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Barrel length and power factor


BillR1

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I'm trying to work up a single load to shoot in my SSP and CCP guns for IDPA, and I had some surprising results today through the chrono.

My load is a 124gr Berrys RNHB with 4.1gr of Titegroup at 1.125" OAL. It's a nice load and very accurate.

My full size P320 (4.7" barrel) averaged 1078fps for a 133+ pf.

When I put the same rounds in my P320 Carry (3.9" barrel), I averaged 995fps for a 123 pf. The SDs on both guns were <15, so it's pretty consistent.

The two tests were shot within minutes of each other using the same bag of ammo.

Is this normal? It's less than 1" difference in barrel length...

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!" wouldn't make a lot of difference in a rifle, but in a pistol it does. Think of it this way, your shorter barrel is only 75% of the length of the longer one.

That's actually a great way to think of it as far as a pistol is concerned. Elegant in its simplicity.

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That is a little more difference than I would have guessed, but nothing crazy. I chrono'd some 9mm loads out of a 4.25" 1911 that I run in USPSA occasionally, and found they were about 5-7% less than a XDM 5.25", and about 8-10% less than a G17L 6". Of course every gun and every barrel is a little different.

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Doesn't idpa allow you to crono with any gun you want?

The test gun has to be in the same division that you're competing in.

I've seen matches where they have a gun at the chrono station with the longest allowed barrel for the division, which is 4.1" for CCP. Only if your ammo fails at making PF do they come and try the ammo through your gun. I've also seen them simply test with your gun.

Edited by BillR1
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