The chamber of the Grendel is fairly unique in designs used in the AR15, in that it has 2 angles into the caliber sized, engraved barrel. The first angle serves to help center the bullet, while the second eases the centered bullet into the bore. This design was used to allow the use of many different bullet designs and weights with the cartridge. Since all those bullets had different ogives, they all shot differently from standard chambers because of the great variation in length and amount of freebore in comparison to that length.
The chamber was a compromise, allowing bullets all the way from 85 grains to 140 grains to shoot well. Some spectacularly well. Some manufacturers have called it a "machine gun chamber" because it seemed so loose compared to conventional wisdom regarding accurate chambers. This tends to directly contradict what some seem to be experiencing with their barrels. However, it does seem to have achieved its design, allow good accuracy with all bullets in the weight group mentioned. Seldom do you hear anyone say, "I can't get this barrel to shoot anything well!"
Les Baer chose to go the other way, making a chamber with a somewhat tighter neck, (though still able to chamber factory ammo without difficulty when properly machined), and with a conventional throat. He wanted ultimate accuracy with either of 2 bullets, the 123 AMAX or the 123 Sierra HPBT. By all accounts, he achieved this with his chamber, so much so that he offers an accuracy guarantee shooting factory ammunition. Many others have used this chamber with good results as well.
Now we seem to have run into an issue with some barrels. The problem is that there has been no consistent measuring or use of measuring tools. There are lots of people trying to measure the depth of the chamber, then posting their results, but that relies entirely upon the bullet used and their technique. There is little doubt that at least a few of the chambers are problematical, but no one has tried to quantify how many that is. Consequently, we have people saying "Mine works great, I can drop factory ammo in, no problem." While others are having difficulty and posting pictures trying to explain what is happening in their barrel.
We have a manufacturer with a quality reputation who is being assailed as the cause of the problem, when no one has actually quantified the problem! Is this 1 barrel, or 4 barrels, or 10 barrels, or 100 barrels?
Is there a way to easily tell if there really is an issue? Until we have 1 or 2 people measuring, using the exact same technique each time, and using the same measuring tools, we really have NO IDEA how big an issue this is. And that's where the real world intrudes on measurements. As an experiment, pull a bolt from a rifle, have a friend or two that you trust measure your chamber, then compare it with your measurements. If you are within .010 of each other, I'll be surprised. If you are within .005, I'll be shocked, and will congratulate you!
These measurements present their own problems in logistics, which is why I recommended that everyone with what they thought was a problem barrel contact the manufacturer and work out some solution.
I still hope that will be the case.
As is pointed out in another thread, the Grendel drawing is not a "plus/minus" drawing. It is a minimal/+.002 drawing. ANYTHING under the minimum is likely to cause problems. However, I still believe, and still count on the manufacturer making it right if there really is a significant problem with even one barrel, and I believe that given the opportunity, he will do so.
We are hearing rumors of a new Grendel reamer, one with a different throat design. Some are calling it Grendel II. The LBC was essentially exactly that, a different throat design. I've talked with several different manufacturers, at least one of whom offers both the LBC and SAAMI Grendel chamber. The consensus is that the SAAMI chamber shoots many bullets exceedingly well, with one manufacturer telling me that he had tested them side by side and found the LBC shot the 123's very well, but that the shorter bullets all shot more accurately out of the Grendel chamber and that even the 123's demonstrated very similar results from both chambers. Some have insinuated that shooting longer bullets, like the 120 grain solids or 130-140 grain bullets out of the new chamber would be possible. That may well be true, but it will be at the expense of loss of the magazine capability, since no mags load past 2.300 with the Grendel case without issues. I load longer than 2.300 with 130 Bergers and don't touch anything in my Grendels, but I single load them, using a sled, so I'm not sure that even a new throat would be helpful in that regard, since I can do it already, with a SAAMI throat!
If you were to go to the local store, pick out a bolt .223 and take it home, and then find that your factory box of .223 ammo didn't fit, what would be your reaction? Would you say, "Well, I'll just polish it up with some Tubbs and it'll be fine."? Or would it go right back to the store? Why is the situation with barrels any different? You are buying a product that is advertised as being built to a standard. If it doesn't meet that standard, why are you considering fixing it yourself? Would you take delivery on a new car, then find out that it only ran on 50% ethanol and decide to do the work yourself to make it run on gasoline, or 10% ethanol? Think this through, folks! Please!
For those that feel a need to post here......Please ONLY POST IF YOU HAVE A BARREL THAT YOU BELIEVE IS OUT OF SPEC. It would be very helpful to actually quantify the issue. If you can't tell if it is out of spec, please take it to a gunsmith who can check it, or to one who will show you how to do it. IF you then find it out of spec, please contact the manufacturer to discuss a resolution.
The chamber was a compromise, allowing bullets all the way from 85 grains to 140 grains to shoot well. Some spectacularly well. Some manufacturers have called it a "machine gun chamber" because it seemed so loose compared to conventional wisdom regarding accurate chambers. This tends to directly contradict what some seem to be experiencing with their barrels. However, it does seem to have achieved its design, allow good accuracy with all bullets in the weight group mentioned. Seldom do you hear anyone say, "I can't get this barrel to shoot anything well!"
Les Baer chose to go the other way, making a chamber with a somewhat tighter neck, (though still able to chamber factory ammo without difficulty when properly machined), and with a conventional throat. He wanted ultimate accuracy with either of 2 bullets, the 123 AMAX or the 123 Sierra HPBT. By all accounts, he achieved this with his chamber, so much so that he offers an accuracy guarantee shooting factory ammunition. Many others have used this chamber with good results as well.
Now we seem to have run into an issue with some barrels. The problem is that there has been no consistent measuring or use of measuring tools. There are lots of people trying to measure the depth of the chamber, then posting their results, but that relies entirely upon the bullet used and their technique. There is little doubt that at least a few of the chambers are problematical, but no one has tried to quantify how many that is. Consequently, we have people saying "Mine works great, I can drop factory ammo in, no problem." While others are having difficulty and posting pictures trying to explain what is happening in their barrel.
We have a manufacturer with a quality reputation who is being assailed as the cause of the problem, when no one has actually quantified the problem! Is this 1 barrel, or 4 barrels, or 10 barrels, or 100 barrels?
Is there a way to easily tell if there really is an issue? Until we have 1 or 2 people measuring, using the exact same technique each time, and using the same measuring tools, we really have NO IDEA how big an issue this is. And that's where the real world intrudes on measurements. As an experiment, pull a bolt from a rifle, have a friend or two that you trust measure your chamber, then compare it with your measurements. If you are within .010 of each other, I'll be surprised. If you are within .005, I'll be shocked, and will congratulate you!
These measurements present their own problems in logistics, which is why I recommended that everyone with what they thought was a problem barrel contact the manufacturer and work out some solution.
I still hope that will be the case.
As is pointed out in another thread, the Grendel drawing is not a "plus/minus" drawing. It is a minimal/+.002 drawing. ANYTHING under the minimum is likely to cause problems. However, I still believe, and still count on the manufacturer making it right if there really is a significant problem with even one barrel, and I believe that given the opportunity, he will do so.
We are hearing rumors of a new Grendel reamer, one with a different throat design. Some are calling it Grendel II. The LBC was essentially exactly that, a different throat design. I've talked with several different manufacturers, at least one of whom offers both the LBC and SAAMI Grendel chamber. The consensus is that the SAAMI chamber shoots many bullets exceedingly well, with one manufacturer telling me that he had tested them side by side and found the LBC shot the 123's very well, but that the shorter bullets all shot more accurately out of the Grendel chamber and that even the 123's demonstrated very similar results from both chambers. Some have insinuated that shooting longer bullets, like the 120 grain solids or 130-140 grain bullets out of the new chamber would be possible. That may well be true, but it will be at the expense of loss of the magazine capability, since no mags load past 2.300 with the Grendel case without issues. I load longer than 2.300 with 130 Bergers and don't touch anything in my Grendels, but I single load them, using a sled, so I'm not sure that even a new throat would be helpful in that regard, since I can do it already, with a SAAMI throat!
If you were to go to the local store, pick out a bolt .223 and take it home, and then find that your factory box of .223 ammo didn't fit, what would be your reaction? Would you say, "Well, I'll just polish it up with some Tubbs and it'll be fine."? Or would it go right back to the store? Why is the situation with barrels any different? You are buying a product that is advertised as being built to a standard. If it doesn't meet that standard, why are you considering fixing it yourself? Would you take delivery on a new car, then find out that it only ran on 50% ethanol and decide to do the work yourself to make it run on gasoline, or 10% ethanol? Think this through, folks! Please!
For those that feel a need to post here......Please ONLY POST IF YOU HAVE A BARREL THAT YOU BELIEVE IS OUT OF SPEC. It would be very helpful to actually quantify the issue. If you can't tell if it is out of spec, please take it to a gunsmith who can check it, or to one who will show you how to do it. IF you then find it out of spec, please contact the manufacturer to discuss a resolution.
You seek escape from pain. We seek the achievement of happiness. You exist for the sake of avoiding punishment. We exist for the sake of earning rewards. Threats will not make us function; fear is not our incentive. It is not death that we wish to avoid, but life that we wish to live. - John Galt