Barrel fouling and groups

[luke5678]

I had a new remington sendero 7mm Mag for about a year. I broke in the barrel cleaning every shot for a box, then every 3 shots for the next two boxes.

I now handload with IMR4350 (60.5g.), COAL 3.343, Nosler accubond 160s. For the first year my cleanbore shot was the same as the next 15. All .5 inch groups at 100. I understand this is unique.

All of a sudden everything changed about two months ago. Now my groups have slid to .75 and my first couple of shots just go wherever. Then it settles down. I have a total of about 300 rounds through the gun.

Why would this change? I clean my barrel every 20 shots.

Second question:
It also seems that each time I clean my barrel my zero changes to a half inch low and half inch left. I reset my zero and shoot my groups. Next day, clean barrel and shoot again only to adjust the nightforce scope the same amount.

The only thing I changed was last time trimming my brass to 2.480 where I used to just make sure it wasn't more than 2.5 and had variances. Will minor brass lengths make any difference?

Thanks

 

[Mikecr]

When you 'reset your zero' and go to group shooting, does the zero settle back to original setting? When shooting next time out, is your needed zero adjustment countering the last adjustment?

I ask because I had a NF scope cause a similar issue, that had me tail chasing for a couple months. Finally, I bought another NF scope just for comparison/troubleshooting scope suspicions, and identified with it that my original scope had an intermittant shift. Sent it to NF, they found a glass bedding issue, fixed it, and relieved me of the shifting zero.
NF service was outstanding(3day turnaround, no charge).

 

[Rimfire]

I had a new remington sendero 7mm Mag for about a year. I broke in the barrel cleaning every shot for a box, then every 3 shots for the next two boxes.

I now handload with IMR4350 (60.5g.), COAL 3.343, Nosler accubond 160s. For the first year my cleanbore shot was the same as the next 15. All .5 inch groups at 100. I understand this is unique.

All of a sudden everything changed about two months ago. Now my groups have slid to .75 and my first couple of shots just go wherever. Then it settles down. I have a total of about 300 rounds through the gun.

Why would this change? I clean my barrel every 20 shots.

Second question:
It also seems that each time I clean my barrel my zero changes to a half inch low and half inch left. I reset my zero and shoot my groups. Next day, clean barrel and shoot again only to adjust the nightforce scope the same amount.

The only thing I changed was last time trimming my brass to 2.480 where I used to just make sure it wasn't more than 2.5 and had variances. Will minor brass lengths make any difference?

Thanks

If the only thing you changed was trim length and it started after that, than that is where I would start. It's been a while since I shot a 7rm but I believe Min. trim length is 2.490"

 

[luke5678]

It doen't return to zero. I have to keep adjusting it each shooting out. It is countering. The new nosler brass is 2.480 out of the box and that is why I trimmed others to that. Otherwise I would have done at 2.490 but then it would take a couple of shots each to extend the new brass that far.

I would hate to think the $2K scope has a defect. It holds perfectly until I clean the barrel. That is what makes me think something weird is going on with pressures or something barrel related.

I am actually thinking of trading the sendero for a savage long range hunter at this point but want to try every possible solution first.

Thanks for the help.

 

[elkaholic]

I had a new remington sendero 7mm Mag for about a year. I broke in the barrel cleaning every shot for a box, then every 3 shots for the next two boxes.

I now handload with IMR4350 (60.5g.), COAL 3.343, Nosler accubond 160s. For the first year my cleanbore shot was the same as the next 15. All .5 inch groups at 100. I understand this is unique.

All of a sudden everything changed about two months ago. Now my groups have slid to .75 and my first couple of shots just go wherever. Then it settles down. I have a total of about 300 rounds through the gun.

Why would this change? I clean my barrel every 20 shots.

Second question:
It also seems that each time I clean my barrel my zero changes to a half inch low and half inch left. I reset my zero and shoot my groups. Next day, clean barrel and shoot again only to adjust the nightforce scope the same amount.

The only thing I changed was last time trimming my brass to 2.480 where I used to just make sure it wasn't more than 2.5 and had variances. Will minor brass lengths make any difference?

Thanks

It is not at all unusual for POI to change after cleaning, but as you stated, it didn't do that at first. It DOES sound like a fouling issue, however. Sometimes the barrel can be otherwise clean but have a carbon ring build up in the throat which throws accuracy out the window, but if this were the case, it wouldn't likely come back after a couple of shots. For whatever reason cleaning didn't change POI at first, I would still tend to think it was a normal "clean vs fouling shot issue". You might try soaking a patch with a good overnight solvent "even Kroil" and leaving it in the throat. Take it out and rotate a brush in the throat and then do the same with a clean patch to see if it comes out black.Make sure everything is clean BEFORE you do this so you can tell where you are with the carbon ring removal "if any".......Rich

 

[luke5678]

Thank you Rich and others.