FX barrel liner run out.

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srtmat

srtmat

Member
Dec 28, 2018
358
66
Wausau, WI United States
Just wondering if any of you guys have checked the run out on your FX barrel liners?

Today I noticed some marks in the moderator on my Crown, it appears I have some clipping.

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As long as I had the 700mm barrel off (which I believe is the culprit) I thought I do some checking.

I made up some roller blocks at work and did a little indicating. I was seeing about .009” run out in the middle and at the end of the barrel. It is a little tricky measuring the STX liner with the rifling on the outside but I’ve indicated enough things I felt pretty comfortable with my numbers. I spent about an hour rolling and checking pressing and straightening...

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I was able to get the run out down to .003” I’m pretty happy with getting .006” out. When the liner goes back into the barrel sleeve I believe that also helps to straighten it out a bit. Previously I did index this barrel at 35 yds. At that distance the circle of groups it printed was about 5” in diameter. I’m pretty sure this will help shrink that a bit.

I’m hoping to do a little testing tomorrow I will also check the 380 mm barrel when I have it out. I haven’t indexed that one yet.






 
srtmat,

First what you are measuring is not run out. It is a simple bend. The correct definition of run-out is the amount that is out of round. To do that, you must measure concentricity and you are not doing that. Furthermore, bends are NORMAL. Just shipping the barrels or liners can and usually do cause some bend. Bend is really not an issue, just shoot it. If you are really care, you can straighten them. It is easy to do, but small bends do not effect accuracy at all.

Let me give you an example, I recently bought a .177 barrel kit for my Crown through the mail. When it arrived the barrel was sticking out through the box. It was of course bent a bit, so I used an indicator and a pair of roller blocks and straightened it. It tool all of 30 minutes.......what problem. I toured the H&K factory in Germany back in 2010. A large percentage of their new barrels after returning from heat treatment are bent and are routinely straightened as a manufacturing process. Here is another heads-up, they do it optically, as with a painted "X" on the wall and their eyeball. They don't use a dial indicator. It isn't necessary. Mind you, the barrel straighteners are the highest paid workers on the factory floor.
 
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Mat, I'm not sure the marks on the moderator are from clipping. The hangers used in the finishing process cause such marks. If it is indeed clipping, you should be seeing some very significant flyers. I had one experience with clipping, and the pellet would completely miss the target frame at 25 yards, maybe by several feet, as I never saw where the pellet went. But I'm sure there are slighter degrees of it, so it's possible. I expect even the slightest clipping would result in very poor accuracy. 
 
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Clipping generally makes itself obvious in that you're going to see a major accuracy issue, as elh0102. I would just note that a single pellet passing that hole could have easily scrubbed that lead onto the inside, if that in fact what it is. And that could have happened at any point for any reason. If I were looking for runout though, I'd be looking for it on those barrel supports, because that is what is going to get your barrel off-center in there. 

Just a thought. 
 
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Sorry “run out” probably not the correct term for what I was trying to measure. I also didn’t mean to imply a slightly bend barrel is inaccurate. Heck we’ve all seen this gun before.
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However if the barrel is bent enough that I'm seeing clipping that’s a problem. I was a bit surprised that in just a few inches from the end of the barrel to the end of the moderator things were that far off. Not sure if that’s from the .009” of bend but getting it down to .003 can’t hurt.

I tried running JSB 34’s through it last week knowing they may not shoot the best “A-liner” and the accuracy was pretty poor. After seeing the moderator I knew I had to at least check how straight the barrel was. The marks in the moderator are definitely from pellets. That picture is after pulling multiple tight patches through it. The anodizing was flawless when I got the gun. 

Sometimes it’s just about eliminating variables. Hopefully this will help. Only testing will tell.

STO thanks for the tip. I think I’ll slide those off put them on a dowel pin and check them in a lathe at work
 
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From my point of view, the FX barrel liners are pretty thin and easily bent if not treated with care. I wish there were a spec indicating how much torque should be applied to the barrel nut. I think if you tighten it too much, you can bow the barrel.

In answer to another person's comment, yes, all gun barrels are not perfectly straight after manufacture. The last step taken is to straighten them, a job usually done by a skilled worker they eyeballs the bore for straightness then tweaks the barrel on a hand operated press.
 
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I couldn’t agree more. That’s why I was surprised to see a 5” spread at 35yds when I indexed the barrel. I figured when all 3 bushing are well spaced and put in the sleeve it should help straighten up the barrel a bit or conform to the sleeve I suppose.

I figure by getting the barrel as straight as I can. I help to put this whole system in a more relaxed state. More bend seems like it would just add more tension.

I’m hoping to try and index the barrel next week and see if it tightens up the group a bit.

Maybe after I get my slug liner I should get the pellet liner shooting real nice then take it out and purposely bend it a bit and see how much it changes things.
 
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From my point of view, the FX barrel liners are pretty thin and easily bent if not treated with care. I wish there were a spec indicating how much torque should be applied to the barrel nut. I think if you tighten it too much, you can bow the barrel.
Click to expand...

According to the FX liner replacement manual, the nut is supposed to be thighten aprox a quarter turn. https://fxairguns.com/wp-content/uploads/2019/06/liner-replacement-eng.pdf
Click to expand...

That seems excessive.
Click to expand...

If you try it, it is not much. 
 
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