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Thread: Massive POI shift without suppressor

  1. #1
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    Massive POI shift without suppressor

    I've been doing a bit of searching and see that this has come up before but mostly in a way that can be taken care of with scope adjustment. Shooting my Tikka 243 I can sight in and shoot more than happily with the suppressor on. Now, when I take it off the POI shifts off the target board completely. Seems a bit excessive. Has anyone had any experience trying to adjust a load or any other way of getting the POI at least close so that it can just be dialed out? Right now the POI is 600mm+ off at 100M. It's also shooting high so when I zero with suppressor on I can't go back past my zero stop. I'm only asking as I prefer to leave the suppressor off in the bush and use it for more volume type shooting or around stock.

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    A different load may or may not be less susceptible to the harmonic changes that occur when the suppressor is, and is not installed.
    There is really no way to tell without testing it.
    Hanging any weight off the end of the barrel can have an effect on harmonics and there is really no way to tell exactly how those changes will affect anything without testing.

  3. #3
    Member 199p's Avatar
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    What rifle do you have mate?

    is it free floated? pressure point bedding will make a bigger difference with suppressor on vs off as it changers the harmonics a lot
    even on my weatherby heavy barrel 223 there is a massive difference with suppressor on vs off as its pressure point bedded
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    Cheers guys, may have to do a bit of trial and error. Rifle is a Tikka 243 with factory fluted barrel and stug stock. Scope is aVX5-HD and then a DPT modular suppressor on the end. Currently shooting 95gr Targex.

    May have a play with adding and removing baffles to see if that makes much of a difference.

    Really just want to be able to accurately shoot a quick handling suppressor-less rifle in the bush and then be able to put the suppressor back on without having to go through massive amounts of scope adjustment. Even with a quality scope I feel that's just adding potential for inconsistencies.

  5. #5
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    Every rifle is different. I’ve found most the difference + or - can is only a few inches. But like @199p my Weatherby MkV ultralight 7mm08 the poi shifts by 8 in or so, high and right. And I think the standard set up with these in a B&C stock they come with is pressure point bedded. Thanks for the insight @199p, that does make sense
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    Make up a different load for spook and shoot, carry 2 different loads.

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    Quote Originally Posted by chainsaw View Post
    Every rifle is different. I’ve found most the difference + or - can is only a few inches. But like @199p my Weatherby MkV ultralight 7mm08 the poi shifts by 8 in or so, high and right. And I think the standard set up with these in a B&C stock they come with is pressure point bedded. Thanks for the insight @199p, that does make sense
    I've got a 300 WM in a B&C, tried it without the supressor the other day and was surprised to see there was bugger all diference in POI. My 308 Howa (freefloat) has around a 75mm shift.

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    GWH
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    The way i understand the POI shift with can on to can off, mainly comes down to the the threading of the barrel, normally a machinest would machines the thread true to the bore, potentially the outside of the barrel may not be true to the centre of the bore. If that is the case, and the rear bush in the suppressor happens to be too tight a fit over the barrel then as the suppressor is screwed up tight it can tweak the barrel slightly.

    You can test this by removing the bush from the rear of the suppressor and fitting the suppressor with out the bush and check to see if that changes the point of impact, compared to shooting it with the bush fitted. Assuming you are running a suppressor that has a bush that can be screwed out.
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  9. #9
    ebf
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    600mm at 100M is a massive amount... 60 mil or around 20 MOA

    are the holes in your paper target round, or is the projectile tumbling ?

    another test you can do is to put a cleaning rod up the barrel from the chamber end and see if it is perhaps touching any part of the suppressor ? not foolproof, but worth a try.

    also have a very close look at the suppressor, preferably under magnification

    are the group sizes you getting with the can on and off similar ?
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    Quote Originally Posted by ebf View Post
    600mm at 100M is a massive amount... 60 mil or around 20 MOA

    are the holes in your paper target round, or is the projectile tumbling ?

    another test you can do is to put a cleaning rod up the barrel from the chamber end and see if it is perhaps touching any part of the suppressor ? not foolproof, but worth a try.

    also have a very close look at the suppressor, preferably under magnification

    are the group sizes you getting with the can on and off similar ?
    Yeah I think you're recognising what I'm talking about. My 308 had a spread but about 150mm or so and that could be dealt with. First time I shot this rifle without the suppressor was last week. Have had about 150 rounds through it before that. At 100M I couldn't even see the impact as it was over the backstop so far, at 50M was completely off the paper. Did re zero without suppressor and group size is similar and no scuffing on the suppressor baffles or anything like that. Did not think about the rear bush potentially being a bit off. Holes are all round as they should be, no signs of tumbling.
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    Quote Originally Posted by GWH View Post
    The way i understand the POI shift with can on to can off, mainly comes down to the the threading of the barrel, normally a machinest would machines the thread true to the bore, potentially the outside of the barrel may not be true to the centre of the bore. If that is the case, and the rear bush in the suppressor happens to be too tight a fit over the barrel then as the suppressor is screwed up tight it can tweak the barrel slightly.
    The only real issue with a rear bush touching the barrel is a -variable- zero when you refit it. Even having it completely clear doesn't in any way guarantee the POI won't change significantly with the can fitted versus unfitted. To my way of thinking, it's surprising that the zero doesn't change markedly when you add that much mass to the end of a barrel.

  12. #12
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    all of my rifles change by poi lifting ABOUT 3" at hundy......not enough to worry about.... took me awhile to get head around difference when using collimetre/bore sighter....cross hairs now sit pretty much bang on whereas they were 3 squares up before....figures when you think about it... 600mm=2 feet that is a HUGE amount of difference,something else going on here.
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  13. #13
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    The weight of the suppressor typically has an effect barrel harmonics hence the POI shift.
    Similar to how a bench rest barrel tuner works. There are some light weight barrel tuners available these days with micrometer adjustman so it just shows it doesn’t take much..

    Even with the ‘truest’ thread job on earth, there should be a difference between even screwing the suppressor on half way and screwing it up to the shoulder. Not that I’d recommend trying that!

    600mm at 100 is a crazy POI shift. 1-3 inches would be typical. If you had someone fit it for you I’d send it back.
    Last edited by Tui4Me; 01-08-2018 at 03:53 AM.
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    how heavy is the can?

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    I too would say throw the bush away. I got rid of them years ago. They fuck up things after a couple shots. Also it allows heat to escape from that chamber.

 

 

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