07-16-2022, 04:26 PM
The M4 feed ramps are part of the solution to feeding 6.5 Grendel reliably. M4 ramps are lowered relative to the bore axis, which allows the fatter case to index correctly.
The feeding cone in the breech is also a critical geometry that needs to be machined right, otherwise you will get the situation with larger meplat bullets like 603 Country did with Nosler 64gr .223 Rem.
There are a lot of things that have to come together, starting with feed lip geometry, magazine index height relative to the bore axis (controlled by the placement of the magazine catch hole in the lower receiver), then the placement of the feed ramps, their angle, their height, and then the feed cone in the breech of the barrel.
This really turns into an argument for a competent manufacturer who has worked all these issues out and established their own TDP for Grendel or whatever cartridge theyre chambering, vs the DIY/parts market.
As DIYers, we tend to want to assume that all we need to do is Lego some parts together with the best of intentions, entitled to the stars aligning for us, and expecting it all to work out.
This expectation is especially optimistic when we buy bottom-barrel parts.
For my personal approach to this, I look for barrels from companies that have been around for a long time and have a reputation for reliability #1, followed by accuracy.
My first barrel/bolt combo was from Alexander Arms.
My 2nd was from Lilja with the 1st Group Buy we did here.
I dont want to change the angle of the feed ramps or mess with that geometry, but just take the sharp edges off the teeth along the sides of the ramps and polish the ramps so the coefficient of friction is reduced and especially my BTHP meplats arent damaged as much.
One problem I have seen is that when fitting the barrel extension to the upper receiver, the bottom edge of the ramps can sometimes be proud of the corresponding M4 ramps in the upper receiver.
For those who are unaware, the AR15/M16 family never had extended feed ramps in the upper until the Colt Model 727 (M16A2 Carbine), which then were carried over to the M4.
Reason for that was on AUTO or BURST fire, the action would start to out-run the spring rate of the magazines, and cartridges would be prematurely fed before they could lift into feed lip presentation, so they would hit the flat face of the upper receiver right under the barrel extension.
The serendipity of that for 6.5 Grendel is that the larger, lower feed ramps of both the upper receiver and barrel extension played well with the fatter cartridge.
These aspects of the AR15 have been constantly looked at throughout the life of the program by DoD, gaining more scrutiny as more carbines were fielded in the 1990s, with most of the emphasis on magazines.
Suppressed carbine combos are the hardest to get to run reliably.
The feeding cone in the breech is also a critical geometry that needs to be machined right, otherwise you will get the situation with larger meplat bullets like 603 Country did with Nosler 64gr .223 Rem.
There are a lot of things that have to come together, starting with feed lip geometry, magazine index height relative to the bore axis (controlled by the placement of the magazine catch hole in the lower receiver), then the placement of the feed ramps, their angle, their height, and then the feed cone in the breech of the barrel.
This really turns into an argument for a competent manufacturer who has worked all these issues out and established their own TDP for Grendel or whatever cartridge theyre chambering, vs the DIY/parts market.
As DIYers, we tend to want to assume that all we need to do is Lego some parts together with the best of intentions, entitled to the stars aligning for us, and expecting it all to work out.
This expectation is especially optimistic when we buy bottom-barrel parts.
For my personal approach to this, I look for barrels from companies that have been around for a long time and have a reputation for reliability #1, followed by accuracy.
My first barrel/bolt combo was from Alexander Arms.
My 2nd was from Lilja with the 1st Group Buy we did here.
I dont want to change the angle of the feed ramps or mess with that geometry, but just take the sharp edges off the teeth along the sides of the ramps and polish the ramps so the coefficient of friction is reduced and especially my BTHP meplats arent damaged as much.
One problem I have seen is that when fitting the barrel extension to the upper receiver, the bottom edge of the ramps can sometimes be proud of the corresponding M4 ramps in the upper receiver.
For those who are unaware, the AR15/M16 family never had extended feed ramps in the upper until the Colt Model 727 (M16A2 Carbine), which then were carried over to the M4.
Reason for that was on AUTO or BURST fire, the action would start to out-run the spring rate of the magazines, and cartridges would be prematurely fed before they could lift into feed lip presentation, so they would hit the flat face of the upper receiver right under the barrel extension.
The serendipity of that for 6.5 Grendel is that the larger, lower feed ramps of both the upper receiver and barrel extension played well with the fatter cartridge.
These aspects of the AR15 have been constantly looked at throughout the life of the program by DoD, gaining more scrutiny as more carbines were fielded in the 1990s, with most of the emphasis on magazines.
Suppressed carbine combos are the hardest to get to run reliably.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com