Need advice about shifting point of impact.

Assuming you're not using a genuine Aimpoint or EOTech "dot sight" the elevation change could very well be the effect of air temperature on the sight. You can rule this out by shooting with the iron sights and comparing POI on different days.

Humidity will also affect external ballistics although I'd not expect to see a 2" difference from day to day.

-- Chuck

I thought about this too, or at least thought it could be the case. It's a very valid point. What I will do is if the shifting continues I will put my Aimpoint with Bobro mount on the M&P 15-22 just to take away that variable.
 
Well I got a good chance to wring out the rifle again today. I was one click off for windage and one click for elevation. The windage error was expected based on when I sighted it in last and really the elevation could be a reasonable error in my aiming down a 1x sight. This is considerably better then the shifting I was getting before. I also learned not to bear down on the rifle to much, being that it is only nylon really pushing into the rifle will changes its POI (this of course includes shooting slings).

Suffice it to say I am quite happy with the consistency so far and I am thinking that I have solved my POI shifting. I also think that the biggest problem I had was the fore end cap. As I keep shooting the carbine I will keep up on this post with any updates.
 
guys if you're not used to AR style sights the problem is quite simple. Short range shots will vary from your zero exactly 2 inches most of the time when your zero is out to about 50 yards. If your zero is 50 yards, a shot inside that say at about 10 to 20 yards you'll need to aim low. A shot thats wayyy past 50 yards and you'll have to aim high until the round starts to lose energy. A bullet crosses the trajectory line 2x in flight. This threw me off tremendously when I first started out with my 15-22 as I'd never shot an AR platform. It has to do with the sights sitting so high over the bore. Hope this helped
 
guys if you're not used to AR style sights the problem is quite simple. Short range shots will vary from your zero exactly 2 inches most of the time when your zero is out to about 50 yards. If your zero is 50 yards, a shot inside that say at about 10 to 20 yards you'll need to aim low. A shot thats wayyy past 50 yards and you'll have to aim high until the round starts to lose energy. A bullet crosses the trajectory line 2x in flight. This threw me off tremendously when I first started out with my 15-22 as I'd never shot an AR platform. It has to do with the sights sitting so high over the bore. Hope this helped

There is a good trajectory calculator on handloads.com that will tell you where the round will be hitting by inputing your sight height, bullet weight and speed etc. Works quite well.

However all my shots were taken at 25 yards and the .22 was sighted in for that range to hit POA/POI.
 
Well I got a good chance to wring out the rifle again today. I was one click off for windage and one click for elevation. The windage error was expected based on when I sighted it in last and really the elevation could be a reasonable error in my aiming down a 1x sight. This is considerably better then the shifting I was getting before. I also learned not to bear down on the rifle to much, being that it is only nylon really pushing into the rifle will changes its POI (this of course includes shooting slings).

Suffice it to say I am quite happy with the consistency so far and I am thinking that I have solved my POI shifting. I also think that the biggest problem I had was the fore end cap. As I keep shooting the carbine I will keep up on this post with any updates.

Were you able to shoot enough to get the barrel fairly warm? I was thinking this may also be a factor considering the build material of the rifle.
 
Were you able to shoot enough to get the barrel fairly warm? I was thinking this may also be a factor considering the build material of the rifle.

Warm to the touch but nothing close to hot. The barrel being just a bit warm didn't seem to have a big effect. The first time I took this .22 out I burned through lots of ammo fast on a very hot day. The groups opened up like crazy. So I definitely agree heat a pretty big factor.
 
I have come to the conclusion in my case that carring my 15-22 with a sling attached on one end to the far end of the forearm may cause my shifting impacts. While slung over my shoulder and bouncing around while ridding my atv may provide enough torque on the forearm to shift the point of impact somewhat. Only a theory for now though.

I am a little afraid to free-float my barrel when the barrel without some support from the forearm is only attached to a poly receiver and may flex the barrel in the receiver. On a real ar15 a metal receiver can support the barrel much better when the barrel is free-floated.
 
I am a little afraid to free-float my barrel when the barrel without some support from the forearm is only attached to a poly receiver and may flex the barrel in the receiver. On a real ar15 a metal receiver can support the barrel much better when the barrel is free-floated.[/QUOTE]

That is exactly the worry I would have with the idea of free floating the barrel. Frankly, as easy as it is to float the barrel, seems to me that S&W would produce it that way if 1) it helped accuracy and 2) the extra support the barrel recieves from the handguard was not needed.
Figure S&W knows what stresses are excessive more so than I.
 
I am a little afraid to free-float my barrel when the barrel without some support from the forearm is only attached to a poly receiver and may flex the barrel in the receiver. On a real ar15 a metal receiver can support the barrel much better when the barrel is free-floated.

That is exactly the worry I would have with the idea of free floating the barrel. Frankly, as easy as it is to float the barrel, seems to me that S&W would produce it that way if 1) it helped accuracy and 2) the extra support the barrel recieves from the handguard was not needed.
Figure S&W knows what stresses are excessive more so than I.[/QUOTE]

I think the biggest reason not to free float the barrel is if you use the iron sights. The fore end will flex and will throw off your shots if you free float and try to use the front sight.

As far as strength is concerned, working off memory, it's true that the weakest part of the fore end is going to be at or near the connection point, but not necessarily the point that is being compressed by the barrel nut. Besides that nylon seems to have a excellent elasticity and it's yield strength is pretty good, outside of straight abuse I don't think it will matter much.

however just to be on the safe side I am going to bore out the fore end cap to a larger inside diameter so that if the fore end wants to flex a lot it will contact, but under normal conditions it will be free floating... best of both worlds I think.
 

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