Thompson/Center QLA - Why Is This An Issue?

Maybe I should rephrase my title. I know what the QLA is, and I've seen the diagrams posted here by somebody (sorry, I can't remember who) that shows how the QLA is offset from the barrel rifling.

Here are my questions:

1. Are ALL T/C's with QLA's off-center? I don't understand how a barrel's rifling can be made (cut, forged, etc.), but for some reason, the QLA is off-center. I mean, it obviously goes in some sort of lathe or fixture, correct?

2. Even IF the QLA is off center, why does it affect conicals and not sabot rounds? Isn't the inside diameter of the QLA larger than the sabot or conical's diameter? In other words, isn't the QLA nothing more than a really deep recessed muzzle crown?

Thanks,

Emrah

emrah said:

Maybe I should rephrase my title. I know what the QLA is, and I've seen the diagrams posted here by somebody (sorry, I can't remember who) that shows how the QLA is offset from the barrel rifling.

Here are my questions:

1. Are ALL T/C's with QLA's off-center? I don't understand how a barrel's rifling can be made (cut, forged, etc.), but for some reason, the QLA is off-center. I mean, it obviously goes in some sort of lathe or fixture, correct?

2. Even IF the QLA is off center, why does it affect conicals and not sabot rounds? Isn't the inside diameter of the QLA larger than the sabot or conical's diameter? In other words, isn't the QLA nothing more than a really deep recessed muzzle crown?

Thanks,

Emrah

Click to expand...

This is copied and pasted here from another thread - see if this might help you with some of your questions..

The 'crown' at the bottom of the QLA - is exactly the problem. TC understands this and knows it. That is why they will tell that their rifles are for sabots and not conicals.

Here is what I am trying to convey...

The way TC chooses to bore and install lands and grooves is different that most other barrel manufactures. What they choose to works very well but on occasion the bore does not come out in the middle of the barrel. They have a +/- number of thousands that it can be off center. The fact that the bore might be off-center to the barrel has nothing to do with accuracy at this point. It will shoot sabots and conicals equally well. The problem is that for most consumers the cosmetics of the bore being off-center would not be acceptable. To hide this slight problem TC chose to install the QLA to cover the slight descrepency.

This does not happen in every TC bore it does in some.

Here is a picture of a cut off QLA... I believe in this picture you can see that bore is just slightly off center of the barrel.



While on this end the QLA looks just fine at it install in the center of the bore.



Then this is the picture of the bore recrowned and now able to shoot conicals as well as sabots, but notice it is still slightly off center...



I talked to a TC Tech about all of this and from that conversation I created this simplistic picture as a representation of the problem.



Again TC is aware of this and if you were to call them they would tell that their rifles are built for sabots.

I would also tell you that you do not find this in all TC/QLA rifles but enough of them to make you a little leary of the problem.

CVA uses and al lot of other companies, such a
Green Mountian Barrels choose to use a different type of boring to insure this problem does not exist. Yes CVA uses a form of QLA but the bore and the QLA are concentric - not a problem...

To summerize:

1) Not all are bores are off center

2) The QLA IS cut in the center: When an uncentered bore doesn't line up there is a bigger space on one side of the bullet as it enters the QLA. Therefore more gas passes the bullet on that side of the barrel kicking the bullet sideways. Sabots pictures really show how that happens

3) I suspect that the plastic in sabots is hot enough to expand in the QLA and hold the gasses better and doesn't allow the bullet to be deflected.

Before I cut mine off, I got 8 inch groups at 25 yards and some bullets went through the target sideways!

Thats interesting

That may explain why I had a problem with my old ML. I had the QLA added at a gun shop a few years after I bought it. Never shot the same after that. Thanks for the info. :shock:

Actually I think the off center ones are kind of rare. I have had 6 with the QLA and none of them a off center as far as I can tell, since I have never had a problem I have not gone to the trouble of making a casting of them so I could mike them. The 3 I have now will shoot a minute of angle when I am holding steady and I have several conicals they will shoot almost as good at 100 yds as the sabots, it is true that they are picky about conicals but so are a lot of other guns as long as I have a few for Colorado hunts it does not bother me I do not like them any how.

If that is really true, then they would be money ahead to replace barrels like mine. If it really were a rarity, they would probably do just that and not try and say it is the twist rate.

For those that do have T/C QLA guns that are NOT off center with the bore....could you give the brands and weights of the conicals that DO work well with your guns?

http://www.hornady.com/store/50-Cal-350-gr-FPB/

http://muzzleloading-bullets.com/index_ ... age319.htm
The .503 460gr.

Bullshop 445gr UC Short
Bullshop 460gr MT Nex
[email protected]

Nimrodder said:

http://www.hornady.com/store/50-Cal-350-gr-FPB/

http://muzzleloading-bullets.com/index_ ... age319.htm
The .503 460gr.

Bullshop 445gr UC Short
Bullshop 460gr MT Nex
[email protected]

Click to expand...

Thanks!

It was these ( http://muzzleloading-bullets.com/index_ ... age319.htm ) that were giving me 8 inch groups at 25 yards, so you can see what a difference it makes

txhunter58 said:

It was these ( http://muzzleloading-bullets.com/index_ ... age319.htm ) that were giving me 8 inch groups at 25 yards, so you can see what a difference it makes

Click to expand...

Thanks txhunter..

Don't get me wrong. The no excuses bullets are great/well made bullets. Just won't shoot if the bore/QLA are misalligned. Chances are the bullshops would do the same. The only one in that group that shot decent before cutting off the QLA was the FPB.

txhunter58 said:

Don't get me wrong. The no excuses bullets are great/well made bullets. Just won't shoot if the bore/QLA are misalligned. Chances are the bullshops would do the same. The only one in that group that shot decent before cutting off the QLA was the FPB.

Click to expand...

What about the Thor bullets? They are a bit pricey, but on the same idea as the FPB's..

TC has recently discontinued it's Hawken rifle due to sales. Had they not put the much hated by traditional shooters the QLA on this rifle they may have not need to discontinue it. I won't buy any rifle with a QLA! Other companies do not put it on their products for a reason, it is not needed.

Thanks for the reply guys. Man, when I bought my Impact, I had no idea about any of this, as I'm as brand spankin' new to MLs as it gets. Of course I do love my Impact. Ridiculously accurate, even with me behind the wheel.

I think the QLA/bore thing was explained very well. It appears they are cut at different times and on different jigs/machines. As I understand your explanations, it's not the QLA cutting operation that's the problem, but the rifling operation that precedes it. Is this correct? If that's the case, why doesn't T/C (or S&W or whoever owns T/C now) update that machine or jig? I can't for the life of me figure out why it would be acceptable or within "tolerances" to have a barrel blank rifling cut off-center and NOT fix the jig?

One last thing: The reason that sabots are not affected was touched on briefly. Are there any other (or verified) explanations? One would think the back, hollow portion of the sabot would be more susceptable to getting knocked sideways, up, down, whatever, than the solid base of a lead bullet.

Emrah

I own a Thompson Center Black Diamond XR with a QLA. And it is an exceptional conical shooter.



I first want to state that this was not 100 yards as I listed on the card. This was before my range finder. I later checked the distance and it was 88 yards. Shows you how far off pacing can be.

This was during deer season. I had been hunting that morning with a 375 grain Buffalo SSB (the small hole far right). I decided I was going to go into my marsh that afternoon and wanted a big fat chunk of lead to plant things..

So I sat down in a lawn chair with my shooting sticks and a good back rest.. and shot the 460 grain No Excuse Conical bullets out of the Black Diamond XR. That rifle just flat out shoots about anything you stuff down it. I knew that this big lead could anchor a deer and stop them from dashing into the marsh deeper. But my luck was poor that day. Could have been the weather.. I never got to try the lead out on a deer.

Dave, does your Black Diamond XR referenced above happen to have a blued steel barrel. I ask because I've got the impression, based upon my own limited experience and reports from others, that TC seems to have a much harder time putting out good SS barrels than they do the blued steel.

That may be a false impression, but humor me.

Yes ... mine is a blued barrel. And I have looked at the QLA and it looks as dead center as can be.

oldfox said:

[ What about the Thor bullets? They are a bit pricey, but on the same idea as the FPB's..

Click to expand...

Thors shot decent from my Omega before removing the QLA as well. Best terminal performance conical out there IMO, so worth a look.

txhunter58 said:

oldfox said:

[ What about the Thor bullets? They are a bit pricey, but on the same idea as the FPB's..

Click to expand...

Thors shot decent from my Omega before removing the QLA as well. Best terminal performance conical out there IMO, so worth a look.

Click to expand...

Thanks txhunter...they are sending me there bore size kit.