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Posted: 9/13/2009 10:30:40 AM EST
Posted this in Precision Rifles, but this is a specific AR problem. So:

Here's the Rifle: Krieger Barrel, DMR trigger



The following are all 4 round groups:

69gr BH, 100 yds, WITH Smith Vortex FH:



Same ammo, FH removed:



77gr BH 100yds, WITH Smith Vortex FH:



Same ammo, FH removed:



According to the factory, the Vortex should be no more than finger tight. I have been using it exactly that way; also tried it with 10lbs torque.

I have used Vortexes in the past without anything like these results. Is mine damaged? What FH would you try next?
Link Posted: 9/13/2009 11:05:53 AM EST
yhm flash hider?
Link Posted: 9/13/2009 11:17:19 AM EST
We ran some tests a while back using a Vortex, Blackout, and QCB on a quality barrel with quality ammo. The QCB performed better, but not as dramatic a differential as you are presenting.

The gist of it is that muzzle devices can most certainly influence precision.

Your target type changed for one of the strings. I am not suggesting that made all the difference, but please remember how important variable isolation is for further testing. Thanks for the data.
Link Posted: 9/13/2009 11:52:52 AM EST
Seems obvious, but are you seeing any strikes? Doubtful, but worth asking.
Link Posted: 9/13/2009 12:05:33 PM EST
There was nothing obvious in terms of strikes. I will check again.

since I and many others have had good results with Vortex, I am thinking one of the tynes got knocked out of line, or something? Not sure if that would cause what I was seeing.

The difference in the targets is noted, and in the future I will try to compare apples to apples; of course, in this case we went from 2.4in to 0.45in, far more than the target itself could account for.
Link Posted: 9/13/2009 12:29:21 PM EST
Your barrel might just not like the Smith FH.

I'd get a whole bunch of FHs and try them out. Keep the winner and sell the losers on the EE. BSW
Link Posted: 9/13/2009 2:44:29 PM EST
Interesting results - everything I've ever read on the Smith Vortex Flash Hiders is that they "increase" accuracy? Can you post a close up pick of the Vortex from the front and the back? I'm wondering - as you suggested, if one of the prongs is off alignment compared to the others? Or, is there some excessive fowling/carbon build up on one side that's affecting the gas flow and causing irregular turbulence when the bullet exits the muzzle?

Sakic #19
Link Posted: 9/13/2009 3:03:38 PM EST
Barrel harmonics can change when different torques values are used when installing a FH. I had a 16" carbine barrel with a standard GI FH that I had replaced with a XM177 Slipover FH. I torqued it on (no measurement, just torqued until it felt solid).

Prior to the Slipover the barrel groups were so so. After I put on the slipover, it shot amazingly tight groups. I never took that slipover off because I was afraid I would never find that "sweet spot" of torque again.

Try torquing it at different amounts, if that still does not fix it, ditch it and try another FH.
Link Posted: 9/13/2009 4:33:17 PM EST
You got me. Try a small spark plug ring as a crush washer. This might take out any variance between the two mating surfaces.
458
Link Posted: 9/14/2009 3:37:33 AM EST
1. No flash hider can improve accuracy by design.
2. Adding any weight to your barel can casue a random alteration of accuracy based on barrel harmonics.

You can just as easily get better groups as worse when adding a Vortex. Would like to know how much your torqued it on if at all. Excessive torque on the threads is bad.
Link Posted: 9/14/2009 4:17:21 AM EST
I tried it finger tight, as Smith indicates it should be, as well as with 10 lbs torque as applied by a torque wrench
Link Posted: 9/14/2009 5:11:25 AM EST
Link Posted: 9/15/2009 10:20:17 PM EST
[Last Edit: 9/15/2009 10:31:22 PM EST by Green0]
Link Posted: 9/17/2009 4:34:18 PM EST
Will try an A2 fitted and reamed. I'll let you know how it goes.
Link Posted: 9/17/2009 4:55:57 PM EST
Just a guess, could it be bad threads on the barrel? Way off center perhaps?
Link Posted: 9/17/2009 4:58:40 PM EST
Yes this is possible and is being checked; however, after talking with Krieger about how they do their threads, it would be extremely hard for their system to fail, especially since each barrel is done one at a time by hand.
Link Posted: 9/21/2009 2:30:16 AM EST
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