point of impact changes with heat...help!!

[mocos]

I have two socom 16s one GI tiger striped wood stocked the other synthetic..they both operate very well with an occasional feeding and ejection hiccup every so often. I shoot both of them in 3 gun and run-n-gun matches. As a result they can get pretty hot to the touch because of the number of rounds fired in a realatively short period of time. Both are zeroed at 50yds with milsurp ammo, currently South African and generate 1.5 - 2 inches at that distance..and 4-5 at 100yds....iron sights...national match fronts and GI rears.

At 40-50 rounds..the point of impact starts to shift. The targets engaged are usually clays at 50-60 yds...which is not a problem. Once the rifles are warmed up, point of impact shifts toward 2'o clock and the clays need to be basketball before I can hit them with a center hold. I also have a mini-G in .308(16" garand) that exhibits the same thing.

Is this typical of m14s or garands any barrel length and how do I go about dealing with this impact changing.

 

[JSTARSZ]

Re: point of impact changes with heat...help!!

If the 40-50 rounds are fired very quickly then yes the barrel will heat up and can change the POI. I find this even more so when I use suppressors as that really heats up the barrel. Now, knowing what your weapon does when it heats up is knowing your weapon well. If you know that after that 40-50 rounds it changes the POI and it is repeatable then you do what out Grandfather's called "Kentucky Windage." If you know it moves 2" right then shoot 2" left.

is it normal - yes it is normal that when steel heats up it does change the impact of a round. If you could look at your weapons as you fire them in slow motion you would see just how much the barrel can arch and move during firing but knowing what they do on a consistent basis under certain conditions makes you an informed shooter.

 

[ORD]

Re: point of impact changes with heat...help!!

+1 to JSTARZ's comments.

This problem becomes even more pronounced when you have a rifle, like the Garand, M14/M1A, etc. that has a non-free-floated barrel, additional heat from the gas cylinder, etc., more moving parts to wreak havoc on accuracy, and often, a wood stock.

The best thing you can do is to range-test your rifle under competition conditions. Run it up to 40-50 rounds so that your barrel gets hot enough to cause the POI shift and then put it on paper at the ranges you need to know the what the POI shift is and see if you get a repeatable, consistent measurement. Once you know the data, you can either accomodate for it with a hold-over or (less likely in a high-speed comp setting) make an iron sight adjustment so that your POA and POI match up.

If for some reason your POI shift is NOT repeatable/consistent or, instead of only cause POI shifts your groups open up and go to hell, then you have an entirely different problem and you probably want to consider an alternative carbine/rifle for competition use.

 

[mocos]

Re: point of impact changes with heat...help!!

thanx..got it...start with a 0 hold and when things start going bad..(in my case)adjust to a 7:00 hold...or use the top right corner of the front sight and a skosh lower etc...and if I read between the lines, once the barrel has heated up enough for the impact to move, it generally stabilizes at that point? or will it continue to move elsewhere?

Will the techniques mentioned in forums like: unitizing the gas assembly to the barrel or bedding the action "cure" this or will only delay the inevitable impact shift?

I typically shoot an AR setup but really like going at it with a big bore ...it's not about winning but more about learning how to shoot with what I have ....

 

[longshotbml]

Re: point of impact changes with heat...help!!

Match accurizing the rifle by unitizing the gas system, bedding the stock, ect. will reduce the effects of heating. Rapid fire will still change POI but to a lesser extent.