Air barriers with suppressed 300?

[Rancid Coolaid]

http://i250.photobucket.com/albums/gg279/rancidcoolaid/whispertarget.jpg


I've shot a few groups that look like this now, and it is an unusual thing.

I talked with a guy who has more suppressor (and subsonic) experience than me and he said it looks like an air barrier issue with a slanted baffle can.

Anyone else seen this?

Rounds were not rapid fired but were shot with short interval between. Nothing went super-, all were hand loads, should have been right around 1025FPS. All loads made at the same time, same components.

It was a windy day. The rifle has shot very nice groups, but there was more time between rounds that day (barrel break-in.)

Next trip to the range will be to shoot groups without can, shoot groups with can with chrono, and shoot groups with can and with Cor Bon factory subsonic.

Any help or insight would be greatly appreciated.


The rifle

http://i250.photobucket.com/albums/gg279/rancidcoolaid/whisper.jpg

[Rikky Lee]

Do as described. In particular, shoot without the can as you describe and tell us what happens. A factor to bear in mind is also the change in barrel harmonics with the heavy weight on the end.

Air barrier issue is a new one for me though.

[Spook]

I am dumb, what is an air barrier :confused:

[Rancid Coolaid]

Air barrier is a pressure differential due to the baffle design. I've been told slanted baffles can cause air barriers and can show stringing in groups like this.

Then again, it could just be high winds.

More to come when I get to the range and do some test shooting.

[Alleycat]

Air barrier = barrel touching the stock due to the extra weight of the suppressor and insufficient clearance. :grin:

[Rikky Lee]

Also try with the silencer on at 50 yards and compare group sizes.

I'm thinking a weight issue still tho'.

[PFDD]

You know I saw the vertical stringing and I wonder if Alleycat isn't on to something?

I had a Husqvarna rifle that would exhibit the same groupings until I identified that the stock inletting was insufficient on the forend and it was binding and reseating with each shot. There was no suppressor involved just a hunting rig in 7MM Mag but after restocking in a McMillan stock all the stringing issues disappeared. I could have cleaned up the forend on the old wood stock but wanted to switch it out anyway so it was a good excuse.

I wasn't aware of a theoretical air barrier issue but my cans are all traditional stack baffles. You may want to double check on the stock clearance as Alleycat suggests.

[Rancid Coolaid]

Alleycat, the definition was provided to me, it could be off.


I hope to have the rifle on the range tomorrow or day after for some evaluation -sub and supersonic.


The barrel channel seems to be adequate to keep the barrel off the fore end.


More to come.

[amafrank]

As a simple test you can take some very true shims to change the orientation of the suppressor on the barrel. Try a number of different locations by changing the thickness of the spacers. Put a line on the top when you start and try at least 90, 180, and 270 degrees from there. If the baffles are truly the problem you will find that the stringing changes each time but remains a measureable issue. If its just a weight or ammo issue than it will change but not necessarily in the same order or arrangement. Suppressors normally change the point of impact in relation to the point of aim unsuppressed. I have heard people say that the baffles and jets in the can will create issues with accuracy but I've not seen but very few cases where that seemed to be the real cause.

Good luck and keep us posted as you find things.

Frank

[Rikky Lee]

The other advice is to put a piece of tape over the suppressor. See if the bullet is leaving dead center. If not shim the mount 180º from the area where the bullet is off center. Then see if the tumbling continues.

[Rancid Coolaid]

Um, perhaps there is some confusion, there is no tumbling, those are 2 rounds side-by-side, not one round keyholing.



On the range soon, will follow up.

I swapped the stock recently, maybe the stock needs to be bedded, it ain't bedded yet.

[Rancid Coolaid]

Took the rifle to the range and shot several strings with different conditions. I now have a conclusion, but it ain't conclusive.

1. Shot reloads (1050FPS) 220gr SMK with can: groups about 1MOA with some vertical stringing, almost no horizontal stringing.

2. Shot Cor Bon factory (220 subsonic) with can: same - vertical stringing, tight horizontal spread, about 1MOA.

3. Shot reloads without can: same vertical stringing, same tight horizontal dispersion.

4. Shot Cor Bon factory without can: same.

Obviously, the observation at this point is that the rifle tends to string some, not due to can, not due to particular ammo. the stringing is about 1MOA, but the rifle could easily shoot .5MOA if I could fix the stringing.

Here's the kicker: with or without can, if I let gun rest between shots, it is dead nuts every time, literally hitting the "X" every shot, no more than .25 inches off dead nuts.

Final thought, the rifle should be bedded to the McMillan HTG, now, it is not.

Thoughts?

[Rikky Lee]

So the rifle is not bedded at all? Have you checked for obvious flexing by pulling and pushing the barrel against the stock (left and right and up and down) and also clearance in the barrel channel?

Also, what are your 50 yard groups like?

Based on what you have described (and without looking at the rifle and shooting it myself) I would suggest a bedding job is required.

[Alleycat]

http://www.midwayusa.com/Search/#bedding____-_1-2-4_8-16 :grin:

[LouBoyd]

Took the rifle to the range and shot several strings with different conditions. I now have a conclusion, but it ain't conclusive.

1. Shot reloads (1050FPS) 220gr SMK with can: groups about 1MOA with some vertical stringing, almost no horizontal stringing.

2. Shot Cor Bon factory (220 subsonic) with can: same - vertical stringing, tight horizontal spread, about 1MOA.

3. Shot reloads without can: same vertical stringing, same tight horizontal dispersion.

4. Shot Cor Bon factory without can: same.

Obviously, the observation at this point is that the rifle tends to string some, not due to can, not due to particular ammo. the stringing is about 1MOA, but the rifle could easily shoot .5MOA if I could fix the stringing.

Here's the kicker: with or without can, if I let gun rest between shots, it is dead nuts every time, literally hitting the "X" every shot, no more than .25 inches off dead nuts.

Final thought, the rifle should be bedded to the McMillan HTG, now, it is not.

Thoughts?

To get vertical sringing one either the bullet has to be changing velocity between shots. (slower = more drop) or
The barrel has to be pointing at a differnt point than the scope at the time the bullet leaves the muzzle.

The bullet velocity as a barrel heats can be due to canges in bore friction (larger ID as the barrel heats) or changes in the powder burn rate as the action heats each cartridge before firing.


Questions:
Have you shot over a chronograph to see if the bullet velocity is changing. If the problem is only caused by velocity spread it takes 25 to 30 fps change in muzzle velocity (relative to 1025 fps) to get 1 MOA of stringing. at 100 yards. A chronograph should easily measure that.

Are the bullet impacts climbing or dropping (or random) as you fire the group? Which way it goes can be a clue to the problem.

What did you torque the barrel to. (in ft-lbs)? Has the action been squared by a competent smith? If the barrel isn't square in the vertical plane to the face of the receiver or the recoil lug has wedge it could cause the symptom.

What is the torque on your front and rear action screws? Most Remingtons seem to like the front screw fairly snug (50-60 in-lbs) and the rear maybe 1/2 to 1/3 that. If the action is resting on a hump between the front and rear screws (stock or magazine) it will never be stable.

An MOA at the target could be the result of 1 MOA of bending between the bore at the muzzle and the line of sight of the scope. That isn't much. You might try shooing a group with the rear action screw as tight as the front and one with it loose. If the stringing doesn't change thats probably not the problem. It wouldn't be a bad idea to bed the action whether it's the actual cause of the problem or not.

Are the rail, rings and scope snug and free of stress?

[Rancid Coolaid]

Another update:

Went to the range today and shot my 300 Whisper with my can (YHM Phantom) and a friend's Gemtech HVT.

With my can, same result: impacts grouping into 3 distinct vertical groups, no real horizontal stringing. Groups do not print sequential, meaning 3 rounds down't hit same spot, then next 3 hit another with vertical distance between them. A 10-shot string yields 3 tight groups with roughly 0.75-1.0 inches between groups at 100 yards.

With the friend's can, one group, no stinging, group was just at 1MOA at 100 yards. Cold bore (cold shooter) was low, but the remaining 6 rounds all went into a 1x1 square with nothing touching any edges.

First round out the gun is always dead nuts, folow-up start to string vertically.

My theory at the moment stands: pressure differences due to gas in the can and barrel are causing the bullet to leave the barrel at varying speeds - but speeds that replicate. All shots taken when the can is cleared of gas are good shots. All shots taken in rapid succession exhibit vertical stringing, but they group into discreet sets, almost always with one ragged hole at each of the 3 vertical heights.

I've now spent months on this, tried everything (but chrono, need to chrono) and this is unbeleivably consistent.

The same can shoots on a 0.50 MOA 40X in .308 with no stringing, and shoots on an AR10 and AR15 with no vertical stringing, but all are supersonic.

I need to chrono to know the full story, but...

[egraham]

I had the same issue with an AAC Cyclone can. It drove me nuts. I tried bedding, new scope, new mounts, new ammo. To make a long story short the threads on the suppressor were not concentric with the bore. The can was way out of spec. I never had a baffle strike. AAC ended up giving me a new can because that one could not be fixed.

My degroat whisper can made the gun shoot better.

Good luck.

[Rancid Coolaid]

I've considered that, but why does it shoot so well when everything is cool and not gas-filled? And why does the can shoot great with other guns?

[Alleycat]

Have you tried a bug hole? It may just change the harmonics enough to tell you if you're heading in the right direction.