AR-15 Questions: Feed Ramps / Lower Differences

[GBMaryland]

Ok, a few questions for folks that actually have exterience...

...yeah, I was in the USAF, NO, we didn't spend a lot of time with M16s when I was in...

Question 1:

I've got an Armalite upper with very deep feed ramps. I've noticed that replacement rifle (not carbine) barrels seem to have feed ramps that exist only within the barrel itself; they are not cut deep enough match up with the upper reciever.

Does anyone make a good 1:9 rifle barrel (20 inch) with the extended feed ramps?

Question 2:

I have a few lower recievers. One is a Rock River and the other is an Essential Arms lower...

I extected to have to put in an AccuWedge for the RRA lower, but I was supurised when it had a VERY tight fit... and that the lower basically didn't have any room for something like an AccuWedge. (It obviously doesn't need it...)

Is there a reason that the Essential Arms lower would have significantly more room under the rear push pin area than the RRAlower? My curiousity is more along the lines of: Was the Essential Arms lower designed with a military application in mind, vs the RRA being a civilian sporter lower??

Thoughts?

GB

 

[widnerkj]

Re: AR-15 Questions: Feed Ramps / Lower Differences

for your barrel. they are actually kind of easy to find

http://www.rainierarms.com/?page=shop/detail&product_id=1631

http://www.rainierarms.com/?page=shop/detail&product_id=1635

http://rockriverarms.com/index.cfm?fuseaction=category.display&category_id=272

That should get you going in the right direction for your barrel.
the fit of the RRA is famously tight. I don't think they are low shelf "RDIAS" ready. Which would be the reason you can't get an accuwedge in there.

 

[GBMaryland]

Re: AR-15 Questions: Feed Ramps / Lower Differences

Thanks, I appricate it.

In my case, I'll need to find a HBAR type barrel, with M4 feed ramps (or so it appears).

So it's called "a low shelf" on the lower reciever when it's there is no real space under the rear pin?

GB

 

[Oodin]

Re: AR-15 Questions: Feed Ramps / Lower Differences

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GBMaryland</div><div class="ubbcode-body">So it's called "a low shelf" on the lower receiver when it's there is no real space under the rear pin?</div></div>No, that's a high shelf.

A high shelf is not compatible with a DIAS (Drop In Auto Sear) whereas a low shelf receiver (presumably like your Essential Arms receiver) IS compatible with a DIAS (there is enough space for one).

I hope that clears it up.

 

[4thPointOfContact]

Re: AR-15 Questions: Feed Ramps / Lower Differences

"M4" feedramps are an adaptation necessary to get the carbine system to feed reliably. The original M16 configuration existed for close to 30 years without requiring them. I believe there is one major manufacturer that has stated that unless you have a combination of full-auto capability and worn springs then M4 ramps are not a necessity and can even be a liability.

Since the start-point and end-point of barrel extension are fixed in space, the only way to get a 'longer' feed ramp is to make the angle steeper and more abrupt. Depending on bullet type and overall length this may not be advantageous.

 

[GBMaryland]

Re: AR-15 Questions: Feed Ramps / Lower Differences

Neat, so I guess the Essential Arms story is true... That they were making them for a military contract, and then opted to started selling them publically again.

 

[Oodin]

Re: AR-15 Questions: Feed Ramps / Lower Differences

AR-15 lower FAQ It's really just a design choice. Many manufacturers use a low shelf, many others use a high shelf.

IIRC the high shelf design came about during the AWB.

 

[widnerkj]

Re: AR-15 Questions: Feed Ramps / Lower Differences

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Oodin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GBMaryland</div><div class="ubbcode-body">So it's called "a low shelf" on the lower receiver when it's there is no real space under the rear pin?</div></div>No, that's a high shelf.

A high shelf is not compatible with a DIAS (Drop In Auto Sear) whereas a low shelf receiver (presumably like your Essential Arms receiver) IS compatible with a DIAS (there is enough space for one).

I hope that clears it up. </div></div>

I was afraid I had it backwards.

 

[GBMaryland]

Re: AR-15 Questions: Feed Ramps / Lower Differences

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 4thPointOfContac</div><div class="ubbcode-body">"M4" feedramps are an adaptation necessary to get the carbine system to feed reliably. The original M16 configuration existed for close to 30 years without requiring them. I believe there is one major manufacturer that has stated that unless you have a combination of full-auto capability and worn springs then M4 ramps are not a necessity and can even be a liability.

Since the start-point and end-point of barrel extension are fixed in space, the only way to get a 'longer' feed ramp is to make the angle steeper and more abrupt. Depending on bullet type and overall length this may not be advantageous. </div></div>

Interesting. My interest are the relatively sharp edges where the "M4" sytle upper reciever meets the non-M4 feedramps. They're actually somewhat sharp... Generally, barrels are cheap, so I was considering just keeping things consistant. I'm not sure that Armalite is carrying the 20 inch HBAR sytle M4 barrel that came with the upper anymore... [I bought it new from someone that had it sitting around for awhile.]

As for the second part of your answer: I gather the implication is that if I where using something like a 68gr Hornady BTHP... it the nose might deform due to the steep nature of the M4 sytle ramp?

I have no interest in a select fire AR, or spending the insanely stupid amount of money the want for that trigger group. (If I want something like that I'll save the cash an attempt to find an MG34 or MG42... -smile-)

 

[Oodin]

Re: AR-15 Questions: Feed Ramps / Lower Differences

GBMaryland, you're saying that the upper receiver you have now HAS M4 feed ramps, correct? Then you will really want to go with a barrel extension with M4 feed ramps. Exhibit 1:

Using a barrel with standard feed ramps creates the situation depicted in the lower left picture, bullet noses tend to get caught in the "gap" created by the M4 feed ramps.

 

[GBMaryland]

Re: AR-15 Questions: Feed Ramps / Lower Differences

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Oodin</div><div class="ubbcode-body">GBMaryland, you're saying that the upper receiver you have now HAS M4 feed ramps, correct? Then you will really want to go with a barrel extension with M4 feed ramps. Exhibit 1:

Using a barrel with standard feed ramps creates the situation depicted in the lower left picture, bullet noses tend to get caught in the "gap" created by the M4 feed ramps. </div></div>

And the lower left aka "bad" picture is exactly what I've got...