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Question for gunsmith on barrel hood lenght


Josh Biondi
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Usually the STI side has a hood space of 1.315 as showend in the picture. The ideal fit is to get a barrel hood sligtly short that works tight.

But...but if you have a barrel with hood length of 1.311 due to the use or because you cut too much material whats your opinion...is it too short and in that way its necessary to welder little material on the back of the hood to recover the right measure or this could be considerate as a tollerance?
Anyway whats are the trouble that a gun can get from similar fit?

Your opinion will be appreciate. Thanks ahead!!20191002_203909.thumb.jpg.932376ddb116bea0e834419254b320c6.jpg20191002_203109.thumb.jpg.e97b224d6d3967dd931cb092bbe392b6.jpg

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I messed up the first match barrel I tried fitting.  I did cut the hood too short.  I had it welded up and I refit it.  It worked fine.  A little while later I was reading an article about hood length.  Bullseye shooters said it had to touch the slide for best accuracy.  Competition shooters said BS, why take the chance that a little debris could keep the gun from going into battery.  Some said they want .001" clearance.  Others said no, it should be .003".  Bullseye said interference fit.

 

In the mean time I had fit a new Barsto barrel to the gun.  I cut the hood so that when it went into battery it would scrape half the thickness of a magic marker film placed on the slide.  So essentially I had about .0003" clearance.  The barrel shot fine.

 

So I had the original barrel lying around and decided to experiment.  I shot it for group, then cut .001" off the end of the hood and shot for group again.  Same size.  Next I cut another .003" off.  Same group size.  I cut another .003" off and another.  At.013" too short I gave up.  Group sizes were exactly the same as the bullseye fit hood length.  Everything else about the barrel was fit perfectly.  It locked up perfectly.  That's why I think the hood length didn't matter.

 

If everything else is okay with your barrel and you are happy with the accuracy, just shoot it .004" short.  If you are not happy with the accuracy, I'd look for problems elsewhere.  It is very unlikely to be hood length.

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As zzt stated, it's not a big deal.  Optimally, I would go with an exact fit for the length, as there's no real downside to doing that.  But the upper and lower lugs, plus the sides of the hood are far more important than the length.  The reason is, accuracy comes from secure lockup and repeatability.  Once the barrel is securely locked in the lugs, the hood length really doesn't matter.  If you're stuck on it, you can weld the hood and recut it.  But personally, I wouldn't bother.  Just be more careful with the rest of the fitting and be sure to get that right.

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On 10/3/2019 at 5:09 PM, sauza45 said:

I have heard that when the barrel hood length get around .008 or more it can crack the slide due to beating between the hood and slide

 

I don't understand this.  If the hood is .008" short and the sides have clearance, the hood never touches the slide.  How could it beat it?

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19 hours ago, zzt said:

 

I don't understand this.  If the hood is .008" short and the sides have clearance, the hood never touches the slide.  How could it beat it?

With a too short hood the slide slam the barrel on the back of the hood (because the barrel moves ahead with a not correct closure). This is because the recoil spring pull ahead the slide. Plus there are other trouble because all the force push on the barrel and the barrel lugs apex works critacally, and the link barrel works under force due to the thrust foward of the slide on the barrel hood.

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First of all don't get to attached to spec numbers as they are all over the place with different manufactures.   What happens when the barrel hood to breech gap is large, as the gun is fired the bullets friction in the barrel rifling pushes the barrel forward and the rear of the round case forces the slide rearward  which causes the two upper lugs to collide, so the larger the hood to breech gap the more movement between these two upon firing.  This can affect accuracy if the gap gets too large but also another affect is the peening of the slides upper lugs with the barrels upper lugs which will cause the gap to grow more. Here's a simple way of looking at it, say you have a hammer and hold it above a surface then hit the surface, if the hammer is held 5 inches above or held 1 inch above which would cause more surface damage?   .004 gap is not that much compared to the guns I see across my bench everyday.  Usually after a lot of rounds are fired through higher pressured guns the barrels second upper lug will make contact with the slides second lug and any more peening                                                                                 Now bullseye guns need a narrower gap for extreme accuracy while game guns can and do have a little more clearance.   

 

MP Custom

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  • 4 months later...

I took Bob Marvel’s class on building a 1911’s, we used .001” feeler gauge between the barrel hood and breach face. That should be a tight fit. so the short answer is it should be less than .001” between the barrel hood and breach face. If you really want to understand building a 1911 you can’t do better than Bob’s class. 

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