What have you guys experienced when your Norinco M305 heats up? Mine with the synthetic stock they now come with shoots about 3 in low at 100 when barrel heats up. I`m talking 20 rds or more to heat up barrel, and as soon as she cools down impact goes up again to where i have it sighted. My other Norinco M305`s over the years were wood stocked and always shot high when hot..
Point of Impact change when Hot?
- Thread starter y2k
- Start date
Heads up by the way,
POI not only is affected by barrel heating, but can also be impacted by how warm or cold your cartridge is at the time of the shot. This is mostly as a result of the type of powder used in the cartridge. It may not be much, but have been known to make a difference.
Although not related, directly to your inquiry, please see attached Youtube info to clarify or support my comment.
[video=youtube;aWg92Nuob3A]http://www.youtube.com/watch?feature=player_detailpage&v=aWg92Nuob3A[/video]
POI not only is affected by barrel heating, but can also be impacted by how warm or cold your cartridge is at the time of the shot. This is mostly as a result of the type of powder used in the cartridge. It may not be much, but have been known to make a difference.
Although not related, directly to your inquiry, please see attached Youtube info to clarify or support my comment.
[video=youtube;aWg92Nuob3A]http://www.youtube.com/watch?feature=player_detailpage&v=aWg92Nuob3A[/video]
How does your synthetic stock fit? The following is from Hungry's helpful hints.
2009 Poly/Norc Plastic Stock Ferrule Reduction
Some of you may realize that your plastic stock might be a tad "Long" for the ferrule that kisses up to the front band. M14Doctor suggests this quick fix:
the plastic poly stocks are a bit of a bugger to get the ferrule off. essentially a small flat blade instrument and yes, pry her off. may require some fine tuning with pliers to straighten any kinks out that may form during removal.
then with a file, carefully remove material from the forstock from both the ferrule lip face, the part it goes on, and the main body of the stock. This is to allow for the ferrule to be seated farther back on the stock.
once the modifications are done, put the ferrule back on without epoxy and assemble to rifle, observing the VERTICAL gap between the front 90 degree face of the ferrule and the gas assembly band.
if you want to be technical and by the book... this vertical gap should be 15thou optimally but for the layman...... as long as you see light through it and have at least a milimeter of space between the vertical face of the ferrule and the gas band.... yer good to go. use a reliable 2 part epoxy paste and reseat the ferrule, ensuring the face is 90 degrees to the top plain of the stock.
those with fiberglass and wood stocks (chinese ones included) most likely can skip this whole thread as the problem we are discussing primarily affects the plastic stocks..... every single one i've seen as a matter of fact. We are talking about fixing a problem that is inherent to the plastic stocks, this ferrule "re seating" is not an NM modification.... it is a correction.
now..... as for actual NM modifiations of the stock and ferrule....... this is a DIFFERENT procedure and applies to all stocks and pertains to clearancing the ferrule around the gas cylinder to relieve any contact points between stock and action. This can be done with a rat tail file or careful application of a dremmel with a cylindrical grinding stone. Essentially, looking at the nose end of the stock with ferrule in place.... it appears as a "U" shape...... and you want to make it look more like a circle with the top missing . So, remove only enough material from the side wals and bottom of the "U" of the ferrule until you see a visible gap all around the cylinder.
Now the only part of the stock that should be in contact with the gas cylinder is the bottom outside of the ferrule, where it engages the lip on the gas band..... a location where NO MODIFICATIONS should take place.
Helping prevent ####-loss one M14 at a time!
Fail to Train; Train to Fail!
Yes I would agree almost completely with this statement although stringing can also be even more amplified when you have a hot plastic stock and a over tight gas lock. Flip it around and get another more ridged stock.
RememberTheSomme
CGN Ultra frequent flyer
- Location
- Nova Scotia
The old rule of thumb with points of contact is if the pressure is increased(say barrel heating for one) the rounds will tend to be shifted in opposite direction of the pressure point generated.
A perfect teaching/demonstration example of this and one you can experience through a full range of adjustment is with the Remington 742/7400 Semi Auto Rifles. I figured this out over 30 years ago with a 7400.243W I had just bought and thus never had a complaint with these rifles for accuracy or their wandering zeros and I still own one in 30 ought-six.
Was zeroing for Deer just this fall, had her POI exactly at 200 yards with the cheapest ammo I could find Winchester 150s, then realized I hadn't gone through my yearly clean under forearm, re-tighten and mildly locktite the forearm screw ritual, that stays put till Deer season is over.
I applied the 1/8 turn necessary to do this right on the bench and then wondered just how high she would fly now from my established zero, remember she's going opposite the pressure so up she should go with it applied to the bottom of the barrel in the gas lug by the Screw.
Fired again from the bench rest and my 200yard zero went from point of aim on my 200 yard lower target to point of aim into center of the bull on my upper .270 target,..... a full 2 feet!!!. See what a little tension does to a whipping barrel LOL.
This is a roundabout way to tell you if your ferrule, or anything for that matter,.. starts to exert a tiny bit more pressure on top of your barrel during heating, your rounds are going to fly 180 opposite from this, so they go down, lower impact if the old rule of thumb applies here.
I'm guessing by the barrel heat up procedure guys speak of before shooting for groups, this pressure only reaches a certain point and then stabilizes there.
The post with Thomas' correction to a plastic stock is what you should do to your stock and be aware of contact points that will shift zero opposite them on increase of pressure caused by heating.
A perfect teaching/demonstration example of this and one you can experience through a full range of adjustment is with the Remington 742/7400 Semi Auto Rifles. I figured this out over 30 years ago with a 7400.243W I had just bought and thus never had a complaint with these rifles for accuracy or their wandering zeros and I still own one in 30 ought-six.
Was zeroing for Deer just this fall, had her POI exactly at 200 yards with the cheapest ammo I could find Winchester 150s, then realized I hadn't gone through my yearly clean under forearm, re-tighten and mildly locktite the forearm screw ritual, that stays put till Deer season is over.
I applied the 1/8 turn necessary to do this right on the bench and then wondered just how high she would fly now from my established zero, remember she's going opposite the pressure so up she should go with it applied to the bottom of the barrel in the gas lug by the Screw.
Fired again from the bench rest and my 200yard zero went from point of aim on my 200 yard lower target to point of aim into center of the bull on my upper .270 target,..... a full 2 feet!!!. See what a little tension does to a whipping barrel LOL.
This is a roundabout way to tell you if your ferrule, or anything for that matter,.. starts to exert a tiny bit more pressure on top of your barrel during heating, your rounds are going to fly 180 opposite from this, so they go down, lower impact if the old rule of thumb applies here.
I'm guessing by the barrel heat up procedure guys speak of before shooting for groups, this pressure only reaches a certain point and then stabilizes there.
The post with Thomas' correction to a plastic stock is what you should do to your stock and be aware of contact points that will shift zero opposite them on increase of pressure caused by heating.
Bazzoka_Joe
Regular
- Location
- PRQ(People Replublic of Quebec)
mine did something similar and it was a over thight gas lock
