Hot M305 Hitting Low

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theDuck

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I used a black plastic stock Norc M305 at a SR clinic using US made iron sights. The elevations were on at each yardage to 500 yards on the sighters. When we fired 10 shots rapid the groups dropped at least a foot to 18". Lately I put a good quality scope (for me) on and sighted it progressively out to 500yards to get the come ups marked on the tactical dials. Again the rifle was 'on' doing sighters but as soon as I did rapids the group dropped the same 12' to 18". My sight picture is fine and the rifle is rested.
I'm wondering if the heating is causing something to push on something to lower the group. I'm thinking of switching to a wood or fibreglass stock and giving that a try.
Has anyone run into this lowering of the group by a large amount issue before?
 
Check the ferrule to gas cylinder gap. The metal band on the nose of the stock should have cleance between it and the plate at the gas assembly.
Most , if not all, chinese plastics stocks I've run into are tight in this location. It's plausible to suggest that if pressure exhists here, it could affect group consistancy as the rifle heats up.

Gap should be about 1/16" , no more, between the vertical face of the ferrule and gas band plate.

If that doesn't make an improvement, maybe a new stock is in order?
Try it and let us know.
 
How "rapid" are you shooting? If you are shooting too quickly its possible that you might start jerking the trigger or might not be following through properly with your shots. 12" to 18" @ 500 yards equates to 2.4 to 3.6 MOA, which makes this a plausible explanation (especially with a heavy trigger pull). There are many possible factors that can cause this to happen ranging from marksmanship, stock fit to even your scope mount setup/rings.
 
45ACPKING said:
Check the ferrule to gas cylinder gap. The metal band on the nose of the stock should have cleance between it and the plate at the gas assembly.
Most , if not all, chinese plastics stocks I've run into are tight in this location. It's plausible to suggest that if pressure exhists here, it could affect group consistancy as the rifle heats up.

Gap should be about 1/16" , no more, between the vertical face of the ferrule and gas band plate.

If that doesn't make an improvement, maybe a new stock is in order?
Try it and let us know.
Click to expand...

Exactly what he said.

Also - tuned m14's tend to shoot lower as the barrely gets hotter.
 
I checked for the gap and there is none. Can't get a .001" shim in. Likewise on my Norc plastic stock shorty. The chu wood M305 has a gap of more than 1/16" and less than 1/8". Likwise with the one with a USGI fibreglass stock and USGI barrel and fore end parts. 45ACPKING's observations of the plastic stock fit hold true for me.
Is there an easy way to take the metal nose band off? I'd like to try trimming it and giving that a go.
 
I use a key stock punch and small hammer. Any kind of object that is flat at end and bit wider than a bigger flat head screw driver will work.
Start inside the stock at the bottom of the "U" shape and start tapping forward. Then once a small amount of movement is observed, switch to the inside walls of the "U" shape and repeat the tapping till movement is observed. Repeat , moving from walls to bottom until a gap starts to form at bottom. Then it's pretty straight forward manipulation to wiggle it off.
Work slowly so as to keep the ferrule in excellent shape.
Once off, use a flat , wide point plier to straighten the side retaining divots of the ferrule.

I believe that in the stickies, somewhere, Hungry inserted my "how to" on setting the ferrule back on the plastic stocks, I'll try and find it and post the link.

There are many theories and methods of stock tensioning. One observation I have absolutely witnessed is the before and after effect of modding the stocks to allow for the desired gap. The results have always been positive

As for the front vertical face of the ferrule? It was never designed to be a recoil surface and correcting the stock for appropriate gap is an often over looked "first step" in modifying or tuning a rifle with the purpose of producing consistantly repeatable groups

Here the link to my post, from Hungry's sticky on M14 FAQ's
http://www.canadiangunnutz.com/forum/showthread.php?38722-M14-FAQ-Tips-Help-amp-Info/page2
 
Last edited:
45ACPKING said:
I use a key stock punch and small hammer. Any kind of object that is flat at end and bit wider than a bigger flat head screw driver will work.
Start inside the stock at the bottom of the "U" shape and start tapping forward. Then once a small amount of movement is observed, switch to the inside walls of the "U" shape and repeat the tapping till movement is observed. Repeat , moving from walls to bottom until a gap starts to form at bottom. Then it's pretty straight forward manipulation to wiggle it off.
Work slowly so as to keep the ferrule in excellent shape.
Once off, use a flat , wide point plier to straighten the side retaining divots of the ferrule.

I believe that in the stickies, somewhere, Hungry inserted my "how to" on setting the ferrule back on the plastic stocks, I'll try and find it and post the link.

There are many theories and methods of stock tensioning. One observation I have absolutely witnessed is the before and after effect of modding the stocks to allow for the desired gap. The results have always been positive

As for the front vertical face of the ferrule? It was never designed to be a recoil surface and correcting the stock for appropriate gap is an often over looked "first step" in modifying or tuning a rifle with the purpose of producing consistantly repeatable groups

Here the link to my post, from Hungry's sticky on M14 FAQ's
http://www.canadiangunnutz.com/forum/showthread.php?38722-M14-FAQ-Tips-Help-amp-Info/page2
Click to expand...

I have rebuilt many of the new plastic stock norstinkos, grinding down the rear of the ferrule, then sanding down the front end of the plastic stock to match , to obtain the necessary gap.

In almost all of them when reassembled the necessary minimum 5 lbs ferrule lip pressure and spring was not there. This i think is because the receiver bedding area is not to spec in relation to the front on those new stocks.

I recommend to all my clients to go with G.I. fiberglass as soon as they can.
 
"...10 shots rapid the groups..." Operator failure. It takes practice to be able to shoot quickly. A scope won't make any difference either. You'll just be able to see the target better.
 
I set the ferrule back and have about a .035" gap. (Easy to do once you get started) However the front band lip does not contact the bottom outside of the ferrule give zero stock tension. I searched the interwebs and put .020' shims on either side of the bottom of the reciver at the forward end of it. That tensioned things when I put the trigger group in.
I went to the range and gave it a go at 100 meters. The grouping was inconsistent so I took the shims out from under the receiver. That improved things but then when the rifle was hot the group dropped about 2" then started to open.
I noticed my black stock shorty also has no contact between the outside bottom of the ferrule and the front band bottom lip. It does however have full contact between the front ferrule face and the back of the front band as other have poined out these black stocks tend to do.
I'm tempted to epoxy an piece of .020" shim material to the outside bottom of the ferrule to give the front band lip something to latch on to. I can always take it off if it doesn't work.
Anyone have any experience adding tension to the front band other than using another stock?
Thanks.
 
theDuck said:
I set the ferrule back and have about a .035" gap. (Easy to do once you get started) However the front band lip does not contact the bottom outside of the ferrule give zero stock tension. I searched the interwebs and put .020' shims on either side of the bottom of the reciver at the forward end of it. That tensioned things when I put the trigger group in.
I went to the range and gave it a go at 100 meters. The grouping was inconsistent so I took the shims out from under the receiver. That improved things but then when the rifle was hot the group dropped about 2" then started to open.
I noticed my black stock shorty also has no contact between the outside bottom of the ferrule and the front band bottom lip. It does however have full contact between the front ferrule face and the back of the front band as other have poined out these black stocks tend to do.
I'm tempted to epoxy an piece of .020" shim material to the outside bottom of the ferrule to give the front band lip something to latch on to. I can always take it off if it doesn't work.
Anyone have any experience adding tension to the front band other than using another stock?
Thanks.
Click to expand...

I have tried the epoxy shim ( go thicker and file down to appropriate tension ) - Doesn't last - eventually the epoxy lets go - even with normal toothing of the bonding surfaces. Silver solder perhaps ?
 
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