Progressive PoI shift with Suppressor and Heat

[Wingge]

I'm having an issue with a rifle and/or suppressor that I'd like some feedback on before I start bleeding cash to resolve or replace.

The nature of the issue is a progressive shift in PoI of 2+ moa as the barrel/suppressor heats up, but only with the suppressor installed. Without a suppressor attached, the PoI shift due to barrel heating is very minimal.

Some specific information:

• Rifle in question is a Christensen Arms MPR in 6.5 CM with a 24" carbon fiber barrel. Entire rifle remains "stock original", no modifications on this rifle.
• Suppressor in question is a SilencerCo Hybrid 46 with 30 caliber end plate
• Rifle maintains acceptable zero and accuracy (< 1 moa), with or without a suppressor on "start from cold" 3 or 5 round group fire
• Without a suppressor, POI shifts very minimally up (0.1-0.2 moa) as the barrel heats up (could be explained by powder heating in chamber)
• With a suppressor, POI shift approximately 2 moa diagonal down and left as the barrel heats up.
• By "heats up", the specific scenario is 20 rounds fired in succession from cold barrel, with rounds fired within 10 minutes. For testing I've been firing a 3 round group at 50 yards, then 14 rounds on steel downrange, then a final 3 round group on target at 50 yards, with same aim point as first group. All groups from bench. At the end of the sequence the barrel is too hot to hold, but you can touch it briefly with some discomfort but no burn. I did not measure temp.
• The suppressor has been tested on several guns, including 2 other Tikka CTRs in 6.5 CM, and this behaviour is not seen other than on the MPR. However, the other guns all have shorter steel barrels (16"-20")

Just to reiterate, all guns show a repeatable PoI shift from the suppressor as compared to "no suppressor". The specific issue I am concerned with is the additional PoI shift due to barrel/suppressor heating, that does not manifest when the suppressor is not installed.


My questions are:

• Is this issue common and/or to be expected with the weight of a suppressor on a relatively long barrel?
• If so, would a shorter barrel mitigate the issue to any beneficial extent? By short, I'm considering a 20" barrel which I've been wanting to do in any case as this is a hunting carry rifle.
• If not common, is this perhaps a CF barrel issue that doesn't manifest to the same extent in steel? I'd like to stay with the lighter CF barrel if possible.

Thanks. Apologies if this has been covered before, but when using search functions all I can seem to get are articles on PoI shift due to suppressor installation. Any real world experience on this issue is appreciated.

 

[FisherT&C]

The can maybe too heavy for the carbon fiber barrel. I ordered a sendero profile barrel from proof a few years ago and was asked if a surpressor was going to be used, I replied no. The man I spoke to said ok, we like to go a with a little heavier profile if a can is going to be used. That may be your issue.

 

[jcmullis2]

Maybe Carbon fiber barrels don’t dissipate heat as good as traditional barrels. You can touch it because it doesn’t conduct heat like regular barrels so the cf becomes an insulator. But what do I know I haven’t thought about thermal dynamics since college and that’s been a really long time ago.

 

[Wingge]

The can maybe too heavy for the carbon fiber barrel. I ordered a sendero profile barrel from proof a few years ago and was asked if a surpressor was going to be used, I replied no. The man I spoke to said ok, we like to go a with a little heavier profile if a can is going to be used. That may be your issue.

Yah, that's my main crux here. The question I'm asking myself is whether this is a CF barrel trait, or alternatively just an issue with my specific barrel.

Just ran the test again with a Tikka T3x A1 (24" x 13/16" diameter steel barrel), also in 6.5 CM, to compare to the Christensen Arms MPR. The Tikka maintained PoI hot or cold, with the only observation being that the groups opened up with the suppressor.

Interestingly enough, the CA MPR PoI moved significantly from cold to hot barrel, with and without a suppressor. However, the suppressor did seem to magnify the PoI movement of the hot barrel. The CA MPR with suppressor moved 2.39 moa from cold barrel to hot barrel

Interestingly enough, for reasons I cannot explain the CA MPR "cold to hot" PoI drift was up and left during this test, rather than down and left that was observed while testing last weekend.

Graphic of test below:

 

[hollywood1981]

I have a CF sendero light 24" long on my new bolt action rifle. Use a rugged surge that is pretty heavy. My POI shift is no greater than .5 to 1 when warm to my CB shot. Interesting