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Does porting reduce velocity?

Discussion in 'Uncategorized Threads' started by microbrew44, Dec 25, 2007.

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  1. microbrew44

    microbrew44 TS Member

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    Does porting reduce velocity? Anyone know?
     
  2. whiz white

    whiz white Strong Supporter of Trapshooting Banned

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    Since the powder is most likely all burned in the first 18", I would suspect that any reduced muzzel velocity is neglible.

    Others may chime in with additional info. I believe Neil may have some data.

    Whiz
     
  3. Neil Winston

    Neil Winston Well-Known Member

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    Whiz, the trouble is, barrels themselves vary so much, the only valid test would be to test, drill, and then test again. But on the average, I've found no difference. That's comparing some ported 303's with unported ones, and the same with three 682 barrels, two ported and one unported which performed about the same.

    Neil
     
  4. likes-to-shoot

    likes-to-shoot Well-Known Member

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    My BT-99 didn't have ported barrels. When I bought my Citori Combo I didn't have a choice, it came with them. I wish I would of had a choice, I would have elected to pass on the porting. I can't see or feel any difference between the two but I just don't care for the porting. My personal opinion.

    Bill
     
  5. Easystreet

    Easystreet Well-Known Member

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    Yes, porting will reduce velocity, but not a significant amount. No, I haven't drilled any holes in my barrels in order to test this, but it has to be true based on other testing and observations.
     
  6. phirel

    phirel TS Member

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    Easystreet- I understand your logic, but if porting does reduce velocity slightly why does changing from a 32 inch barrel to a 30 inch barrel not reduce the velocity. Is it possible that the shot charge has reached maximum velocity in the first +-20 inches of the barrel?

    Pat Ireland
     
  7. halfmile

    halfmile Well-Known Member

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    Pat, there is a change but probably negligible.

    Rifle barrels operating in the 50-60 KPSI range will change with barrel length about 2 percent or so per inch when shortening the barrel. There are other factors to consider (powder burn rate, bullet B. C. and drag coefficient) so this is not an absolute figure.

    With a shotgun operating on one fifth the amount of pressure I feel the change, while there, would not be noticeable.

    HM
     
  8. Gargoyle!

    Gargoyle! TS Member

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    The best way to find out is to get a barrel and some factory shells. Get two boxes of the same lot number. Without porting fire and list the speed with a chrono and then send the barrel off and have it ported and then shoot the other box with the chrono and then compare.
     
  9. Neil Winston

    Neil Winston Well-Known Member

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    Here's one consideration, based on Pat's comment above.

    A stack of 30-inch 870 barrels produced speeds of 1179 to 1188 feet per second. A 34-inch one clocked 1201. If you take the midpoint of the short ones as 1183, you get about 5 ft/sec loss of speed per inch.

    So if porting got _all_ the gas out, which you can see by watching at night is far from the case, you might expect a 10 ft/sec drop in speed. But since only part of the gas escapes, it'll be less than that.

    If you test the same shells twice, you will get a variation in average speed which will often be close to the less-than-ten ft/sec difference we guess at here. In other words, even testing before and after porting in not sure to tell you unless you do several speed tests at each condition.

    Neil
     
  10. Capt. Morgan

    Capt. Morgan TS Member

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    The answer to you question depends on how many ports there are in the barrel. I have a card-shoot barrel with 180 ports in it...2 groups of opposing pairs of 36 each and a group of opposing pairs of 18.

    I guarantee that they reduce the velocity...a LOT!

    Morgan
     
  11. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    I'd love to have a good supply of primers and powder combos that would give the same numbers every time! Close is the best hoped for, ported or otherwise. Hap
     
  12. Hipshot 3

    Hipshot 3 TS Member

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    No chance!
     
  13. jsteenson

    jsteenson Member

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    I don't know but what about all the shot you lose out the sides?
     
  14. M-16

    M-16 TS Member

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    Take it for what it's worth.
    Just completed tests for penetration into phone books
    short barrel modified choke 6" longer barrel full choke at 60yds the shorter barrel penetrated 50 more pages. Findings the tighter choke slowed the shot down. So if the porting is before the choke yes it would slow it down. porting after the choke should not unless burnning some slow powder. All of the shells I shot were all hand loaded and each weighed out/ match style loads.
     
  15. Neil Winston

    Neil Winston Well-Known Member

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    Interesting result, m-16. Fifty pages is how much of a change? A lot or a little?

    Neil
     
  16. gcbluerock

    gcbluerock Member

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    yes it does reduce the velocity. How much depends on what style of porting, and how many ports. Some ports actually grab and shred the wad as it goes by. Which powder is also a big factor. The slower the powder the more porting will reduce it. Which wad is used has a big effect as well. Not all wads are created equal.

    Years ago one of the old timers decided to have his new Browning o/u ported since he was starting to be bothered by recoil. He figured if a little was good then a lot was better, and twice as much was just right. When he got the gun back he couldnt hit a thing. He tried and tried but just couldnt hit targets anymore. He decided that the porting was to blame and so he bought another new Browing. Same model, same everything as before. He went right back to grinding out 25 straights. I tested the 2 guns over my chronograph, side by side with his reloads. In the new gun with no modifications his shells clocked off 1400 fps one right after the other. In his ported gun they were in the low 900's. we didnt bother to pattern test, just made a lamp out of his ported barrel.
     
  17. Old Cowboy

    Old Cowboy Active Member

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  18. smartass

    smartass TS Member

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    gcbluerock, now that was quite a tale. Are you by chance a fisherman?
     
  19. ou.3200

    ou.3200 Well-Known Member

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    I don't think penetration into telephone books can be equated with velocity. Deformation of shot at higher velocity may retard penetration. Soft point jacketed rifle bullets penetrate farther into paper bundles at 1800 fps than at 3000 fps. Try it.
     
  20. Easystreet

    Easystreet Well-Known Member

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    Pat Ireland wrote: "Easystreet- I understand your logic, but if porting does reduce velocity slightly why does changing from a 32 inch barrel to a 30 inch barrel not reduce the velocity. Is it possible that the shot charge has reached maximum velocity in the first +-20 inches of the barrel?"


    First, I know of no proof that 32 inch barrels have the same velocity as 30" barrels (all else being equal). Do you?

    Second, it would make no difference if the shot charge HAD reached maximum velocity in the first 20 inches of the barrel. Venting out some of the gas which is pushing the shot charge down the barrel before the shot charge gets to the end of the barrel will just result in FURTHER slowing of the shot charge (if in fact it is slowing once it passes the 20 inch mark).
     
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