View Full Version : Acurracy issue/possible chamber problem
I was shooting today a previously accurate load for this rifle. 55gr Vmax bullet seated to 2.250 OAL, 25.3 grains xbr, rem 7.5 primer. Acurracy went totally to hell, 10ft wide and people reported seeing bullet puff out at 50ish yards but I was still getting impacts as far as I could tell. So when I recovered the bullet I ejected it showed marks that look like it was impacting something in the chamber (see pics). I took the remaining rounds and after cleaning the rifle chambered a round again and when I went to eject it it had resistance and the same markings. I then took another round and chambered it into my other rifle and it was easier (not sticky) to eject round and no marks were left on bullet that were unusual just the normal marks from chambering and ejecting. I looked in bore and didn't see anything there with my eyes and a flashlight. Has anyone ever had a bit of brass come off and jam itself in front of the rifling? I am thinking I may have had a bit of brass get stuck just before the rifling starts and I am unable to see it. This barrel has about 3-5k rounds through it and has been very reliable, I am leaning towards an ammo problem. Any suggestions are welcomed.
https://uploads.tapatalk-cdn.com/20190526/cc0906b5e29845cee18ba774a35ee2d3.jpg
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You are saying that you had misses 10' wide? A chamber issue isn't going to cause that. Not only that, brass stuck at the edge of the rifling would make chambering pretty difficult. I've had rifles that have key holed and still hit within inches at 50 yards after wearing out barrels. I'd start looking for other issues.. barrel nuts coming loose, sights or optics coming loose, etc..
also you might make some dummy rounds with different seating depths to see if you can make the ring go away.
10' was a guess but was off enough for my buddy to come up and call cease fire. I will try the dummy round trick and see what happens. I was thinking jacket was being torn open and causing bullet to come apart shortly after leaving barrel? Optic was tight, don't think barrel was loose. Switched to 55gr Hornady fmj and started getting hits. This was at 100ish yards.
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I would locate someone with a bore scope and check the chamber/leade/bore, before I shot that again.
I would be concerned with a catastrophic failure due to excessive chamber pressures.
Something is different, something has changed/failed/etc.
lordmorgul
05-26-19, 10:42
Clean the barrel with a copper remover not just a basic carbon solvent. Look for blue/green to stop coming out of the barrel on patches, if you’ve managed to get a good pileup of shaved plating in there like you think it’ll be obvious you’re taking awhile to dissolve all that. I doubt that is the issue.
Look for muzzle device hits?
Andrew - Lancaster, CA
NRA Life Member, CRPA member, Calguns.net contributor, CGF / SAF / FPC / CCRKBA / GOA / NAGR / NRA-ILA contributor, USCCA member - Support your defenders!
lordmorgul
05-26-19, 10:46
Regarding that bullet pic, is that mark only on one side? Is it present before you try to lockup the bolt if you ride the charging handle in slightly to prevent the bolt lockup? I’ve got a gun that leaves marks on the side like that front feed ramp, needs some light reshaping/polish.
Andrew - Lancaster, CA
NRA Life Member, CRPA member, Calguns.net contributor, CGF / SAF / FPC / CCRKBA / GOA / NAGR / NRA-ILA contributor, USCCA member - Support your defenders!
Ned Christiansen
05-26-19, 12:24
We should all have a bore scope and now with the Lyman Bore Cam it's pretty painless at under $300. It's not lab-grade optics but it does what is needed at the user level with a lot of convenience and the ability to get pictures.
Something has changed, obviously. Did you add a brake recently by chance? I do see chambers get some buildup once in a while at the freebore and 2" up....but that's usually from near-abuse-level high volume fire. One in this week's Patrol Rifle class, I could actually feel the cleaning patch get tighter as I pulled it back towards the chamber, at about 2".
Those bullets are showing a mark that ought not be there..... that does seem suspicious. The puff might be the result of the jacket being weakened "just enough" by that....? I'm guessing a 7 or 8 twist...?
I just found the scopes at Midway on clearance, $207!
https://www.midwayusa.com/product/1016394299/lyman-borecam-20-digital-borescope-with-monitor
Thanks for the response! Yes 7 inch twist. Never thought about it just being buildup of shavings or whatnot. Hope to get a look at it tomorrow. It's definitely not the drag marks from the feed ramps, it's completely around the bullet and I was able to duplicate it by chambering a round. I also feel some extra resistance when extracting the round. I will absolutely let everyone know what the results are when it gets figured out.
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Can you measure the COAL of the round in the picture? I know you said 2.250, but the one in the pic looks long unless it is my eyes playing tricks. And it looks crooked in the pic?
lordmorgul
05-26-19, 18:38
The one in the pic could be pulled long by the difficult extraction. You’d have to measure some before and after and see the actual 2.250” or less COAL before and it still got stuck.
Andrew - Lancaster, CA
NRA Life Member, CRPA member, Calguns.net contributor, CGF / SAF / FPC / CCRKBA / GOA / NAGR / NRA-ILA contributor, USCCA member - Support your defenders!
This is the round https://uploads.tapatalk-cdn.com/20190527/2b16ea4a33167d687c14617c04b32bd4.jpg
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lordmorgul
05-26-19, 22:46
55 Vmax is not going to separate in flight from 1:7 rifling, it’d have to be damaged before. Are these your reloads that get stuck (I mean by your personally, from previously fired cases), And factory runs fine? Any chance the cases are too long, but crimped (which it appears to be?), and the crimped long case wedges into the free bore? That would create an excessive crimp crease in the bullet of the ones that wedge in.
Andrew - Lancaster, CA
NRA Life Member, CRPA member, Calguns.net contributor, CGF / SAF / FPC / CCRKBA / GOA / NAGR / NRA-ILA contributor, USCCA member - Support your defenders!
Yes, they are reloads trimmed to length with Dillon trimmer to 1.750 and then through Lyman M die. I will definitely take a look and QC some brass again to see if any issues come up. Never tried factory vmax. I hope this ends up being a dirty bore or some junk in there. Not a month or so before same gun shot same load 1.5 at 100. Conditions were similar. Right now I am just running patches with ballisol that I have on hand, every now and again I get a bit of brass bits. If the barrel checks out then I will try the vmax load again maby shoot more of them and see what happens. This was at a match and I was shooting through barricades at 100. They were super cool and let me Mulligan and try with different ammo and got one of the best times overall. I really appreciate the advise, sometimes you won't think of things as other would.
Here is a picture of a group from same load out of same gun, prone at 100 out in the hills off a bag.
https://uploads.tapatalk-cdn.com/20190527/0e711b485ed1656d73580cb2593dae21.jpg
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While you’re waiting on that borescope, remove the upper and pull the BCG, and look through the barrel pointed at a white piece of paper thats reflecting an overhead light. It sounds like you could have something going on big enough to see with that technique.
Here are 2 photos done with a cheapo endoscope. First is the barrel giving me issues and the second is of a known good barrel both are chrome lined. https://uploads.tapatalk-cdn.com/20190528/2d1b81cdc99e0b9f810d551a5f4115c2.jpghttps://uploads.tapatalk-cdn.com/20190528/94997db3b887de3caa472c8d4b41489b.jpg
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Here are 2 photos done with a cheapo endoscope. First is the barrel giving me issues and the second is of a known good barrel both are chrome lined. https://uploads.tapatalk-cdn.com/20190528/2d1b81cdc99e0b9f810d551a5f4115c2.jpghttps://uploads.tapatalk-cdn.com/20190528/94997db3b887de3caa472c8d4b41489b.jpg
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Are these barrels chrome lined bore, but not chrome lined chamber? What kind of barrels are they? I'm trying to make sense of the gray ring around the second shoulder in both barrels.
Are these barrels chrome lined bore, but not chrome lined chamber? What kind of barrels are they? I'm trying to make sense of the gray ring around the second shoulder in both barrels.They are chrome bore and chamber the grey ring is the end of chamber right before the bore starts. It just looks kinda funky due to cheapo camera. One is a hammer forged bcm barrel the other is a Bushmaster barrel. The bcm is the one with what looks like chipping or buildup. Barrel has maby 10k on the high end over 4 or so years no suppressor or full auto. I don't really get my barrels smoking hot on a regular basis. Camera is inserted from chamber end of course and it has reflections from light.
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Can you check this ammo with a case gauge?
Have you checked how the ammo performs in another barrel?
Ammo is good in case gauge, it headspaces and are trimmed to length. Ammo was shooting fine in 2 other guns. I used it just last week in a different rifle and had excellent results.
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I'm interested to see pictures of the freebore / throat through your new borescope (maybe I want one).
Wondering if a good scrubbing with a brush will clear this up.
Also wondering if you remove the bullet from the cartridge then place cartridge in chamber, will the BCG lock easily and extract easily? Through all the Q and A, it seems the answer would certainly be yes, but this would verify some things.
Any velocity data?
Could it be that the light-weight varmint bullet is thin-skinned and being pushed too fast out of that 1:7?
I'm interested to see pictures of the freebore / throat through your new borescope (maybe I want one).
Wondering if a good scrubbing with a brush will clear this up.
Also wondering if you remove the bullet from the cartridge then place cartridge in chamber, will the BCG lock easily and extract easily? Through all the Q and A, it seems the answer would certainly be yes, but this would verify some things.I only have a cheapo endo scope so I still have yet to locate a proper borescope. Empty cases chamberd and extracted fine. If I seated bullet in empty case super long and dropped it in the chamber then ran the bolt home the barrel would hold onto the bullet and the case would come out with bullet still in barrel. It could be possible it was butting into the rifling but bullet only showed scratch marks and not rifling grooves. I tried the same thing in another rifle and it would eject both bullet and case with no issue. It passed a field and go gauge. I have scrubbed it quite a bit so far and will probably clean it some more now it's been pulled. For the time being I am using a spare barrel I had laying around.
Velocity was around 2900 fps if I remember correctly with s 55 grain Vmax. I still believe I had something come off the tip of a case or some other debris and lodged in the chamber lead/freebore area and then was fired into barrel making removal difficult without special tools. I also believe it possibly cause excessive lead buildup in bore due to cutting jackets as it left the case. Time for me to find an AR specific gunsmith and have it checked out. Now I have the rifle back up and running the urgency level is down, but I am damn curious what happened.
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I only have a cheapo endo scope so I still have yet to locate a proper borescope. Empty cases chamberd and extracted fine. If I seated bullet in empty case super long and dropped it in the chamber then ran the bolt home the barrel would hold onto the bullet and the case would come out with bullet still in barrel. It could be possible it was butting into the rifling but bullet only showed scratch marks and not rifling grooves. I tried the same thing in another rifle and it would eject both bullet and case with no issue. It passed a field and go gauge. I have scrubbed it quite a bit so far and will probably clean it some more now it's been pulled. For the time being I am using a spare barrel I had laying around.
Velocity was around 2900 fps if I remember correctly with s 55 grain Vmax. I still believe I had something come off the tip of a case or some other debris and lodged in the chamber lead/freebore area and then was fired into barrel making removal difficult without special tools. I also believe it possibly cause excessive lead buildup in bore due to cutting jackets as it left the case. Time for me to find an AR specific gunsmith and have it checked out. Now I have the rifle back up and running the urgency level is down, but I am damn curious what happened.
Sent from my Moto G (4) using TapatalkIt is a weird situation. I'm curious as well. Neck separation that got perfectly lodged in there? At this point it might be easiest and possibly cheapest to trash the barrel and move on. But that would leave the mystery unsolved.
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