Compensator physics question...

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  • DarkRose

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    May 14, 2010
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    So I'm making a foray into machining my own compensator for a new build because I didn't like what I found on the market...

    Still fitting the prototype (unfortunately a Glock barrel in battery is not centered in the slide opening, causing my comp to have an offset, if not for that, It would be close to finished, as it is I'll be making another as I had to move the bore down .028" for the offset).

    I've got an idea, but not sure about the physics of the thing...

    If I angle cut (slash cut) the end of the comp, will the escaping gas affect the accuracy, as the exit bore would have more material on the top (or bottom, depending how I go)?

    For crude example, cutting the end of the comp either _/ or _\ (Might try to match grip angle or slide serrations)

    If it would affect the bullet exiting, would a shallow counterbore negate this? And if that works, how deep/shallow would it need to be?


    Slide started...
    34210389160_1ef7bb1f91_b.jpg


    Roughing it...
    34596412525_1e7c34e4b5_b.jpg


    Comp profiled and bored...

    34210393680_80d81e0de1_b.jpg


    Profiled and test fitting for thread depth and setback (close but not quite...)
    Will be using the blank slide in the first image to eliminate the nose radius and allow a seamless look (or close to it, needs to have a little clearance.)
    34210388560_a0609ff327_b.jpg
     

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    Alpo

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    As long as the muzzle crown is perpendicular to the bore axis, you should not affect accuracy. Where are your compensator ports located?
     

    DarkRose

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    So far I haven't located them. Just roughing and fitting. Will be machining the comp to match whatever I do with the sides of the slide so I haven't figured my ports yet...
    So the end of the compensator shouldn't matter at all since the barrel crown should be good (brand new) and the bore is also over bullet diameter (research indicated .380-.390" for 9mm compensator)

    One I get my shape and sizing and threading and shoulder depths set, then I'll do my slide and comp machining together.

    I'm expecting to do one or two ports each side (depending on size) and 2 maybe 3 on top.
     

    55fairlane

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    Good looking machining.......what kinda steel?what kinda mill are you using....it's the tool and die maker in me

    .020 to .035 over bore size and keep the comp muzzle true,flat parallel, and square to the the barrel and crown

    Might wanna if possible finish machining the comp muzzle crown with the barrel in place and as your locator to keep everything true

    Just my 2 pennys

    Aaron
     

    DarkRose

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    Good looking machining.......what kinda steel?what kinda mill are you using....it's the tool and die maker in me

    .020 to .035 over bore size and keep the comp muzzle true,flat parallel, and square to the the barrel and crown

    Might wanna if possible finish machining the comp muzzle crown with the barrel in place and as your locator to keep everything true

    Just my 2 pennys

    Aaron

    That comp was machined on a Haas CNC. Now that I've got my programs tweaked I did what I hope is a good one tonight (accounting for the barrel offset) on the Fadal CNC.
    416 stainless, comp used 1/4 and 1/2 4 flute uncoated endmill, running around 2k rpm @ 8-10 ipm.
    Slide machining used smaller cutters, higher speed, slower feed. Also done on the Fadal.
    Programmed with MasterCAM 8 and 10

    The exit bore finish size is done on a Clausing manual mill with DRO, with the barrel in a 3 jaw and comp screwed on, using an indexable boring bar.

    Hoping the barrel OD is true to the barrel ID...

    Dig the username, got a 79 Fairmont Futura with only 40k on it...
     

    AllenM

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    One thing I dont see covered but you may have. There needs to be extra material on the top of the comp to be removed once the comp and barrel are together and in battery.
    The tilt that happens when the barrel goes into battery will cause the nose to sit lower so the top of the comp should sit taller other wise your top plane will start to dive.
    On 1911 it is a 1 degree tilt when in battery. most people compensate on 1911's by making a cut on the end of the slide since a pre fab comp is being installed. but you could cut the angle on the comp at this point.

    As far as the angle on the end o the comp I "feel" it should be square with the bore but this would be a good time to experiment. It wouldn't take much to try it both ways. cut it with an angle, shoot it and cut it square and shoot it. leave extra material so you could go either way after shooting it.
    I would test it before porting even. just me.

    Lastly the barrel bore is never concentric with OD but you can get away with threading on a live center if you have to and make a plug to go in the chamber end to find center and hold that end of the barrel.
    But it is better if you can indicate off the bore 2" from the muzzle to the muzzle end to make certain your threads are concentric to the bore
     

    DarkRose

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    Well internal single point threading is beyond me, and with most of the markings on our lathe at work long gone I wouldn't attempt it...
    The first comp I made I didn't realize about the barrel angle in battery, that's why I made a second and offset the bore to compensate, leaving a bit of stock.
    I read somewhere there should be a gap of around .020 between the comp and barrel, but that seems a little excessive. At the moment I've got the threads and shoulder set so that it basically flush and plan to mill the backside down to get whatever gap I really need...
    Once I get everything set and locked in place, I'll skim .001 or .002 off the top and sides to even it all out, then machine my windows and panels and angles in the slide.
     

    AllenM

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    the .020 is the difference between bullet size and exit hole in the comp. A tap is fine for the comp I would just indicate off the bore of the barrel vs the OD or use live center
     

    DarkRose

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    the .020 is the difference between bullet size and exit hole in the comp. A tap is fine for the comp I would just indicate off the bore of the barrel vs the OD or use live center

    Ok. Somewhere I read gap between slide and compensator or it wouldn't go into battery properly... Might have just been a safety thing to make sure your setback isn't causing the comp to hold the slide back... Good to know, now I really can make it almost seamless...
     

    rvb

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    back when ipsc had a modified division, angled comps/barrels were a common thing to get the guns to fit in the box.
    always thought those guns looked cool... lots of creativity to get them in the box. I never shot the division or had a gun for it, but never read of accuracy issues due to angle cuts on the barrels/comps.

    Some builders would keep the crown square, but as you can see below, some wouldn't. I don't think SVI infinity would make a gun inherently inaccurate...

    MCO_1720copy.jpg


    mod_17.jpg


    post-4907-1170302066.jpg


    maxresdefault.jpg


    Now as far as angles on the baffles/ports, I've never read of any benefit. Seems perpendicular baffles/chambers still gets the best work out of gas to reduce recoil and muzzle rise...

    -rvb
     

    Alpo

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    Interesting SVI comps. I googled a bit to see if accuracy was reported as a problem (didn't find anything), but I did see that second gen guns went back to a square crown (at least I think these are later pics than rvb's posted pics).

    right_350_350.jpg


    While an interesting exercise, and novel in approach, and even cool looking, I still prefer perpendicular crowns.
     

    rvb

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    not a lot of modified guns on US soil... was more of a European/ipsc thing vs a US/USPSA thing. you'll find lots of configurations out there. I don't know that SVI offered a "production" version... most were probably custom builds, or mods done by smiths on existing guns... imagination/style/tooling of the owner/smith was probably more of a factor than accuracy...

    -rvb
     

    Alpo

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    Handguns and reddots. I've always had a bit of an issue quickly acquiring the dot (vs. iron sights). Could be lack of practice. This little Browning I have is a lot of fun to shoot at steel.

    33oleol.jpg
     

    Alpo

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    Thanks. I hadn't followed that thread very far. That barrel (and all the hardware on it) came from my son. He moved to California and couldn't take his threaded barrel with him. I gave up my 6" TacSol which was a great barrel. This iteration is a little too post-Industrial/Millennial for me.
     

    DarkRose

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    @rvb Those SVI comps are kind of the look I was going for, reminds me os some of the slash cut AR brakes/comps... But was thining about giving it a back slash similar to the Desert Eagle, but was afraid of accuracy and escaping gas not directed by the ports coming out downward negating the effects of the ports (though I'm not sure that would be much of a problem considering it's a G34, and an extra 1.5" of steel comp on the end). If I angled the front backwards I could match the slide serration angle and grip angle (since it's a blank slide I can match the serrations to the grip angle, etc.)

    @AllenM that seamless blend is slick, and that's the whole point of this learning endeavor... Worked on the new iteration a bit last night, got it cut and milled to length (for now), and drilled and tapped for set screw to anchor it in place, with a slight flat surface ground square into the bottom of the barrel threads (only had to take .008 to get a good flat for an 8-32 screw). Now I just need to bore the exit to size, blend the sides to the slide (left it oversize), figure what I'm doing about ports, and then figure out the overall slide machining pattern... Trying to decide on front serrations or no... Will play with a few ideas when I get time, since this is all off-clock work...
     
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