Air barriers with suppressed 300?

[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.

[LouBoyd]

Originally Posted by 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?

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?