SD = Standard Deviation = A little harder to explain, or even grasp, for me at least!
In simple terms, it is the measure of how close each shot’s velocity in the shot string will be to the “average.”

rcmodel

 

[ambidextrous1]

I'd like to know more about the Chrono numbers: Do you have a bimodal distribution, with a lot of values at the low end and the rest at the high end?

I'd suggest that you edit your data, as a means of understanding what it means. What is your edited extreme spread if you delete two values from your data: the slowest and the fastest?

ES and SD are good indications of performance if you have a normal, or bell-shaped distribution, or a good approximation.

If you'll post your data or PM it to me, we can look for process aberrations, then suggest what might cause them.