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Discussion Starter #1
I shot over a chrono. with my Beretta 682 30" .727 bore full choke and 18gr 700X,windjammer wad,AA hull,1 1/8 oz shot and got 1170 f.p.s average with 5 shots. Now keeping the same ammo a 34" K-80 .033 choke .748 bore (allor) I get a speed of 1263 f.p.s 5 shot average! Too fast! What did I do wrong or is it the longer barrel that makes the difference?

Thanks in advance.

Fred.
 

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Maybe this is why the K 80 barrels explode....? Only kidding. Like your post; Neil? I think it may have something to do with forcing cone shape and removal.
 

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digger1dog,if you go to the above link and scroll down to section 3 and thence to "choke and barrel effects" you will see that I tested both bigger bores and longer barrels and the effects of both combined were far less than you report. I can't account for your data.

When I chronograph I write down all the individual speeds and see if they are reasonably close together, say within 30fps or so. If they aren't it's a do over. Otherwise a single deviant (and usually wrong) speed can move the average too far.

If the individual speeds were consistent enough, I'd just say that's you got and plan to replicate it sometime when you are chronographing something else.

Parenthetically, it is not true that larger bores always produce higher shot-speed readings. I tested two 870 barrels which were factory oversize with choke tubes and those funny chokes and both were slower, not faster, than similar 0.730/0.735 870 barrels.

Neil
 

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Interesting results.

I'm not trying to stir the pot now, but I'm curious because this raises an interesting issue about the ability to enforce ATA rules.

Now how would the ATA deal with this?

Lets just say there was an issue somewhere (how 'bout Kentucky! JUST KIDDING), about the velocity of someone's reloads. How would the ATA test them - out of a test gun? Out of that shooters gun?

How would the apparent "rules violation" (1250fps max. for 1 1/8, avg of 1263fps chronographed) be dealt with? Eighteen grains of 700X (or similar powders, Clays, Red Dot, Promo), under an 1 1/8 oz of shot, is just about a standard light target load by just about all standards. So technically, its hard to say the person knowingly violated the rules when the reloading book speed would be about 1145-1170fps!

I'm sure someone somewhere would complain the shooter using this load in their gun and getting 1263fps out of a light target load would say its an "unfair advantage", but still.

Thanks,
D (ever curious)
 

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A shell to be tested would be done according to SAAMI standards. The speed limit, D, is 1290 fps for one and an eighth ounce loads.

Neil
 

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Not only that but the big bore should generate more of its energy earlier than a standard bore developing equal velocity, giving more of a "punch" than a "shove." This is because the recoil force is equal to the pressure multiplied by cross-sectional area and the cross-sectional area is bigger. The pressure drops off quicker in the big bore as the gas expands into a larger volume, therefore the big bore has to get its work done sooner.
 

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Big bore recoil less even with more velocity? Same reason full choke has more felt recoil than a skeet choke. The force it takes to shove the wad and shot thru and out the barrel is a component of the perceived recoil. I know I'm going to get flamed for this but the best analogy I have is when you squeeze a garden hose to get the water to squirt further you can feel the hose push back (recoil) just a little more.
 

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Discussion Starter #11
O.K it looks like the only problem I caused was in my own head this sounds like it is somewhat normal. And the ammo is not illegal. So don't worry about it. And put the chronograph away!
 

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Bustedemall,

The hose has more recoil with more velocity, not less recoil.

I never noticed full choke having more recoil. The friction at the choke is pulling the barrel forward away from your shoulder, so it should subtract from the recoil, not add to it.
 

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digger1dog, try again from further away from the chrono, a minimum of 6' between muzzle and the first screen. 8' or 10' may be better. I think a little bit of blow-by in the larger barrel caused your anomaly.
 

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Make sure the chrono has the same direct sunlight or you'll get different readings as well, cloudy vs sunshine. Same day, same light, or throw your results away.

ol 12
 

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One obvious question that has not been asked yet:

How far from the muzzle was your chronograph placed in each case? If it was the same distance from the bench in each test, it would be 4" closer to the muzzle for the longer barrel, and that could easily account for a 93 fps higher reading.
 
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