.223 Chrono Results - Acceptable Consistency???

[Knuckle Dragger]

I’m curious as to the chrono results I’ve been getting as I start loading .223 and whether or not the range of velocities I’m seeing is reasonable.

The extreme spread for the two loads I’ve tested (H-335 24.5gr. or 25.0 gr.) is 130 fps and 160 fps respectively. Is this variation within the bounds of what most people see and would the use of mixed brass be enough to account for the range of velocities?

Other facts:

Bullet: 55gr MG FMJBT
Powder: H-335 24.5gr. or 25.0 gr.
Primers: WSR
Brass: Mixed once fired
Press: Dillon 550B w/RCBS x-Size and Lee Factory Crimp

 

[rep308]

That is about twice what I got from using Win 748, WSR primers and 62 gn SS109 bullets.
I was aiming for 2800 fps and with 24.6 gns of 748 got a 2785-2859 range on a 10 shot string. Again I'm no expert here please be careful when working up loads.

I was using new IMI brass

 

[RKG]

By itself, extreme spread tells you little. Can you give us the actual sample data?

 

[Knuckle Dragger]

Can you give us the actual sample data?

Sure

Sample 1 (24.5 gr H-335)
2765
2782
2790
2821
2831
2841
2854
2887
2895


Sample 2 (25.0 gr H-335)
2788
2816
2817
2847
2854
2855
2867
2880
2923
2948

These may be very reasonable results under the circumstance. However, my handgun loads are much more uniform. But I've been doing that longer, use a different press, etc.

 

[Adam_MA]

Maybe take a look at your powder measure first. You can take that out of the equation completely by hand filling the cases to see if you are getting the same results, but my first stop would be to verify how accurate, and consistent my powder measure was.

 

[jkelly]

It's been a long time since I've loaded for the .223 so I couldn't comment on the velocity spread but using mixed brass can lead to inconsistent velocities.


Respectfully,

jkelly

 

[RKG]

Analyzing your data give the following information:

Set # 1:
Ave. = 2829.6
SD = 45.2
Max = 2895
Min = 2765
ES = 130
R-squared = 0.9832
Eq: 2748 fps + 16 fps/shot

Set # 2:
Ave = 2859.5
SD = 48.7
Max = 2948
Min = 2788
ES = 160
R-squared = 0.9334
Eq: 2774 fps + 15.6 fps/shot

All other things being equal, the SDs are a bit large, and might tell me, for instance, that your powder measure was a tad loose. However, look at the R-squared values (and, if you can, at a graph of your data). They show a nearly perfect correlation to increasing velocity with each shot. My guess is that you were firing these shots without allowing the rifle to cool down, and that the increasing temperature of the weapon was affecting velocity.

If you PM me with an email address, I'll send you the data analysis and graphs. (Or, if someone wants to tell me how to do it, I'll attach the Excel file so that all can see; the graphs are quite illustrative.)

 

[Knuckle Dragger]

PM Sent, thanks for the input.

I did not provide the data in the order shot, they were sorted by value. The actual values were much more random.

I'm also leaning towards brass as the biggest variable. I'm only checking it with a case gauge to ensure it's within tolerance and not trimming it.

 

[doobie]

Are you properly trimming and expanding all the same?

What type of scale are you using? Try an electronic one. One of those balance scales generally isn't super accurate and could throw loads that differ by upwards of .2 grains. Or are you using a powder thrower? Those are even worse.

 

[Knuckle Dragger]

Are you properly trimming and expanding all the same?

Expending yes, trimming no. I'm using a 550b, so a powder thrower, I'm not measuring each charge independently.

To put this in prospective, I'm using this for IPSC rifle, not long range precision. The accuracy is perfectly acceptable at this point. I just need to reliably and consistently make a certain velocity required for minor power factor.

I may well be that within these parameters my results are to be expected. But I'd be interested in others' opinions on this.

 

[doobie]

I'm using a 550b, so a powder thrower, I'm not measuring each charge independently.

My guess is this is the issue. Try measuring each charge then going out again.

 

[bpm990d]

If they are surplus bullets they may be off dimensionaly as well as their weight may be off quite a bit. Just changing the bullet to something match grade might give you better results.

B

 

[RKG]

PM Sent, thanks for the input.

I did not provide the data in the order shot, they were sorted by value. The actual values were much more random.

I'm also leaning towards brass as the biggest variable. I'm only checking it with a case gauge to ensure it's within tolerance and not trimming it.

Well, that explains the high R-squared and renders the conclusion unsupported.

Even though you're not going for tack driving accuracy, you might want to satisfy yourself by doing the following:

Sort your brass and load your sample rounds from the same headstamp.

Gauge and trim as necessary

For this run, use a single-stage press and a good powder measure, checked for consistency.

Tip: after loading the powder measure, I always through 10 charges back into the can, and then I don't let the measure get more than 1/3 down in the hopper before refilling.

Space your record shots at least 3 minutes apart.

You should be able to get SDs in the 20-40 fps range.

 

[Knuckle Dragger]

Thanks everyone - especially RKG. I have a batch of uniform, once-fired brass that I'll use for a more controlled test and will hopefully be able to set a consistent baseline. If I can do that I'll be more willing to accept the variation as a trade off for convenience and output.

 

[Gammon]

I load my .223 on a 550 (actually a 450 converted to 550). I use the powder measure for all my loading so don't see much sense in hand weighing the charges. Using 69gr Sierra bullets, WCC 844 and once fired (and trimmed) miltary brass I am getting an extreme spread of 62 fps and just a tad over 1/3 moa accuracy. That's good enough for me. I think one of the keys to using the Dillon powder measure is to find a powder that meters extremely well.