View Full Version : LaRue .308's and popped primer issue
gamewarden
10-21-13, 22:30
After reading John McPhee's AAR i'm seriously questioning my purchase.
This is what i'm talking about:
The Course: Training Day 2
Before td2 started, we had a weapon down from the day before. As I beat the bolt apart the story started to unfold. The cause was a LaRue OBR, which was having issues with Federal Gold Medal Match 175gr loads from the day before. This OBR was brand new (purchased and used for the course) and had major over pressure issues. Because the weapon had too much chamber pressure, each round was blowing out the primers into the Bolt face. Generally, any type of blown primer is an ammunition issue; however, the pressure from the chamber was also deforming the brass so bad that brass from inside the bullet casing was bulging out of the hole where the firing pin touched the primer. (See Pic 1). The pressure was so great it was pushing the primer pieces into the firing pin hole. This eventually jammed and locked the bolt up to where the weapon no longer functioned. There was about 5-10 small perfectly shaped primer pieces exactly sized to fit through firing pin hole. The OBRs are known to have over pressures issues. Nonetheless, it ran Mil-Spec M118LR ammunition just fine, due to the ammo being ruggedized with harder primers and thicker casings. This is something for future students to consider when bringing OBR’s to this course.
The FIX is to lower the chamber pressure to a more tolerable pressure that common ammunitions can shoot. Yes, this rides the line of accuracy versus less chamber pressure and the line between accuracy versus reliability. One student commented, "I wish I knew more before I bought this OBR and knowing what I know now, I would not have bought a Larue OBR.” I personally always go for reliability because if the gun doesn’t go boom why carry it. Also, I will sacrifice accuracy first because I would rather have a Reliable 2MOA gun than a .5 MOA that doesn’t shoot. Dually noted about this weapon’s failure is ammunition. The LaRue OBR works best with MIL-Spec Ammo, not everyone has access to Mil Spec ammo, and I always bring some for this reason. Hardly seems fair for the guy who bought a high-end rifle to end up not participating due to these kind of problems. Gun and gear manufactures watch your products because I'm writing AARs for every class. "Your manufacturing or production problems should never be the customers!”
I have a PredatOBR on order of course, but at a good price I have been stocking up on Federal 175 grain GMM and am only planning on running premium ammo from Federal, Hornady and Black Hills in 168 and 175 grain in the rifle. I'm also only using the rifle for long range shooting 1,000 plus and possibly some elk hunting.
Is the above issue common in other high end .308 gas guns with tighter chamber specs designed for precision (LRP-07, GAP-10, Noveske, KAC ECR) or is this something that has been happening more with LaRue rifles? I know a lot of different schools have run OBR's and this is the first I've heard of this issue. I also thought the Xtraxn chamber fluting would help alleviate an issue like this somewhat...?
Please educate me!
thanks you.
OrdnanceLocker
10-21-13, 23:40
I never had that issue in my GAP-10, nor have I seen it in any of the numerous LRPs, SR25s, or POF's.
Popped primers are typically a "reloaded a case too much" issue, or maybe a "too much pressure" issue.
Nothing to do with the rifle...
Now a popped primer totally jamming up a trigger group... yeah, that's the fault of the AR.
ETA... see the over pressure in your post... humm... call Larue, I wouldn't shoot that anymore for risk of damage to the rifle if not a kaboom...
That sucks and I hope (and I'm pretty sure) if there's an issue Larue will make it right.
I take it this was factory loaded ammo? With that said, I recently got my hands on a precision rifle, 700 action, Krieger barrel, Bell & Carlson stock in .223, custom built for another fellow and he'd never shot it. I had something he wanted real bad! It came with 10 boxes of Hornady Match 75gr ammo. 2 boxes were a different lot than the other 8. I started breaking it in with the 2 odd ball lot. Well and good and sub-moa with this factory ammo. Got into the other lot, in the first 10-15 I was seeing some pierced primers and this lot wasn't supposed to be as hot as the first lot. What wasn't pierced were cratered like you see in over pressure conditions. No other pressure signs and a strong action, I continued. A couple rounds later had a mis-fire, light primer strike. Hummmmm?...Fired the second hit, a couple more shots, another light strike, then another, then it would not fire at all even with 3 or 4 hits. Well crap, probably busted a firing pin. Got her home, tore it apart, firing pin looked fine. Cleaning out the bolt, found little brass donuts from the pierced primers blown back into the bolt just as you did. Did some research and found others had had the same issues with Hornady match in AR! From what I could tell they used a bad batch of Winchester primers. So, it's not just AR's that can have this happen and a warning for when we see pierced primers, it could be the primers themselves and no matter what rifle type, (or brand of ammo it appears) it may cease to function....O.L.
It's an issue with the LaRue. Not an ammo issue.
I hosted McPhee for his "Heavy Carbine Marksmanship" course 3 weeks ago here in IL and every 7.62 LaRue in the class (5 total) displayed the same over-pressure issues except for one. All with factory loaded ammo.
I shot M118LR thru my 7.62 PredatAR and didn't have any stoppages but each of my fired casings showed bulged primers. Another student with a PredatAR had his gun completely lock up on TD1 due to a popped primer lodged inside of the cam pin hole. He was running 175gr Fed GMM. Luckily he happened to have 500rds of LR that he finished the class with without any further stoppages but it also showed bulged primers.
John's conclusion was that even if it runs with M118LR it is still way over-pressured and will burn out the chamber much sooner than it should (approx 2,000-2,500rds max). John believed that this is exactly what happened to the gun Larue submitted for the Mil evaluation that didn't finish. The chamber was toast at 2,000rds.
I don't know about any issues with the 7.62 guns specifically.
There are two possible primer related issues
Blown primers
The whole body of the primer is loose or comes out. Usually ends up jamming the trigger.
Causes:
Over pressure ammo
Tight chamber / Tight bore
Soft brass / Loose primer pocket
Over gassed action
Early extraction
Pierced primers
A small chunk of primer is extruded into the FP hole in the bolt. Usually ends up jamming the firing pin.
Causes:
Over pressure ammo
Tight chamber / Tight bore
Primer cup thickness / strength / non mil-spec primers
Loose fit between the firing pin hole and the firing pin
With all the interrelated causes here, it's more difficult to nail down the specific reason.
Didn't Mark Larue FINALLY come clean and say that making barrels was harder than it looks, hence all the issues with getting rifles out the door?
My money is on the barrel and Larue in general.
Glad I've moved on from them...
Didn't Mark Larue FINALLY come clean and say that making barrels was harder than it looks, hence all the issues with getting rifles out the door?
My money is on the barrel.
Completely separate issue. The over-pressure issue has been present since day one with the OBRs with their original Lothar barrels. McPhee seemed to think that it was the size of the gas port in conjunction with a few overly tight tolerances in the chamber, bolt face and a couple other places inside of the gun.
evoutfitters
10-22-13, 08:47
Just another data point: KevinB at KAC has stated before that FGMM brass is too soft for reliable use in semi auto rifles. I don't know if this has changed in the last couple of years, but this is the reason I stayed away from the stuff when I had my SR25 EMC.
It's an issue with the LaRue. Not an ammo issue.
I hosted McPhee for his "Heavy Carbine Marksmanship" course 3 weeks ago here in IL and every 7.62 LaRue in the class (5 total) displayed the same over-pressure issues except for one. All with factory loaded ammo.
I shot M118LR thru my 7.62 PredatAR and didn't have any stoppages but each of my fired casings showed bulged primers. Another student with a PredatAR had his gun completely lock up on TD1 due to a popped primer lodged inside of the cam pin hole. He was running 175gr Fed GMM. Luckily he happened to have 500rds of LR that he finished the class with without any further stoppages but it also showed bulged primers.
John's conclusion was that even if it runs with M118LR it is still way over-pressured and will burn out the chamber much sooner than it should (approx 2,000-2,500rds max). John believed that this is exactly what happened to the gun Larue submitted for the Mil evaluation that didn't finish. The chamber was toast at 2,000rds.
Bingo.
C4
it is kind of curious why he jumped to the conclusion popped primers were ammo issue. assuming factory ammo and not somebody's hot reloads, my immediate thought would be the chamber. when you have 5 guns doing the same, it's obviously the chamber.
it's not clear how it could be related to the gas port either.
and... i am extremely skeptical that hot rounds will drop the barrel life on a 308 from 8000+ to 2000-2500 rounds. i would love to see the firing schedule for that test. it's not a belt fed.
and ffs, if you think rounds are "way overpressure" why would you continue shooting them?? or allow people in your class to continue shooting them?
it is kind of curious why he jumped to the conclusion popped primers were ammo issue. assuming factory ammo and not somebody's hot reloads, my immediate thought would be the chamber. when you have 5 guns doing the same, it's obviously the chamber.
He never said that he though it was an ammo issue. He said it is a gun issue. Everyone in the class was running premium factory loaded ammo. The biggest issues with popped primers/bulged primers appeared to be with factory Fed 175gr GMM. Factory M118LR functioned but still showed heavily bulged primers
it's not clear how it could be related to the gas port either.
Too much gas in-conjunction with the other mentioned tight tolerances.
and... i am extremely skeptical that hot rounds will drop the barrel life on a 308 from 8000+ to 2000-2500 rounds. i would love to see the firing schedule for that test. it's not a belt fed.
He stated that the OBR that LaRue submitted for the Mil trial dropped out right around 2,000rds because of throat erosion and that was the reason it failed the trial.
and ffs, if you think rounds are "way overpressure" why would you continue shooting them?? or allow people in your class to continue shooting them?
Again, it's not an issue with the various factory ammo that he has seen run thru the 7.62 LaRue guns in his classes. He said the issue is with the guns and he has not had a LaRue OBR 7.62 detonate in any of his "Heavy" classes. He said that he has seen the identical issues in every one of his "Heavy" classes with LaRue 7.62 guns. The over-pressure issues cause primers to pop and the guns to lock up due to those popped primers ending up causing the stoppage.
He also said that he considers Mark LaRue a friend and has no "Agenda" with Mark or his company, and is only reporting what he has seen in his classes.
ok thanks for the clarification. perhaps i misread the OP which I thought was quoting McPhee's AAR when he wrote "Generally, any type of blown primer is an ammunition issue;" and went on to say it was soft brass and primers. The 3rd post in this thread seemed to continue and support that supposition, so that's why I responded.
if your problem is "overpressure" or "blown primers", how could too much gas affect that? "too much gas" is often a contributing factor to extraction issues when the bolt unlocks before the pressure subsides, but I still don't see how it could cause overpressure in the first place, or blown primers, or be relevant to this conversation. Thanks for the education.
my last point was not ammo or gun related. it's a safety issue. it's a liability issue. the fact that he hasn't witnessed a particular model of rifle blow up is nice, but this is one of those cases where after one does blow up and somebody gets hurt, everyone will look back on this and say it was a really really dumb idea to keep shooting and that there were plenty of warning signs.
I don't know Larue or Mr. McPhee and have no agenda either. (though I have plenty of Larue product, dillo dust and bumper stickers)
I had both an early 762 OBR and PredatAR. Both had running issues that were never fully resolved. I would have thought that they'd improved by now.
Has anyone dropped a "no go gauge" into one of these offending rifles?
ok thanks for the clarification. perhaps i misread the OP which I thought was quoting McPhee's AAR when he wrote "Generally, any type of blown primer is an ammunition issue;" and went on to say it was soft brass and primers. The 3rd post in this thread seemed to continue and support that supposition, so that's why I responded.
if your problem is "overpressure" or "blown primers", how could too much gas affect that? "too much gas" is often a contributing factor to extraction issues when the bolt unlocks before the pressure subsides, but I still don't see how it could cause overpressure in the first place, or blown primers, or be relevant to this conversation. Thanks for the education.
my last point was not ammo or gun related. it's a safety issue. it's a liability issue. the fact that he hasn't witnessed a particular model of rifle blow up is nice, but this is one of those cases where after one does blow up and somebody gets hurt, everyone will look back on this and say it was a really really dumb idea to keep shooting and that there were plenty of warning signs.
I don't know Larue or Mr. McPhee and have no agenda either. (though I have plenty of Larue product, dillo dust and bumper stickers)
Taliv,
To be clear, now that I think about it more I don't think McPhee ever specifically mentioned the LaRue guns being "Over Gassed", that may be me reading too much into what I observed at the class. He specifically said there was an "Over-Pressure" issue inside of the LaRue guns causing the problems with the ammo and the throat/chamber area of the guns.
It's obviously a headspace or chamber dimension problem.... barring something crazy... has anyone stuck a no go gauge in one of the offending rifles?
gamewarden
10-22-13, 21:11
I would be very interested to find out more info on head spacing...especially if there are people that could compare multiple .308 gas guns.
Thanks for the discussion so far.
Anymore OBR owners out there?
That would be interesting to find out. I don't have either of my Larue 7.62s anymore to help. Both of mine had smooth chambers, but I'm pretty sure they added some sort of spiral fluting to them later on. I assumed it was to help out some of their running issues?
My 7.62 PredatAR has the XTRAXN chamber treatment as did every other LaRue gun in the class that was showing pressure issues. The only one that didnt show any issues was a 2+ year old/pre-XTRAXN OBR.
I have an OBR with approximately 300 rounds on it. I've primarily run 175gr FGMM though I ran some 168gr FGMM when I first picked it up.
I haven't observed any of the pressure issues noted above, though it sounds like a I have a few rounds to go (~2000?). I did have some issues with the 308 Pmags (FTF), but since going to the Larue supplied ones I haven't had any issues.
Also, I don't know if it increases or decreases the problem, but I run suppressed (762 SDN6) with the switch settings suggested by Larue.
I have an OBR with approximately 300 rounds on it. I've primarily run 175gr FGMM though I ran some 168gr FGMM when I first picked it up.
I haven't observed any of the pressure issues noted above, though it sounds like a I have a few rounds to go (~2000?). I did have some issues with the 308 Pmags (FTF), but since going to the Larue supplied ones I haven't had any issues.
Also, I don't know if it increases or decreases the problem, but I run suppressed (762 SDN6) with the switch settings suggested by Larue.
Have you noticed flattened primers? Bulging brass towards the case head?
When was it bought and does it have the "XTRAKTION" treatment?
If it was a problem... you would have noticed it if you are paying attention.
A match grade .308 (that doesn't have F'd up pressure problems) can shoot with match grade accuracy for up tens of thousands of rounds before the groups open up and accuracy goes to shit if it's kept cool and taken care of.
So if you don't have the problems then you're good...
After reading John McPhee's AAR i'm seriously questioning my purchase.
This is what i'm talking about:
The Course: Training Day 2
Before td2 started, we had a weapon down from the day before. As I beat the bolt apart the story started to unfold. The cause was a LaRue OBR, which was having issues with Federal Gold Medal Match 175gr loads from the day before. This OBR was brand new (purchased and used for the course) and had major over pressure issues. Because the weapon had too much chamber pressure, each round was blowing out the primers into the Bolt face. Generally, any type of blown primer is an ammunition issue; however, the pressure from the chamber was also deforming the brass so bad that brass from inside the bullet casing was bulging out of the hole where the firing pin touched the primer. (See Pic 1). The pressure was so great it was pushing the primer pieces into the firing pin hole. This eventually jammed and locked the bolt up to where the weapon no longer functioned. There was about 5-10 small perfectly shaped primer pieces exactly sized to fit through firing pin hole. The OBRs are known to have over pressures issues. Nonetheless, it ran Mil-Spec M118LR ammunition just fine, due to the ammo being ruggedized with harder primers and thicker casings. This is something for future students to consider when bringing OBR’s to this course.
The FIX is to lower the chamber pressure to a more tolerable pressure that common ammunitions can shoot. Yes, this rides the line of accuracy versus less chamber pressure and the line between accuracy versus reliability. One student commented, "I wish I knew more before I bought this OBR and knowing what I know now, I would not have bought a Larue OBR.” I personally always go for reliability because if the gun doesn’t go boom why carry it. Also, I will sacrifice accuracy first because I would rather have a Reliable 2MOA gun than a .5 MOA that doesn’t shoot. Dually noted about this weapon’s failure is ammunition. The LaRue OBR works best with MIL-Spec Ammo, not everyone has access to Mil Spec ammo, and I always bring some for this reason. Hardly seems fair for the guy who bought a high-end rifle to end up not participating due to these kind of problems. Gun and gear manufactures watch your products because I'm writing AARs for every class. "Your manufacturing or production problems should never be the customers!”
I have a PredatOBR on order of course, but at a good price I have been stocking up on Federal 175 grain GMM and am only planning on running premium ammo from Federal, Hornady and Black Hills in 168 and 175 grain in the rifle. I'm also only using the rifle for long range shooting 1,000 plus and possibly some elk hunting.
Is the above issue common in other high end .308 gas guns with tighter chamber specs designed for precision (LRP-07, GAP-10, Noveske, KAC ECR) or is this something that has been happening more with LaRue rifles? I know a lot of different schools have run OBR's and this is the first I've heard of this issue. I also thought the Xtraxn chamber fluting would help alleviate an issue like this somewhat...?
Please educate me!
thanks you.
what?
OBR's are not .5 rifles
Milspec 118LR is not SUBMOA ammo
I wish a SME would reply to this thread. It's my understanding a lot of them are using larue 308 guns in austere situations.
It's an issue with the LaRue. Not an ammo issue.
I hosted McPhee for his "Heavy Carbine Marksmanship" course 3 weeks ago here in IL and every 7.62 LaRue in the class (5 total) displayed the same over-pressure issues except for one. All with factory loaded ammo.
I shot M118LR thru my 7.62 PredatAR and didn't have any stoppages but each of my fired casings showed bulged primers. Another student with a PredatAR had his gun completely lock up on TD1 due to a popped primer lodged inside of the cam pin hole. He was running 175gr Fed GMM. Luckily he happened to have 500rds of LR that he finished the class with without any further stoppages but it also showed bulged primers.
John's conclusion was that even if it runs with M118LR it is still way over-pressured and will burn out the chamber much sooner than it should (approx 2,000-2,500rds max). John believed that this is exactly what happened to the gun Larue submitted for the Mil evaluation that didn't finish. The chamber was toast at 2,000rds.
Just curious what test/evaluation was this? Mark has avoided every opportunity that has come up in the past three years to submit any of his weapon systems for Army testing citing that it would not be worth it. It would be nice to actually see one come in for either a competition or private industry testing.
Just curious what test/evaluation was this? Mark has avoided every opportunity that has come up in the past three years to submit any of his weapon systems for Army testing citing that it would not be worth it. It would be nice to actually see one come in for either a competition or private industry testing.
You think Larue has the capacity to fulfill a military contract?
You think Larue has the capacity to fulfill a military contract?
Probably not, and no flame intended, but probably not the R&D and quality departments as well. It's a smaller operation than some others. There's some genius about bigger, but still mid sized business models.
no issues in mine. It eats everything and shoots like a laser.
Roughly 1,950 rds so far: mostly factory FGMM 175gr, 168gr, PMC 147gr, M118LR and even cheap SilverBear my buddy gave me.
Also shot 175gr reloads from Southwest ammunition ( "run and gun" loads for semi auto)
specs:
20" OBR/ XTRAXN chamber ( bought 2 years ago new )
Surefire MB
PRS stock/H2buffer
PMAGS and Premier Reticle 3-15X scope.
I'm picking up my PredatOBR 16" next week. I hope it will be as good.
my 0.02 but why would someone go to a class with a brand new rifle ? I would test the shit out of the gun before I go spend my time/money in a class.
You think Larue has the capacity to fulfill a military contract?
honestly, i doubt it. Considering the amount of OBR's that are out there, and the repeated issues that continue to come up (accuracy, consistency, reliability). I doubt LT could ship 12 rifles out for testing that would be able to complete testing.
I am not even talking about the 110 carbine test, they could sponsor a one or two week test. Get some good data, and slap the DoD stamp of approval on it. That would say a lot more about their capabilities than bottle openers, BBQ rub, and stickers.
Much of their hype is generated by users hyper-inflating their performance, I mean really, what the hell does shoot like a laser mean? Do lasers drop like a rock past 800 yards, do lasers get pushed all over the place when there is some mild wind.
It’s a slow 308, and while in reality that round would be a dog in most competitions, somehow in the OBR it has better accuracy at 1000 yards than the 2010.
****UPDATE****
The gun works. Mark LaRue spent a long time with me helping to get this resolved.
Every question I had was answered honestly. I feel very comfortable with what my PredatAR is capable of.
Probably not, and no flame intended, but probably not the R&D and quality departments as well. It's a smaller operation than some others. There's some genius about bigger, but still mid sized business models.
Agreed.
Coming from an engineering standpoint and the description Larue provides of XTRAXN it sounds like it might be due to the reduced friction on the chamber walls is increasing the pressure imparted on the the head of the casing and bolt face. Normally the friction imparts a considerable amount of shear stress in the walls of the casing, which reduces the axial load delivered to the back of the casing. Decrease the friction in the walls, and more of the load is transferred to the back. While the chamber pressure is still at a safe load, the high strain rate and extra load may be deforming the primer pockets, etc. creating new problems that weren't foreseen. Of course this is all conjecture without seeing any real data, but considering that the chamber differences between 7.62 NATO and 308 WIN have caused case head separations when using WIN ammo in a NATO chamber, I would guess that it's possible. There's an animated model that shows the internal stress of a 308 WIN casing during the firing process in both a NATO and WIN chamber, and the models clearly show that the NATO chamber results in a stress above the tensile stress of 70/30 alpha brass. I wish I had the url saved. Any one have any ideas about this? To be clear I am saying this phenomena might not be a result of a chamber dimension or machining issue, but with a decreased friction between the chamber walls and the casing.
7.62x51 Federal ammo is commercially available. I've fired it through an OBR with XTRANX/LW barrel suppressed and unsuppressed and it functioned fine. As did .308 win 175 Federal ammo.
I've fired several types of reloads through one and have found that the gun has functioned well with a variety of ammo, but accuracy is best at a lower node, as are pressure signs. That is the nature of DI .308 semi-auto rifles, though.
The only ammo I've seen that was a problem, besides hot hand loads, was hot hunting loads. No blown primers, but ejector marks on the brass.
For what it's worth, I've seen 175 gr Federal be too hot for Remington 700s with loose factory chambers.
I don't think putting a go/no-go gauge will be a good indicator as the pressure is likely being created by the fluted chamber and a short throat in an attempt to gain every last ounce of accuracy out of them.
Interesting thread. My PredatAR 762 only has a couple hundred rounds of 147gr ball through it, but no issues. My PredatAR 556 had a few popped primers a couple years ago but it was with a specific lot of ammo that another friend had doing the same in his Colt. That company took back all the ammo left over from our cases and replaced it all on their dime. No issues with the PresatAR 556 with the replacement ammo, or a variety of others for close to 1,000 rounds. Small sample size of course, but I'll be paying attention in the months to come.
As for .gov contracts, LaRue has provided 7.62 rifles to FBI Indian country offices out west. Can't recall if they are OBR's or tOBR's. They have NF glass though and the folks who have gotten their hands on them have been pleased. And these tend to be the gun enthusiasts of the offices since a typical employee wouldn't know the difference between an OBR and an M1 Garand.
I have a co-worker who owns an OBR. When looking at the fired cases of FGMM, 175gr, I observed "cratering" around the firing pin strike on the primer. Using the same lot of ammunition fired out of my SR25 ECC, I see no cratering or primer flow. Something is going on, I don't know what.
This OBR has the XTRAXN chamber.
Todd
Interesting thread. My PredatAR 762 only has a couple hundred rounds of 147gr ball through it, but no issues. My PredatAR 556 had a few popped primers a couple years ago but it was with a specific lot of ammo that another friend had doing the same in his Colt. That company took back all the ammo left over from our cases and replaced it all on their dime. No issues with the PresatAR 556 with the replacement ammo, or a variety of others for close to 1,000 rounds. Small sample size of course, but I'll be paying attention in the months to come.
As for .gov contracts, LaRue has provided 7.62 rifles to FBI Indian country offices out west. Can't recall if they are OBR's or tOBR's. They have NF glass though and the folks who have gotten their hands on them have been pleased. And these tend to be the gun enthusiasts of the offices since a typical employee wouldn't know the difference between an OBR and an M1 Garand.
What does this even mean? Considering that we are in a shortage of Navaho code talkers these days, can anybody actually give a clear answer as to who is using these rifles, and to what standard they were selected and or tested?
It takes about 3 minutes to find pictures of Delta force, SEAL team 6, and the CIA's SAD and get an idea of what they are using, but for some reason, the official use of the OBR is more closely guarded than the Presidents book of secrets.
Dirtyboy333
03-08-14, 12:13
any updates or answers to this?
sounds like the gun, as I never had a problem with my sr-25 with 175 smks
I have a co-worker who owns an OBR. When looking at the fired cases of FGMM, 175gr, I observed "cratering" around the firing pin strike on the primer. Using the same lot of ammunition fired out of my SR25 ECC, I see no cratering or primer flow. Something is going on, I don't know what.
This OBR has the XTRAXN chamber.
Todd
To me this seems to indicate the firing pin hole in the bolt may be bigger than necessary. Signs will be a raised rim around the firing pin indent and in some extreme instances blanking the impact point (putting those little round bits of primer cup into the firing pin channel).
Armalite gets around this with their 7.62 guns by using a tapered-point firing pin and a small firing pin hole in the bolt (AR-10 pin above, M16 pin below):
http://starbase4.com/album/albums/Private/normal_DSCN0392.JPG
Primer cratering (the raised rim around where the firing pin point hits the primer cup, starting the chemical firing chain) will give a false impression and look like overpressure vice being a firing pin hole drilled too large.
In these images there's a raised rim around the pin indent -- yet the primers are still radiused and there's no ejector smear on the case head:
http://i667.photobucket.com/albums/vv35/wcw308/primers/primer_2.jpg
http://img155.imageshack.us/img155/7706/308primer1.jpg
If you have an OBR you can check by inside mic-ing the firing pin hole, then finding the diameter of the firing pin.
http://www.shootingillustrated.com/wp-content/uploads/2011/03/xW5756_SI_LaRueTacticalOBR_8786.jpg
You can visually see the difference in firing pin holes between an LMT MWS on the left and a JP 308 on the right:
http://i752.photobucket.com/albums/xx166/jasonusvi/308bolts1.jpg
You can see the tight fit of an LMT firing pin point in an MWS bolt face:
http://i744.photobucket.com/albums/xx87/rginidaho/face.jpg
Colt's 308 pin looks like a duplicate of the Armalite:
http://looserounds.files.wordpress.com/2012/06/002.jpg
Armalite gets around this with their 7.62 guns by using a tapered-point firing pin and a small firing pin hole in the bolt (AR-10 pin above, M16 pin below):
http://starbase4.com/album/albums/Private/normal_DSCN0392.JPG
Your pic isn't showing up, but I think LMT does this as well as I just looked at a pic of my MWS bcg broken down and it appears to have a very similar design. I'm always learning something new from you, thanks for info.
http://i888.photobucket.com/albums/ac81/trident1982/3333/DSC02551-1.jpg (http://s888.photobucket.com/user/trident1982/media/3333/DSC02551-1.jpg.html)
Dirtyboy333
03-14-14, 23:07
Very interesting sinister. Here's another example of LMT vs. JP pin hole size.
http://i1230.photobucket.com/albums/ee498/Dirtyboy333/71EC5294-7B25-49B3-B356-A8EC40248FDA_zpshp6qsaee.jpg (http://s1230.photobucket.com/user/Dirtyboy333/media/71EC5294-7B25-49B3-B356-A8EC40248FDA_zpshp6qsaee.jpg.html)
http://i1230.photobucket.com/albums/ee498/Dirtyboy333/1ADDEE57-2235-4808-959C-426BA1FD67BF_zpsrkcafqon.jpg (http://s1230.photobucket.com/user/Dirtyboy333/media/1ADDEE57-2235-4808-959C-426BA1FD67BF_zpsrkcafqon.jpg.html)
Also, I know this doesn't belong in this thread but I figured I would ask it here instead of starting a new one. Notice the bevel on the back of the lugs of the bolts. The LMT and JP have the bevel on opposite sides. Which side is most benificial for locking/unlocking?
http://i1230.photobucket.com/albums/ee498/Dirtyboy333/8577456C-1E2F-4E16-B183-AE64FAA2A3ED_zps2kuie9ww.jpg (http://s1230.photobucket.com/user/Dirtyboy333/media/8577456C-1E2F-4E16-B183-AE64FAA2A3ED_zps2kuie9ww.jpg.html)
The LMT bolt is a thing of beauty!
Recent photo of a case fired from one of the new DPMS GII 308 rifles.
doekilr [Member]
3/4/2014 5:08:34 PM MDT
Yesterday, i went out to the range to shoot my new DPMS G2 Hunter in .308. I forgot my handloads at home, so i could only shoot 20 rounds of 150 gr Remington core-lokts while sighting in my scope. Everyone of the 20 rounds had the primer issue seen in the attached picture.
http://i1312.photobucket.com/albums/t528/doekilr/remington308_zps2760c28c.jpg
This photo is captioned to be Larue 308 parts, so its pin is also tapered:
http://emptormaven.com/img/OBR_BCG.jpg
Dirtyboy333
03-15-14, 02:06
Larue even puts his name on his cam pins!!! :no:
Usually the only way you can tell if you're getting a genuine or counterfeit.
Shady Jake or Scrood-ahn Wong will crank out tens of thousands of Bubba-spec parts, while Mark will put his thumb print on his stuff.
Unlike subbing out everything you know where it came from.
thopkins22
03-16-14, 14:25
****UPDATE****
The gun works. Mark LaRue spent a long time with me helping to get this resolved.
Every question I had was answered honestly. I feel very comfortable with what my PredatAR is capable of.
Late question I know, but did they tell you what they did?
TurretGunner
03-19-14, 12:10
That's good to hear. Not to long ago mark told a ptobr customer to sell his rifle if he didn't like how it performed. Good to see some people are getting support from the factory.
honestly, i doubt it. Considering the amount of OBR's that are out there, and the repeated issues that continue to come up (accuracy, consistency, reliability). I doubt LT could ship 12 rifles out for testing that would be able to complete testing.
I am not even talking about the 110 carbine test, they could sponsor a one or two week test. Get some good data, and slap the DoD stamp of approval on it. That would say a lot more about their capabilities than bottle openers, BBQ rub, and stickers.
Much of their hype is generated by users hyper-inflating their performance, I mean really, what the hell does shoot like a laser mean? Do lasers drop like a rock past 800 yards, do lasers get pushed all over the place when there is some mild wind.
It’s a slow 308, and while in reality that round would be a dog in most competitions, somehow in the OBR it has better accuracy at 1000 yards than the 2010.
I've often wondered why LT gets so much hate. So I bought one. And after 500 rounds and one Mammoth Sniper Challenge in, I love it. It shot .444 moa at LaRue and I have a recent group of .410. Accurate gas guns are perfect for field events like Mammoth as a secondary shooter's weapon engaging targets from 600 yards and under from less than ideal positions.
As far as winning in competition, two SOTIC instructors win the 2010 International Sniper Challenge with a pair of OBR's. As far as using them in service, I've competed with some SF guys as well as a couple of Ranger teams who have deployed with OBR's.
I certainly hope I dont have some of the issues described here, if I do I will report them. Until then I will report the good in an effort to counterbalance the overrunning hate ☺️
LaRue ships with 3 round targets. You really can't say that it's even a group to call it .444 MOA because it is statistically insignificant.
For the record, I shot 80 rounds through my OBR yesterday and was making 75% hits on 12"x16" plates at 1k with 15 mph winds. They are good rifles love or hate Mark.
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31272
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Just finished turning 175smk's to dust at Mammoth followed by a couple of days at SHOT. Like the gun I had to buy because so much shittalk, I heard so many bad things about Mark I had to visit him. Second year in a row and he greeted me with "how was your sniper competition?" Guy is awesome, talks as long as you want (if not longer) and is passionate about what he does- and does it well. 31273
With the "Field Grade" barrel on my Predatobr I have gotten 5 shot groups in the .4's and put 9 consecutive shots into .6. I just finally got the match grade barrel and it came with a 3 shot test group of .162! I know it's only 3 shots and a sample of one but it looks promising. Have only fired 30 rounds through the new barrel 20 FGMM 175 and 10 HSM 175. Both shot very well. Had only about 300 rounds through the field grade barrel and had no problems with blown primers etc. Years ago I had a GAP AR in 308 and I did have blown primers using factory ammo (FGMM) with that rifle.
This is a problem in a lot of AR10's because the AR10 was never engineered around a long bearing surface or heavy projectile with slow-burning powders.
The AR10 was designed around the Army Ordnance Corps/NATO service rifle cartridge developed in the 1950's, which became the 7.62 NATO with 147gr FMJBT going as fast as they could get it to go. It's a fast-burning powder, short bullet shank combo that punts the pills out quickly, with a very fast conversion rate.
A gun with a gas port, reciprocating mass, and recoil system built around M80 147gr is ill-suited to shoot loads that were really worked up for bolt action sniper systems, where no consideration for gas operation is accounted for.
We see this in AR10 variants in .308 Winchester with the 175's pushed to the max, .260 Remington, 6.5 Creedmoor, 6.5x47 Lapua, and other slow burning powder/long bearing surface combos. You can cut the port for 147gr-165gr fast loads, or for 175gr/slow burning powder loads, or go with adjustable gas.
I have experienced the primer piercing condition in .260 Remington, where molten primer material flows over the firing pin into small rings once they go back solid. The biggest contributing factors are:
* .080" firing pin hole on the bolt face
* Elongated burn curve where the peak pressure isn't necessarily higher, but the duration of higher pressures lasts longer, and the large firing pin hole simply can't support the primer as it transitions from a solid to a liquid
* Soft brass with weaker metallurgy that doesn't sink heat as well as higher density brass alloys
I deal with this all the time, and have had to pay very close attention to how I load for the AR10-sized gas guns with modern target bullets, no matter the caliber. Just because a box of ammo says ".308 Winchester" and your gas gun is chambered in .308 Winchester does not mean that load will run safely in it. We also see this with the Hornady Superformance ammunition in many cases, but I think Hornady has been responsive to this knowing that a lot of their ammo is being run through gas guns more and more.
If you look at a lot of the high-end, well-engineered guns, many of them have had problems with slow-burning powders and longer bearing surface or heavier projectiles. There have to be compromises if you build a gun around a certain burn rate and bullet combo. As soon as we engineer the gun around 175gr SMK or 178gr A-MAX with a medium slow powder, the rest of the folks shooting 147gr NATO surplus start seeing short-stroke malfs.
It is my understanding that chamber dimensions and the gas port diameter of the LaRue OBR was designed around the M118LR load. Is that not true?
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I don't know what specific design considerations where taken into account with the LaRue OBR.
Another thing to consider is that the M118 173gr FMJBT load had to be functional in the M14/M21 system, which is really finicky once you depart from the M80 ball load it was built around.
To me, I was really disappointed when I saw the muzzle velocity for the M24 listed at 2500fps with the 173gr M118, and I wasn't the only one who saw the lackluster performance of M118 in terms of trajectory and its horrendous danger space. Along came the M852 OTM, then the M118LR with the 175gr SMK pushed really hard, thinking about M24's and M40's. This was around the time between transitioning to the M110.
If you settle on one load, agree that this will be the load fired through the system, then you can engineer everything around it. We're all over the map when it comes to civilian market AR10 variants when looking at reamer specs, QC, gas port dims, bcg's, gas system lengths, recoil systems, friction points, and firing pin hole diameters/pin sizes.
ArmaLite Inc. has one of the best engineered BCG's, as do LMT and KAC. ArmaLite and LMT use a .068" firing pin hole. The engineering work that went into the 1996 ArmaLite Inc. AR10 was done by David Dorbeck, and Karl Lewis was heavily involved in the program at the time since Eagle Arms was the retail front for LMT. Mark Welstrom bought Eagle Arms, acquired the "ArmaLite Inc." name from Elisco Tool & Machine from the Philippines, and began marketing the new AR10 in the initial wake of the 1993-released Knight's Armament SR-25 Match Rifle. They even used an SR-25 upper in the RDT&E for the ArmaLite Inc. AR10, but since it was done during the Clinton AWB, they had to source a surplus magazine if they were to offer 20rd capacity for civilians.
So these big 3 names are a lot closer related than most people know, when speaking about KAC, LMT, and ArmaLite Inc., and they all have very solid engineering behind the guns. Think about Stoner himself working with Reed, who was also a firearms designer and major Stoner collector, then Karl Lewis, and David Dorbeck, and you don't have to wonder why these companies ended up with well thought-out guns.
LaRue also isn't known for half-cocking on his rifles, and has a professional team that has pushed the innovation driving a large part of the industry. I don't own one, and have no dog in this fight. I just have been watching this market very closely since the 1980's before there was even a US production AR10 available. I've owned 5 different AR10's and custom-built large frame AR's, including an Eagle Arms 24" from way back, but I would own and recommend production rifles from any of the above companies based on what reputation they all have established for themselves over the years.
Mark would have to answer what design considerations were taken into account with the chamber and gas port, gas system, and operating system. As the end-user demand for more long-range shooting with .308 gas guns increases, all of these companies have had to address it some way or another.
gamewarden
02-01-15, 19:44
I did finally get a PREDATOBR and have fired an entire case of Federal 168 SMKs, about 200 175 SMKs, and another 250 Hornady 155 AMAX without any issues with the field get barrel...it's a wonderful rifle.
Just got the Match barrel and have about 300 rounds of Blackhills TANKs, 100 rounds of Mk 316's, 100 Federal 7.62x51 175 SMKs (civilian Mk 316),100 rounds of Applied Ballistics with 175 Bergers...we will se how it goes. I'm expecting smooth sailing.
gamewarden
02-01-15, 19:45
Damn auto correct...Field Grade Barrel, Tipped SMKs
Hope to add a suppressor to the mix too and see how it runs with that. One thing not so good about the AR10/SR25's I've seen is they are hard on brass.
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