1911 in 40 S&W jamming

[greatgoogamooga]

I built up an Essex in 10mm and it runs fine. Decided that converting it to .40 would make shooting cheaper and should be a matter of changing barrels. Fitted a .40 S&W barrel and I'm getting failure to feed about 1 out of 5 rounds. Here are the details:

Barrel: non-ramped Olympic Arms
Slide: Essex .40/10mm breechface
Extractor: Ed Brown .40/10mm
Mags: Mec Gar and Metalform .40

The barrel ramp is just slightly less than .030 ahead of the frame feedramp. When the jam occurs, the nose of the bullet wedges itself against the barrel feedramp, with the base of the case low against the breechface. It does not make it far enough to interact with the extractor.

The fit of the barrel looks good. There was little fitting to be done with this barrel. While it says NM on it, it was not oversized. The .278 link allows the barrel to ride on top of the lower lugs without riding the link at lockup. I "polished" the ramp with 400 grit sandpaper on a dowel to remove any roughness. It's shiny, but dimensionally, untouched.

With snapcaps, the gun cycles fine, manually. It has the same jam with any ammo (CCI or American Eagle) either hand cycling or live firing. The only thought I have at this point is to try loading some roundnose bullets.

What causes this kind of jam? Will a roundnose bullet cure it?

TIA

Goog

[swampertwo]

When you switched to 40, did you install a lower poundage recoil spring?
The 10 should take one with a higher rating and the 40 may not drive the slide far enough to the rear and may cause misfeeds.
Jeff

[greatgoogamooga]

Yup. I've tried, 18 and 20# recoil springs. It happens why hand cycling, so I don't think that's the problem, though.

Goog

[Tap]

Are you using those weird angle pointed 40 bullets? If so I would try and find some round nose and see if that was the problem