M14 - Possible Causes of Vertical Stringing

[Rosco7002]

My M14 build / accurization project is coming along and, although it’ll probably be a “work in progress” for the Summer months, the main areas that I wanted to tackle are nearly done.

This weekend I shot some groups to assess the rifle’s accuracy potential and determine if using Winchester or IVI brass made any sort of performance difference. Seemed like the M14 was happy with whatever brass I fed it BUT one thing that did show up was a tendency for vertical shot stringing.

This issue can be be brought on by shooter error, the rifle itself and/or equipment setup but by the time I ran out of ammo I wasn’t able to diagnose the exact cause... wondering if a group brainstorming session might help.

I’m inclined to believe that shooter error PROBABLY wasn’t coming into play (I’ve received a LOT of weapons training and vertical stringing isn’t something that manifests on other weapon systems) but the M14 is a new platform... so I’m not ruling anything out.

On background:

- rifle was shot at 50 and 100 yards using a rest positioned halfway between the sling swivel and mag well.
- ammunition was 168gr SMKs, 41.5gr H4895, BR2 primers and Win/IVI cases with an OAL of 2.800.
- brass was trimmed to uniform length with flash holes de-burred and uniformed.
- 50% of groups were shot in quick succession, 50% were shot by allowing the barrel to cool completely.
- a Bushnell Elite 10x40 is mounted on an aluminum CASM rail that stayed tight for the whole session.
- 3 and 5 round groups were shot.
- approx. 40% of groups were in the 1.2 - 1.6 MOA range, the remainder exhibited vertical stringing.
- semi-auto fire was used throughout (i.e. the gas systems was turned off).

Right now it looks like this rifle could end up being very accurate if the vertical stringing can be eliminated so what say you fellow M14 enthusiasts - any suggestions as to where I can look to find the cause?

 

[Dake21]

Try 5 and 10 shot group. 3 holes doesn't say much.

 

[eaglesnester]

Mine shoots about the same with a 10 shot group. It is mounted in a Sage stock with Sadlak gas plug, Sadlak rod guide and spring. No other mods, my load is 41.2 gr H4895. As for possible causes of vertical stringing, not enough rounds to give a good answer. My best guess is, its you.

 

[goldenbb]

Rosco7002,
What kind of stock are you using? Is it plastic?
See Post #15, this is a common problem.

https://www.canadiangunnutz.com/forum/showthread.php/38722-M14-FAQ-Tips-Help-amp-Info/page2

 

[Rosco7002]

Try 5 and 10 shot group. 3 holes doesn't say much.

This photo shows 3 shot groups but it’s only an example, I shot 5-rounders that showed the same issue (as per the comments in my original post).

 

[Rosco7002]

Rosco7002,
What kind of stock are you using? Is it plastic?
See Post #15, this is a common problem.

https://www.canadiangunnutz.com/forum/showthread.php/38722-M14-FAQ-Tips-Help-amp-Info/page2

Appreciate you pointing me to this post but the front ferrule mod has already been done (have also bedded the receiver, reinforced the forend and completed the NM cleanrance modification to the ferrule/gas cylinder).

 

[Claven2]

Most common cause of vertical stringing in the M14 is a nose cap that touches the gas system on its face.

What is your setup? What stock? What barrel? What brand receiver? Can you post a photo of the setup? It would help narrow things down.

 

[Rosco7002]

Most common cause of vertical stringing in the M14 is a nose cap that touches the gas system on its face.

What is your setup? What stock? What barrel? What brand receiver? Can you post a photo of the setup? It would help narrow things down.

Norinco M14 with standard barrel and receiver. Polymer stock with reinforced forend, bedded action and modified ferrule (including NM clearance + length ajdusted to eliminate ferrule to front band contact). Here’s an older pic, will check later to confirm that the nose cap isn’t contacting on the front.

 

[Claven2]

Are the tabs for your stock band touching the top of the ferrule?

Also, is that a Norinco stock, or a USGI or McMillan? The Norinco plastic stocks aren't exactly precision stocks, even if "reinforced". Also, is the gas system unitized? If you bed the action, do the NM clearance cut, etc. and then don't unitize the cylinder, that is likely the weak link.

I would also mention, for a stock norinco barrel and gas system, 2MOA is actually really good.

 

[Merovingian]

1.2 - 1.6 MOA is incredibly good for mostly a stock Norinco.
Mine has the stock barrel (chopped & crowned) & gas system as well and I have never experienced vertical stringing.

Blackfeather chassis, upgraded guide rod & spring and changed the bolt to a HRT after my original bolt (mim) blew up on me.

Did your rifle show the same behavior before you started accurizing it?

 

[Rosco7002]

Are the tabs for your stock band touching the top of the ferrule?

Also, is that a Norinco stock, or a USGI or McMillan? The Norinco plastic stocks aren't exactly precision stocks, even if "reinforced". Also, is the gas system unitized? If you bed the action, do the NM clearance cut, etc. and then don't unitize the cylinder, that is likely the weak link.

Thanks Claven2 don’t touch, angle of the pic isn’t helpful but there’s actually a gap of about 1/8”. Stock is a Norinco (for now), GAS system hasn’t been unitized YET. Anyone able to recommend a good go-to for the latter? Ideally Ottawa area?

 

[Rosco7002]

1.2 - 1.6 MOA is incredibly good for mostly a stock Norinco.... Did your rifle show the same behavior before you started accurizing it?

Didn’t note any stringing at the get go... but at that point I wasn’t shooting tuned ammo and the MOA wasn’t stellar, coulda masked the issue.

I am really happy with how it’s shooting right now, seems like it’ll be a tack driver if I get the stringing licked. Here’s the first group I shot with some FGMM after I swapped my TRW bolt in, would love to see this every time!

 

[Claven2]

Thanks Claven2 don’t touch, angle of the pic isn’t helpful but there’s actually a gap of about 1/8”. Stock is a Norinco (for now), GAS system hasn’t been unitized YET. Anyone able to recommend a good go-to for the latter? Ideally Ottawa area?

Gunco can do welded unitizing.

 

[Rosco7002]

Thanks man, I’ll give Jason a call.

 

[m14medic.ca]

Well, here’s my $.02, in addition to what’s been mentioned.....

Case capacity: theres a differance between the cases you mentioned testing.

Milspec cases have less internal volume than commercial cases as the brass is thicker and the external dimesnsions are, for all practical purposes, the same. The IVI was the group that is stringing, and it’s been my expericance (as well as several well known individuals in the M14 world, this topic has been done adnausium) that loads should be reduced as much as 1 grain when going from commercial cases to military cases.

My load data, for the same powder, same bullet and primer combo you posted is 41.0 grn in military cases and 41.8 in commercial cases.

You could quite simply be off the accuracy node.

John

 

[1-trident-1]

Well, here’s my $.02, in addition to what’s been mentioned.....

Case capacity: theres a differance between the cases you mentioned testing.

Milspec cases have less internal volume than commercial cases as the brass is thicker and the external dimesnsions are, for all practical purposes, the same. The IVI was the group that is stringing, and it’s been my expericance (as well as several well known individuals in the M14 world, this topic has been done adnausium) that loads should be reduced as much as 1 grain when going from commercial cases to military cases.

My load data, for the same powder, same bullet and primer combo you posted is 41.0 grn in military cases and 41.8 in commercial cases.

You could quite simply be off the accuracy node.

John

I have been chasing that node, best I can do is 4 at 1 1/2 moa and the 5th a flier at 3moa. first cold shot is always 3moa high. at some point I'll accept the limitations of the platform and my budget.

 

[Claven2]

I have been chasing that node, best I can do is 4 at 1 1/2 moa and the 5th a flier at 3moa. first cold shot is always 3moa high. at some point I'll accept the limitations of the platform and my budget.

Or go hog wild, get a medium or heavy krieger tube, put it in an EBR chassis, all USGI parts, high end mount like a Sadlak Airborne and some high end glass in rings that cost more than the mount.

You would not be the first.

And with quality ammo, it would drive tacks if a credible gunplumber assembled it for you.

 

[Rosco7002]

Case capacity: theres a differance between the cases you mentioned ..... You could quite simply be off the accuracy node. John

Roger that John. I have OCW tested the IVI and Win cases, the 41.5gr h4895 showed up as a good node with both cases. The stringing was also evident with both as well. If that hadn’t been the case I’d have just mag-to-grid the one brass type... not so lucky unfortunately. Think this is either down to the rifle or shooter.

 

[notsorichguy]

Sorry, don’t have the “medic” phone on me right now....

When i accuracy test an M14 pattern rifle, I always fire 5 to heat up the rifle, then shoot 10 for score.

This platform is renowned for poor cold-bore to warm rifle groupings.

That said, vertical stringing is “always” solved by the gas system portion of the rifle. If unwanted contact occurs between the gas cylinder or barrel band and the stock/chassis you’ll get vertical. Gas cylinder and gas piston Mis-matched, vertical. Too much or too little draw pressure, vertical..... you get my drift. It’s pretty common for a gas piston to be the culprit. You can get everything “right” with the rifle and still get vertical stringing. Swap out the piston and keep trying it until the vertical goes away.... That’s where witchcraft and sorcery come into play....

Groups shifting left to right, are either too much torque on the barrel instal or shooter error.

John

 

[45ACPKING]

to understand vertical stringing and how it is remedied at the gas system.... google Gus Fisher and soak it all up.
I'm not giving M14 advice anymore....... but i guess i just did.
you'll be banging your head against a wall trying to solve a stringing issue with stock bedding and ferrule tinkering and unitizing is no guarantee either.
It's a "timing" issue 90% of the time.