12-12-2013, 05:47 PM
Buying Billet vs. Truing Yourself
As far as buying versus truing your own receiver face, JP, LaRue, Seekins Precision, Mega Machine, and Precision Firearms come to mind as excellent billet sets. I still will check every upper to see that the face is true, but unless you are an anal-retentive machinist, one of the most critical arrangement of parts is totally out of your hands with the AR15: The barrel extension and barrel mating.
OCD
I have a friend who will let a lathe spin with dial indicators on it for 45 minutes before he even thinks about cutting threads on a barrel. Most of the barrel extensions on the AR15 market are mass-produced units meant for volume, not precision. Furthermore, most AR15 barrel makers simply are not going to take the time to ensure that the threads are perfectly true to the center of the barrel's bore, which is not straight in a lot of rack-grade barrels anyway.
Everything really works outwards from the bore center, and the high-end barrels will have a true, straight hole drilled through them in top-end steel, then rifled nicely by a gifted machine craftsman. Some companies that make top-end barrel blanks will totally louse up the profiling and chambering if you let them, because it isn't a core competency for them.
If you hand an AR15 barrel job over to a comfortably OCD machinist or smith, who worships at the throne of having everything centered, trued, and concentric, the attachment of a top-quality barrel extension to a top-quality barrel blank that he has profiled will make a difference in the accuracy potential of the barrel/BE.
At the moment of ignition and peak pressure burn, the real force of the recoiling energy on the chamber and bolt is driven rearward against the receiver face, from the barrel extension flange, so support there is more important than support around the extension, but I still love a fit where the extension is very tight after ensuring the receiver face is true. + 1 for using lubricant in the pilot that inserts snugly into the carrier tunnel/raceway. These lapping tools have no movement off of true once they are inside the upper, so they need a nice thin oil in there.
Tempered Fits
Some companies use a tempered fit of the extension into the upper, like Mega and JP, where the tolerances are such that the upper won't let the barrel extension fit into it without thermal contrast between the parts, and that gives you a super-tight fit that is probably superior to bedding a sloppy mating.
Accuracy Lessons From BR and F-Class
Klem makes a number of really good points that indicate a strong F-class and benchrest train of thought, where we have really pushed the capacity of the custom industry to improve accuracy potential in barrels, receivers, and bolts. The same principles apply to the AR15 in many ways, which is where a lot of the tricks come from for accurizing the Black Rifle.
Realistic Accuracy Expectations for AR15
Most Grendel shooters are not under the illusion that they will be winning benchrest competitions against BAT machine actions with Kriegers and the 6mm PPC, but we will take all the accuracy we can get in the AR15, whether it means the difference in our confidence level as we cleanly break the trigger with the center of our crosshairs on the heart of a trophy beast, or on a small steel plate at a match.
Here are some other basic tools I use for smithing the AR15:
![[Image: 2013-12-04143136_zpse3a8ba17.jpg]](http://i1085.photobucket.com/albums/j422/LRRPF52/2013-12-04143136_zpse3a8ba17.jpg)
As to the D-Fender and enhanced silicon extractor buffers, you can over-tension bigtime in my experience with these units, so just check the extractor to ejector balance in your particular bolt. These were really meant for aiding harsh extraction in the military CLGS commando variants, where port pressure is high with 5.56 NATO loads, and the case fights to be pulled before it has rebounded back to memory as the extractor tries to pry it from the chamber. This is especially true with the 10.5" guns, suppressed.
The Grendel barrel length and gas system configurations where this is more likely to be an issue are:
* 10.5"/CLGS with a large port
* 18"/MLGS with a port larger than .076"
* 20"/MLGS (Saber actually cranked out a bunch of these for some reason)
* 28"/RLGS
We generally fight these guns with buffer and carrier weight, and then an increased power recoil spring.
As far as buying versus truing your own receiver face, JP, LaRue, Seekins Precision, Mega Machine, and Precision Firearms come to mind as excellent billet sets. I still will check every upper to see that the face is true, but unless you are an anal-retentive machinist, one of the most critical arrangement of parts is totally out of your hands with the AR15: The barrel extension and barrel mating.
OCD
I have a friend who will let a lathe spin with dial indicators on it for 45 minutes before he even thinks about cutting threads on a barrel. Most of the barrel extensions on the AR15 market are mass-produced units meant for volume, not precision. Furthermore, most AR15 barrel makers simply are not going to take the time to ensure that the threads are perfectly true to the center of the barrel's bore, which is not straight in a lot of rack-grade barrels anyway.
Everything really works outwards from the bore center, and the high-end barrels will have a true, straight hole drilled through them in top-end steel, then rifled nicely by a gifted machine craftsman. Some companies that make top-end barrel blanks will totally louse up the profiling and chambering if you let them, because it isn't a core competency for them.
If you hand an AR15 barrel job over to a comfortably OCD machinist or smith, who worships at the throne of having everything centered, trued, and concentric, the attachment of a top-quality barrel extension to a top-quality barrel blank that he has profiled will make a difference in the accuracy potential of the barrel/BE.
At the moment of ignition and peak pressure burn, the real force of the recoiling energy on the chamber and bolt is driven rearward against the receiver face, from the barrel extension flange, so support there is more important than support around the extension, but I still love a fit where the extension is very tight after ensuring the receiver face is true. + 1 for using lubricant in the pilot that inserts snugly into the carrier tunnel/raceway. These lapping tools have no movement off of true once they are inside the upper, so they need a nice thin oil in there.
Tempered Fits
Some companies use a tempered fit of the extension into the upper, like Mega and JP, where the tolerances are such that the upper won't let the barrel extension fit into it without thermal contrast between the parts, and that gives you a super-tight fit that is probably superior to bedding a sloppy mating.
Accuracy Lessons From BR and F-Class
Klem makes a number of really good points that indicate a strong F-class and benchrest train of thought, where we have really pushed the capacity of the custom industry to improve accuracy potential in barrels, receivers, and bolts. The same principles apply to the AR15 in many ways, which is where a lot of the tricks come from for accurizing the Black Rifle.
Realistic Accuracy Expectations for AR15
Most Grendel shooters are not under the illusion that they will be winning benchrest competitions against BAT machine actions with Kriegers and the 6mm PPC, but we will take all the accuracy we can get in the AR15, whether it means the difference in our confidence level as we cleanly break the trigger with the center of our crosshairs on the heart of a trophy beast, or on a small steel plate at a match.
Here are some other basic tools I use for smithing the AR15:
As to the D-Fender and enhanced silicon extractor buffers, you can over-tension bigtime in my experience with these units, so just check the extractor to ejector balance in your particular bolt. These were really meant for aiding harsh extraction in the military CLGS commando variants, where port pressure is high with 5.56 NATO loads, and the case fights to be pulled before it has rebounded back to memory as the extractor tries to pry it from the chamber. This is especially true with the 10.5" guns, suppressed.
The Grendel barrel length and gas system configurations where this is more likely to be an issue are:
* 10.5"/CLGS with a large port
* 18"/MLGS with a port larger than .076"
* 20"/MLGS (Saber actually cranked out a bunch of these for some reason)
* 28"/RLGS
We generally fight these guns with buffer and carrier weight, and then an increased power recoil spring.