Musing on Polishing Feed Ramps

[ggibson511960]

This forum and other sources of gunsmithing knowledge advocate for polishing feed ramps to cure FTF stoppages. As a mechanical engineer who over-analyzes such problems, I see three sources of friction as a slide pushes a cartridge to battery; feed ramp friction on the bullet nose, magazine feed lip friction on the case walls, and breech face friction on the case head, not to mention the extractor's spring resistance and friction as the rim snaps into place under the extractor. All the breech faces of my numerous automatic firearms are not nearly as smooth as the typical feed ramp that generally gets polishing attention. The surface angles are such that the breech face could much more easily cause trouble than feed ramp or magazine lips. In a free-body diagram of a moving case (sorry to implore engineering wonkiness) the breech face forward vectored force must match the opposing forces from magazine and feed ramp, at least until the case clears feed lips and feed ramp.

Have we been missing an opportunity to fix feed problems? I've never heard anyone advocate polishing a breech face, and yet the case head must slide upward across it, albeit aided by magazine spring pressure.

Thoughts from this learned group? Life is good when this is all you have to worry about.

 

[ContinentalOp]

I've seen polished breech faces before, though usually on 1911s. Terry Tussey does that as part of his reliability package. I've seen other gunsmiths do that, though I can't remember specific names. Still others will deburr/smooth the breech face if not polish it. Tussey also bevels the bottom edge of the breech face, as well as polishing the slide's center rail where it rides over the top round of the magazine and the striking surface of the hammer where the slide rides over it. IIRC, I believe he also relieves the disconnector well in the slide's center rail so it rides over the disconnector more smoothly.

I also know of gunsmiths who will radius the underside of the extractor hook and polish the inside for reduced friction, but I've read of at least one gunsmith who says he prefers to leave toolmarks inside the hook for better traction on case rims (Kim Ahrends, I think, when he worked on guns).

I can't remember the names of what specific gunsmiths do because a lot of what they do overlaps so I can't remember who does what, for the most part. The main reason I know Tussey does it is because I met him at a gunshow several years ago and he showed me examples of his work and explained why he does it. His 1911s are known for being able to cycle empty cases from the magazine. His work really stuck in my mind.

 

[rwsmith]

Start with the most obvious.....

Polish the feed ramp if you are having problems. Not too much at first.

I'm not a gunsmith, but I believe that the main source of friction is as the nose of the bullet is first contacting and traveling up the ramp. When the cartridge lays flat in the ramp, the force is almost linear with the ramp. If the edge of the mouth of the properly taper crimped case catches on something, I'd be concerned over such a poorly polished ramp, but a little polishing should clear that up it it's not to bad, or I'd ask for another barrel.

The breech face is a different matter, as the edge of the case rim has to ride a short distance up the face of the breach until the cartridge is heading straight into the chamber. If this is not smooth, a little polishing on the breech face will help, but I wouldn't mess with it if it wasn't causing a problem. Again, if a breech face is so rough as to cause failure to feeds from not allowing the rim to slide on the face, it can be polished, but I'd wonder about the gun and whether or not the factory should look at see why it's so rough and if there are other spots as poorly machined.

 

[2152hq]

Many don't completely polish the breech face to clean up all the tool marks. Doing so on many assembly line pistols would end up increasing the headspace in the pistol to & past the No-Go point, the marks being that coarse & deep at times.

Simply smoothing out what is there can be very helpful in feeding as can a very slight bevel at the bottom of the breech face,,,a very slight bevel.

Polishing the magazine feed lips is another. They often have coarse corners or edges inside from the forming operation. Polishing can really reduce friction betw the mag and the case as they are stripped out.

These are often over looked in many kitchen-table upgrade jobs performed to better the reliability of a semiauto.

The Dremel being the primary tool involved for these jobs, feed ramp work seems to get the most if not all the attention.
The breech face and magazine don't lend themselves too well to Dremel enhancement. Therefore the latter are left undone or at best get a swipe or two with a bit of grit cloth wrapped around the end of a file and that's about it.

You're right,,,there's a lot to it and much more that can be tinkered with than just the feed ramp itself.

The 'smiths,,amatuer and pro, that specialize in this really get into the fine points, study it and do everything possible to improve performance.

 

[Tom S.]

Unless a feed ramp has some kind of serious issues, it's been my experience that feeding problems were most often caused by other issues, with magazines being the number one cause. In probably 95 to 98% of cases, polishing the feed ramp is mere window dressing as opposed to an actual cure. I would apply that same principle to any work on the breech face.

 

[federali]

I had some F-T-F issues with all four magazines furnished with a new Kahr T-9. Three mags came with the gun and the fourth was a free promotional issue. I judiciously polished the feed ramp using automotive rubbing compound followed by polishing compound. The problems went away. However, this particular gun does not like 9mm 147 grain sub-sonic ammo as it has a wide, gaping hollow point. Federal Critical Defense and ordinary ball ammo work just fine.

 

[RGVshooter]

The only FTF problems I've experienced over the years was due to either ammo selection or a magazine issue. Polishing a feed ramp IMO was never intended to "cure" a mechanical problem in a auto loading pistol rather it was to enhance function.

 

[Protocall_Design]

OK- you heard it here first folks. I have figured out a way to make just about anything go up the feed ramp. If you study the problem as our engineer OP and I have, you will find that certain types of bullet shapes just don't feed well. On these, you can see a wide line in the soot on the feed ramp because the bullet has a wide contact area with the ramp. That equates to friction. Even a polished ramp with a wide contact area can be problematic. The question is then, what can be done to make a minimal contact area with less friction, or resistance to the bullet sliding up the ramp?

The answer is pretty simple, once you understand the concept. To get a thin line of contact, you have to change the shape of the ramp so the bullet doesn't conform to it, either by being the same to begin with, or by deforming to be the same shape when the slide jams them together.

The way to do this is to mill a flat in the middle of the ramp with slightly smaller radii on each side of the flat. To set this up, you put the barrel in the mill vise with the ramp exactly vertical. Then use a regular endmill to come in and touch off the center of the ramp and go sideways an equal amount each side of center. You don't want to change the angle of the ramp or make it deeper, just make a small flat going up the center. Then polish the ramp and it will feed any bullets and often empty cases. The bullets or cases now have only thin line contact when going up the ramp, therefore very little friction or resistance.

For a 9 or 10 mm, use a 5/16 endmill and make (approx.) a .06 wide flat. For a .45, use a 3/8 endmill with an approx. .09 wide flat. It is safer to use a ball end mill to keep from running into the sides of the chamber.

In addition to the other things mentioned above, I like to put a slight edge break on the firing pin hole, as that is sometimes a catch point for the rim of the case as it travels upward if the hole has a burr, or even just a sharp edge.

 

[Bullet Bob]

"Have we been missing an opportunity to fix feed [cause more] problems? I've never heard anyone advocate polishing a breech face"

Couldn't help myself, all you bright guys proceed.

 

[nachogrande]

POLISHING NOT A MIRACLE CURE ALL.

Sure polishing a feed ramp can make a gun that works to start with work betterer, but will not fix ALL the other areas of problems, real or potential.

 

[armorer951]

Most feeding problems can be mitigated or eliminated by replacement of the recoil spring with a new, OEM spring.....or a slightly heavier aftermarket spring. Dirty magazines, damage to the feed area of the magazines, and old magazine springs can also be contributing factors. If done properly, polishing the ramp will not harm the gun, but is just one piece of a very complicated mechanical process. Improper polishing or alteration of the feed ramp can actually worsen the problem, and can actually compromise the striuctural integrity of the chamber.

Proper cleaning and lubrication of the gun itself is also critical in terms of reliable feeding. This is even more important if the gun is to be used on duty or for carry. Many more feeding problems are caused by filth and neglect that are caused by some imagined mechanical issue.

Please function check, shoot, and clean, clean, clean your carry guns often. (with the ammo you are carrying) Trust but verify.

 

[federali]

.357 SIG Solution?

On the subject, I'm curious if owners of .357 SIGs have fewer feed ramp or feeding issues. The bottle-necked cartridge should make contact a bit higher on the ramp, which should help feeding. The .357 SIG is often touted as minimizing feeding issues.

Would .357 SIG users offer any comment pro or con?

 

[colt_saa]

"Have we been missing an opportunity to fix feed [cause more] problems? I've never heard anyone advocate polishing a breech face"

Couldn't help myself, all you bright guys proceed.

I have polisheed the breach faces on many of my 1911s

Not to try and solve anything, I just thought it looked cool

 

[colt_saa]

On the subject, I'm curious if owners of .357 SIGs have fewer feed ramp or feeding issues. The bottle-necked cartridge should make contact a bit higher on the ramp, which should help feeding. The .357 SIG is often touted as minimizing feeding issues.

Would .357 SIG users offer any comment pro or con?

I am a big fan of the 357SIG cartridge.

I can not recall feeding issues with any of my or my associates 357SIG firearms.

Starting the mid 90s, I used to go through about 6,000+ rounds per year personally. In recent days it has dropped below 2,000 per year.

My 357SIGs include a P224, several P226s, many P229s, many P239s, an X-5, a USPc, aP2000SK, a Shorty 357, a MP5/357 SMG, several SW357Vs, Several M&P357s, a M&P357c and probably others that do not come to mind at the moment

 

[nachogrande]

A HOW TO BUBBA YOUR OWN GUN???

OK- you heard it here first folks. I have figured out a way to make just about anything go up the feed ramp. If you study the problem as our engineer OP and I have, you will find that certain types of bullet shapes just don't feed well. On these, you can see a wide line in the soot on the feed ramp because the bullet has a wide contact area with the ramp. That equates to friction. Even a polished ramp with a wide contact area can be problematic. The question is then, what can be done to make a minimal contact area with less friction, or resistance to the bullet sliding up the ramp?

The answer is pretty simple, once you understand the concept. To get a thin line of contact, you have to change the shape of the ramp so the bullet doesn't conform to it, either by being the same to begin with, or by deforming to be the same shape when the slide jams them together.

The way to do this is to mill a flat in the middle of the ramp with slightly smaller radii on each side of the flat. To set this up, you put the barrel in the mill vise with the ramp exactly vertical. Then use a regular endmill to come in and touch off the center of the ramp and go sideways an equal amount each side of center. You don't want to change the angle of the ramp or make it deeper, just make a small flat going up the center. Then polish the ramp and it will feed any bullets and often empty cases. The bullets or cases now have only thin line contact when going up the ramp, therefore very little friction or resistance.

For a 9 or 10 mm, use a 5/16 endmill and make (approx.) a .06 wide flat. For a .45, use a 3/8 endmill with an approx. .09 wide flat. It is safer to use a ball end mill to keep from running into the sides of the chamber.

In addition to the other things mentioned above, I like to put a slight edge break on the firing pin hole, as that is sometimes a catch point for the rim of the case as it travels upward if the hole has a burr, or even just a sharp edge.

Giving instructions en masse to "some people" who don't have the skill to change a light bulb, let alone the correct gun smithing tools or experience??? What could possibly go wrong here?

 

[Protocall_Design]

The instructions are for those who have the skills and equipment to do the procedure. For those who don't, they will be spending money with those that do. Win win.

All the guns I have done this on (maybe a dozen) that were problematic feeders where the rounds jammed on the feed ramp were super reliable afterwards.

 

[armorer951]

Not sure, but I'm guessing these milling operations are probably going to have a negative impact on the S&W lifetime warranty.