Hood length

[Iron bottom]

I have a question regarding hood length. Let's say the hood is really short. I saw a new pistol (1911 clone) that had close to an eighth of an inch clearence between the the back of the hood and the breech face. If the head space was good, the barrel probably was being pushed into battery by the the round. Guess I should have looked closer, but at that moment I had seen enough.

Just how important is the hood length for timing the barrel and slide lug engagement? Or does it matter at all? I know Tuner recommends 0.003 clearence. Feel free to chime in here, Tuner.

[twin oaks]

I'm still learning, but here's my thoughts:
The slide shouldn't connect the rear of the hood at all. Hence the clearance. The excessive (?) gap between the slide and the hood is probably more of an issue with case support than it is with timing or lugs.

[niemi24s]

For a mid-spec 1911A1, the barrel is driven out of link-down and up into battery by contact between the breechface guide blocks and the rear surface of the chamber (on either side of the hood). I think headspace would have to seriously short for the round to drive the barrel into battery.

When in battery, this same mid-spec gun will have a 0.00175 inch gap between the hood and breechface. For other non-mid-spec (but in-spec) guns, this gap could be as large as 0.0165 inch, LOTS less than than one you recently saw. The gap could also be zero (in which case hood/breechface contact drives the barrel into battery).

Suspect hood length has little or no affect on timing and lug engagement simply because: all the barrel locking lug horizontal distances on the Army blueprints are referenced to the aft surface of the chamber (not the hood); all the slide locking lug horizontal distances are referenced to the breechface guide blocks (not the breechface).

The amount of vertical locking lug engagement is determined by the vertical relationahips among the frame, slide stop pin, link or barrel feet, barrel and slide dimensions.

A hood that's too long won't allow the barrel & slide lugs to engage. As for a hood that's too short, well, er, uh, .... you could probably (I'm just guessing here) cut it completely off and not affect the gun's operation - unless it would goof up feeding. Maybe the hood's there just to contain the big chunks in the event of a case rupture.

FWIW, most fitting of truly oversized (National Match) barrels involves carefully trimming a too-long hood to just barely allow locking lug engagement. This provides for the absolute minimun amount of "end-shake", or virtually zero. This can be also done with a standard barrel by welding up the hood to lengthen it. While this helps develop maximum accuracy, most say it's not the best for reliability. So it's done mostly, I guess, on bullseye target guns where the shooter gets an "alibi". Cuz there's no "alibi" in personal defense, guns for that purpose are fitted with a small hood-breechface gap, like 1911 Tuner's of 0.003 inch.

Maybe they made the hood super short on the one you saw so it'd be easier to see if there was a round in the chamber! :D Cheers.

[twin oaks]

and that's why I said I'm still learning :)

Thanks Niemi24s for an outstanding analysis. I'm learning all I can, and explanations like yours REALLY help my search for knowledge.

[Iron bottom]

Niemi, in the case of the hood being too long, it is my belief that the breech face "pushes" the back of the hood, and does in fact have the barrel lugs pushed too far foward and out of time preventing them from meshing properly. I see no other way for the barrel to go to battery properly without a "push" on the back of the hood from the breech face. I don't think this "push is really a "push", but is in reality a knock out punch taking into account slide speed. A hood that is so short that the breech face will be "pushing" the back of the round and go to battery correctly is what I was wondering about. With very little hood and a correctly reamed chamber in relation to the barrel lugs, in other words. As I looked at this pistol, this thought went through my mind.

[Iron bottom]

Well, Niemi, You are right. I was thinking of my situation. I just looked at two slides and barrels. With no endshake, Barsto and Schuemann barrels, they both are being pushed into battery by the hood. Even the original barrel would be pushed by the hood if the endshake were removed. I thought the Schuemann combined with some +P would develope some endshake, But it hasn't. I really hate to add any endshake, that Schuemann is really accurate. Going to battery with no hood finally sunk in. What do you think of shooting these barrels some more and trying to get a little more endshake or just putting them back in spec. And yes, I am really that dense once in a while.

[niemi24s]

Hi IronBottom: WAIT! What you just described in your last post is barrel-fitting perfection!! You've got no endshake - and that's a good thing. Good? No - it's a GREAT AND GLORIOUS THING !!!

Endshake (or at least too much of it) is what causes lug setback when the barrel slams forward in the slide when the gun's fired. The more the barrel can move forward, the faster it's going when its lugs contact the slide's lugs, the greater the impact and the quicker the lugs get set back.

If there's little or no endshake, the barrel can only move a tiny bit (or perhaps not at all) and there's little (or no) locking lug impact and locking lug setback won't occur - at least to any significant extent.

You may be thinking of some post where I said a mid-spec USGI 1911 will have 0.0125 inch of endshake. This figure was derived from U.S. Army blueprint specs for a gun that was designed to go together with little or no hand-fitting or trial-and-error selection of parts in the factory. And, these guns had to work in the mud, snow, dirt & dust of any combat theatre. Our finely fitted and tuned 1911's would no doubt fail miserably in this environment.

In short: too much endshake is bad; a little endshake is tolerable; zero endshake is wonderful; if you have zero endshake on a reliable, accurate gun do NOT do anything to create some endshake - unless you need to shoot it right after pulling it out of a mud puddle!

The two barrels you describe that get driven into battery by hood/breechface contact are properly fitted. There's only one other alternative, and . . .think how difficult it would be to fit a barrel for zero endshake by trimming the aft end of the chamber for good contact with two breech face guide blocks. Just the thought gives me the heebie-jeebies! Cheers.

[gbw]

Hi IronBottom: WAIT! What you just described in your last post is barrel-fitting perfection!! You've got no endshake - and that's a good thing. Good? No - it's a GREAT AND GLORIOUS THING !!!

................

The two barrels you describe that get driven into battery by hood/breechface contact are properly fitted. There's only one other alternative, and . . .think how difficult it would be to fit a barrel for zero endshake by trimming the aft end of the chamber for good contact with two breech face guide blocks. Just the thought gives me the heebie-jeebies! Cheers.

I'm wondering if this is the best fit for any extended use - in this case, the slide forward travel is stopped by the end of the hood, alone. It seems possible that this would batter a hood-shaped recess into the breechface over time, until the guideblocks do come into play. While I don't see that this would hurt anything much, it's avoidable.

What I'm wondering is, does it make more sense to go ahead and fit the hood end such that blocks are in the game, or very very close to it, from the git-go?

[Maybe it's acedemic - I know that with the Colt slides I use, and with both Kart and Schuemann barrels, that the true ideal often happens - fitting the hood to a brush contact with the breech (barrel full forward after lug engagement) also brings the blocks into contact. I'm thinking of trying a Bullseye pistol next so I'm very interested in the exact fitting business. I'd love to hear 1911Tuner's or a Bullseye smith's take on all of this.]

[niemi24s]

Well, as GBW wondered about, there is indeed a third alternative: Fit the barrel for little or no endshake and so that it's driven into battery by both hood/breechface contact and chamber rear/breechface guide block (BFGB) contact.

Sounds like (in theory, at least) this would be the very best way to minimize wear on these surfaces - by spreading the impact load over the largest possible area. Now, however, the fitter's got 3 separate surfaces on the barrel to fit to the slide (after any necessary lug fitting) instead of 1: hood; left side of chamber's rear; right side of chamber's rear. There's also the possible complication from the barrel lifting up at the rear through 52 minutes of angle during the process of being driven into battery - so it's axis is perpendicular to the forward-leaning breechface and BFGB's.

Never tried fitting a barrel myself with this as a goal. IMHO, it would tremendously complicate the fitting process and I'm not sure the benefit would be worth the added effort.

Anybody out there in 1911 Land ever try it? Ever just think about trying it?? Cheers

[robot1911]

For all of my Bullseye building life, starting in 1950, I've always fit the hood to the face of the bolt and disregarded the side ledges (blocks)completely. If they contact...good...if not, that's okay too. As you said, I suspect trying to fit all 3 could be very interesting...and probably not very useful.
This is the way the Navy had me trained to make match pistols and I've just always done it...except I did try the 'new' .003 clearance idea a year or so ago. It didn't make any difference in 50 yard groups and I returned to the old-fashioned way, even though it's a bit more difficult. I just feel better about it.

[niemi24s]

Should have put the following pix in Post #3. Dimensions were derived from the U.S. Army's Rock Island Arsenal blueprints for a USGI M1911A1 slide and barrel (not the National Match slide or barrel). The dimensions posted are the mid-spec values which (by definition) lie at the center of the tolerance band, are in inches, and have not been rounded. The drawings are not to scale, and tolerances have been omitted.

If the hood length is toward the upper limit of its tolerance band and the breechface guide blocks are toward the lower limit of their tolerance band, it is possible for the hood to contact the breechface. They're still in-spec, but not at mid-spec, as is shown.

http://i129.photobucket.com/albums/p232/niemi24s/P075230001c.jpg

The barrel and slide locking lugs are engaged in both illustrations. The distance the barrel can move fore and aft in the slide is the "endshake", or
0.0125 inch for this mid-spec barrel in a mid-spec slide.

[Iron bottom]

I'll put that little hood fitting task on hold, NIEMI. I've started clamping slides and barrels in a small machinist vise and using a height gage to measure the lugs. So far results have been far better than expected. With that gage, I can get two lugs dead on and leave the other < 0.001. Should have went for all three, but decided not to push my luck. Leave the hood a smidge long and adjust until the barrel can be pushed in battery. I love that gage. It was just a little more expensive than a caliper with offset adjustable jaws.

[niemi24s]

Hi Iron Bottom: A height gauge, huh? (drool, drool) Always wanted one. What kind did you get? Got a granite surface plate to use it on? (more drooling). Cheers.

[gbw]

For all of my Bullseye building life, starting in 1950, I've always fit the hood to the face of the bolt and disregarded the side ledges (blocks)completely. If they contact...good...if not, that's okay too. As you said, I suspect trying to fit all 3 could be very interesting...and probably not very useful.
This is the way the Navy had me trained to make match pistols and I've just always done it...except I did try the 'new' .003 clearance idea a year or so ago. It didn't make any difference in 50 yard groups and I returned to the old-fashioned way, even though it's a bit more difficult. I just feel better about it.

I do it this way too...as others have said, it would be a misery to try to get all 3 hitting at once, and the hood hitting first doesn't really hurt anything.

It's just dumb luck, but with the parts I've used, on 3 of the 5 guns I've done the guide blocks were also so close to the barrels that I couldn't measure a clearance. The other 2 were .001 - .003 out, not to worry.

All of this brings up a related question, and I don't pretend to know the answer.

Is there a point in fitting the lugs horizontally where we introduce so much endshake that the extra slop makes it not worth getting the extra lug(s) in contact? Can (does) that ever happen? I don't see how with the hood fitted last to a contact fit. Asked another way - is it better to have one lug bearing with zero endshake than to have 2 or 3 bearing and introduce the shake?

That end-shake induced crash has to be a very bad thing if the slide gets enough of a runniing start, but I've no idea how much is too much.

(Like Neimi, I'm jealous of the height gauge too!

Mr. Robot, any bullseye building tips you care to pass along I sure like to hear. I want to try a true bullseye gun next.)

[robot1911]

Well, IMHO zero endshake is preferable in a true bullseye pistol. I've always fit to the first lug and ignored the other 2 because with light, midrange loads used in BE matches, it takes a lifetime to move into 2 or 3 lug contact...and by that time, the pistol needs a new build anyhow.
I might add that because of the zero-build, I always put a very small bevel on the slide lugs sharp corners to facilitate lockup and unlock.
And yes Tuner, I know it isn't really "lockup."
Another small tip. On a BE gun, do not concern yourself with firing pin strike location...it isn't important. Be concerned with getting a nice, deep lock with the lugs and if the barrel winds up a bit high, which makes for an off-center strike, it's still good to go...even if you're using a 9mm firing pin size. But I always change that little firing pin too. I like something big and fat striking that primer.

Bob

[gbw]

Thanks, Bob. That's exactly the sort of help I was hoping for.

Not meaning to hijack, but if you don't mind, what barrels do you prefer, and what do you consider to be a good accuracy result for a BE gun? Thanks again.

[robot1911]

I've been using Fred Kart's barrels exclusively for about 20 years. I've tried others during those years...some good, some not so good...but the Karts seem to be the most consistent. There have been periods when his barrels were not good but he has discovered the problem and corrected it.
As for accuracy, 2" at 50 yards is the standard for a .45 bullseye gun but with a good barrel, 1" is about as good as it's possible to make a bullseye gun using quality handloads. I've seen some 3/4" groups but they are the exception...and 1/2" is rare.
BTW, before I started using Kart barrels, I was using Colt barrels, welded at the hood and lug areas but not at the top lugs as is done with today's match dimension barrels.
Colt used to make excellent barrels...today, I don't know.

Bob

[gbw]

Once again, Thank you.

[Iron bottom]

http://i116.photobucket.com/albums/o16/gwilliams20/heightgage.jpg

Not a good picture, but here it is. Just zero (no math involved) on the first lug and check the other two. Repeat with the slide. You may be able to see the depth attachment I made up on the vise. This one is the Mitutoyo Digimatic Absolute model. Fourteen inch. I got it from Penn Tools. They had the best price I could find on the web. $420.00 and a few bucks for shipping, If I remember correctly. This thing seems to be very accurate. Lots of things you can do with it. Depth attachment will check the lugs in the slide, lug engagement etc. This thing is a big improvment over calipers in my opinion. I have a piece of glass out of a high end copy machine I have been using until I locate a little granite.

[niemi24s]

Had (another) brain cramp when doing the drawing and verbage in Post #11, but edit time is over. In the first line change "Rock Island Arsenal" to read "Springfield Armory". The drawing does show the older SA-derived gaps, but had intended on showing the newer RIA-derived gaps.

Too many pages of calculations based on two slightly different sets of specifications and got everything all bass ackward. Will post a drawing with the newer RIA gaps in a day or so.

Iron Bottom: Ooooooooohhhh! (still more drooling) Cheers

P.S.: Edit time wasn't up, so here's the drawing (side view this time) of a mid-spec regular old run-of-the-mill U.S. Gov't Issue 1911. Clearances were exaggerated for clarity.

http://i129.photobucket.com/albums/p232/niemi24s/P525001d.jpg

FWIW, 1911 Tuner, in the thread "Springfield Barrel fit question. HELP!! hehe", said endshake of "More than about 0.010 is excessive". Maybe 0.0125 is close enough.

[twin oaks]

re : Maybe 0.0125 is close enough :
. . .a few thousandths here, a few thousandths there . . .pretty soon you're talking about real movement.
I know in the world of BE super tight building is expected, but seriously, how close to perfection do you need?

[niemi24s]

Hi Iron Bottom: Picked up a 12x12x1 1/4 inch granite counter top sample my local kitchen cabinet/counter shop was going to discard. It's not very flat (curves 0.005 & 0.001 inch along its axes), but at 1 1/4" thick it is quite rigid.

Just a suggestion as a possible temporary replacement for your piece of copier glass until you get a real granite surface plate (if glass flexing causes problems). Cheers.

[Iron bottom]

Good idea, NIEMI. And as usual, your drawings were right on.

Took that Barsto barrel to the range today. It was perfect with hard ball. So I decide to shoot a few Gold dots to see how they would feed. I didn't have any with me, so I went around to the retail area (indoor range) and axed for some .45 ACP Gold Dots. Lane six? Yep. I'll put them on your range tab. I loaded up a mag and commenced firing. Smooth. Then a malfunction on the forth round. It was standing straight up in the front of the mag caught between the barrel and slide. Mag wouldn't drop and the slide would not move. Finally got things cleared up. I was shooting .45 GAP. A nice low recoil little round.

Now to clean up and check things out. Hope I have better luck with the proper ammo. I know I fired one that was in front of the extractor, and it ejected and loaded the next. Could have been dangerous but turned out OK.

[niemi24s]

Hi Iron Bottom: Don't get me wrong on the countertop sample. With about 50 times the "humpiness" of a regular toolroom grade surface plate - it's a terrible surface plate. The price was right, though. Tried a 12x12x1/2 inch granite floor tile a while back and it had only about a 0.002 inch curvature, but it wasn't heavy enough for its intended use (non-height gauge).

45GAP, huh? I'll have to try some. Be like when I was a kid shooting rats at the dump with a 22 and a pocket full of shorts, longs & long rifles. Always wanted to save some long rifles in case I just nicked one with a short and the darn thing charged at me! :lm:

Cheers

[Iron bottom]

Ah, yes, NIEMI. The ability to turn mundane things into high adventure.