Is there a minimum barrel hood width that is needed for a 45 round? I know the Gold Cup uses a .385 width hood, is there any problems associated with going to .300 to .350 width? What could it cause if it was too narrow?
Some barrels are fitted to a slide so there's barely enough clearnace (perhaps 0.001") for the hood to fit between the tops of the breechface guide blocks. This is said to help position the barrel in the same lateral position for every shot and thus promote the ultimate in accuracy.
The average GI barrel hood (0.4155" wide) has 0.0225" of wiggle room in between the average GI guide blocks.
The extreme would be cutting the hood off completely, but this might lead to feeding problems with no hood to perhaps deflect a frisky round into the chamber. As such, I'm guessing the minimum hood width would be that which still deflects the round into the chamber - and not be narrow enough to deflect it off to the side. I've no idea how narrow that could be, however.
There are a couple of schools of thought on barrel hood width and its fit-up to the slide. Some advocate (old school) a close lateral fit-up to improve accuracy by making the hood align the barrel. The other school (Kart barrels) mentions in their fit-up instructions that lateral tolerance can be generous, i.e. and not affect accuracy. I've fit up a "few" barrels, including Kart, and my experience also concurs with this "generous tolerance" school. I've tried both schools and like generous hood clearance.
Likewise, It has been stated by Pat Yates, Mechanical Engineer and designer of the Detonics 1911, that the torquing of the barrel (counterclockwise viewed from the rear) caused by the bullet entering the barrel can delay the unlocking of a short barrel from the slide. Therefore, in my view, a tight hood/slide fit-up (particularly with short barrel 1911s) would delay the barrel/slide unlocking process. The hood needs to have the proper clearance with the slide. When you look at the impact marks of how the top barrel/slide lugs mate together it becomes clear that the accuracy comes from consistent lug alignment. To help this alignment, the Kart barrel uses two pads on the barrel (i.e. 3-point contact) to locate it consistently and precisely the same at each battery. This is similar to what the late gunsmith Swenson did by welding two pads on the barrel. And finally what Gustin did, with his patent of using two screws through the slide to locate the barrel precisely, at every battery.
I think that Kart has recently changed their Easy-fit hood width . I fit one last year that had a NM hood width in the .450s and required a lot of fitting. The one I fit last month had a hood width of .428. I call Kart about it and they said that this is how they make their Easy Fits barrels now. The .428 is .013-.018 wider than the standard barrel hood width and fit my .440 slide just fine at .006 per side. The accuracy is outstanding.
What I am taking away from this is, is that in maybe more important than the hood fitting snug, is the lower lug position/location when in battery? I'm after a bit more accuracy out of a officer model .45 I am working on.
Lower barrel lug fit is important. But the top barrel lug fit into the slide lugs is key. Typically, the radius of the barrel female lug is different than the radius of the male slide lug. So when the slide and barrel are placed together (male lug fits into female lug), there are only two points of contacts between them. As an example, if you place a large diameter cylinder into a smaller diameter gutter/trough, the large diameter cylinder will make two points of contacts. Now when the lower barrel lugs make a third contact on the slide stop pin, you have a 3-point contact for the barrel and accuracy results. Every time the barrel goes into battery, it should always have a consistent 3-point contact.
If you remove the blueing from female barrel lug, magic mark it, then lay it in the slide in battery, and gently tap the barrel with a mallet, two impact marks should appear in the barrel female lug. If the barrel sets a little low, relative to the firing pin hole in the breechface , the two impact marks can be filed slightly to insure the firing pin hole is concentric with the center of the barrel.barrel. I use a gauge that slides in the barrel and aligns with the firing pin hole. Once that's done, you can fit the link to insure the lower barrel lugs sit on the slide stop pin and MOST importantly the rear of the lower barrel lugs MUST hit the vertical impact surface in the frame (VIS). There should be a slight clearance of the bottom of the barrel with the horizontal bed of the frame. In the real world, if the lower barrel lugs don't sit on the slide stop pin, all is not lost. In that case, as long as the link keeps the barrel against the slide at two contact points some reasonable accuracy should result. Also, when you don't have the lower barrel lugs hitting the VIS, you WILL break links and have feeding malfunctions.
Quote:
...when the slide and barrel are placed together (male lug fits into female
lug), there are only two points of contacts between them.
Unless you have some slide & barrel blueprint data that differs from the Army Ordnance data, there cannot be two points of contact if the parts are within spec. Ordnance specs are:
* Slide bore (male lug) radius = 0.3495" + 0.0015" for a minimum of 0.3495" in the GI or NM slide.
* Barrel lug cut (female lug) radius = 0.348" - 0.005" for a maximum of
0.348" in the GI barrel. I've no NM barrel data for this. Using your analogy, the smallest diameter trough is larger than the largest diameter cylinder. Therefore the cylinder (barrel) can roll back and forth a little bit in the trough (slide) - because there's only one point of contact.
Of course that's just the blueprints talking. How barrels & slides actually get made nowadays is a different matter entirely.
For a NM barrel, the radius of the female barrel lug, closest to the breechface, is 0.355"/0.350"R, i.e. 2 points of contact for a NM barrel in a standard issue slide. I would assume this larger radius was specified to improve accuracy, which is what NM 1911s achieve. Likewise, it is a simple task to carefully file this female barrel lug a few thousands at the top to achieve the desirable two points of contacts without affecting safety. After seeing some of the groups fired by Swensons, Gustins, and NM 1911s I view this very minor filing mod to be a worthwhile effort to obtain 2-points of contact between barrel and side.
In my experience, on the majority of barrels that I have personally fit-up, the 2-point contact was already there and no filing was required. It is simple to test a specific 1911 for the 2 points of contacts and more meaningful than looking at drawing dimensions. The gun in hand is the one you're working not the one the drawing says it's suppose to be.
In my experience, on the majority of barrels that I have personally fit-up, the 2-point contact was already there and no filing was required. It is simple to test a specific 1911 for the 2 points of contacts and more meaningful than looking at drawing dimensions.
(The gun in hand is the one you're working not the one the drawing says it's suppose to be.)
CJR;
I agree. I strive for full contact, with a small flat machined at 12 oclock.
I find getting full contact requires the lapping of the slide lugs to a true
radius, which usually brings that radius to .351/.353 depending on the
slide..and then duplicating that radius on the barrel. Todays aftermarket
barrels are not usually a true radius. Matching of the two radii C/L, along
with the C/L of other dimensions, allows a closer fit between the hood and
slide. The reason for the loose clearance recommendations, is most fitters do
not or cannot align all the necessary tolerances to permit reliable function.
Many of the old timers you mention, silver soldered a stop to the left upper
side of the slide to provide additional support for the rear of the barrel.
This modification had much merit, and Iam working on an improved version,
similar to the BoMar Tuner.
Quote:
For a NM barrel, the radius of the female barrel lug, closest to the
breechface, is 0.355"/0.350"R...
My apologies. Had previously stated I didn't have that dimension for the NM barrel - and there it was, hiding in plain view on page 110 of J.K.'s Vol II!
Do you have any idea where I might obtain an Ordnance drawing for the latest Army Ordnance NM barrel (P/N 7791414)?
No, I don't know where to find an Ordnance drawing on the NM barrel. I would think an Internet search would find the drawing.
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No, I don't know where to find an Ordnance drawing on the NM barrel. I
would think an Internet search would find the drawing.
Been looking online for a few years with no luck. Even Nicolaus Associates didn't have one - and their fine book of 1911 blueprints even had one for the cleaning patch!