I have a T/C Contender barrel chambered for 300 Blackout with 1/8 inch rifling rate. In preliminary testing American Eagle 220 grain loads showed signs of large yaw at short distances. Two other subsonic loads, Nosler 220 grain OTM and Hornady 208 A-MAX produced no noticeable signs with no muzzle device. Today I fired a number of rounds of the Nosler load at 70 yards, both with and without a suppressor.

With the suppressor attached (and checked for tightness), the shots were all over the place: up to 6 inches left and right of the point of aim, and significant elevation deviation. Some of the impacts also showed obvious excessive yaw. One shot even grazed the exit hole of the end cap of the suppressor, but fortunately caused no material damage.

Without the suppressor, the accuracy was far better and my last group measured about 0.7" at 70 yards.

My question is why a load that shoots as good as I could want without the suppressor produced such horrific variations when the suppressor was used. I am wondering if that because the load in question is subsonic (factory data 1020 fps), could the discharge gas get ahead of the bullet in the suppressor and disrupt its flight—especially if the bullet is marginally stable? The can is a TBAC 30P-1 that was recently recored to the Ultra 9 configuration while using the same tube.

Thanks for all responses.

Update on this page.

This message has been edited. Last edited by: sigfreund,

If the bullet is stable and punches clean holes with no can, and is producing strikes with a can, your barrel thread is probably crooked.

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Originally posted by exx1976:
If the bullet is stable and punches clean holes with no can, and is producing strikes with a can, your barrel thread is probably crooked.

Thanks. That possibility occurred to me, but I can’t see any problem. I am using a TBAC flash hider that screws onto the barrel and the suppressor screws onto that so I tried to check everything before firing the gun. I will take another look.

Are you testing from a rest?

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Originally posted by kilyung:
Are you testing from a rest?

Yes.

quote:

Originally posted by sigfreund:

quote:

Originally posted by exx1976:
If the bullet is stable and punches clean holes with no can, and is producing strikes with a can, your barrel thread is probably crooked.

Thanks. That possibility occurred to me, but I can’t see any problem. I am using a TBAC flash hider that screws onto the barrel and the suppressor screws onto that so I tried to check everything before firing the gun. I will take another look.

Have you successfully used a can on this rifle before, or is this a new to you rifle? You mention the recore.. When it was a 30p-1 did it work fine on this rifle?

though very unlikely due to how good TBAC cans are, the possibility does exist that the recore wasn't perfect and the crooked thread is in the can...

The best I could by just looking, I checked the can on three different barrels. The “recore” was primarily so I could use it on hosts with different threads by installing an adapter between the suppressor and barrel. Two of the adapters are muzzle brakes and one is a flash suppressor when the can isn’t used. The two brakes fit Sako and Tikka rifles, and I’ve used the can and both adapters on different rifles with no apparent problem. As part of my session yesterday I checked the zero of a particular load with the Sako to confirm it hadn’t shifted as a result of the alteration from the original threading of the 30P-1; the POI was the same.

The flash suppressor is a different thread and is installed on the Contender barrel. The suppressor itself would not fit the Contender barrel before it was modified, so it wasn't tried then.

Short of using a proper diameter rod through the barrel is there a better way of checking the alignment of everything other than just trying to look through and keeping all the circles visually centered?

It's difficult to explain, but you should be able to look down the bore and tell.

I've also shined a flashlight in the breech and pointed the muzzle at the wall with the can on. If you don't get a perfect circle, something is amiss.

Okay, thanks. I'll be looking again and try the flashlight trick.

quote:

and I’ve used the can and both adapters on different rifles with no apparent problem.

was this after the recore or before

quote:

Originally posted by HRK:

quote:

and I’ve used the can and both adapters on different rifles with no apparent problem.

was this after the recore or before

It would have to be after since a 30p-1 was direct thread and didn't use adapters.

quote:

Originally posted by HRK:
was this after the recore or before

After.

In addition to changing the internal design to make it more effective (as I understood it), the primary reason I had the recore work done was to have one suppressor that would work with different muzzle threads via intermediate adapters between the barrel and the can. Although the Sako TRG-22 and the Tikka T3 that I’ve used the system with have the same muzzle thread, I used two different muzzle brake adapters with them and everything was fine. I had also used the suppressor with both rifles before I had it modified.

My story: My 22LR can was flawless until I started swapping hosts. Bullets all over and baffle strikes.

I then remembered my FFL warning me to make sure my new can seated tight to the barrel and stayed tight. I found the problem to be gunk in the can threads not allowing the can base to make firm contact with the barrel or adaptor. Shorter host thread length will expose can threads to primer gunk that a longer host thread will subsequently try to thread into. It would tighten but not seat. When I held firearm up to the light, I could see a little daylight between the can and the host. Used a shotgun brush to clean the can threads between swaps and all was good.

Update.

I sent the barrel and flash hider to Thunder Beast for their analysis after deciding that the suppressor was misaligned with the barrel bore.

I got a call today advising me that the barrel threads were the cause. I had previously told them if that was the problem to rethread the barrel and now the runout is 0.003 inch. I’m not sure what that means, exactly, but it sounds pretty good. I’m looking forward to getting the barrel back and working more with subsonic loads.

Barrel runout measure the straightness of the hole drilled through the barrel concentric to the outside profile of the barrel. It's nearly impossible to drill a perfectly straight hole through a barrel. My last custom barrel was .002. So I would say they did a good job threading your barrel concentric to the bore.

Thanks, swage, for all that. I suspected something like that explanation, and I am glad to hear that it’s a good number.