Air barriers with suppressed 300?

[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/#bed...__-_1-2-4_8-16

[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?

[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.