HELP Mark II Y Horrible groups all of a sudden

Ive had my mark II for about 11 years only thing not stock is I clearance the stock to float the barrel when I first got the rifle and put a scope on. Has always been a .75 or less MOA rifle at 50 yards. Has roughly 2500 rounds through it. Well yesterday just wasnt grouping very well was seeing 1 to 1.5 MOA @ 50yd. Then today my first 5 shots was .75. Then 1.5 and then 5.25 MOA. After every group was a walk to the target and a reload for cool down time. That was with Aguila super extra 40gr. So I tried some Federal automatch and it shot 1.5 to 4.5 MOA at 50yd. I cleaned the barrel and tried agian and same results starts with a .75 or less group and then goes crazy. Swapped scopes no change. Scope and rings and bases are tight. Action torque at 15in lbs. Went through Federal automatch, aguila super extra, winchester super x, federal champion, federal gold match, armscore. All had the same results groups 1.25 or less then out to 5+ even after the first group. Cleaned and not cleaned between groups. These are all done from a bench rest. Took all ammo and shot out of another rifle and it was consistent 1 MOA or less shooting 5 shots groups 4 times with just reloads for cool downs. Ive noticed a small ring at the end of my chamber before the rifling starts that Ive never noticed before today but only after it has been shot cant see it after running a patch. Even had my dad come out to the house and shoot it with the same issue. Has any one got and idea what it could be? PS yes its a youth model i actual prefer the shorter stock on the mark II.

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Originally Posted by musclecar76

Ive had my mark II for about 11 years only thing not stock is I clearance the stock to float the barrel when I first got the rifle and put a scope on. Has always been a .75 or less MOA rifle at 50 yards. Has roughly 2500 rounds through it. Well yesterday just wasnt grouping very well was seeing 1 to 1.5 MOA @ 50yd. Then today my first 5 shots was .75. Then 1.5 and then 5.25 MOA. After every group was a walk to the target and a reload for cool down time. That was with Aguila super extra 40gr. So I tried some Federal automatch and it shot 1.5 to 4.5 MOA at 50yd. I cleaned the barrel and tried agian and same results starts with a .75 or less group and then goes crazy. Swapped scopes no change. Scope and rings and bases are tight. Action torque at 15in lbs. Went through Federal automatch, aguila super extra, winchester super x, federal champion, federal gold match, armscore. All had the same results groups 1.25 or less then out to 5+ even after the first group. Cleaned and not cleaned between groups. These are all done from a bench rest. Took all ammo and shot out of another rifle and it was consistent 1 MOA or less shooting 5 shots groups 4 times with just reloads for cool downs. Ive noticed a small ring at the end of my chamber before the rifling starts that Ive never noticed before today but only after it has been shot cant see it after running a patch. Even had my dad come out to the house and shoot it with the same issue. Has any one got and idea what it could be? PS yes its a youth model i actual prefer the shorter stock on the mark II.

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I usually see action torque numbers in the 30 to 35 in/lb range for best groups, but it is odd that they start good and degrade quickly.

I might try scrubbing the chamber with a brush.

Hi MC - As jkv suggested, and you indicated, you may have a 'Carbon Ring' developing at the cone of the chamber. I have found that Boretech C-4 will dissolve that pretty well, especially if you put a wet patch in that area and leave it o-nite. Much gentler than brushing the h--- out of the chamber. You don't want wear there as most .22s especially have quite a leade to start ;-) The C-4 is pricey, at least in Canada, I bought a 8-oz bottle for about $40 CDN. But you only use a few drops at a time and only need to 'de-carbon' once in a while. I bought a cheap borescope ( Teslong .2 bore -$69CDN on amazon) and can see when I need to clean it. You'ld be surprised to see how poorly the 'regular' type of cleaning leaves the bore. Higher power guns also get copper fouling that is hard to remove properly and the Carbon build-up often goes throughout the barrel on these. Again, soaking and leaving sit a long time makes for easy cleaning.

PS - I suggest you search on-line for Carbon Barrell fouling to get further info, there are several threads and articles out there.

Marlin 60 Leade after cleaning
[IMG]https://i.postimg.cc/jWqPmHrC/M60-First-rifling-2.jpg[/IMG]

Ruger .223 mid-bbl copper and Carbon fouling
[IMG]https://i.postimg.cc/sMmZYMZz/5-16-R...-1-nr-chbr.jpg[/IMG]

Well i posted pics but they never got approved. I scrubbed it real good and that ring is still there. Looks like the chamber is separated from the barrel making a little gap where the rifling starts

Hey Musclecar - I just wanted to come back to this problem of yours. Were you able to get some C-4 or similar Carbon solvent? And do you have or know someone who does have a bore scope? That will show you exactly what's going on inside the bore/chamber. I found a couple threads about carbon rings by searching i-net, too. There are differing views on what/how it builds up, and how to remove it. Here's one - htt p://www.rimfireaccuracy.com/Forums/showthread.php/9488-Carbon-Ring!!
As I said, I use the C-4 letting a wet patch soak for overnite or at least a few hours. An alternative would be to use something like Remington 40-X Bore Cleaner or JB Bore paste on a tight patch, and spun in the chamber on a drill. I did that before I got onto C-4. Using a bore paste pushed thru the barrel (Not Drill) can smooth the barrel similar to lapping. Here's a thread to that effect - see Post #20 - http s://benchrest.com/showthread.php?97313-Rimfire-Cleaning-Is-Brushing-Bore-Absolutely-Necessary/page2& - If you read the whole thread you'll see the different opinions on this, but I think it's a 'real problem' and proper cleaning can solve it. Just using a brass brush and #9 may not be the answer.
Hope some of this can help you,
Ed

Back again :eek: You said that you 'scrubbed' and the ring was still there. Is it something like this pic? It's from my .223 Ruger but I had similar rings on my .22s before cleaning. Using the C-4 cleared them up and I've done the same to the Ruger now. I used to use a brass brush in the chamber, on a drill, but I've read that doing so creates too much wear and can increase the Leade jump to the rifling.
I have a Teslong borescope - about $70 CDN) from amazon.ca. Here's the page from amazon.com - http s://www.amazon.com/s?k=teslong+rifle+borescope&crid=1U8U2EJ9WME3I&spr efix=teslong%2Caps%2C179&ref=nb_sb_ss_ac-a-p_6_7
Pics of Ruger "ring
[IMG]https://i.postimg.cc/Y0hSBg8D/5-14-Ruger-bore-1.jpg[/IMG]
[IMG]https://i.postimg.cc/ydfNGnhS/4-21-R...-rifling-1.jpg[/IMG]