Suppressors Suppressor POI change?

[timelinex]

I'v been using my 338BA suppressor on my savage 308 for a while now. The POI change has always been very minimal. The POI would be 0.2 mils higher with the suppressor than without.

Now, out of nowhere, the POI with suppressor is almost a full mil lower. Groups aer still just as great as before.

Anyone ever had something like this happen?

 

[itieknots7]

How heavy is the can (before/after)?


Some people depending on reloads really collect a lot of carbon in their cans and need to clean them.

 

[Zak Smith]

Whenever there's a change in your POI or ballistics on a precision rifle, you always start with "what changed" ?

The 0.2 high suppressed vs. unsuppressed stands out. Upward shifts are pretty unusual, but not unheard of.
Shifts up usually indicate either a vibration/harmonic change in the barrel/rifle, or a node/antinode change in barrel vibrations, or some other movement during firing, that is being affected by the added mass of the suppressor.

If this were the case, I could see how perhaps changing the load a little bit might throw it off, to a different position in the node/antinode setup in barrel vibration or something like that.

Another thing to check-- have you removed or replaced the muzzle brake recently? Is there any carbon or gunk on the external shoulder of the brake that might not let the can seat square?

If all else fails give us a call.

 

[timelinex]

Whenever there's a change in your POI or ballistics on a precision rifle, you always start with "what changed" ?

The 0.2 high suppressed vs. unsuppressed stands out. Upward shifts are pretty unusual, but not unheard of.
Shifts up usually indicate either a vibration/harmonic change in the barrel/rifle, or a node/antinode change in barrel vibrations, or some other movement during firing, that is being affected by the added mass of the suppressor.

If this were the case, I could see how perhaps changing the load a little bit might throw it off, to a different position in the node/antinode setup in barrel vibration or something like that.

Another thing to check-- have you removed or replaced the muzzle brake recently? Is there any carbon or gunk on the external shoulder of the brake that might not let the can seat square?

If all else fails give us a call.

Sorry, your right about the upward shift. Its a downward shift. I zeroed with the suppressor on and I would have to put 0.2 mils DOWN for the unsuppressed zero. So that would make a downward shift with the suppressor.

How does your advice change with that in mind?

When your talking about the external shoulder, your talking about the slanted part right after the threads end right? That parts really clean, so its not that. There is alot of crud on the front of the muzzle break, but don't think that effects anything.

The only thing that 'changed' is I've put 200 or so rounds of 338lm through it, since last time I used it on this rifle. Looking through the can, there aren''t any obstructions and accuracy is still great, so I don't think its anything to do with the actual can?

How heavy is the can (before/after)?


Some people depending on reloads really collect a lot of carbon in their cans and need to clean them.

I've never weighed the can, but I was under the impression that centerfire suppressors go thousands of rounds before needing a cleaning of any sort?



How large of a POI change is generally normal? I use to use it on my savage 110 and there was barely a POI change on that either. However on my AX338 I just got recently, there is a .7mil change. I can't test the savage 110 as I've already taken all its ammo apart in preparations for selling it.

 

[ZombieMonkey]

I've never weighed the can, but I was under the impression that centerfire suppressors go thousands of rounds before needing a cleaning of any sort?

Generally they can, however certain powders can increase the amount of buildup quite a bit. Some cans may gain a couple ounces and level off, others may continue to build them up a bit. Really can depend on specific combos and I'm sure Zak can give you much more advice.

When did you develop your 338 load? Temps have been climbing here in AZ again and it may be possible that you were right on the edge of that node and the can / temps have causes you to exit the node. Something clearly changed which is great you picked up on it.

Have you ensured your brake attach is not coming loose?

 

[timelinex]

Generally they can, however certain powders can increase the amount of buildup quite a bit. Some cans may gain a couple ounces and level off, others may continue to build them up a bit. Really can depend on specific combos and I'm sure Zak can give you much more advice.

When did you develop your 338 load? Temps have been climbing here in AZ again and it may be possible that you were right on the edge of that node and the can / temps have causes you to exit the node. Something clearly changed which is great you picked up on it.

Have you ensured your brake attach is not coming loose?

Its not coming loose and this is the same load I've been using for atleast 2 years now. Same lot of powder in the last year. So it's not the load. I had to recently push my bullet out .01, because I'm pretty sure lands eroded that much. But that shouldn't change anything to do with POI.


Top 2 are unsuppressed and bottom one is suppressed. I'm gad there was a target to the bottom right or I wouldn't even of seen it! I did a couple more groups throughout the day to confirm.

 

[Zak Smith]

We have cans here that we swap between multiple rifles but they come back to each rifle's zero/POI. I've swapped my .338 can around a whole bunch with no similar problems.

I would recommend to weigh the 338BA can to see if it happened to pick up disproportionate weight on the .338LM. I would not expect that it would, and your comment about not needing cleaning for thousands of rounds is right in most cases. The stark exception we've found so far is that loads with H1000 foul way, way more compared to just about everything else.

Did you ever remove the brake from this rifle?

 

[timelinex]

We have cans here that we swap between multiple rifles but they come back to each rifle's zero/POI. I've swapped my .338 can around a whole bunch with no similar problems.

I would recommend to weigh the 338BA can to see if it happened to pick up disproportionate weight on the .338LM. I would not expect that it would, and your comment about not needing cleaning for thousands of rounds is right in most cases. The stark exception we've found so far is that loads with H1000 foul way, way more compared to just about everything else.

Did you ever remove the brake from this rifle?

The can weighs 25oz now. Unforunately I don't know the exact weight before using it.

I use retumbo for my 338lm. I have moved it between refiles all the time bfore too and didnt have this issue.

Lastly, No I have never removed this brake from this rifle. I'm guessing the brake has a good 500-1000 rounds through it. It's caked up, but clean around the threads and shoulder.

 

[Zak Smith]

Not much weight change at all.

If you can't figure it out by all means give us a call and we can take a look. It might be impossible to debug without your rifle(s) though

 

[timelinex]

SO.... BIG UPDATE. Today I went to the range and all hell broke loose. Unsuppressed Im shooting bugholes with my 308 and then I put the suppressor on and I'm shooting 2-3 inch groups!! So now it went from the POI change changed to shotgun groups.

Looking down the suppressor, it doesn't look like there are any baffle strikes of any kind. At the advisement of a friend at the range, I looked down the bore, and voila! It looks like the top part of the suppressor can be slightly seen! Here are some pictures:

1. No suppressor on

2. Suppressor on. You can now see slight shaddowing up top

3. Another picture with the suppressor on. Its taken outside where its brighter, so its easier to see the shadowing on top

4. This is a picture taken a little bit above the centerline of the bore. So even then, you cannot see any shadowing at the bottom of the bore (from the bottom of the suppressor).

I put the suppressor on my 338 and everything seems to be normal. No shaddowing unless I go off center from the bore.

So it's gotta be the mount on the 308 then...? What could it be? For hundreds of rounds the suppressor only changes POI .2mils and accuracy was great. Then it changed POI to over a mil away, while accuracy stayed tight.. Then accuracy degraded. What problem with the mount could cause the suppressor to be off axis like this and cause a decline in integrity of shooting like it did?

 

[Zak Smith]

I can't really tell anything from the photos.

Suggestions:

1. Make sure there is no damage to the 308 brake or anything preventing the suppressor from seating fully against the brake shoulder

2. Make sure the brake is mounted correctly on the muzzle threads and that the brake to peel washer to barrel shoulder is tight and solid.

If all else fails you know it shoots good with the brake on the 338- you could swap the brake from that rifle (don't bother using a peel washer for testing: brake straight against muzzle shoulder), and see what happens. That would either rule out the .30 cal brake or how it's mounted, or suggest focusing on those.

Something changed over time, we just have to figure out what it is.

 

[timelinex]

I can't really tell anything from the photos.

Suggestions:

1. Make sure there is no damage to the 308 brake or anything preventing the suppressor from seating fully against the brake shoulder

2. Make sure the brake is mounted correctly on the muzzle threads and that the brake to peel washer to barrel shoulder is tight and solid.

If all else fails you know it shoots good with the brake on the 338- you could swap the brake from that rifle (don't bother using a peel washer for testing: brake straight against muzzle shoulder), and see what happens. That would either rule out the .30 cal brake or how it's mounted, or suggest focusing on those.

Something changed over time, we just have to figure out what it is.

You really can't see the difference in the pictures? They are pictures looking through the bore of the rifle. Here they are cropped, zoomed in and placed side by side. The first is without the suppressor and the next two is with the suppressor. You can see that in the first picture the light through the bore is nice and round. With the suppressor, the bore looks a bit oval, as the top is cut off with what is the edge of the suppressor. My best guess is that its not actually striking, but coming very close and because of this being throw off coarse.

The rifle had hundreds of accurate rounds through the suppressor before this started happening. Nothing has changed. The brake is still on there tight and no crud on the shoulders. There is a bunch of carbon buildup on the outside of the brake though(everywhere but shoulder). The suppressor screws on and sits tight against the shoulder.

I will screw the 30ba brake off my AR and put it on this rifle, to see if this fixes it I suppose.

 

[Zak Smith]

I do see it offset in "with2". These things are always easiest to see with the naked eye.

With respect, if there were no change in any part of the system, then it would still be shooting the same, right? It's not, therefor something changed. We just don't know what part of the system changed yet. If the can still shoots accurately on the other rifle, then it points at something other than the can. If you can swap a different brake to the rifle it shoots good, then it points to the brake or brake mounting. Once we have a little more data we can go from there.

hope this helps
Zak

 

[timelinex]

Ok so I tried it on the other rifles and when I try to apply side pressure and move the suppressor in its threads, it won't. However when I try to do the same with the 308 rifle that's having issues, there is definitely play in the threads. Applying pressure allows the suppressor to move up and down a little bit, even though it's tight and snug against the shoulder.

Is this the problem? Do I need to replace the brake?

 

[Zak Smith]

Without having it in front of us, it's hard to diagnose the exact problem.

Can you tell if it's moving on the brake, or if the whole brake is moving on the rifle?

If it's the former, without having seen it and just speculating, I'd guess that something is preventing it from really seating against the shoulder on that particular brake. It might look like it's bottoming out but not really doing so for some reason. If it were against the shoulder it couldn't move. That could be due to the brake or something on the brake itself, or due to a combination of factors with the brake and can.

Please give me a call tomorrow with whatever you find.

thanks
Zak

 

[timelinex]

Without having it in front of us, it's hard to diagnose the exact problem.

Can you tell if it's moving on the brake, or if the whole brake is moving on the rifle?

If it's the former, without having seen it and just speculating, I'd guess that something is preventing it from really seating against the shoulder on that particular brake. It might look like it's bottoming out but not really doing so for some reason. If it were against the shoulder it couldn't move. That could be due to the brake or something on the brake itself, or due to a combination of factors with the brake and can.

Please give me a call tomorrow with whatever you find.

thanks
Zak

There is a major amount of carbon buildup on the front and sides of the brake, which shouldn't be touching or effecting anything since its not on the shoulder. However I thought about what you said and how it might not be sitting flush even if it seems like it is. So I cleaned the brake outside completely of all the carbon buildup. I had to get out a piece of brass and literally scrape it off!

I tried putting the brake on and it seems to sit on there much more solid! I will do another range trip sometime this week and test it out. If it doesn't fix it, I'll give you a call zak.

Thank you for helping me through this diagnosis. I will give you an update when I test it again.

 

[timelinex]

Just went to the range after the cleanup and all is good. Back to almost no poi shift and good groups.

Moral of the story, clean your brakes!

There was no buildup on the shoulder, but regardless, one way or another the buildup on the front of the brake was somehow preventing the suppressor from seating completely.

Thanks again Zak for all the suggestions and helping me diagnose this.