Of Reamers, Chambers, and Real World measurements

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  • bwaites
    Moderator
    • Mar 2011
    • 4445

    Of Reamers, Chambers, and Real World measurements

    There has been great consternation recently over barrels and chambers.

    Some have barrels that seem to allow factory cartridges to drop right in, straight from the factory. Others have claimed that their barrels do not allow them to chamber factory ammunition, but do allow short seating of bullets, and seem to shoot very well.

    There have been conflicting reports that manufacturers may be using SAAMI spec reamers, and not getting SAAMI spec chambers, or that the chamber design itself may be at fault.

    Unfortunately, all of the above, and all the "remedies" are nothing but speculation from everyone involved.

    There are some terms that are somewhat confusing:

    Some refer only to the area occupied by the cartridge case itself as the chamber, while others define the chamber as the entire area filled by a loaded cartridge as the chamber. In the second case, this includes the area filled by the cartridge case, the area in front of the case (often called the throat, and which includes the angle that guides the bullet into the caliber sized, engraved portion of the barrel), and the area occupied by the ogive of the bullet.

    SAAMI defines the dimensions of the case itself.

    The drawings of the chamber are also defined by SAAMI, and in the case of the Grendel chamber, that includes the compound throat, and the designated angular changes within that throat. In order to properly be called a SAAMI chamber, all those dimensions must be consistent with the SAAMI drawing. In a typical chamber, the dimensions include an area ever so slightly larger than the bullet diameter, this is called the "free bore". This is an area prior to the caliber diameter area where the bullet is moving freely before it is forced into the caliber engraved barrel itself.

    In attempts at ultimate accuracy, this freebore area may be nearly nonexistent, or the handloader may load his bullets long, thus engaging them into the rifling so that the bullet does not ever have that "free" jump before engraving. This is a bit of a gamble on the handloaders part, accepting that there is a pressure increase, but that the gain in accuracy is worth it. VLD bullets are typically loaded in this manner. Modern metals are so good and so strong that many long range competitive shooters "JAM" the bullets significantly into the lands and get away with it because of that strength.



    Here are the facts about ALL chambers:

    A proper SAAMI chamber will allow a proper SAAMI cartridge to chamber properly. This means it should not take excessive force for the cartridge to chamber. The bullet should NOT be engraved by the lands doing so. There is NO SAAMI chamber that I am aware of that allows a factory loaded cartridge to do so. The area directly in front of the case mouth may very slightly "kiss" or rub the bullet, but in doing so it should not deform or scrape the bullet. (Those seeking ultra accuracy often have a "tight necked" chamber built, where they must turn the neck of the cartridge itself to allow loading, but no SAAMI cartridge or design I can find is on the books in this manner.) Even when they do so, the area in front of the neck must remain open to the bullet itself, although as noted above, that area may be very short.

    We have reports of barrels that do not allow loading of SAAMI factory ammunition.

    There are TWO and only TWO possibilities:

    1) The chamber is incorrect.

    2) The ammunition is incorrect.

    Number 2 is pretty easily checked. Try a cartridge from another case lot, or several different case lots, and several different loadings.

    If ONLY the one cartridge doesn't fit, you can be relatively sure that the cartridge itself is out of spec.

    If more than one, or multiples, don't fit, then there are only 2 possibilities:

    1) You have multiple case lots of ammunition out of spec. (Highly unlikely, especially if you use different loadings and bullets.)

    2) You have a chamber that is out of spec.
    Last edited by bwaites; 02-04-2014, 06:17 PM.
  • bwaites
    Moderator
    • Mar 2011
    • 4445

    #2
    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.
    Last edited by bwaites; 02-04-2014, 10:07 PM.

    Comment

    • mongoosesnipe
      Chieftain
      • May 2012
      • 1142

      #3
      While this is wondering slightly off the intended topic of this thread I bought one of the 18" barrels from brownells while I quickly threw it together ran a patch down the bore and tried to chamber a round and it stuck a little, I had to hit the charging handle on the under side of my bench to extract the round and there were some marks on the case mouth my first thought was out of spec since that seemed to be going around... I scrubbed the chamber with a bronze brush an sprayed it out with brake cleaner and rounds then chambered and extracted better but it still didn't feed very well, so I did a bolt polish up and polished the feed ramps and now everything is gravy

      Other than a thuroghly cleaning I did not do anything to the chamber or throat

      I think one thing people forget when they are putting these guns together is that we are assembling components and not dealing with a finished and test fired product, when these barrels get made the chamber gets cut blown out with air and a go/no go test gets done most likely with a bolt with extractor and ejector removed and if it passes the barrel is good to go and gets an assembled bolt put in it and goes out of the shop

      It is out job as home gunsmiths to make things work from there, one thing I would recomend I order to cheek the throat/chamber of these new barrels is to load up a dummy round and cheek it with a case guage to ensure it should chamber then with the bullet seated quite long and the ejector and extractor removed from your bolt chamber said round jamming it into the lands and let the bolt push the bullet into the case then remove bolt and tap round out from the muzzle with a cleaning rod this should give you a rough estimate of your throat profile, or you could do a chamber cast and take your measurements that way

      In the end it's very difficult for even the best mind to diagnose and or solve a problem with a tangible item sight unseen through a computer screen
      Punctuation is for the weak....

      Comment

      • dammitman
        Warrior
        • Dec 2012
        • 647

        #4
        so if you have a very well cleaned brand new barrel that you can NOT drop a factory hornady round without it sticking (and i dont mean just barely, you have to tap it out) due to the bullet touching the barrel, is it in spec or out? i have one like that but i really think i could tubbs it or just shoot it some and it would "clean" up that part of the barrel. of course as i hae stated already though my bolt is out of spec enough to not pass the go/no go gauges. it wont go but a LBC bolt will and i have more than one extra of those to try. my dilemma is should i just tubbs it or shoot it with a good bolt or not? i wish i had a great way to polish the throat that was perfect. and yes i have already contacted satern and they are more than willing to do whatever i deciede.

        Comment

        • mongoosesnipe
          Chieftain
          • May 2012
          • 1142

          #5
          I have not tried factory hornady as I handload everything I have on box of AA 123 scenars and they chamber, I have some 123 amax but haven't loaded any off them what's the oal for hornady factory amax I will load some up and try it tonight
          Punctuation is for the weak....

          Comment

          • bwaites
            Moderator
            • Mar 2011
            • 4445

            #6
            Originally posted by mongoosesnipe View Post
            I have not tried factory hornady as I handload everything I have on box of AA 123 scenars and they chamber, I have some 123 amax but haven't loaded any off them what's the oal for hornady factory amax I will load some up and try it tonight
            2.245-2.250

            Comment

            • mongoosesnipe
              Chieftain
              • May 2012
              • 1142

              #7
              I loaded up an 123 amax dummy round to 2.250and it has zero resistance entering or leaving the battery, the 123 lapua and 120 smk both have a very slight resistance opening the bolt but no markings on the bullet

              So assumably the barrels from brownells are not affected in the same way as the midway and liberty barrels but I would still recommend doing a little scrubbing with a bronze brush in case there is a little bur or something in the throat

              The first round I chambered was a loaded 120 smk and it stuck to the point of using the under side of the bench hit the charging handle and after a little scrub and slick up its gravy so I think I had a bur others may not be so lucky but it is certainly worth beating up a 1.99 270 bronze brush to see it it helps followed by brake cleaner, rinsing in hot water and the blowing dry with compressed air and running a patch down the bore
              Punctuation is for the weak....

              Comment

              • WildBill3/75

                #8
                I measure my factory 123 amax @ 2.245 COAL

                With my Satern cut rifle barrel using 123gr amax I measure 2.230 tell I get resistance in the chamber.

                With my old barrel chambered by PF I was getting 2.271 @ point of resistance in the chamber using 123 amax.

                Comment

                • txgunner00
                  Chieftain
                  • Mar 2011
                  • 2070

                  #9
                  Originally posted by WildBill3/75 View Post
                  I measure my factory 123 amax @ 2.245 COAL

                  With my Satern cut rifle barrel using 123gr amax I measure 2.230 tell I get resistance in the chamber.

                  With my old barrel chambered by PF I was getting 2.271 @ point of resistance in the chamber using 123 amax.
                  How long have you had your Satern barrel? I just remeasured mine (20" Satern cut rifled purchased 2010) a few days ago and I was getting 2.270+ to the lands with 123 amax.
                  NRA life, GOA life, SAF, and TSRA

                  "I ask, Sir, what is the militia? It is the whole people, except for a few public officials. To disarm the people is the best and most effectual way to enslave them."

                  George Mason, co-author, 2nd Amendment.

                  Comment

                  • WildBill3/75

                    #10
                    Originally posted by txgunner00 View Post
                    How long have you had your Satern barrel? I just remeasured mine (20" Satern cut rifled purchased 2010) a few days ago and I was getting 2.270+ to the lands with 123 amax.
                    It's a newer one, purchased in 2013.

                    Comment

                    • rickOshay
                      Warrior
                      • Apr 2012
                      • 784

                      #11
                      My 24" cut rifled Satern measures like TXGUNNER's. Mine purchased in 2012.

                      Comment

                      • Tedward
                        Banned
                        • Feb 2013
                        • 1717

                        #12
                        Originally posted by dammitman View Post
                        so if you have a very well cleaned brand new barrel that you can NOT drop a factory hornady round without it sticking (and i dont mean just barely, you have to tap it out) due to the bullet touching the barrel, is it in spec or out? i have one like that but i really think i could tubbs it or just shoot it some and it would "clean" up that part of the barrel. of course as i hae stated already though my bolt is out of spec enough to not pass the go/no go gauges. it wont go but a LBC bolt will and i have more than one extra of those to try. my dilemma is should i just tubbs it or shoot it with a good bolt or not? i wish i had a great way to polish the throat that was perfect. and yes i have already contacted satern and they are more than willing to do whatever i deciede.
                        dammitman, wish I read your question more thoroughly earlier. You state the bolt is out of spec. Why? Is the HS .130 and the bolt OAL 2.800? If so, you might have the same batch of bolts I got with my barrels. Satern did receive out of spec bolts from there new supplier and I returned them. All were from .129 to.132 but 90% were .130 head space, not .135 and OAL of 2.800 rather than 2.810. I think we all know who the new bolt supplier to Satern is from previous post so hopefully they make the bolts in the future correctly.

                        I bought bolts directly from Maxim Firearms. He has bolts for sale on his website and are made from 9310 Steel. http://www.maximfirearms.com/online-...-grendel-bolt/
                        I am not promoting the product (yes I am) but if you want a bolt and extractor made from a reputable manufacture, he has them. The first batch of bolts thet he supplied had Satern 6.5 Grendel extractors without markings on them. They currently have there in house manufactured extractors that are easily identified with the same 4 rings as the bolts. Also notice he eased the edges on the lugs prior to finishing them.
                        IMG_1156.jpg

                        Mark at Precision Firearms also has bolts from Maxim and is doing different finishes but not sure if they are available. Either way, you can get correct bolts. AA also has bolts, I got mine in 40 amazing days just to see if they are shipping them. Not sure if it will continue but they also have a quality product. Les Baer Custom too is a source for bolts and I have had great success with theirs but they ARE NOT 9310 steel that I know about.

                        Comment

                        • dammitman
                          Warrior
                          • Dec 2012
                          • 647

                          #13
                          yes my bolt is out of spec and as i see it totally unusable. i would hate to have a barrel that was headspaced to use some kind of bastard bolt. i am sending both barrel and bolt back to satern this week. i have talkd to them and they know that they have a bad batch of bolts. the one thing i am really unsure about is their description of what they are going to do with the barrel. they are going to "scrape" it. WTF is scrape it? they described to me that they have a tool bit now that will as i see it just removing more material from the throat. i sure hope this is a good idea.

                          Comment

                          • dammitman
                            Warrior
                            • Dec 2012
                            • 647

                            #14
                            [/QUOTE]Mark at Precision Firearms also has bolts from Maxim and is doing different finishes but not sure if they are available. Either way, you can get correct bolts. AA also has bolts, I got mine in 40 amazing days just to see if they are shipping them. Not sure if it will continue but they also have a quality product. Les Baer Custom too is a source for bolts and I have had great success with theirs but they ARE NOT 9310 steel that I know about.[/QUOTE]

                            i wonder what the les baer bolts are made from? its actually all i have.

                            Comment


                            • #15
                              Originally posted by Tedward View Post
                              dammitman, wish I read your question more thoroughly earlier. You state the bolt is out of spec. Why? Is the HS .130 and the bolt OAL 2.800? If so, you might have the same batch of bolts I got with my barrels. Satern did receive out of spec bolts from there new supplier and I returned them. All were from .129 to.132 but 90% were .130 head space, not .135 and OAL of 2.800 rather than 2.810. I think we all know who the new bolt supplier to Satern is from previous post so hopefully they make the bolts in the future correctly.

                              I bought bolts directly from Maxim Firearms. He has bolts for sale on his website and are made from 9310 Steel. http://www.maximfirearms.com/online-...-grendel-bolt/
                              I am not promoting the product (yes I am) but if you want a bolt and extractor made from a reputable manufacture, he has them. The first batch of bolts thet he supplied had Satern 6.5 Grendel extractors without markings on them. They currently have there in house manufactured extractors that are easily identified with the same 4 rings as the bolts. Also notice he eased the edges on the lugs prior to finishing them.
                              [ATTACH=CONFIG]4612[/ATTACH]

                              Mark at Precision Firearms also has bolts from Maxim and is doing different finishes but not sure if they are available. Either way, you can get correct bolts. AA also has bolts, I got mine in 40 amazing days just to see if they are shipping them. Not sure if it will continue but they also have a quality product. Les Baer Custom too is a source for bolts and I have had great success with theirs but they ARE NOT 9310 steel that I know about.


                              How do you know they are not 9310 bolts? I've never asked directly did you?

                              Comment

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