Need advice about shifting point of impact.

[FullEffect1911]

I figured this would be by far the best place for advice about my M&P 15-22. First I would like to say that mine has been flawless for function and capable of surprising accuracy. It is stock except for a Primary Arms M4 style red dot.

Now the problem I am running into is a wandering point of impact for elevation only. I sighted it in at 25 yards dead on one day, and a few days later it was shooting consistently 2 inches low. The funny thing is the precision of the groups is great, just not the location.

The first time I took the rifle out it was 92 degrees and sunny, the rifles groups opened up a whole lot. I figured that was just due to barrel heat.

I guess either the barrel nut is loose, the rifle is really sensitive to heat, the barrel plug is really effecting the POI or something else I haven't thought of. It is possible that it is my shooting and I won't completely rule that out. The PA red dot seems to be holding zero in relation to the iron sights. The ammo I have been using is Blazer lead RN (my rifle really likes this ammo).

If anyone can steer me to some likely suggestions I would very much appreciate it.

 

[OKFC05]

Shot in the dark:
Are you resting or holding the rifle differently?
Rifles rested on a firm surface tend to shoot away from the contact point.

Also, are all screws, bolts, nuts torqued to spec? My RWS 34 air rifle suddenly shifted zero because of a loose stock bolt.

 

[FullEffect1911]

It appears that the POI shift is consistent through all 4 shooting positions, though I tested it properly shooting prone, no sling or bipod. As full disclosure, when I sighted it in a few days ago I was using a vertical table leg as an extra support, I suppose it is possible that had an effect.

The only screw or nut that really could be loose is the barrel nut, but I would suspect that would cause the groups to open up as opposed to move the POI vertically.

What I plan on doing is making a barrel nut wrench to torque the barrel nut to 15 ft-lbs and opening up the fore end cap on the lathe to be a true free float. Just don't want to bother with the work if neither will help.

From my observations I am starting to think that any slight temperature change seems to really affect this rifle, but that doesn't make a whole lot of sense to me.

 

[true_shooter]

i know you said you were using blazer ammo both times but just to throw it out there, were the projectiles the same weight both outings ie 36gn when you sighted it in and 36gn when you noticed the problem? Did you remove your optic then put it back on in the wrong rail accidently? check that the optic is mounted good and tight. My thought is that the dope on your sight either got messed with or it lost its dope in the car/truck on the way to or from the range going over a bump. My advice would be to sight it in again, after your point of aim and point of impact match up run a few more 5 rnd groups through it as a confirmation. then go home and cross your fingers and hope that when you go back out to the range all is good. good luck to you

 

[FullEffect1911]

All good points. However the ammo was all 40 grain and from the same brick. The optic hasn't been removed since it was sighted in the first time, however I will double check the tightness of the mounting bolt. While I'm at it I will look over any mounts that were factory tightened in the event that they just missed something.

It's an M4 style red dot so it came with an integral mount but it doesn't hurt to take a look.

If the rain holds off I think I'll send a few rounds down range tonight.

 

[team sidewinder]

I have experienced the same problem and I am using a 4X32 Mark III NcStar scope. I would sight in at the range take the gun out to shoot gophers a couple of days later ( carring the gun in the truck gun rack then on my back while on the atv ) and sometimes the gophers wouldn't even move or go down their hole when I was shooting at them so I knew I must have been WAY off target. Take the gun back to the range and it would be either a couple of inches high or low but right on line. This happened several times which drives me crazy and then the other day it started moving point of impact right but elevation perfect. All my groups are not bad and good enough for gophers to 40 yards if I could just keep them the same. I have checked the scope mounts and everything is tight on the rail and with my scope the mounts are part of the scope body so nothing loose there either.

I was able to slip a bent pick in one notch of the barrel nut to see if the barrel nut was loose but it seems tight to me without buying a barrel nut wrench. I blamed my scope but now I don't know what is causing the problem. Hate to take my rifle out gopher hunting ( 10 miles round trip ) after sighting it in and the gophers just laugh at me. LOL If you find your problem maybe I will find mine.

 

[Star4Ever]

Are you using the same Magazine? Pre and post Point of Impact...

Have you added/removed anything to the rifle since sight in, such as a bipod etc?

I have noticed that if I "play around" with the tip of the forearm by applying pressure to the forearm, it moves slightly enough to press against the barrel.

That said, your idea about free floating probably is worthy of a test or two.... you may be onto something there.

 

[FullEffect1911]

I am going to make a barrel nut tool and remove the fore end "spacer" and really give everything a once over. I will get to the bottom of this.

There is one common theme to days I went shooting, and that is different temperatures. I think the temperature is effecting the fore end (possibly even the connection point with the upper receiver) and pushing on the barrel just slightly. This is of course all theory, but worth investigating.

"Are you using the same Magazine? Pre and post Point of Impact...
Have you added/removed anything to the rifle since sight in, such as a bipod etc?"

I have been using two magazine, both 30 rounders. Everything else is the same, no bipod or sling.

ETA: sorry I meant 25 rounders, been around my Stag carbine to much =)

 

[Dead eye 22]

Be sure you rest/hold the forend at the exact same point each time you shoot. Holding or resting the forend at different locations can change the point of impact. I would try benchrest shooting the rifle in order to reduce the human variable as much as possible for your tests.

 

[FullEffect1911]

Alright, I made a barrel nut wrench and disassembled my rifle. The bolts on the red dot were certainly tight, so barring a mechanical flaw with the sight I don't think it was that. The barrel was pretty tight so it wasn't likely the culprit either. I removed the forend cap and then took the rifle out shooting.

I got it sighted in for 25 yards again, it's relatively cold and windy here right now but the red dot returned nearly to zero with only a 3 click change in elevation and 1 click for windage (windy day). It shot consistently well in a variety of prone positions, both supported and unsupported. I may have to shift the windage back one click on a nice day. The rifle certainly didn't shoot any worse with the plug absent.

So in a few days I will take the rifle out and see if anything shifted.

I suspect I know what the problem is though, Nylon has a thermal expansion of about 3 times that of aluminum, so if the joint between the barrel and the receiver expand (even slightly from the ambient temp the rifle was sighted in for) it might flex the whole system up and down changing POI vertically. This would also show up when the barrel gets hot as Nylon also doesn't conduct heat well so it wouldn't cool at the same rate as steel or aluminum.

I'm hoping I'm wrong with my theory and the removal of the fore end cap solves any of my POI problems. Time will tell. The ambient temperature could also have affected the forend cap causing it to push on the barrel in a strange direction. When I had the barrel clamped in a vice I noticed that both the barrel and the fore end were capable of flexing without much effort, so it wouldn't take a lot of force for that cap to move the barrel.

 

[team sidewinder]

You may be on to something alright. Sounds logical.

I am thinking my problem is scope related as the last time at the range with the left/right shift I tried to bring the impact point from 2 inches right by turning the left/right knob left and the impact point kept moving more right. Go figure. So I started moving the L/R knob right and the impact moved back to the left and to bullseye zero so that is where I left it. Went out the next day to the range and it was still at zero but will see where it shoots after traveling to the next gopher hunting trip. The scope seemed to work as designed the first time I sighted it in but I have had to sight it in 4 times since.

 

[FullEffect1911]

I never did trust that the adjustments on cheaper scopes are repeatable. I have never had a problem with them going out of zero, but I always just assumed that if I go x clicks up and then x clicks back down that it won't likely be in the same spot it was when I started.

I'm really hoping for the both of us that just removing the forend cap will solve our problems, would be great if it were that simple.

 

[team sidewinder]

The temps for all my sight ins were probably not more than a 15 degree ambient temp spread. Although my groups are all that great and I could live with them I would just be happy if they were where I was aiming.

 

[Star4Ever]

You did good.... lets see what happens in a few days time.
Report back.
thanks

 

[team sidewinder]

Took the 15-22 out today and wasn't expecting much but it layed a few gophers low ( some at 50 and 25 yards ). I R a happy camper and this is the only thing I use my 22 rimfires for. Now if it will just stay there. If my rifles are on I may only shoot 100 22 rimfire rounds a year as I am not a high volume shooter and 50-70 gopher a summer are enough.

This M&P 15-22 is just the best looking AR .22LR out there and people compliment its looks but can't believe it is a .22LR.

 

[paulj2]

I'm really hoping for the both of us that just removing the forend cap will solve our problems, would be great if it were that simple.

Did you test your rifle any further without the cap? I have been watching to see your results, I have had the same issue.

 

[FullEffect1911]

"Did you test your rifle any further without the cap? I have been watching to see your results, I have had the same issue."

I haven't yet. I plan to this week, but I have been getting ready for my first IDPA match early next month and have been focused on my M&P9.

 

[team sidewinder]

I have not tried my rifle at the range without the end cap. Not sure why but my last hunting trip out the rifle was close enough to zero that my misses could have been shooter caused error. I can tell when it is me or the rifle is off far enough there is no doubt where the problem lies. So I have just left the end cap on so far and have not shot any paper ( which I hate to do ) to see where it is shooting but it has taken way more gophers so it must be real close to zero.

I also began to wonder if cleaning my rifle after every range session trying to get it sighted in on paper ( sometimes not more than 50-70 rounds ) may have somehow cause the rifle to shift point of impact on my next time out because I have not broken the gun down and cleaned the barrel bore since and just cleaned the bolt face without the point of impact shifting. I would always push down on the barrel handguard to break open the rifle to give it a real good cleaning ( scrub bore, clean and lube bolt, slides, clean/lube trigger group ) and maybe causing the point of impact shifting. This is the only thing that I can think of that I have quit doing and it is keeping the zero so far. Next time the rifle needs a good cleaning ( for me 200 rounds ) I will try another method of breaking the rifle open for cleaning and see what happens to the point of impact. Before after sighting the gun at the range to get it back to zero I would take the rifle home to really clean and the next time out hunting gophers the gun was way off zero. All this is just speculation on my part.

 

[paulj2]

I am with you about shooting paper, I guess I don't hate it but prefer reactive targets, like rockchucks.

On my rifle, I pulled the end cap and opened the hole up, giving it approx 1/8" clearance around the barrel and then reinstalled. I haven't been able to give it a real test yet. I fired about 40 rounds and it seemed to hold at "minute of rockchuck" while hunting, but need to print a little paper to be sure.

I will post the results when I can get out again.

 

[chuck s]

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