Dinged Crown and Accuracy - Zero Issue

N

Nishgriff

Sergeant
Full Member
Minuteman
Aug 11, 2013
113
21
Denver CO
www.nishnalbandian.com
#1
So when I bought my 20" Rem 700 Tactical .223, the muzzle face had marks on it, but the crown was intact. Now I notice this big ding on the crown and I also notice that my accuracy has gone down. I went from shooting .5-.75 MOA (probably averaging .65-.7MOA) to now struggling to shoot under 1MOA. All things being equal (I rechecked torques etc on Rings and base and action screws), would the crown ding have this much effect? I'm gonna drop it off at a smith on Tuesday, but just wanted to see. The accuracy is just not consistent now, and I can't seem to make it better by slowing down and going back to the fundamentals. I'm fairly new at precision rifle, but I know I can shoot sub MOA most of the time, and my groups have opened up big time. I struggle for 1MOA at 200 and 300 yards now too.

Second issue. I installed a Nightforce 20MOA base, and I can't zero at 100 yards, the scope doesn't have enough travel (Nikon M223). I like the scope, but down at the very bottom of the click range it's kinda mushy. Would switching to a flat base solve this? I'm guessing yes :D

Here's a pic of the muzzle:
Sep272013_9572.jpg


300 Yard group from before with one sighter with Black Hills 69 Grain HPBT:
TgtGfx300-1.jpg


100 Yard group from before with Black Hills 69 Grain HPBT:
TgtGfx-copy.jpeg


100 Yard Group yesterday (Fouled Bore): Black Hills
9-26-13-04.jpeg


Best 100 Yard Group yesterday (Clean bore): Federal Gold Medal Match 69 grain
9-26-13-01.jpeg


I fear that cleaning has caused this, not just the ding, but also in other ways.
 
#7
Ring said:
man, you could have recowned that with a case deburring tool....

The Over-Rated Crown
Click to expand...

Well, SOMEONE could, but I'm not really that handy with stuff like that...

Mile high was cheap and helpful. The takeaway for me is that I was dragging the jag or brush back over the crown too roughly and damaged it. They pointed out where bits of the crown were dinged 'in'. Have not taken it to the range yet, but will post pics of groups to see what the difference might be. So learn from me, over-zealous cleaning damages barrels more than shooting!!!!
 
#11
Target112913002.jpg

Best hour of the day at P2K today. I wanted to start going above 5 round groups, so this is my first attempt at a 15 round group. Close to an MOA, but I threw some.

Target112913003.jpg

Another 10 shot group

My best group of the day was .49 MOA, biggest was this 1.16MOA 15 round group, and my average was .786 MOA over 100 rounds. I had one group of five larger than 1MOA. THis was off a bench and bipod with rear bag with FGMM 69gr.

I am gonna start going back out to longer distances and using a sling and other positions. I think this rifle (really me) shoots better at 300 yards, and I shoot better without these shoot n c targets. I'm gonna go back to regular paper NRA highpower targets. I am finding I really do not like to see where my group is when I'm aiming. The scope I'm using (Nikon M223) has a shitty thick reticle, but at longer distances it subtends the center and I aim better with it.

Hoping someone wants to go shoot at South Bay or Pala next week :D
 
#12
Ok, I do not mean to hijack this, however, I need another point of view from someone smarter than me.
Follow me for a second and lets discuss this:
Accuracy follows consistency. Therefore is everything from the shooter up is consistent, then we are accurate. Yes?
If we were to use different rounds with different powder charges, that would be an example of inconsistency, therefore inconsistent (inaccurate) grouping ant any given distance.
Same as if the shooter is doing something inconsistent; we would have a formula for an inefficient shooter/rifle combo, therefore producing inaccuracy.
if you have a cut/knick/scrape on a barrel crown, wouldn't that be a consistent change on the efficacy of the rifle? It would essentially be affecting every bullet the same. Right?
My thinking is that would change the "accuracy" of the rifle the same way changing another variable rifle piece would.
Please feel free to call me an idiot or point out the obvious, but I think this might have been a mental thing as to why your (OP) groups opened up?
 
#13
I have had one of my match rifle barrels crowned with a 45 degree 'break' in the rifling/face area of the muzzle crown. The theoretical advantage is to make the crown less vulnerable to dings. It didn't affect accuracy, that much I can say with confidence. Anything else would need to be conjecture.

Greg
 
#14
0311 Hesco said:
this might have been a mental thing as to why your (OP) groups opened up?
Click to expand...

No, I think it's a good question, and I'm not always the consistent part of the equation! However, I didn't notice the ding, I noticed my accuracy decreasing. Over time my groups opened up on average, and I couldn't figure out why. By really focusing back on the fundamentals of marksmanship I was able to SOMETIMES make 1 MOA, but was average 2 or so, when before I was averaging .6 or .7. I finally looked at the crown and saw the ding, so I don't think that on average this particular instance was a mental thing.

As for whether a ding would cause a consistent change, the answer is yes, it consistently made my groups bigger :D It consistently negatively affected accuracy by causing point of impact to differ more greatly than before from point of aim. Once the barrel was recrowned, I could average back where I was.

Disclaimer, I'm posting in the Stupid Marksmanship questions section because I am not a perfectly consistent shooter, and am learning to be better, so it's entirely possible that I could just have been shooting poorly. However, I have been keeping my average, and the changes correlated to the ding and the repair.... AND while this rifle was in the shop, I was shooting another rifle with my old average.
 
#16
Hesco, you bring up a valid point. Here's a theory:

Remember though that bullets themselves and actual velocities vary.

When we have a very accurate load with extreme velocity spread under 20fps, the world is dandy. But assuming we have an uneven release of thrust from the bullet at the muzzle, combined with a 10 or 15 fps variance. The error effect is compounded.

To say another way, assuming every single shooter-related fundamental is followed and a rifle is somehow fired absolutely perfectly for a group; Exact same poa, exterior pressures, environmental conditions...etc....
There is still the variance of the projectile, the velocity, and the stability.

Without pyscho-high-speed photography or screen-shooting, I think it would be very difficult to approximate the overall effect of an imperfect crown. Looking at the one in the above pics, though, and comparing to carbon deposits on AR15s... I would wager more of his accuracy improvement came from HIM than the spec on the crown.

For shits and giggles a few years ago, we cut my cousin's .30/06 savage sporter barrel from 22" to 17" with a tubing cutter. Looked horrendous. Peened and abraded metal for his crown. We sighted it in so it could be used as the "swamp gun". We shot all 50 rounds of reloads through it sighting it in...actually shooting for groups. We couldn't believe that it's previous accuracy (0.6s) was absolutely maintained with our new atrocity of a crown.
 
#17
smokebomb said:
We sighted it in so it could be used as the "swamp gun".
Click to expand...

Having lived in Colorado for the past 22 years, I am not familiar with this 'swamp gun' of which you speak. Seriously, what is a swamp gun? I am laughing out loud as I write this! Please don't think I'm trying to be a dick! I have an image in my head of a criminal from an old Scooby-doo cartoon dressed up as a swamp creature waving a gun with the mystery machine in the background....

As to your other points, I can't argue, as I said, it's entirely possible I could have been shooting poorly. However, on the same day that I could barely get under one MOA on this rifle with the ding, I got several .25-.5 groups out of my other rifle. I understand there is some controversy about how much a crown or damage on the crown affects accuracy...
 
#18
Haha, Scooby Doo Monsters...

One of the places we have access to hunt is swamp land. The longest reasonable shot in that entire plot is maybe 80 yards. It is thick, dense, congested and dark. We cut that particular cheap-o barrel down for maneuverability.

As for crowns, I'll perform a crown experiment next year and report back.
 
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