Muzzle Brakes and normal POI change

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smilloy

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First off, let me say I am relatively new to this, so while some of this may seem simple to some, I am still learning.

I recently purchased a RPR in .308.

I took it out and zeroed it at 100. Lets say it was within 1" after the first time out.

I then installed a Cadex MX1 brake on the gun.
Took it out today and missed a 12x18 paper, aiming at the center (100 yards).
Brought it back to 50, and shot at the paper again and was 5" low. I adjusted the turrets up, then went back to 100 to zero it again. 5" low at 50 yards, is 10MOA at 100 if i am not mistaken.

I ended up moving my turrets a full 10 MOA up from where it was a few weeks ago.
Does this seem right? obviously the results font lie, but that seems like a lot to me.



Secondly, with me having to adjust my scope up 10 MOA, I now have roughly 38 MOA up, and 40+ down. Not a big problem as I likely dont have a range to shoot very logn distance, but is this normal? (the RPR comes with a 20MOA rail), so without the rail I would have less than 18 MOA in adjustment up (from 100 yard zero) Again is that normal?

Does it matter where i mount my scope on the 20MOA rail? It was originally put at the very back, but i moved it forward a few inches. i assumed it wouldnt matter, but maybe it does?

The accuracy was not effected by the brake, just the fact that they were significantly lower, so I dont think its a problem, was just curious if its normal?
 
I haven't seen more than a minute or two of POI change from installing a brake.. I would have to guess that something changed when you played with the scope. Also, might be something wrong with the scope, I would think that with the 20 MOA you should be have a lot more elevation to play with
 
I would double check to ensure your scope rings are fully seated down into the picatinny rail. 10 moa is a pretty big change in elevation for just a brake I think.
 
CanuckR said:
I would double check to ensure your scope rings are fully seated down into the picatinny rail. 10 moa is a pretty big change in elevation for just a brake I think.
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I should also note, the first time i was shooting off a bag. This time it was with a bipod.

Could the weight of the bipod + brake cause that?

Once it was zeroed it was shooting consistently.



I cant see the scope rings being a problem, all very tight and if it was moving due to firing i would expect it to constantly be out of zero. As soon as i zeroed it today, it was fine. Either way, no idea how i could test to see if thats a problem. Nothing moves when i use my hands to try and move it.
 
I put a genII lilbastard brake on my RPR, negligible zero change, also minimal change shooting off bag or bipod..I'd focus on brake installation problems , rings or scope.
 
APA LB GENII is 4.2 oz
this brake is 9.2 roughly...similar to a .338 Lapua in a FTE at 9.3 oz roughly...on a .750 RPR that will change the POI for sure. plus its a 30/338 brake so the bore is very large for a 30 cal bullet. Might add up to a big point of impact change from on to off. Once zeroed either way it should be fine...keep us posted
 
Maybe check the brake and be sure the bullets are not barely grazing it?

I bought and installed my first ever brake recently and had zero elevation change at 200M shooting distance before and after. Moving that much seems like a lot.

EDIT: My brake is also a 30/338 brake on a 30 Cal
 
Accuracy isnt reduced with the brake as far as i can tell.
Didnt shoot much today but measured my last group at 100. 0.364" measured to center of impact, 3 shots.

Good or bad, I have only ever shot 65 shots over 22lr in my life in a rifle, and all were on this one, so i assume I have room for improvement.
 
furtaker said:
APA LB GENII is 4.2 oz
this brake is 9.2 roughly...similar to a .338 Lapua in a FTE at 9.3 oz roughly...on a .750 RPR that will change the POI for sure. plus its a 30/338 brake so the bore is very large for a 30 cal bullet. Might add up to a big point of impact change from on to off. Once zeroed either way it should be fine...keep us posted
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Thanks for the education. I wonder why there is no great change in zero when I take off my Boss device from my 338win mag. It's definitely heavier than most muzzle brakes I'v seen ( It's the solid, non-muzzle brake Boss fitting).I have a Boss for same rifle that is vented, don't use it because it's way too load. Never noticed any big change in zero with it on/off. Curious.
 
smilloy said:
I should also note, the first time i was shooting off a bag. This time it was with a bipod.

Could the weight of the bipod + brake cause that?

Once it was zeroed it was shooting consistently.



I cant see the scope rings being a problem, all very tight and if it was moving due to firing i would expect it to constantly be out of zero. As soon as i zeroed it today, it was fine. Either way, no idea how i could test to see if thats a problem. Nothing moves when i use my hands to try and move it.
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I am not saying that the rings aren't tight. There is a chance that one of the rings isn't fully seated into the slot, but is still clamping onto the rail. I made this mistake a few months ago when moving some scopes around. Rifle still grouped well, but the amount of elevation I used up to get zeroed again didn't make sense. After further investigation it turned out to be one to the rings not fully seated onto the rail.
 
CanuckR said:
I am not saying that the rings aren't tight. There is a chance that one of the rings isn't fully seated into the slot, but is still clamping onto the rail. I made this mistake a few months ago when moving some scopes around. Rifle still grouped well, but the amount of elevation I used up to get zeroed again didn't make sense. After further investigation it turned out to be one to the rings not fully seated onto the rail.
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I suppose anything is possible. I am pretty sure that it was all the way on, but who knows, i guess cant hurt to take a look.
So if this was the case, I would assume the front mount to be the problem right?


Will the location on the 20MOA rail matter? I would it matter if i mount the scope at the very back, or forward a couple inches? I would assume the further forward you go, the closer the scope gets to the barrel, which should mean more MOA to play with right? Or am i way off here?
 
As far as I am concerned a big change in POI between brake or no brake is due to a poor fit. It is why I like to thread the barrel to fit the brake and then bore the clearance on the brake while it is on the barrel. Pre-threaded barrels and finished brakes don't always give the best results.
 
guntech said:
As far as I am concerned a big change in POI between brake or no brake is due to a poor fit. It is why I like to thread the barrel to fit the brake and then bore the clearance on the brake while it is on the barrel. Pre-threaded barrels and finished brakes don't always give the best results.
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I suppose that may be better, but if the gun is still accurate, and the only issue was an elevation change that can be zeroed out, whats the problem?


Here is a question. If one was to add a significant amount of weight to a barrel, but not change the barrel, or add a brake etc would that cause a POI change?

Just wondering if the weight of the brake is causing the change over anything else?
 
Brake bore is misaligned vs the threads, or the barrel's bore is misaligned vs the threads.
It's rare to see more than a 1 Moa shift with any quality brake.
 
To answer your last two questions, yes a break can and will change your POI due to the change in barrel harmonics. It is surprising that it changes that much though but there could be a number of things causing that.
Did you take the barrel and action out of the stock after your first outing to clean it? If so torque changes on the action screws when you put it back together could affect it.
Is the scope properly seated like mentioned before?
Are the action screws torqued properly? I had a 308 and the front action screw would come loose (about 3 inch pounds) and that would change my POI.
Is everything bedded and free floated that should be?
Could the weight of the brake be enough to make the barrel contact the stock when firing?
Misalignment of the break could be a possibility but I would suspect you would get any groupings at all if that was the case.
Are you using the same ammo from the first time to this time Brand, weight, design?
 
Did you take the barrel and action out of the stock after your first outing to clean it? If so torque changes on the action screws when you put it back together could affect it.
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No. I removed the bolt, folded the stock and cleaned it that way.

Are the action screws torqued properly? I had a 308 and the front action screw would come loose (about 3 inch pounds) and that would change my POI.
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I have not checked this. Its a new gun, right out of the box with 40 rounds the first day and 25 the second.

Is everything bedded and free floated that should be?
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I am not sure what you mean by this specifically.

Could the weight of the brake be enough to make the barrel contact the stock when firing?
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I dont think so. Didnt notice anything unusual.


Are you using the same ammo from the first time to this time Brand, weight, design?
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Now that I think harder about it, the last 5-10 rounds I shot on day 1 were a different brand. I brought the same stuff out for day 2 that i shot at the start of day 1. The stuff at end of day 2 was 7.62x51. It was supposed to be higher quality but I didnt like it. Totally forgot about it.

So now I feel like a moron.

My guess is the Brake caused part of the change, and the bullet caused the other.



Still a bit concerning however that I have used up almost half of my scopes MOA adjustment to zero at 100 yards (considering i have a 20MOA rail). If the scope was mounted too high would that use up part of its MOA? The scope was mounted for me, and I was told he had to go to extra high rings because it wouldnt fit with the high rings. I haven't measured the distance, but it might be 1cm?
 
guntech said:
As far as I am concerned a big change in POI between brake or no brake is due to a poor fit. It is why I like to thread the barrel to fit the brake and then bore the clearance on the brake while it is on the barrel. Pre-threaded barrels and finished brakes don't always give the best results.
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I wish there was a like button for comments like this. Fitted brakes yield much better results than the available pre-fits. Not to knock the available pre-fits, they have their place.
 
Schecter 81 said:
I wish there was a like button for comments like this. Fitted brakes yield much better results than the available pre-fits. Not to knock the available pre-fits, they have their place.
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Absolutely. Just keep in mind the RPR is an entry level rifle, that has a lot of features for low cost. If one was building from scratch, sure get it fitted but that isnt why someone would buy this gun (at least IMO)
 
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