grouping opens with flash suppressor attached - M14 Forum

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grouping opens with flash suppressor attached

This is a discussion on grouping opens with flash suppressor attached within the Accuracy forums, part of the M14 M1A Forum category; Subject says it all. I have a SA standard with a few NM parts swapped and mounted in a Sage chassis. @100 yards, I am ...


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Old January 29th, 2017, 08:18 PM   #1
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grouping opens with flash suppressor attached

Subject says it all.
I have a SA standard with a few NM parts swapped and mounted in a Sage chassis.

@100 yards, I am shooting a 1/2 MOA group with nothing on the end of the barrel.
When I add the factory flash suppressor, the group opens to >=4 moa and drops about 6 inches.

Thoughts? No, I have not tried another FS as I do not have handy.

TIA

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Old January 29th, 2017, 08:47 PM   #2
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Question

MO638,

#1, Have you inspected the inside of your flash suppressor for rounds strikes?

#2, Is the flash suppressor attached correctly and on center axis..

#3, Have you thought about installing a NM flash suppressor, which has been reamed larger that standard dia. flash suppressor?


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Old January 29th, 2017, 09:52 PM   #3
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Originally Posted by XXIV Corps View Post
MO638,

#1, Have you inspected the inside of your flash suppressor for rounds strikes?

#2, Is the flash suppressor attached correctly and on center axis..

#3, Have you thought about installing a NM flash suppressor, which has been reamed larger that standard dia. flash suppressor?

#1, Yes I have and no strikes

#2, it's installed with a dab of lube and tapped down until slightly bottomed on barrel. Nut is tightened with proper pliers and with gas cylinder wrench used as well. I do not have a FS alignment tool but my #2 white grease pencil fits snug in bore and shows @ equal clearance in all 360°.

#3, yes but as stated in my original post, I do not have one handy at this time and will the larger opening really help me in this case since I have clear margins and no projectile strikes?

Thanks again,
Mike

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Old January 29th, 2017, 10:04 PM   #4
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In addition to what XXIV Corps has mentioned, check the tightness of the flash suppressor castle nut. Make sure it is tightened down. I once had a problem similar to yours. The rifle was shooting lousy groups when I already knew it had shot better. The castle nut was loose, which resulted in a loose flash suppressor. Don't forget to retighten the castle nut retaining screw if necessary.

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Old January 30th, 2017, 02:01 AM   #5
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5 ounces of steel on the end of a barrel will change the harmonics and lower the POI.

Make sure the crown is clean before installing the FS.

Use a mallet to seat the FS while turning the castle nut.

Use a proper set of castle nut pliers to tighten it.

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Old January 30th, 2017, 05:23 AM   #6
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Try working up a load. I like KurtC's response, because mass on the barrel tip will change the harmonics, so I agree that it could be that without a suppressor your harmonics happen to match your load nicely, while they do not suppressed.

If you tune the load to the barrel with the suppressor attached, it might go back to 1/2MOA.

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Old January 30th, 2017, 05:41 AM   #7
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1/2 MOA with a standard? That gives me hope for my standard.

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Old January 30th, 2017, 06:55 AM   #8
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How do you do your accuracy testing? Are you using 5 consecutive 5-shot groups?

I would re-check everything, from the chassis mounting bolt to the gas plug, including any scope mounting. Since you are doing testing, try the rifle again without the FS, see if you can duplicate the 1/2 moa.

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Old January 30th, 2017, 07:03 AM   #9
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The POI changing is not surprising.

What load are you using? Bullet, powder & weight, MV, etc.
My thought is that if the load is especially 'slow' then the change in barrel harmonics due to the flash suppressor might be enough to cause such a large change in accuracy.

But I think there is some sort of mechanical problem that happened when the FS was installed.

Jay Kosta
Endwell NY USA

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Old January 30th, 2017, 08:10 AM   #10
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Quote:
Originally Posted by KurtC View Post
5 ounces of steel on the end of a barrel will change the harmonics and lower the POI.

Make sure the crown is clean before installing the FS.

Use a mallet to seat the FS while turning the castle nut.

Use a proper set of castle nut pliers to tighten it.
- Crown clean and no rough edges felt or see
- Rubber mallet has been used each time
- I use a set of castle nut pliers from brownells

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Old January 30th, 2017, 08:40 AM   #11
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Quote:
Originally Posted by KurtC View Post
How do you do your accuracy testing? Are you using 5 consecutive 5-shot groups?

I would re-check everything, from the chassis mounting bolt to the gas plug, including any scope mounting. Since you are doing testing, try the rifle again without the FS, see if you can duplicate the 1/2 moa.

I do the following
- 1 mag
- 6 rounds per group
- 2 or 3 groups (in this case it does not matter since the grouping only opens when I add the FS and closes right back up when I remove it)
- I have gone back through the EBR stock and rifle 2 additional times assuring alignments, torques and clearances are set. The exception to this statement is only 1. I have left the whip screw at .250 clearance this last time to see if there would be a difference and there was not.
- Yes, I have installed and removed the FS several times and the 1/2 MOA returns when the FS is removed.

The rifle is new from SA and before I shot a single round out of it, it was installed in the Sage EBR. I know.... I know.....
The first couple range days were ugly since the issue appeared optics related so mounts were changed and alignments and leveling was triple checked again. Several optics packages were used and all with the same results.
After the first range day, the system was completely disassembled and inspected then re-assembled.
2nd range day yielded same results.
3rd range day happened with a few alterations like change of piston for a group and then back to factory. Also tried a few positions with the barrel whip screw from just touching while barrel warm to .005 clearance and finally .250 where it is now. (no change to grenade grouping)
4th range day, I removed the FS to see and the first group fired moved from center mass to high / right but tightened up to 1/2 moa. I adjusted optics to bring back to bull and there it stayed for remainder of the day.
5th range day, I started with unchanged rifle and dirty bore. (100 rounds through it without cleaning) The results were the same. MOA good and on bull. When I added the FS back, the rounds impacted low left and in a 4 + sized area.

Thanks from leonmckee

Last edited by MO638; February 2nd, 2017 at 06:18 PM.
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Old January 30th, 2017, 08:56 AM   #12
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check it for cracks also

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Old January 30th, 2017, 09:08 AM   #13
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The Browning B.O.S.S. system works by adjusting a barrel extension in and out until you get the best barrel harmonics that match the specific ammo you are using and you are not moving the extension very much at all. Apparently with your rifle adding the FS changes the harmonics a very great deal. You have not stated what ammo you are using for these tests. If you are using commercial rounds, you may find that a change in manufacture, bullet weight, or going to Federal's M14 load may work to re-tighten your groups. If you are using reloads, consider reducing 1-2 grains and work up a ladder until you reach one that works(without exceeding max recommended for the service rifle). You at least know that you have a very accurate rifle. The problem is finding a load that works when you have the FS installed. These rifles are not as easy to troubleshoot as a bolt gun-too many moving parts. Sometimes you end up chasing your tail until you catch it.lol Good luck.

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Old January 30th, 2017, 09:10 AM   #14
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Quote:
Originally Posted by JayKosta View Post
The POI changing is not surprising.

What load are you using? Bullet, powder & weight, MV, etc.
My thought is that if the load is especially 'slow' then the change in barrel harmonics due to the flash suppressor might be enough to cause such a large change in accuracy.

But I think there is some sort of mechanical problem that happened when the FS was installed.

Jay Kosta
Endwell NY USA
In the beginning I tried a few to see if weight was the factor but never changed loads while going from tight grouping to large grouping.

I have gotten very good results with NO FS using the following loads

mine
168gn SMK
43.0gn RL15
2.800" COAL
210 Fed primer
LC brass

Freedom munitions
168gn hpbt new and reman

Federal
Premium Gold Medal 168gn BTHP

and even some PPU 168gn match

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Old January 30th, 2017, 09:41 AM   #15
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Sounds like you have a defective FS. If nothing is obvious then use the SA warranty or simply purchase a different one. Issued M14's over the last 10 to 15 years either use a USGI (NM), SEI DC or SureFire DC. Just saying!

Leon McKee

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