Effect of brass on velocity

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Effect of brass on velocity

Post by desben on 3/25/2017, 6:25 pm

Different brass can vary velocity by 100fps with the same load. That's what I get reading a document from CamPro (http://campro.ca)

CamPro is a Canadian (Québec) bullet manufacturer of swaged copper plated bullets. In an email exchange, one of their engineers shared with me some load data they have developed for their 148 gr hbwc. One interesting part of the document is the effect different brass can have on velocity. Thicker brass offers less volume and thus more pressure and velocity. The effect is quite pronounced! Almost 100 fps difference between Winchester Brass and Winchester +P Nickel.

What do you think? Extreme case, or good reason to sort by head stamps?

Sorry about the French: Laiton=Brass. FPS scale on the left. Loads were identical, with 3 grains of titegroup. The velocity for each casing type is obtained as the average of multiple shots (11 to 19 shots depending on the brass).

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Re: Effect of brass on velocity

Post by LenV on 3/25/2017, 7:01 pm

Hi Desben, I suggest more time dry firing and less time sorting. I ran your high and low velocity through my handi dandi on line free ballistic calculator and POI difference was less then .80" at 50 yards. In my opinion that is good enough. That is just my opinion YMMV
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Re: Effect of brass on velocity

Post by desben on 3/25/2017, 7:24 pm

Good advice Len. Thank you for putting that in perspective. My hold at 50 is not yet sub inch.
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Re: Effect of brass on velocity

Post by SteveT on 3/26/2017, 9:10 am

That's more of an effect than I would expect, but I've never looked at case vs velocity specifically. I shoot single headstamp almost all the time.

A couple of thoughts...

As mentioned at pistol distances velocity has a small effect on POI.

Case volume will have a greater effect with hotter loads. Were these target loads? or self-defense?

Did they control for other variables? Bullet length and seating, chamber temperature, powder position in case etc. With small charges tipping the gun forward or backwards before shooting changes the position of the powder in the case and can affect velocity by 100-200 fps (in my testing).
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Re: Effect of brass on velocity

Post by desben on 3/26/2017, 10:13 am

Steve, the load was 3.0 gr of titegroup with a hbwc. "Heavy" target load? They make no specific mention of the variables you discuss, but since their goal was to measure the effect of brass, I think it's safe to assume they were all loaded and shot the same way. But I know what they say about assuming... I'd be happy to share the entire document with you if you are interested, but it's in French  Razz
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Re: Effect of brass on velocity

Post by SteveT on 3/26/2017, 2:46 pm

Titegroup is very dense, so the volume is quite small. It was Titegroup that first showed me case position sensitivity. A friend was chrono'ing TG loads and seeing a lot of variability. After some discussion and testing he found that the difference between tipping the pistol down and tipping the pistol up before a shot resulted in nearly 200fps difference. This was with light 45ACP loads.

I don't read French.
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Re: Effect of brass on velocity

Post by Magload on 3/26/2017, 3:01 pm

SteveT wrote:Titegroup is very dense, so the volume is quite small. It was Titegroup that first showed me case position sensitivity. A friend was chrono'ing TG loads and seeing a lot of variability. After some discussion and testing he found that the difference between tipping the pistol down and tipping the pistol up before a shot resulted in nearly 200fps difference. This was with light 45ACP loads.

I don't read French.
I had the same results testing with my Labradar.  Wasn't noticeable in a 9mm but really noticeable in a 38.  Don
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Re: Effect of brass on velocity

Post by Rob Kovach on 3/27/2017, 10:14 pm

I've heard rumors of Tite Group being position sensitive in .38spl.  Perhaps powder orientation was a factor in this experiment.  If they would repeat the tests with a slower, bigger powder, maybe that would show tighter velocity range.
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Re: Effect of brass on velocity

Post by SteveT on 3/28/2017, 12:43 pm

Just for the record, I'm not saying the data presented is wrong. It is larger than I expected, but it's reasonable. I just posted a few questions I had in my head and things I'd try to account for if I was going to repeat the experiment.
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