Help requested!! Weird grouping with 6.5 Creedmoor (advice/ guidance welcome)

[Corey0372]

First off.... Sorry there's no pictures to help illustrate this but I'll try to make it as easy as possible.....

Bought a Bergara HMR Pro in 6.5 creedmoor a while back, it's a great gun and I've shot them a bunch before buying mine. I've been messing around with it seeing which factory loads it likes, which one of my suppressors it prefers, etc..

A couple of weeks ago I took it out with a YHM Resonator K (30 cal) suppressor and put about 80 rounds thru it..
-40 rounds Hornady 140 grain ELDMs
-20 rounds Hornady 143 grain ELDX
-20 rounds 130 Federal Terminal Ascent

After I zero'd, my shot groups were tight and I was making nice little right at, or sub-MOA, 5 shot groups at 100 yards. Groups definitely could've been a little tighter (I hadnt messed with the adjustable trigger yet, and was shooting off a bag as my harris bipods hadnt come in yet) but overall pretty happy first day on the range. No worries, nothing shocking...

Today I went back to try out a different suppressor, this one an AAC 762 SD, today 60 rounds....

-20 rounds Hornady 140 grain ELDM
-20 rounds Hornady 143 grain ELDX
-20 rounds Federal 130 grain TSX

THIS IS WHERE THE WEIRD STUFF STARTS...

As anticipated, my first impacts were a little off from last trip (different can , different zero). Impacts were about .2 mils right, but elevation good, no big deal. Shot 1, Shot 2, both about .2 mils right....

Shot 3 - .5 mils low
Shots 4, 5 - .8 mils low


All about .2 mils right... in a nice vertical row

I did it again and got basically the same results

So I did it some more, the next 2 times I did it with about a15-20 second pause between each shot and it basically became predictable.

Shots 6, 7, and 8 also .8 low... in a nice tight group

Got essentially the same results with 140 grain, 143 grain, and 130 grain.

Shooting at 300 yards my dope called for 1 mil in elevation for the 130s.... which became 1.9ish after a couple rounds... consistently.


This didnt happen with the YHM suppressor or unsuppressed.

My best guess... is the gradual increase in temperature of the can settles at about 3 or 4 round mark.... and creates a different harmonic somehow. But I really don't know.

Thanks for reading.

 

[ActionBob]

First thing I would go is re torque all the action and bedding screws. And check is the suppressor is tight.

 

[Mekaniks]

I bet you are getting some copper build up in the rifling. I would start by cleaning the bore with some copper remover solvent.

 

[perttime]

...

This didnt happen with the YHM suppressor or unsuppressed.
...

So, the weirdness only happens with that particular suppressor. How different is it from the other suppressor? Length, weight? No damage on the suppressor?

 

[HookMeUpII]

OK here we go...I'll take a whack at this. I'm somewhat new to this but I've been really digging into precision rifle shooting over the last 5-6 months.

You didn't mention break-in although with that many rounds, it's broken in.

To your point about heat, from a bench or dead rest (if you're on), you'll notice the gun start to throw rounds in a circular pattern as it heats. This was taught to me by a precision match shooter. Unless you're shooting a super heavy match barrel it will heat up. You may not feel it on the exterior but those rifling grooves and lining of the barrel get a wee-bit toasty with shots in succession. Metal expands, rifling doesn't cut as well, etc. I will typically shoot 2-3 shots, then break for a while, rehearse my setup on sticks, then back at it. The day I was taught this the guy who taught me was shooting an 18 lb 300WM match rifle. He was only taking 1-2 shots every 5 minutes. The barrel alone probably weighed as much as my gun. Patience is not something I was graced with but had to learn.

If it were me, and what I've done, is establish a pattern of cleaning, fouling, and then stick to one ammo. I broke in with Hornady ELDM, and went right to zeroed with Barnes TTSX. Usually, when I re-foul after cleaning I used something cheaper like Norma in the same weight bullet. I typically disregard the foulers and then right to Barnes TTSX. I figured use $2.50/rd to foul before going to the $4/rd stuff. One thing I didn't know, and no one told me, was NOT just elevation is affected with ammo changes. I've noticed Norma pulls left in comparison to my zero with the Barnes. Why? I don't know? Difference in copper composition? Difference in molding of the bullet? I really don't know.

The cleaning, well, huge topic of debate. Some people says it ruins the bore. Some people say do it every time. Some people say just do it within reason. You hear stories of "I never cleaned the rifle and then when I finally did, the barrel was done?" Well, that's probably because there was a mountain of copper built up in it. You removed it, now you have a bare bore that's been shielded.

I'd personally eliminate the variables. This is my routine, every time.

- Bore is cleaned with Bore-Tech components with a nylon brush (never metal). Several soaked solvent patches, brush soaked in solvent passed 20x. Sit for 15 min, run one more soaked patch through. Dry completely with dry patches.
- 3 foulers of Norma Bondstrike 180gr, polymer tipped (same style as Barnes)
- 20-30 rounds of Barnes TTSX, 3 shot groups, pausing for some time between each group. Anymore than 20 rounds I find the barrel starts to heat unless I'm there for 4 hours which is quite a while.

I do this every time. Repeat.

Another thing that @ActionBob mentioned is torqueing of the action. Browning X-bolts are spec'd at about 45 in/lbs. Of course the manual tells you "snug." The folks at Griffin and Howe taught me that the X-bolts need to be torqued in sequence, and at 35 in/lbs, which yields the best MOA. Front screw seat, back screw seat, torque front to 35, torque rear to 35. I would call Bergara. On a nice fresh rifle those screws could be over torqued, under torqued, and/or not in the right sequence. They also could have worked loose slightly. If you don't have one, get yourself a nice Wheeler torque driver. Bergara, which is mind-blowing, has an article on their site specifying they want the rifle disassembled brand new. Bit of a head scratcher.

Rifle Care, Maintenance, and Storage - Rifles Bergara International

Author: Aaron Ryan Editor: Al Louangketh As a hunter, sport shooter, and a moderator for the Bergara International Facebook group, I seem to always be asked the same questions; what’s the best way to break-in my rifle? What solvents and oils seem to work the best for protection? How do I best...

www.bergara.online

After that I'd look to scope mounts, bedding issues, or a problem with scope holding zero.

 

[BourbonTrail]

Sorry my test engineer brain would tell you to take off the can and repeat the shot pattern and see the results. Do that 1-2 times to establish if it’s when that specific can is on the rifle. On, off, on, off, etc. Then I would check torque, etc. The can may be causing the shift when it heats up.

Also, you are using a 30 cal suppressor, weird shifts *can* happen with sub caliber rounds because of standing wave harmonics inside of the can. I’m not saying this is the case, but it’s not unheard of either.

 

[gillettehunter]

I have heard of a string of shots like you describe as the group "walking". The culprit may be the barrel rubbing against the stock in the barrel channel. As the barrel heats up and expands it changes the pressure against the barrel. If the barrel is not completely free floated then thats a good place to start. Also bed the action if that hasn't been done.
I would also suggest allowing the barrel to cool a lot longer after 3 rds fired. The smaller the barrel the more likely heat/expansion may affect groups.
Like mentioned above cleaning needs to be considered. I had one rifle in a .300 WSM. After cleaning it was a honest .35 MOA rifle. After 9 rds of TTSX's it was a 1.5-2 MOA gun! An extreme example but the truth non the less. Bore tech is a great cleaner and will work well for you. A little experimenting should tell you how often you need to clean your rifle. Like mentioned check the torque on your action screws. That can make a huge difference.
Bruce

 

[Inline6]

1st question, are you running suppressor covers on your cans? If no, that is more than likely your problem. Get good covers, several people make good ones if you need advice let me know I'll help point you in that direction.

2nd, I'm going to assume the can was tight. Hopefully assume does not live up to its name here. If you need a way to prove 1, pull the can off and shoot for groups without it. If you need to prove 2 shoot the rifle without the can.

Reading what you have written, the more you shoot, the hotter the can gets, the more visual mirage (in the scope) comes off the can. The harder it is to see the target almost like it gets fuzzy. With my SS cans it's not as bad, my Ti cans it does not take long.

 

[Still alive]

Just my two cents? I have always used a crono to record everything while developing loads to find the sweet spot in the nods? To get on target and dialing in the scope I used factory loads. Had the same thing happened. Measured factory loads and they were all different out of the box? Because I’m in California I have to develop non lead and lead loads for the rest of the country.
I really love my 6.5 creedmoor. 397 yards and 457 shots are deadly

 

[Corey0372]

First thing I would go is re torque all the action and bedding screws. And check is the suppressor is tight.

Everythings tight!

 

[Corey0372]

Sorry my test engineer brain would tell you to take off the can and repeat the shot pattern and see the results. Do that 1-2 times to establish if it’s when that specific can is on the rifle. On, off, on, off, etc. Then I would check torque, etc. The can may be causing the shift when it heats up.

Also, you are using a 30 cal suppressor, weird shifts *can* happen with sub caliber rounds because of standing wave harmonics inside of the can. I’m not saying this is the case, but it’s not unheard of either.

I did this...

did about 4 separate iterations of the "drill" for lack of a better term

With the can on the first 2 shots would be basically point of aim, point of impact (minus the .2 right which is just bc im using a different can than last time)

3rd shot would be .5 low

4th, 5th, and consecutive shots would group nice and tight .8 low from the initial first 2 shots


I would let everything cool down for a few minutes... then run the test again with the same results



Take the can off..... and I wouldnt have the issue

 

[Corey0372]

1st question, are you running suppressor covers on your cans? If no, that is more than likely your problem. Get good covers, several people make good ones if you need advice let me know I'll help point you in that direction.

2nd, I'm going to assume the can was tight. Hopefully assume does not live up to its name here. If you need a way to prove 1, pull the can off and shoot for groups without it. If you need to prove 2 shoot the rifle without the can.

Reading what you have written, the more you shoot, the hotter the can gets, the more visual mirage (in the scope) comes off the can. The harder it is to see the target almost like it gets fuzzy. With my SS cans it's not as bad, my Ti cans it does not take long.

I know what you mean, and this can become an issue with longer strings of fire, but for 5 shot groups the mirage wasnt really bad

 

[Corey0372]

I have heard of a string of shots like you describe as the group "walking". The culprit may be the barrel rubbing against the stock in the barrel channel. As the barrel heats up and expands it changes the pressure against the barrel. If the barrel is not completely free floated then thats a good place to start. Also bed the action if that hasn't been done.
I would also suggest allowing the barrel to cool a lot longer after 3 rds fired. The smaller the barrel the more likely heat/expansion may affect groups.
Like mentioned above cleaning needs to be considered. I had one rifle in a .300 WSM. After cleaning it was a honest .35 MOA rifle. After 9 rds of TTSX's it was a 1.5-2 MOA gun! An extreme example but the truth non the less. Bore tech is a great cleaner and will work well for you. A little experimenting should tell you how often you need to clean your rifle. Like mentioned check the torque on your action screws. That can make a huge difference.
Bruce

It's a pretty stout barrel, and I didnt have this issue with my other suppressor or with no can at all

 

[Corey0372]

Thanks for everyones input so far, i like these scavenger hunts

 

[Corey0372]

So, the weirdness only happens with that particular suppressor. How different is it from the other suppressor? Length, weight? No damage on the suppressor?

Correct, only with this one, it doesnt do it with the other suppressor or when shooting unsuppressed, This can doesnt have any damage and after the 4th or 5th shot the group really doesnt move anymore

 

[Corey0372]

OK here we go...I'll take a whack at this. I'm somewhat new to this but I've been really digging into precision rifle shooting over the last 5-6 months.

You didn't mention break-in although with that many rounds, it's broken in.

To your point about heat, from a bench or dead rest (if you're on), you'll notice the gun start to throw rounds in a circular pattern as it heats. This was taught to me by a precision match shooter. Unless you're shooting a super heavy match barrel it will heat up. You may not feel it on the exterior but those rifling grooves and lining of the barrel get a wee-bit toasty with shots in succession. Metal expands, rifling doesn't cut as well, etc. I will typically shoot 2-3 shots, then break for a while, rehearse my setup on sticks, then back at it. The day I was taught this the guy who taught me was shooting an 18 lb 300WM match rifle. He was only taking 1-2 shots every 5 minutes. The barrel alone probably weighed as much as my gun. Patience is not something I was graced with but had to learn.

If it were me, and what I've done, is establish a pattern of cleaning, fouling, and then stick to one ammo. I broke in with Hornady ELDM, and went right to zeroed with Barnes TTSX. Usually, when I re-foul after cleaning I used something cheaper like Norma in the same weight bullet. I typically disregard the foulers and then right to Barnes TTSX. I figured use $2.50/rd to foul before going to the $4/rd stuff. One thing I didn't know, and no one told me, was NOT just elevation is affected with ammo changes. I've noticed Norma pulls left in comparison to my zero with the Barnes. Why? I don't know? Difference in copper composition? Difference in molding of the bullet? I really don't know.

The cleaning, well, huge topic of debate. Some people says it ruins the bore. Some people say do it every time. Some people say just do it within reason. You hear stories of "I never cleaned the rifle and then when I finally did, the barrel was done?" Well, that's probably because there was a mountain of copper built up in it. You removed it, now you have a bare bore that's been shielded.

I'd personally eliminate the variables. This is my routine, every time.

- Bore is cleaned with Bore-Tech components with a nylon brush (never metal). Several soaked solvent patches, brush soaked in solvent passed 20x. Sit for 15 min, run one more soaked patch through. Dry completely with dry patches.
- 3 foulers of Norma Bondstrike 180gr, polymer tipped (same style as Barnes)
- 20-30 rounds of Barnes TTSX, 3 shot groups, pausing for some time between each group. Anymore than 20 rounds I find the barrel starts to heat unless I'm there for 4 hours which is quite a while.

I do this every time. Repeat.

Another thing that @ActionBob mentioned is torqueing of the action. Browning X-bolts are spec'd at about 45 in/lbs. Of course the manual tells you "snug." The folks at Griffin and Howe taught me that the X-bolts need to be torqued in sequence, and at 35 in/lbs, which yields the best MOA. Front screw seat, back screw seat, torque front to 35, torque rear to 35. I would call Bergara. On a nice fresh rifle those screws could be over torqued, under torqued, and/or not in the right sequence. They also could have worked loose slightly. If you don't have one, get yourself a nice Wheeler torque driver. Bergara, which is mind-blowing, has an article on their site specifying they want the rifle disassembled brand new. Bit of a head scratcher.

Rifle Care, Maintenance, and Storage - Rifles Bergara International

Author: Aaron Ryan Editor: Al Louangketh As a hunter, sport shooter, and a moderator for the Bergara International Facebook group, I seem to always be asked the same questions; what’s the best way to break-in my rifle? What solvents and oils seem to work the best for protection? How do I best...

www.bergara.online

After that I'd look to scope mounts, bedding issues, or a problem with scope holding zero.

Yea it wasn't throwing rounds pre say... like no buckshot grouping going on

HMR Pro does have a heavy match barrel which helps,

It wasnt doing this with the other can, or without a can

And you could almost say it wasnt truly an INconsistency, because it would consistently put the first two shots point of aim point of impact, 3rd shot about .5 low, and then after that it would be consistently .8 low

 

[Inline6]

Correct, only with this one, it doesnt do it with the other suppressor or when shooting unsuppressed, This can doesnt have any damage and after the 4th or 5th shot the group really doesnt move anymore

You are not seeing it as pronounced with the other can due to it being a K can. The longer can is producing more mirage you have to see through. Looking through mirage is like bow fishing in the water, the fish is not where you see it. Hints why the groups are stringing.

 

[Corey0372]

You are not seeing it as pronounced with the other can due to it being a K can. The longer can is producing more mirage you have to see through. Looking through mirage is like bow fishing in the water, the fish is not where you see it. Hints why the groups are stringing.

I would tend to agree but I've shot with this particular can on other rifles and many other suppressed rifles, I'm confident this wasn't a mirage issue

 

[Inline6]

I would tend to agree but I've shot with this particular can on other rifles and many other suppressed rifles, I'm confident this wasn't a mirage issue

Yeah I thought the same thing until it happened to me. It was out of the blue, once it happened. Well all my suppressors have cover with the exception of my 22.

 

[Corey0372]

Yeah I thought the same thing until it happened to me. It was out of the blue, once it happened. Well all my suppressors have cover with the exception of my 22.

Most of the time mirage will have me impacting high though, was this not the case for you?