Lubaloy's comment last week about a 0.024 inch long feed ramp prompted the thought "How long's a feed ramp supposed to be?" It's not dimensioned on either of the U.S. Army's Springfield Armory or Rock Island Arsenal blueprints. So, after a gob of calculations the feed ramp length in a USGI M1911A1 works out to:
A. Mid-Spec & Tolerance = 0.347 +/- 0.136 inch
B. Dimension & Tolerance = 0.330 + 0.153/- 0.118 inch
C. Min.-To-Max. Length = 0.211 to 0.483 inch
Of course, the goal of frame ramp work is to achieve reliable feeding - not to get the ramp to a certain length. But, knowing how long the blueprints infer it could be might be nice to know - before taking some good linear and angular measurements and then attacking with the (gasp!) Dremel!
That's about right.
.350 is about right for a nominal dimension. Due to the large variations in actual frame dimensions out there (hello Vermont!) there might be cause to cut it lower. For instance, if rounds are feeding out of the magazine and hitting below the feed ramp. Technically that should not happen. The ideal arrangement is that the lower part of the bullet ogive grazes the top edge of the ramp. But how many guns have you seen that actually are cut this way?
Last week I read that someone offers a ".420" x 31 degree ramp". I can't remember who it was, but it was a well known 'smith. If I added correctly, that would fall midway into the range of your calculations. *If* he meant length by the first measurement...
A few conclusions that I've reached on feed ramps...
If the feed ramp is to spec... both as to length from the rear of the magwell and angle... it's not necesary to cut it any deeper than abut .350 inch. Neither is a mirror finish necessary. It should be smooth... but any more than that runs the risk of screwin' it up royally unless it's done carefully and correctly. The Dremel Dans among us need not apply. They may get lucky. They may not.
If the ramp is to spec, both as to length and angle... cutting it deeper also moves the top of the ramp forward... which moves the top corner closer to the lower edge of the barrel ramp... which causes the bullet nose to strike the barrel ramp instead of clearing it... which causes 3-Point Jams... which then necessitates moving the barrel ramp forward to regain the necessary clearance... which, in some guns, destroys enough case head support to become a problem. Several things factor in to this, not the least of which is working headspace and barrel fit.
These are the things that cause me to rail against doing a Dremel-assisted kitchen table "Ramp and Throat Job." Whenever I talk to a 1911 owner/shooter about correcting a feed/RTB issue... the one thing that I dread hearing most is: "Well, shucks! I done done a nice ramp and throat job on it. It shines like a dang mirror... and the thing still won't feed!" Whenever I hear that, I just know that my task will be all the more difficult, if not impossible... depending on how much work was done.
Hi David: A ".420 x 31 degree" ramp seems (to me, at least) a little too long and steep, even though it does fall within the limits of the specification. Some (about 0.011 inch) of that length may be due to the angle being 0.5 degree less (steeper) than the 31.5 degree mid-spec value (with a tolerance of +/- 0.5 degree).
Recall 1911 Tuner saying too steep is better than too shallow - as long as the whole thing's not cut too far forward. Maybe this 'smith also offers barrels that are nicely matched to his frames for good feeding, headspace and minimum unsupported case length.
If I was going to put a Brand A barrel with a Brand B frame I'd want to start on a frame with a ramp cut to 31.5 degrees that's about 5/16 inch long. Easier to fit by removing metal than adding metal.
Another important dimension here is the horizontal distance from the slide stop hole centerline back to the barrel bed/feed ramp corner. This one's not dimensioned on blueprints, but works out to 0.694 +/- 0.017 inch.
David, if you remember details on the ramp offer, we'd like to have a look. The painful part of such an advertisement is that the work is most likely offered as part of a reliability package. In other words, the person is suggesting that any gun would benefit by having its feed ramp cut lower (and mirror polished, of course).
If the rounds are hitting below the .350 point when they feed, it is time to break out the calipers and have a good look at some frame dimensions. If I found a metal 'artiste' who advocated feed ramp lowering as a matter of course, I'd be inclined to look elsewhere for assistance. Unfortunately, I had to learn this lesson in reverse!
quote:
"A. Mid-Spec & Tolerance = 0.347 +/- 0.136 inch
B. Dimension & Tolerance = 0.330 + 0.153/- 0.118 inch"
I believe a decimal point was misplaced here.
Thing one: I messed up after reading that the ramp / barrel junction should be a continuous surface from a famous ammo guy. I'll look for the article tonight.
Thing two: This forum has saved me from messing up so many OTHER things that it makes me shudder to contemplate them.
Hi Lubaloy: No, the decimal points are all in their proper places! These tolerances seem huge, but they're based on doing calculations with toleranced dimensions - about 10 of them. The one with the widest tolerance band is 0.79 - 0.01 inch, and this is the one that locates the ramp from a 31.5 degree line through the slide stop hole centerline.
Good example of tolerance stacking, huh?
Neimi:
In the original post you substituted .024" for .240".
Then you wrote:
"A. Mid-Spec & Tolerance = 0.347 +/- 0.136 inch"
.136" is greater than an 1/8"!
Using the +/- .136" gave you this:
"C. Min.-To-Max. Length = 0.211 to 0.483 inch"
Just over 3/16" to just under 1/2".
No way, Jose!
Your mid-tolerance spec of .347" sounds correct, but the allowable tolerances are incorrect.
Anyways, I always enjoy reading and learning from your posts on dimensions. I just think you made a mistake on this one.
http://www.yost-bonitz.com/pricelist/pistol is the site. Scroll almost exactly to the middle of the page. It's under Auto Pistol Frame Work or something like that.
Quote:
David, if you remember details on the ramp offer, we'd like to have a look.
The painful part of such an advertisement is that the work is most likely
offered as part of a reliability package. In other words, the person is
suggesting that any gun would benefit by having its feed ramp cut lower (and
mirror polished, of course).
If the rounds are hitting below the .350 point when they feed, it is time to break out the calipers and have a good look at some frame dimensions. If I found a metal 'artiste' who advocated feed ramp lowering as a matter of course, I'd be inclined to look elsewhere for assistance. Unfortunately, I had to learn this lesson in reverse!
I did indeed mis-quote Lubaloy's 0.240 as 0.024, so I stand (sit, actually) corrected.
I went over the process of calculating the ramp length again (for the fourth time) and did find an error, so:
A. Mid-Spec & Tolerance = 0.348 +/- 0.135 inch
Not saying you'd ever find an un-tinkered ramp as short as 0.213 or as long as 0.483 inch. Just saying those are the extreme limits based on blueprint data - not manufacturing processes.
If I goofed somewhere, I've not been able to find it. Any error'd be somewhere in these pix.
PICTURE 404
S = Specification & C = Calculation
PICTURE 404
Where did I mess up? Cheers
P.S.: Just noticed the top pic has two specifications labeled S5; The spec for the mag. well angle (17.5 +/- 0.5) should have been labeled S6 in the top pic and in the bottom pic for the calculations of C5, C7 & C10.
I've always enjoyed your posts, Niemi, and I look forward to them. Still, I'm gonna pass on checking your trig homework (not that I could - well, maybe).
I am very, very impressed. THAT'S triggernometry!
Quote:
Had a bunch of other derived specifications in the area of the feed ramp,
so put them together in the pic below.
The seemingly large tolerances are an unavoidable consequence of doing the math with the dimensions and tolerances given on the U.S. Army blueprints (indicated by a check mark). Cheers.
Would it be right to assume the derived base dimensions (without the tolerance allowances) are those derived from the given print mid-spec. values? In other words, 'derived mid-spec' dimensions?
I love these drawings, and the math that goes into them! I'd like to nominate them for sticky-hood, perhaps in a combined form.
Oops!
Original Post after #14 deleted a few minutes ago after discovering an error.
Will post corrected one soon. Dispose of any copy you made. Sorry 'bout that.
Here's the amended version of what was in the deleted post. It's a compilation of other derived specifications in the vicinity of the feed ramp.
PICTURE 404
The seemingly large tolerance values for some of these is a natural and unavoidable consequence of doing the math with the U.S. Army blueprint data.
The blueprint specs (checked) are shown as originally printed, except angles are shown in decimal degrees instead of degrees and minutes. The derived specifications are the mid-spec value followed by the +/- tolerance, each based on a blueprint specification (not all of which are shown in the pic).