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I would think that since the expanding "pusher" gasses are the last thing out of the barrel that porting has no effect on velocity. By the time the "pusher" gasses reach the ports the shot charge has reached max velocity and have left the muzzle.

Eric
 

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Good question, Don, but I'm not aware of any research on this. If anybody has done it, it would be Neil Winston.
 

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It all depends on the barrel length and the speed of the powder being used. If the payload is still accelerating when reaching the ports there will be a reduction in fps as compared to a barrel of equal length and no ports. HMB
 

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As it turns out, I did a test of this perhaps 18 years ago. My son and I shot identical 34" KS-5s except his was purchased used and was ported while mine was not. Our shoulders couldn't tell any difference and neither could the chronograph.

Ed
 

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Every barrel ammunition combination has a barrel length where maximum velocity is reached. Barrels that are longer reduce velocity do to friction. Barrels that are shorter reduce velocity do to incomplete powder burn. HMB
 

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I would guesstimate, Pat, that at some point of barrel length there would no longer be a gain in velocity in longer barrels. I have proven that 34" barrels will produce a noticeable higher velocity than 28" barrels with typical target powders. Then, wouldn't powder "speed" also matter? Id est, a super fast burning powder may run out of steam in a long enough barrel where a very slow burning powder may continue to increase velocity through a very long barrel??....breakemall......Bob Dodd
 

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flincher100 - Answers to questions can be interesting even if they have no immediate practical value.

Pat Ireland
 

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"Would a 32 inch barrel result in a greater shot velocity than a 30 inch barrel?"

Yes. There still is a lot of pressure behind the wad at the muzzle, even in long Trap barrels with normal target loads, regardless of fast or slow powder. A year ago or so someone posted the barrel length where velocity started to decrease. It's long.....
 

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Delbert, the answer to that would have to come from testing. The most rearward ports on a 32in barrel will be more than 2 inches behind the muzzle.
 

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From my testing:

"There were five 30-inch full-choke “trap” barrels with bores ranging from
0.727 to 0.733 inches. They produced speeds from 1179 to 1188 fps.
Two more with magnum chambers also fell within that range. A single
34-inch trap barrel clocked 1201 fps."

I found no porting effect in any of the tests I did - several ported barrels were tested and their speeds varied in a small range unpredictably from similar, though unported, barrels.

Neil
 

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flincher100, I wasn't trying to declare much, just participate in the discussion. My "proof" was over an Oehler 35P and my guestimate was on the considerable difference between the 28" and 34" barrels since I'd wager the smaller distances would, as you say, result in a "so what" finding.......Bob Dodd
 

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Neil has provided some interesting test results. I thought the gain in velocity would be greater, but, when starting with about 10,000 PSI from 18 grains of powder expanding in a 12 gauge chamber and barrel, it shouldn't be surprising. Now, if you're talking about a high pressure rifle cartridge, developing 55,000 PSI from 65 grains of powder, expanding through a small 7mm bore, barrel length and porting would make a much greater difference.

It's to bad flincher100 posted his usual uninformed, unfounded, unable to intelligently contribute posts.
 
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