View Full Version : [B]LAST UPDATE[/B] 16X Mk4 & borescope pics <800 rounds sudden loss of precision
Short story; barrel is a 16" chrome lined from a decent manufacturer/sales unit. Initial results were consistent true sub MOA for 5 shot groups. Changed clean muzzle direct thread suppressor to an AAC BrakeOut, and SR-5 suppressor. Other change was from ACOG to S&B 1.5 x 6. Inspection of crown shows no damage awaiting a friends bore scope evaluation. Rifle is now a 3 MOA POS.
These changes were reversed but inaccuracy remains.
My gut feeling is somewhere in the pipe some chrome came loose.
A fellow shooter suggested that maybe the gas port is an issue.
Any suggestions before yet another tomatoe stake finds it's premature way to the garden?
https://i.imgur.com/Q6bSgKu.jpg
https://i.imgur.com/f0n8VvA.jpg
https://i.imgur.com/31LZhih.jpg
Interesting occlusion, so other than the lands starting at irregular intervals, and the GP showing normal erosion, the crown passable, the little occlusion in that land... what could happen. Still leaning to trying a better optic and the remaining ammunition previously proven.
https://i.imgur.com/A3bhzZ7.jpg
Firing was done clockwise after getting a basic zero (4) rounds of fouling. Round #4 jumped out and #5 was back in. Came one additional click to the left and the first 3 in second group were together, then not :-) Last five above were fired at a quicker pace to alleviate some of the variable wind conditions... Blustery 8 - 12 MPH, squirrely conditions. FWIW, my 11.5 with ACOG 4X shot better with 3,700 rounds logged. Lower is a old Colt with a Jewell trigger that breaks better than my Giessle Hi-Speed match's.
https://i.imgur.com/IQtYAf0.jpg
My thought is you lightly kroil the bore and see what that missing chunk area looks like next.
https://i.imgur.com/hWl3VNP.jpg
Range day 5 13 21, 93F 10%H 12 - 15 MPH @ Desert Sportsman's club Las Vegas, range #9, distance to target: 100 yards:I can live with this level of "precision. Not what was but not unacceptable either.
https://i.imgur.com/91HqPhP.jpg 52 grain Berger FBHP and VV 130 Velocity 2963 SD 13.2/ES 29
https://i.imgur.com/faq021e.jpg 62 grain Hornady BTHP and BenchMark velocity 2960 SD 17/ES 35
I am just pulling this outta the air, could the barrel nut torque have loosened some throughout your shooting. Then installing the muzzle device sorta through everything outta kilter?
This is sorta me thinking outloud, I hope you get it figured out and it not be a pain in the ass or your wallet.
Ned Christiansen
05-07-21, 23:12
Overtorqued the second muzzle device so bad it collapsed the bore to the point of it taking damage that was not undone by removing the device. Gage pin the muzzle and see if it will take like a .219 or .220 but only for the first 1/4" or so.
I actually doubt you did that but..... could be.
Overtorqued the second muzzle device so bad it collapsed the bore to the point of it taking damage that was not undone by removing the device. Gage pin the muzzle and see if it will take like a .219 or .220 but only for the first 1/4" or so.
I actually doubt you did that but..... could be.
This was my initial thought. Rare as it may be, if it changed with muzzle devices.
Another possibility would be ammunition. Has the lot changed? Is it possible in the process of changing the muzzle device enough torque was applied to cause a problem with loosening the barrel nut?
In my experience the manufacturers considers 3 MOA “in-spec” even for precision barrels. I’ve seen it with a brand very reputable around here.
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Another possibility is the optic mount. Make sure it's tight. Use witness marks, if you don't already.
Short story; barrel is a 16" chrome lined from a decent manufacturer/sales unit. Initial results were consistent true sub MOA for 5 shot groups. Changed clean muzzle direct thread suppressor to an AAC BrakeOut, and SR-5 suppressor. Other change was from ACOG to S&B 1.5 x 6. Inspection of crown shows no damage awaiting a friends bore scope evaluation. Rifle is now a 3 MOA POS.
These changes were reversed but inaccuracy remains.
My gut feeling is somewhere in the pipe some chrome came loose.
A fellow shooter suggested that maybe the gas port is an issue.
Any suggestions before yet another tomatoe stake finds it's premature way to the garden?
Who assembled the URG when brand new?
Have you removed the barrel and checked the barrel extension fit to the receiver?
Who makes the barrel? Clearly the barrel is not the issue.
What ammo yielded submoa groups? At what distances? How many rounds fired per grouping?
How was the brake installed?
Has it been fired brake only?
Has the optic been verified on another known good weapon?
What mount are you using?
Have ALL bolts been tightened?
These are just a few questions while grabbing coffee....
NedC & MRad; on the over torque issue I think not at 25 ft/lbs.
MRad; ammunition has not changed, same lot as previous. My omission was that the loss was not immediate after the muzzle device change.
GeoB & Stick; the mount is an Aero Precision, screws tightened to spec.
Stick; I assembled this upper using a Giessle action rod. I've not fully taken it down as yet. I am not blaming the "manufacturer" which is in this case BCM. Ammunition consists of handloads using Sierra 60 grain HP, distance to target 100 yards from benchrest, groups fired SLOWFIRE in 5 shot strings while chronograph in using a LabRadar. No anomalies noted. The scope has not yet been tried on a known good rifle.
Gentlemen tank you for your input and direction. I shall update.
It seems like there was no change made at the exact time that the accuracy was lost.
Have you thoroughly cleaned the barrel since groups went to shit? Although, if it was <1 MOA one day a d 3 the next, copper fouling is unlikely to be the reason. My semi-informed opinion lays the name on the optic or mount.
I'd switch back to the COG or any other aiming device. The only time we had it NOT be optic related was on a crappy Faxon barrel that was trash out of the gate.
I had a similar situation years ago. Had a BCM SS410 barrel that was shooting consistently .75-1 MOA then one day it went to 2+ MOA. I couldnt figure it out and had IraqGunz look at it. He noticed right away that the shop I bought my suppressor from had used a crush washer instead of a standard type washer when installing my mount. It lasted for a bit but eventually started becoming a problem. As soon as he put a regular washer on it the rifle returned to normal.
Yeah if you haven’t tried multiple magnified optics, I would look there first. I’ve had two similar issues, once turned out to be defective chrome lining but I remember the bore scope photos looking very different than yours. The other, I was convinced was a barrel issue but it actually turned out to be a broken optic. I could group sometimes so when I tried to isolate the optic as the issue, it did well enough to pass in my mind. Definitely helped make the case for having more than one magnified optic because diagnosing accuracy issues with an RDS doesn’t go very far.
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Am I seeing this right? A chunk out of the one land? That’s enough to ruin accuracy. If the barrel was made by a reputable company, send them that photo and the barrel back. That’s a no-go barrel.
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Am I seeing this right? A chunk out of the one land? That’s enough to ruin accuracy. If the barrel was made by a reputable company, send them that photo and the barrel back. That’s a no-go barrel.
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The problem is that it DID shoot good, it actually shot exceptionally well. The larger question is what happened to make it stop firing well, and I would guess getting a chip like that didn't help at all. Especially if its towards the end of the barrel.
The problem is that it DID shoot good, it actually shot exceptionally well. The larger question is what happened to make it stop firing well, and I would guess getting a chip like that didn't help at all. Especially if its towards the end of the barrel.
It would be interesting if we had a picture prior to the inaccuracy problems. There were lots of changes which could have provided an explanation but that type of barrel flaw just can’t be ignored.
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Am I seeing this right? A chunk out of the one land? That’s enough to ruin accuracy. If the barrel was made by a reputable company, send them that photo and the barrel back. That’s a no-go barrel.
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Yes I was rather surprised myself to see that, It is located about 4 inches from the muzzle and can be seen with the naked eye now that the barrel is "clean."
I hope to shoot it tomorrow with a known BIG optic, at least that should rule out that line of inquiry. Also hope to this this level of precision return.
https://i.imgur.com/xJjea9w.jpg
Once again Gentleman I appreciate the feedback.
It would be interesting if we had a picture prior to the inaccuracy problems. There were lots of changes which could have provided an explanation but that type of barrel flaw just can’t be ignored.
I agree 100%, but it would be a hard stretch to say the gouge (impression) was present during the great accuracy. Which brings us to a barrel which is damaged, not flawed. It may be semantics at this point, but I think of flaw as an issue when the barrel was new, and damaged being sometimes after. This doesn't help the OP either way, I'm just trying to explain my thoughts.
Yes I was rather surprised myself to see that, It is located about 4 inches from the muzzle and can be seen with the naked eye now that the barrel is "clean."
I hope to shoot it tomorrow with a known BIG optic, at least that should rule out that line of inquiry. Also hope to this this level of precision return.
https://i.imgur.com/xJjea9w.jpg
Once again Gentleman I appreciate the feedback.
Yes please, let us know how it shoots with a clean barrel and known good optic (good magnification). I wish NC would read this one and post his thoughts. Ned knows barrels better than I know cameras.
https://i.imgur.com/hWl3VNP.jpg
Interesting occlusion, so other than the lands starting at irregular intervals, and the GP showing normal erosion, the crown passable, the little occlusion in that land... what could happen. Still leaning to trying a better optic and the remaining ammunition previously proven.Absolutely NOTHING good can come from having that gouge / chunk-hole in your land.
I have no idea how that could have got there. It looks like it has some serious depth. A stray steel pin from wet tumbling, or an old primer anvil or cup would have put in a long, skidding groove vice a pot-hole.
sinister said: "Absolutely NOTHING good can come from having that gouge / chunk-hole in your land."
I have no idea how that could have got there. It looks like it has some serious depth. A stray steel pin from wet tumbling, or an old primer anvil or cup would have put in a long, skidding groove vice a pot-hole.[/QUOTE]
I couldn't agree more. No wet tumbling and as we all can see no skid marks in my undies as yet.
I had a long talk with a dear friend of mine who operates down in Bryan, TX. Bill Wiseman you may know him. The topic was barrel steels and the simple fact is this type of an occlusion could happen simply due to how steel is made. Generally a rare occurrence fortunately, just not rare enough to save me.
Appreciate all the responses and am going to shoot it once more in better conditions when possible.
I had a long talk with a dear friend of mine who operates down in Bryan, TX. Bill Wiseman you may know him. The topic was barrel steels and the simple fact is this type of an occlusion could happen simply due to how steel is made. Generally a rare occurrence fortunately, just not rare enough to save me.I met Bill when he first moved down here in 1979. Former Olympic Team Armorer and Marine Precision Weapons Shop gunsmith-machinist. He did one of my .45s over 40 years ago, and it's still going strong. His shop's down the road maybe ten minutes.
As a barrel-maker he knows this kind of thing happens occasionally in alloying bar stock before it's even drilled to become a rifle barrel.
95fordfleetside
05-11-21, 00:48
Does that gouge have chrome in it? If so then it was like that from factory and was present when accuracy was good. I can't tell from the picture, if it doesn't have chrome then it could have been a flaw in the barrel that was exposed after firing
I doubt the chunk out of the land is the problem, why? Because the gas port has taken a whole land out and not affected accuracy. Have you looked at the rifling in front of the leade?
I doubt the chunk out of the land is the problem, why? Because the gas port has taken a whole land out and not affected accuracy. Have you looked at the rifling in front of the leade?
Yes, and while the rifling starts in a rather irregular pattern, i.e., not perpendicular to the bore... It is not showing any problems.
Yes, and while the rifling starts in a rather irregular pattern, i.e., not perpendicular to the bore... It is not showing any problems.
That's good. Didn't think it would be bad after only 800 rds but it doesn't hurt to check.
You got a buddy that knows how to shoot you could let have a go at it? Sometimes we just lose our mojo for a bit.
I doubt the chunk out of the land is the problem, why? Because the gas port has taken a whole land out and not affected accuracy. Have you looked at the rifling in front of the leade?
Very perceptive and it makes sense!
Mark
You got a buddy that knows how to shoot you could let have a go at it? Sometimes we just lose our mojo for a bit.
So if I'm shooting my Creedmoor on the same day and only getting this at 100 yards
https://i.imgur.com/k2PAhei.jpg
I should ask for help...?
OK I will :-)
Any update to how the gun is shooting with a known good optic?
Yes in the original post
Thanks.
So if I'm shooting my Creedmoor on the same day and only getting this at 100 yards
https://i.imgur.com/k2PAhei.jpg
I should ask for help...?
OK I will :-)
Nice, but ya know some of us aren't mind readers. I'm sorry I said anything.
Nice, but ya know some of us aren't mind readers. I'm sorry I said anything.
Don't be sorry, really!
I do appreciate the input and while confident in my abilities I was serious about having some other shooters give it a run.
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