Is there a way to improve feeding by polishing/deepening/cutting the pre-existing feed ramps in a non M4 feed ramps upper??

Yes it is possible with a dremmel tool, but I believe from the last time this was posted that the consensus was that you would also remove the finish on the lower and make it more susceptible to corrosion and stuff.

[url]http://ntdx.tripod.com/GT/007/001.htm[/url]

Note: Not my rifle, but one of the other members.

Done it many times, corrosion really isn't a concern (electrolosis mebbe) with Al parts.

I've had the best luck with the bullet shaped stones and Cratex bullets.

Pack the chamber and extension interior with a piece of shop rag (or paper towel) make sure to not change the angle of the ramps just cut them deeper and don't over do it.

Now the big question, are you having feed problems?

I think the key is to leave the extended ramp a little "proud" of the barrel extension ramp.  What I mean by this is that don't grind down the extended ramp to be perfectly flush with the extension ramp, leave it a little bit higher.  That way, if there is any wearing down of the bare aluminum, it hopefully won't wear down below the extension ramp thereby creating a ledge for bullets to snag on.

I agree with Tweak that corrosion isn't really an issue with aluminum since it will most likely be coated with lube that has creeped out of the extension.  Even if it does corrode, the oxide created is going to be tougher than the bullet jacket material.  There is a reason sanding paper is made from aluminum oxide.  Plus, the oxidation of aluminum is self-limiting (well unless some sort of galvanic action is going on like Tweak mentioned), it's not like steel whereby it will continue to oxidize even after a surface layer of rust has formed.  

Thanks for the replies and the pics.

"Now the big question, are you having feed problems?"

I went and shot some of that 193 stuff today that I got from Wholesale Hunter.  Had to re zero and check for functionality and reliability.  I used an old GI 20 rnd. mag the first part of the day, loading and firing 3 to 5 rounds at a time and adjusting in between as needed.   Out of 200 rounds plus shot today I had 1 round nose dive into the feedramp so bad it kinda split the nose of the bullet on the lugs.   I beleive it is a magazine issue as my 30 rounders I used the rest of the day functioned fine.  I just wanted to explore this feed ramp work as a way of having a bit more feed "insurance"

Would it be worthwhile?

And how much deeper to go?  ie.. how much material to remove?

20 or 30 mils???

And could you give me any more tips/hints/tricks to get it done properly?

thanks in advance for any and all help offered.

The ramps were added to rectify FtFs that came about during cold weather testing of the XM4.

The only time I've seen them [b]necessary[/b] was in carbines (higher cyclic rate) using short (OAL) blunt projos. If yours doesn't fit into those categories then they're probably not strictly necessary.

Is the rear of your barrel extension flush with, or dam close to flush with, the inside lip of the upper receiver? They're shouldn't be much, if any, of a step there. I'm talking about the portion of the upper that is directly beneath the feed ramps in the barrel extension. Some makers leave the threads on their uppers too long and that sets the barrel too far forward.

A lot of the 20 round mags are far past the end of their service lives. You may want to look at replacing the springs. Remember, originally they were nearly expendable items.

looks flush to me tweak.

I think that I may just leave well enough alone and attribute the 1 FtFd to the old 20 round mag.   If I continue to have issues then I may re-visit this idea.

thanks for your input.

I'd like to direct your attention to the AGI armorer's video on the AR15.  At the end of the video, there is a worthwhile discussion of the issue of feed ramps in the lower.  Even more helpful are a few suggestions on how to tweak your magazines for more reliable feeding.  Recommended viewing.  Thanks.
-WhiteFox

I'me familiar with AGI and their excellent armorers videos.   I bought the Sig armorers video and it proved extremely useful.   I think I may get one of the AR15 armorers videos also.  Thanks for the suggestion.

I had to send my upper back to DPMS and when I got it back I noticed that they made some M4 type feedramps in my upper while they had it. They work great, seems like a dremel or chainsaw file would do the trick since aluminum is very soft.

I only cut the ramps in my 7.62X39 upper. It helped.