Rifle failing to feed on 75 gr ammo

[Singlestack Wonder]

seems to happen more on the right side. I've had the same results with a new bcm carrier.

The receiver feed ramps do not look right, especially the right one. What is the upper receiver brand? Did it come with feed ramps or did someone else cut them?

[SomeOtherGuy]

My guess would be that the upper receiver - the machined forging itself - is out of spec on dimensions and the barrel is sitting higher than normal relative to the lower receiver and therefore to the magazine position. The slightly shorter 55gr cartridges are just able to get enough angle as they leave the magazine to miss the barrel end when going into the chamber, but the slightly longer 75's are not and are hitting the end of the barrel earlier, before they have left the magazine enough to get some angle to enter into the chamber. This is purely a guess. Do you have other uppers that you could compare dimensions to?

[ouchonyee]

It is hard to see the right feed ramp. Perhaps another picture from the bottom?

It looks like your bullet got set back in the first picture.. maybe normal for a round that got hung up.. although I once noticed that many red tipped Hornady bullets I was given, got setback when I cycled through a mag. Didn't measure how much, and I don't know what is acceptable, but I decided to stick with crimped after that.

It also looks like maybe the case mouth is hung up where the transition is? Maybe it gets stuck enough to angle the round downwards and wedge the bullet between the lugs?

[556Cliff]

Hornady Superformance is not for carbines. > https://www.m4carbine.net/showthread...ed-in-carbines

[SomeOtherGuy]

Hornady Superformance is not for carbines. > https://www.m4carbine.net/showthread...ed-in-carbines

OP also said "it will also fail to feed 75gr hornady from a bolt locked to the rear. " That seems to indicate it is a problem of geometry, not of over-pressure or anything else related to the Superformance powder.

[556Cliff]

OP also said "it will also fail to feed 75gr hornady from a bolt locked to the rear. " That seems to indicate it is a problem of geometry, not of over-pressure or anything else related to the Superformance powder.

I see, I would still stay away from the Hornady Superformance though.

[stank]

Is the bullet hitting the feed ramp and getting setback, instead of ramping up into position to feed into chamber. Have you tried other 75 or 77 grain ammo from another manufacturer? On a side not I tried that ammo, was a big no go for me, primer ended up in the magazine.

[farmhard]

I now believe it to be feed ramp geometry, when I compared it to a couple bcm barrels (I can't believe I didn't check this earlier) and the stainless barrel ramps appeared to be a lot steeper. I believe that over time the space between the barrel lugs have wore to the point they are now causing malfunctions. I have contacted the manufacturer and they have agreed to replace the barrel.

[MistWolf]

The bore will wear out long before the feed ramps do

[farmhard]

The bore will wear out long before the feed ramps do

Mist if I can get a good pic ill post it, there is a spot on the ramps where there is what I would call abnormal wear from the ramp being to steep. also to add the manufacture said at the time of purchase, which was during the panic of 2013 they had trouble sourcing barrel extensions and that it might have not been in spec. its bad that they sent it out that way and its bad that I didn't know more about what a proper feed ramp should look like, but are at least making it right.