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Posted: 10/12/2014 5:44:40 PM EDT
Recieved a new Match Grade 16" tOBR barrel Friday, EXCELLENT! Acompanying the upper was a meger .697 test target. ANNNDDDDD.....spent the last two days literally pulling my hair out. Unfortunately some people I don't even know, that I am sure are nice people, probably got called names and for that I apologise. Leupold, Surefire and yes as a last resort Larue were probably involved in those thoughts..... Wife has dinner plans so details can't be posted until later, it will be worth checking back.
ETA: Details (preface, I am by no means a teacher, This post is much longer than needed, because I hoped to take everyone that is interested through the analytical process I used to determine the accuracy robing culprit with my particular scenario in the hopes that someone may gain useful information from my mistakes) Received a new Match grade barrel replacement for a tOBR rifle purchased from RifleGear last NOV. The rifle was a 18" tOBR with a "field grade" barrel. The field grade barrel on this tOBR was an extremely accurate barrel, if a Match grade barrel was never offered I would be fine. This is a 10 shot group fired in less than 1 minute. when I saw that Rifle gear had tOBRs in stock I checked and all that was left were 18"rs. I wanted a 16" tOBR as I already had a 18" OBR that will shoot with most any 308 bench gun out there. Gratuitous proof group shot...10 rounds BTW....... Eventually I recieved a replacement MG barrel from Larue (this past Friday to be exact) Larue was kind enough to announce here in the past that FG owners would be granted a new MG barrel in the length of their choice to replace the so called "burner barrel". Well my FG "burner" was a group burner, not only shooting small, mamsy pamsy, groups from the bench at 100 yards but also making FRH on 1/4 MOA targets beyond 700 yards in less than bench shooting scenarios. Point being the FG barrel was "the shit" pardon the language, but is was a a fantastic barrel that I would not have issue with, if it was not replaced with a MG barrel. I received the 16" replacement barrel Friday and spent Friday night loading ammunition that has generally been the most accurate in all my 7.62 Larues. Starting 1/2 grain lower and up to what I shoot in the aforementioned 18" OBR ringer. The first 3 rounds from the new 16" barrel were in a triangular group in the .7's. The next 3 rounds from a different load was a triangular group in the .8's. Good but not stellar or IMO Larue standard. (As an aside, I have found, even larger equilaterally triangular groups are promising, it shows consistent harmonic oscillations of the barrel, even a small group with two bullets in one hole and a 3rd or 5 th out shows inconsistent load vibration or rifle vibration) Not having any history with this barrel it was important to see what 5 shot groups would do. The groups were all the same...three close together with two far out. It varied what bullets went into the close, 1/2 MOA, groups within the group. However, what this shows is a vibration pattern that is repeatable, but with something making it change occasionally. Immediately when I see these type of groups, 3 together 2 out and 3 together and 2 together a short distance apart, you can bet the farm it is a scope/mount issue. Either a weak erector system in the optic or the optic mounting system is moving. Rarely is this ever a load problem. For instance what is seen here. These are all groups from this 16" barrel. Two rounds in one group three in another within the same 5 round grouping Or a small group of three or four with one or two out an unusual distance compared to the cluster. This is on a copy of the 16" barrel test target. That's the 3 vert strung holes to on the right. There were numerous groups that showed this pattern and frankly no five shots groups even approached 1 MOA. I went back to the range today and took an extra scope after checking the Larue mount for movement (which was not there of course) as I was convinced that the Leupold MK6 3-18 was the culprit. I replaced the scope with a Leupold MK8 CQBSS and fired the first group. The top group in this picture. As you can see 3 are decent with 2 well outside the mean group. Seeing that the group was terrible I immediately wrote off the possibility of the scope being the culprit. I then removed the Surefire 762RC supressor to see if it was to blame. I then fired the second group of the same load, which is the bottom .588 vertical string. WTF? Now im confused. The supressor really? I grabbed the supressor put it back on the rifle and tried to rotate it, looking for some sort of play or movement that could cause accuracy issues. I felt an audible click back and forth, play. For those that are not familiar with how the Surefire supressors index. There is a post on the bottom of the Surefire muzzle device. This post slides I to a female slot in the supressor itself. Then a rotating collar that has an offset opening is rotated until the offset cams up against the muzzle device with a ratchet system. I assumed that the locking ring was not pulling up tight enough on the brake to eliminate the play between the male/female parts. I put the supressor on two other Larue barrels and ZERO play. Why did this one not lock up. I then removed the supressor and fired the next load the group was just at 3/4". I put the supressor back on and fired the group below and it was similar in shape at .835". So no measurable change with and without the supressor??? Really confused now. I have the smallest group fired with the same load without a supressor which was a radical change but now nothing, but still not particularly good groups. I decided to shot two groups from a box of 168g FGMM and see what happens. I put the supressor back on and STILL have a slight bit of rotational play that I have never seen on any of my Surefire cans. This is definately the issue. The next five shot group (on right)(left) has the first shot 1/2" out then the rest in a small .478 cluster. With exception of the first round this is how this rifle is supposed to shoot. (Fliers don't exist, a group is a group) why is this first round out? I then remove the supressor and Fire a five shot group (middle) of the same 168 FGMM. The results are a random, nearly 1.5" group. So I immediately put the supressor back on and fire the beginning of another 5 shot group, (left)(right) I quit after the first 3 shots went into nearly a 2" pattern....?!?! Completely baffled I packed up and left the range. Thinking, sooo what is the problem here....Its the Surefire mount. For some reason this mount allows movement, the brake must be made wrong. Back at the house I cleaned the rifle and while letting it soak I kept putting the Surefire can back on and of seeing if I could get it to lock up correctly. Here is the random way I found the problem. I had my 18" tOBR FG barrel out and was going to remove the brake from it and put it in the 16" barrel. While looking At the 18" barrel I wondered could this gas block be loose? It has 3 set screws but possibly. I took the rail off the 16" barreled complete gun which was locked up in a magazine vise. I grabbed the gas block and tried to twist it, goddamn if it didn't twist, slightly but I could move it in a rotational direction. I grabbed the correct Allen wrench and gave each of the three set screws a try, all solid. Then it hit me....DOAH! It's the barrel, the damn barrel is moving. It was not the supressor at all, the supressor was allowing me to rotate the entire barrel. I grabbed the large cad plated barrel nut and it turned easily with finger pressure. I unscrewed the barrel nut with nothing more than my fingers. The rotational play was the amount of play that is present between the barrel pin and the cutout in the reciever threads where the pin sits. I don't know if the rifle left Larue with the barrel nut loose it if it loosened up after the first 30 rounds I fired or if aliens did it. I can say the nut was one entire rotation from being tight enough to use the barrel wrench The nut was loose. Now I have not shot the rifle since I found the barrel to be loose but I will bet the farm that it will shoot better than I hoped on the next outing. Hopefully this post will help others come up with their own systematic accuracy issue solving methods. ETA: right/left |
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Seriously when is your wife going to pick out her shoes or whatever and head to dinner?!
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Aren't you the same guy Mark was going to send to fix Mr 4" groups
Glad you figured that out. |
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Damn man, you shoot better with a loose barrel than I do with a tight one.
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That is......unfortunate. Lot of wasted ammo. Glad to see you figured it out. When do you plan on trying ot out again?
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Quoted: Hey safetyoff, Thanks for sharing your experience, I for one learned something from it. When I first received mine, I didn't want to take the barrel off because I didn't want anything to have changed to do the Outshoot the LT Shooter challenge, but I ended up taking it off to use my Hornady OAL gauge to measure free bore of the 175 SMK's. Anyway, the barrel nut was really tight and it took my Son and I to break it loose. After I put it back together, I put some witness marks on it, the first one is where it is hand tight (to see if I could get the requisite recommended approximately 1/8 turn tight), and the second witness mark to see if it loosened after firing. See pic below: http://<a href=http://i245.photobucket.com/albums/gg57/30MMchaingun/LT%20PredatOBR/DSC_5516.jpg</a>" /> As you can see, there are 16 castellations, so 2 of them would be the approximately recommended 1/8th turn. As you can see, I am a little over 1 castellation, but when I tightened it, I held the rifle and had my Son tighten the nut. After shooting, I verified no change in my marks and I was curious so I took it off again. It was just as tight as when I received it from LT. When I installed the barrel again after cleaning it, I torqued it myself per the technique by Mark and my witness marks were the same. I also put witness marks (white paint craft pen) on my barrel and suppressors so when I am shooting, a quick glance and I can verify no turning/loosening. Torque is a funny thing especially with dissimilar metals, heating and cooling. You can torque it up then break torque, but if you torque it up, then go heat it up by firing it, then when you try to break toque, it will be much tighter. Anyway, "lesson learned" check torque and or my witness marks prior to shooting! Another lesson I learned the hard way; Don't forget to switch back the Gas Bock PST switch after shooting suppressed! DOH! She didn't eject the spent case and the bolt only came back approximately 1/8" I had to pull really hard on the charging handle to to extract the case! View Quote |
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Quoted: That is......unfortunate. Lot of wasted ammo. Glad to see you figured it out. When do you plan on trying ot out again? View Quote Agreed, however it was time spent shooting so there is a positive side, until I started banging my head off the shooting bench out of frustration I have to be out of town most of this week so it will be the end of the week before I get back to it. I have little doubt that this barrel will be a nice shooter, could be wrong but I have confidence. I have a feeling by the way it tries to stack some bullets together it wants to shoot, something was obviously just keeping it from its potential. After replacing several barrels on various bolt rifles every year for more than a decade (lots of prarrie dog shooting and long range shooting with large cal barrel burning cartridges) a person can get a pretty good feel, seeing the way a new barrel shoots, if it is going to be a shooter or not. I will definitely post the outcome when I get it back on the bench. |
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If you don't mind-also waiting on a match grade barrel for my PredaTOBR also. what was your orig order date?how,when were you notified as to getting your match grade?Just trying to find out how this new barrel situation is progressing.Thanks
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Yeah if anyone has an idea for a permanent index mark for that nut let me know. Also I still think it would be nice for them to ship torqued to ideal torque with an index mark, then you could just look for go/nogo in 2 seconds instead of having to get out the wrench.
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Quoted: If you don't mind-also waiting on a match grade barrel for my PredaTOBR also. what was your orig order date?how,when were you notified as to getting your match grade?Just trying to find out how this new barrel situation is progressing.Thanks View Quote |
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Update....
Got to the bench today after tightening the barrel nut. I took 3 loads that have proven accurate in my other Larue rifles, as well as 168 FGMM. Immediately it was obvious that the random spraying of bullets is gone, much more uniform group shapes. For the most part the barrel did not prove to be an exceptionally accurate barrel. I did get it to shoot one very nice half MOA group but then that same particular load shot two more groups just over 1". I have a 14.5 tOBR that was quite finicky when I started shooting it but proved to be very accurate and consistient once I found what it wanted to eat. I am optimistic that this 16" Match Grade barrel will be the same. I do have concern that the one load that shot the smallest group ended up shooting two more that were not consistient, this is unusual. The best group along with another group from the same load pictured below. ETA: clarification, above I stated that it was unusual for a rifle to shoot an extremely small group then shoot that same load poorly (given the ammunition is consistent of course). When a rifle shoots a load well it is for a reason. The harmonics caused by that load agree with the rifle. The vibrations created beginning with breaking of the sear and the impact of the firing pin on the primer, are uniform and consistent allowing the bullet to leave the muzzle at the same point in the barrel oscillation every shot. Now that is very simplified obviously, but to the point. This is why it is unusual, the same load imparts the same harmonics on a rifle in general, therefore results should be similar. |
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Thank you for taking the time to post such detailed information.
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Quoted: Update.... Got to the bench today after tightening the barrel nut. I took 3 loads that have proven accurate in my other Larue rifles, as well as 168 FGMM. Immediately it was obvious that the random spraying of bullets is gone, much more uniform group shapes. For the most part the barrel did not prove to be an exceptionally accurate barrel. I did get it to shoot one very nice half MOA group but then that same particular load shot two more groups just over 1". I have a 14.5 tOBR that was quite finicky when I started shooting it but proved to be very accurate and consistient once I found what it wanted to eat. I am optimistic that this 16" Match Grade barrel will be the same. I do have concern that the one load that shot the smallest group ended up shooting two more that were not consistient, this is unusual. The best group along with another group from the same load pictured below. View Quote I have some data that you might find interesting. At first, I thought it was just me. Now, I'm not so sure. |
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I experienced this first hand today beautiful 76 degree day with ZERO to light wind and a fresh box of 100 hand loads ready to rock and get some good data. Started off at 100 to verify zero. Doh!! I still had it screwed 5 mils up.
300 yds: First round hit dead center of the 6" plate. Same dope from a couple weeks ago 400 yds: First round hit dead center of the 6" plate. Same dope from a couple weeks ago 500 yds: First round hit dead center of the 6" plate. Same dope from a couple weeks ago 600 yds: First shot missed half a mil low and half a mil right. Damn! I was on a roll! Hmmm. Held the .5U and .5L for shot #2...Missed low. More shots, more misses all over the place and I'm getting pissed My 600 correction ended up .8 mils more than previous engagements. I had wasted 7 shots and I was ready to move on. 700 yds: Same dope from couple weeks ago.... You guessed it! Total crap! Lots of shooting and refocusing on me and my mechanics. My spotter(ex LE sniper for 14 years) was in shock. Grabbed the scope and gave it a wiggle. Not loose. Finally got consistent hits .9 mils higher than it should have been. I am in disbelief and about ready to throw this thing in the trash 800 yds: same crap as 6 and 700. Correction was up to 1 whole mil!! Wtf?? 900 yds: I added 1 mil to start and was darn close!! Hit it the second shot!! Woohoo!! Whatever is happening is maybe I short charged my ammo and I'm running out of gas?? Hence the consistent low hits?? 1000 yds: Total poop. Got a hit holding 1.2 mils more than I should be holding. I am ready to give up. I decided to dial back down to 400 and try to get my swagger back. Can't hit 400 now?? This thread hit my brain like a ton of bricks because something was mechanically wrong here. Grabbed the barrel and Boom!! It was loose... And my wrench is at home. I had vowed to quit disassembling the tOBR unless it needed a major cleaning. Electrical tape wrapped channel-lock pliers to the rescue!! Snugged it up as much as I dared as not to slip and scratch something. Tried a few more shots. Now all my data is total garbage and I re zeroed after the makeshift tightening. It lasted a few more shots. And I lost the handle on it again. I gave up!! And because it needs said again..... Check yo nuts!!! |
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