I may have messed up my build: Feed ramps


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Demos
January 31, 2013, 07:46 PM
Hi guys,
I think I may have messed up my build. I have a Rock River Arms 20" heavy stainless steel barrel (like on their Predator Pursuit and National Match rifle) on order and when I went to my local shop I thought I lucked out since they had a Mega Arms completed upper for cheap since a regular had mounted everything on it and decided he wanted a billet one instead. I bought the upper and now a few days later I think I might have a problem. The upper has m4 ramps, but I'm pretty sure the barrel wont. Does anyone own this RRA barrel to confirm one way or another if I messed up (I tried calling RRA several times at different times and different days and either can't get through or am forever on hold)? If I did mess up, is there a way to resolve the problem other than a new upper which I won't be able to find at a reasonable price for a while?

Thanks,
Demos

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taliv
January 31, 2013, 09:17 PM
a new barrel?


sorry to say it, but it does sound like you're going to have a problem. i don't know for sure but my guess would also be that the RRA bbl won't have the feed ramps

other options would be, get a gunsmith to either replace the barrel extension with an M4 extension, or bubba job to cut ramps in the rifle extension you've got. i personally wouldn't do either of these. i'd find a different upper or different bbl. and since bbl are easy to come by these days and receivers aren't, i know which i would choose.

Caliper_RWVA
January 31, 2013, 09:19 PM
Carefully use a Dremel to cut the feedramps into the barrel, then polish.

rcmodel
January 31, 2013, 09:41 PM
The ramps are not cut in the barrel.
They are cut in the barrel extension.

Myself?

I build it and try it.

It will most likely work just fine, if you don't built a full-auto M4.

See this:
http://www.m4carbine.net/showthread.php?t=193

rc

madcratebuilder
February 1, 2013, 07:40 AM
Adding feed ramps to the barrel extension is a five minute job with a jewelers file. I would not use a Dremel tool unless you had a lot of experience with one.

http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/feedramps2.jpg

http://i32.photobucket.com/albums/d37/madcratebuilder/Temptation.jpg

rbernie
February 1, 2013, 07:44 AM
Adding feed ramps to the barrel extension is a five minute job with a jewelers fileConcur. I've done it, both to add the M4 cuts when the barrel extension doesn't have them as well as to match the extension cuts to the receiver.

It's really not a huge deal if you have any inclination towards that sort of task.

Z-Michigan
February 1, 2013, 09:26 AM
Another vote for adding feedramp cuts to the barrel extension. FWIW I've had a barrel that came purportedly cut for M4 feedramps and they didn't match up to the ones in the upper, so I had to deepen them anyway. It's not a big deal.

However, it is unrealistic to talk about replacing the barrel extension. They are torqued on and only after the extension is installed is the gas port drilled. The gas port must be 180 degrees from the feedramp cuts of the barrel extension if you want a rifle that functions well. There is a very low chance that a replacement barrel extension will just happen to line up so that this occurs.

taliv
February 1, 2013, 09:38 AM
z-mi yeah, i forgot about the gas port. you're right. that would be a bad idea. however, i would not dremel or file ramps in there either.

MrCleanOK
February 1, 2013, 10:21 AM
Build your rifle. Shoot it. If the feed ramp incompatibility causes you malfunctions, then do the jewlers file hack job, or sell/trade your barrel. Chances are good that your rifle will work just fine, and if it still bothers you then you can fix it when the market stabilizes.

Z-Michigan
February 1, 2013, 02:14 PM
however, i would not dremel or file ramps in there either.

To each his own. To the best of my very limited knowledge, the barrel extension is either unhardened or through-hardened, so modifying it doesn't damage a hard surface and expose a soft underlying metal like it does with anodized aluminum or many other internal gun parts (triggers and sears, particularly). I've done it with a Dremel and small oval grinding bit, I just went slow and checked my work frequently to get a perfect match between feedramps on the extension and feedramp cuts on the upper (an VLTOR). The barrel extension had some degree of cuts already, just not quite enough, and I read somewhere (can't remember where) that some amount of custom fitting like that was within the realm of normal and OK when mating a barrel and upper. YMMV, etc.

I've concluded that uppers without feedramp cuts are a perfectly good way to go, they work with any barrel extension and you really don't need M4 feedramps with a .223/5.56* unless you have a SBR or something ridiculously overgassed.

*with cases larger in diameter than the .223 case, like 6.8 SPC or 6.5 G, M4 feedramps may be important for reliability.

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