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Discussion Starter · #1 · (Edited)
What you don't know is behind your backs I've been testing loads in five AR barrels, Faxon, Seekins Precision, BCM LWE and BCM SS41, and Odin Works. The Faxon and Odin Works are 18" barrels, all the others are 16".

I did not finish the test on the Faxon because it produced about the same velocities as the 16" barrels and since it's 2 inches longer and heavier...

But that's not what's strange....

Yesterday I started on the Odin Works 18" barrel. I was disappointed, but don't let that throw you, today was more like it but about as strange as I've seen. Here's the target,



First, notice the upper left "group". I knew after that first shot, something was wrong; it should not have been that high or to the right. So, I checked the suppressor, checked the torque on all the scope screws - NOTHING!

So I shot the 2nd shot and it looked about right so I figured whatever the problem was, what I did fixed it. Then I shot that 3rd shot??? That's where it should be hitting! And, I shot three range ammo warm ups prior to shooting this first group.

Now that is a really strange group!

Then, without doing anything else I shot the top middle dot. The hits are where they should be although the group is a bit large. Then I shot the 3rd dot (top right) - 0.40 MOA! Then the lower left - 0.67 MOA.

Now we're talking, but there's more strangeness...

I've shot these same loads in 5 different AR barrels and four of them showed no pressure signs. I was seeing pressure signs with the 4th charge in the Odin Works - I didn't even shoot the last charge.

I was using Hornady cases obtained from shooting ammo from Hornady, 55 gr SP, in of course Hornady cases. All the other barrels were with a different set of Hornady or Winchester brass. The latter gave pretty similar and consistent results. It may be that the Hornady cases I used from the Hornady ammo was somehow different; perhaps a lower case volume.

Naturally, I'll try the load in the same cases I shot in the other 4 barrels and see if that makes a difference.

So I guess the really strange thing is that first group.
 

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Discussion Starter · #2 ·
I discovered the cause of the strange problem today. I went to the range this morning and got those same strange groups I described in the OP. I would have bet a whole quarter it was a loose barrel nut, but the nut was tight. However...

I had a Kinetics Security tuner mounted behind my suppressor. The tuner screws onto the muzzle threads and the suppressor screws on after that. You would think that would be really secure, but it isn't. I tightened the tuner by hand (there are no shoulders for a wrench, etc.) and then I tightened the suppressor by hands, That almost always holds the suppressor adequately.

But, there's some kind of interaction going on between the tuner and suppressor. When I tried to remove them, they were not loose, but snug - not as snug as they should be. Even as I found them, they should have been snug enough to prevent the huge groups I was getting.

I removed the tuner and reinstalled the suppressor and took off to the range again. The strange, large groups were gone!

I have designed and built about five tuners and none of them caused this problem. The difference in my tuners and most others is my tuners don't screw on. They simply are a tight fit over the threads. A tuner is held in place because it is squeezed between the barrel shoulder and the suppressor (or flash hider or whatever).

So the problem was some kind of interaction between the tuner and the suppressor.
 

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Had kinda the same issue, but with a flash hider adapter. If the can was screwed on the flash hider, it shot a wide group. Took the flash hider off and swapped can end cap, to where it threads straight to the barrel, groups tightened up. Also, when I first got my can, I forgot and left the crush washer on, shot some very strange groups. Guess it's all about the harmonics and how everything works together, whether it's logical or not.
 

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That is the fun part of accuracy. I swear sometimes witchcraft is involved.
 
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