FX FX Impact M3 another attempt to fix POI shift

[mubhaur]

I was watching RTI Mora on the shot show.

The interesting thing is that the person told that the barrel of Mora is free floating. It doesn't touch the block. However if someone needs another point of contact it may be at the point from where the barrel comes out of the block.

Hence maximum two contact points only.

I removed all O rings that hold the barrel of M3 into the block. Then inserted the barrel in M3. The barrel entered butter smooth.

Now I tightened the grub screw at the breach and the barrel holder at the front. No other contact of barrel with the gun.

The POI moved 1.5" upwards at 24 yards. It shows that in presence of O rings there was some stress on the barrel.

Let's see how long it holds POI and what is the behaviour over a longer period.

Just an experiment without any cost.

Bhaur

 

[Revoman]

mubhaur --=--
Ever trying to improve. Quite admirable and thank you for your inventive solutions to many issues, especially on FX Impacts.
Thank you!

Mike

 

[qball]

Have you tried the clamp made for the tensioned barrel? With the clamp the second point of contact is fixed because it doesn't rely on the o-ring which does change enough with temp shift. Also I do prefer the backbone upgrade which stiffen the whole chassis a lot. So far my 700mm impact with the clamp and backbone has been solid with no POI shift for about a year regardless of position and hold.

 

[Bigragu]

Qball I believe Mubhaur has that clamp, the barrel holder version, with the single clamp bolt.

 

[mubhaur]

Have you tried the clamp made for the tensioned barrel? With the clamp the second point of contact is fixed because it doesn't rely on the o-ring which does change enough with temp shift. Also I do prefer the backbone upgrade which stiffen the whole chassis a lot. So far my 700mm impact with the clamp and backbone has been solid with no POI shift for about a year regardless of position and hold.

Yes I have all that.

 

[mubhaur]

Qball I believe Mubhaur has that clamp, the barrel holder version, with the single clamp bolt.

I have barrel holder with double screw holding the barrel.

 

[qball]

I have barrel holder with double screw holding the barrel.

If you have the clamp then don’t think remove the oring would do much since the contact is metal on metal. Did you experience POI shift with clamp and backbone?

 

[mubhaur]

If you have the clamp then don’t think remove the oring would do much since the contact is metal on metal. Did you experience POI shift with clamp and backbone?

Yes but very minimum.

 

[qball]

Yes but very minimum.

Interesting, I’ll have pay closer attention my to zero then.

 

[bucketboy]

Continual poi shift was the number one reason I got rid of my impact, made this modification which did help but I could not eradicate it completely, there are too many parts held together with too many screws for it to anything other than flexible.it was by far the most frustrating gun I have ever owned

What I did was remove the liner crush nut and replaced it with a er13 collet chuck, I then ditched the shroud and made a moderator, not only did it make the gun quieter it made it a lot shorter

 

[mubhaur]

So far so good

 

[bigHUN]

I really cannot see what is that POI shift you people talking about. Either myself or yourself doing something extraordinary to make a contrast.
Ok, me an engineer (sourced to Western World 30+ years ago from Eastern EU), and my Impact was apart in smallest bits and pieces over 20x since 2020 if that would be your explanation.
.25x700 MK2 here if that matters...

 

[mubhaur]

It's not about dismantling the gun and again assembling it.

It is just related to holding the POI as good as any other gun with free floating barrel does.

 

[bucketboy]

I really cannot see what is that POI shift you people talking about. Either myself or yourself doing something extraordinary to make a contrast.
Ok, me an engineer (sourced to Western World 30+ years ago from Eastern EU), and my Impact was apart in smallest bits and pieces over 20x since 2020 if that would be your explanation.
.25x700 MK2 here if that matters...

You must be lucky, every time I took the gun out of its case it’s poi would have moved, adjust the butt pad it moves, touch the shroud it moves, even if I left it on the bench and the temperature changed it moved. It was accurate but it wasn’t accurate in the same place every time.

Now if I had bought a new top rail, a bag rider, a liner stiffener, shroud support, barrel tensioning kit and an harmonic tuner then maybe, just maybe it would have been ok.

Bb

 

[Revoman]

bucketboy​

You have hit the nail on the head!

 

[bigHUN]

There are things your money can't buy.
I think your liners move/shifts inside the liner lock. This what I did with diamond paste, I lapped the liner into liner nut. Won't move ever

chamfer or radius will lock the centerlines together

 

[MongooseV8]

I dont want to burst your bubble but I dont think you have accomplished your goal. By removing the orings my assertion is your liner is now just bowed slightly by tightening your barrel nut, causing a shift in poi. Id expect you to still have poi shifting should your rifle get bumped or jarred or picked up buy the moderator. Mr Rowe himself has been very vocal about not over torqueing your barrel nut to prevent warping your liner and/or barrel housing. The orings are there to help support the straw like barrel liner. There is no way to truly freefloat an FX STX system like a traditional rifle barrel.

The FX barrel system is very modular, but also very flimsy and wiggles around a lot. My poi shift issue were solved by adding the FX carbon fiber liner sleeve and a tensioning shroud of some sort.

 

[mubhaur]

I dont want to burst your bubble but I dont think you have accomplished your goal. By removing the orings my assertion is your liner is now just bowed slightly by tightening your barrel nut, causing a shift in poi. Id expect you to still have poi shifting should your rifle get bumped or jarred or picked up buy the moderator. Mr Rowe himself has been very vocal about not over torqueing your barrel nut to prevent warping your liner and/or barrel housing. The orings are there to help support the straw like barrel liner. There is no way to truly freefloat an FX STX system like a traditional rifle barrel.

The FX barrel system is very modular, but also very flimsy and wiggles around a lot. My poi shift issue were solved by adding the FX carbon fiber liner sleeve and a tensioning shroud of some sort.

I appreciate your concerns. But right now I am using a solid barrel in my M3. So all other factors related to FX barrel system faded out.

Let's see in the long run.

 

[Swish]

I am always amazed at how many people have shifting POI problems with their Impacts and yet no one seems to have figured out why.
I won't claim to have figured it out either but I've always been a little suspicious of the power plenum.
I've always noticed a little bit of play in the threads where the "stem" screws into the plenum. In my mind, this play would transfer into the upper rail/spine of the Impact directly above it and possibly cause some flex.
I've never seen it mentioned before and I'm curious of what you guys think about it.

 

[Vetmx]

I appreciate your concerns. But right now I am using a solid barrel in my M3. So all other factors related to FX barrel system faded out.

Let's see in the long run.

You’re on the right track. If you get a POI shift moving forward, clean the barrel and see what happens. Orings with a barrel clamp when you’re using a solid barrel aren’t necessary. For you guys using the FX noodle, slide your barrel in with the clamp loose. Tighten the clamp a little at a time until the barrel won’t slide. Mark the heads of the screws and block with reference marks so you know how far to tighten them every time. You don’t want to hamfist tighten with FX barrel. You don’t want that barrel on a bind in any way because it will really be affected by temp changes.