M305 Wandering POI

[Glockster]

Took my M305 safe queen out after a couple years. The last outing was giving me 3-4" groups at 350 yards, nothing wrong with that. Fast forward 2 years. First shot is exactly at the point of aim. As it heats up each shot drops about 1 to 1.5 inches until it no longer is on the target. Let it cool right down, same thing. Replaced the scope, same thing, open sights same thing. Stock is Polytec injection molded and it has been bedded. The gas system is shimmed and unitized. No contact with the OP rod anywhere or contact with the upper forend and stock. Replaced the stock with an old beded Norinco Chu wood stock, point of impact shifted three feet to the left.

So, the only other thing I can think of is a bad barrel or the bedding job has gone south. Heads pace is good as well. What do you figure? Rebed, replace the stock or relegate it as a parts gun?

 

[sigrunes]

How many rounds fired through the barrel total so far?

 

[Glockster]

Under 500. Bore looks bright and shinny, no obvious problems, muzzle brake is tight no signs of bullet impact.

 

[300Spartans]

Sell it to me for $250 and the problem is solved.

Your groups at 350yds are awesome. Do you have the replacement op rod spring guide in it? Also, what ammunition were you using?

 

[TacticalTeacher]

How tight is the gas cylinder lock on the gas cylinder assembly?
Where does that gas cylinder lock tighten up to after you turn it PAST bottom dead center?
Gas plug tight at the time of the test firing/grouping?
Gun all greased up in the right places?
Are you running a cylindrical NM style op rod spring guide?
Sights and mounts and bases all tightened down/up?

Get back to us and let's eliminate the variables ONE at a time!

Cheers,
Barney

 

[Dake21]

Try a 10 shot group and see what happens. It will give you a better idea of your accuracy in MOA.
http://m14forum.com/rammac/154524-why-10-shot-groups-better.html

 

[Glockster]

Scope base CASM by M14.ca, absolutely tight.
Bases, Brownells, Med Tactical Steel, torqued to base, rings to 16 inch pounds on new Vortex scope. (third scope same problems)
Gas cylinder tight
Gas plug tight
Gas cylinder locks up at three o'clock position before tdc, tightening lock to 6 o'clock position firmly secures it.
Op rod and spring stock Norinco
Gun properly lubed.
Everything pretty much as it was when it was put in the safe.
Handloads of 168SMK and Hornady 150 FMJ follow the same pattern. First shot cold barrel POI/POA then everything walks south by 1-2 inches for every shot as the rifle warms up.
Absolutely baffled as this rifle was a "tack driver" (yes I know 1.5" groups are hardly a tack driver but for a military pattern made in China rifle I was pretty happy with it) when I put it away.

 

[Glockster]

Try a 10 shot group and see what happens. It will give you a better idea of your accuracy in MOA.
http://m14forum.com/rammac/154524-why-10-shot-groups-better.html

Ten shot group results in a 10-15" vertical string. First shot at point of aim, then each subsequent shot drops 1-1.5"

 

[machman]

The group differences between the Polytechnic & the Chu wood stock might be explained by ferrule (over)tightness.

 

[Odd Shot]

What did you bed with? Any gap under the receiver heel?

 

[TonyBen]

When testing for accuracy with a GI profile barrel, I shoot 20 warm-up shots, then perform accuracy testing. I have seen the same thing happen in my M1A with GI barrel and Blackfeather stock. Pr589 has had it happen too. It's much more noticeable at 300 yds though. Once it warms up, it should group nicely. Barrels cool down faster in the winter, so it doesn't take long for a barrel to go back to a cold-bore shot. I don't think medium weight barrels suffer from this as much as GI profile barrels.

Tony.

 

[Pr589]

When testing for accuracy with a GI profile barrel, I shoot 20 warm-up shots, then perform accuracy testing. I have seen the same thing happen in my M1A with GI barrel and Blackfeather stock. Pr589 has had it happen too. It's much more noticeable at 300 yds though. Once it warms up, it should group nicely. Barrels cool down faster in the winter, so it doesn't take long for a barrel to go back to a cold-bore shot. I don't think medium weight barrels suffer from this as much as GI profile barrels.

Tony.

As TonyBen mentions, I usually have a wandering POI in my Standard barreled rifle - at least for the first 3-5 shots. Usually I am about 2.5 MOA high from a cold-bore and then each successive shot tracks lower until I start to get groupings (1-1.5 MOA). After a long target change I see the same effect and need to warm-up the barrel again.

As a contrast, a buddy with a medium-barreled (Springfield/Criterion barrel) M1A seems to have no issues with consistency of cold-bore shots, easily getting MOA-ish groups from the first shot onward.