Interesting issue with my CZ 457 varmint MTR

[tazman]

The MTR is pillar bedded, but not like you would normally think. It has two pillars that the action screws pass through but there is a third piece of metal at the very rear of the action that fits into a notch behind the rear action screw. This allows for extra support but also allows for a bridging effect if the rear support piece is slightly higher than the pillars.
I can't think of a way to properly test this as it all sits in the bottom of the action/barrel trough and can't be easily seen from the side.

The rear piece is shaped like a horseshoe and sits in a small cutout in the stock. The top of it fits into a notch in the bottom of the action behind the rear action screw.
Because of the pillar bedding, you can torque the screws to higher settings and still have things work. When I torqued the screws down at slightly over 30 inch pounds during testing, the bolt became harder to work. I believe this was due to the action springing slightly. This should not happen if the bedding is even and level at all points.
Relieving the pressure returned the action to normal smoothness.

My last trip to the range, the rifle was shooting less than optimal. When I got home, I thought about things for a while and came up with a plan.
I cleaned the rifle thoroughly. I hadn't done this for about 150 rounds so it probably needed it.
When I put the action back in the stock. I used lighter settings than I had before with this rifle. I decided to use the same settings I use with my wood stocked rifle.
The rifle shot well today. not perfect, but well. While at the range, I increased the torque on the front screw slightly and left the rear one alone.This improved groups some more.
Now my settings are 20 inch pounds on the rear screw and 24-25 on the front screw.
I also found by experimenting that I need to torque the front screw first. If I torque the rear one first and after torquing the front one, I check the rear, the setting is different showing a slight increase in torque. This also indicates a situation with all the pillars and support metal not being perfectly in line.
My problem is I need to leave the stock as it came from the factory to follow the rules of the discipline I want to participate in.

I seem to have found a happy medium where I have not distorted the receiver by over torquing and still getting good results with accuracy.
If someone can think of a way to check if all the support points are at the right heights I would appreciate your ideas.

[barrabruce]

Try a bit of candle black on the action first.
Or mark out blue.
Photo may help a thousand words.

[tazman]

I will try and get some photos posted after tomorrow. I have a competition to go to and I don't want to change anything on the rifle until after the match.

[OS OK]

Trying to visualize your description taz . . . from this manual... https://cz-usa.com/wp-content/uploads/2019/03/cz_457_en.pdf

but I don't see the part your talking about? This below is a blowup of the parts from the above manual...

https://i.imgur.com/Jq1DLxZ.jpg

https://i.imgur.com/q02ZpXG.jpg

[Mk42gunner]

I'm guessing part number 70 is just a bit taller than it should be.

This is the part that makes it a hard fix:

My problem is I need to leave the stock as it came from the factory to follow the rules of the discipline I want to participate in.


I can think of several ways to adjust the bedding, but none are probably legal with your restrictions.

Robert

[tazman]

I am considering just removing it. The action would still be fully supported by the two pillars with the screws. This would remove the stress from an uneven bed.
Part number 70 cannot be seen without dismantling the rifle.

[uscra112]

If it's removable, take it out and reduce its' height by some amount. Who can say whether it was done by you or the factory?

[tazman]

If it's removable, take it out and reduce its' height by some amount. Who can say whether it was done by you or the factory?

Very true.

I will test the rifle with the piece out before actually modifying it and see if having it in there matters. I may find out that piece is causing my fliers.
I wonder if having it in there loose would cause issues from just sitting in the hole with no pressure on it? Kind of like having a marble loose in a hole under the butt-pad.

[uscra112]

Make a dummy that's a bit short. Add shims under it until it just contacts the tang when the main screws are correctly tightened. Measure. Lap off the bottom of the real part to match.

Another way might be to use plastigage instead of the shims.

As for fliers, I dunno. But stressing the receiver as you described cannot be helping.

[Forrest r]

I've always ran my pillar bedded rimfires in the +/-45 inch # range.

A pea sized piece of playdough under the receiver near the pillar will tell you everything you need to know.

[tazman]

I've always ran my pillar bedded rimfires in the +/-45 inch # range.

A pea sized piece of playdough under the receiver near the pillar will tell you everything you need to know.

I didn't know I could take it that high. Now I have more testing to do.

[tazman]

After I got home from the competition today, I took the rifle apart and studied things a bit.
Here are some relevant pictures.
282942282943282944

The small block of steel in the first picture sits in the stock in the crosswise slot at the rear of the receiver channel. The top fits into the slot in the bottom of the receiver at the rear shown in the third picture.

The problem turned out to be the metal piece was slightly too tall. I know this because the rear action screw is visible through the hole it screws into when the bolt is removed from the rifle. With the metal piece removed the screw fit about one thread further into the receiver than it did with the piece in place. With the piece removed, the screw fits flush with the inside of the receiver and does not interfere with the bolt whatsoever.
Apparently, the receiver wasn't sitting solidly on the rear pillar with the metal piece in place. When I tightened the rear action screw down enough, the receiver would flex a bit and begin to bind the bolt slightly. Enough so you could feel it when working the bolt.
Not certain what purpose it really serves except to complicate the bedding. With the metal piece removed the receiver fit nicely and solidly onto the pillars with no rocking or sliding around.
I am going to work with the rifle without the metal piece for a bit and see how it shoots. I can always put it back if things refuse to work. I can also remove some metal from the height of the metal piece if I need to put it back.

[uscra112]

Beats me what purpose that part could have. Recoil shoulder? For a .22???

Does CZ build more powerful rifles on that action?

Think of the screw as a micrometer, do a bit of simple trigonometry, and you'll know how much to take off it that block.

[OS OK]

After I got home from the competition today, I took the rifle apart and studied things a bit.
Here are some relevant pictures.
282942282943282944

The small block of steel in the first picture sits in the stock in the crosswise slot at the rear of the receiver channel. The top fits into the slot in the bottom of the receiver at the rear shown in the third picture.

The problem turned out to be the metal piece was slightly too tall. I know this because the rear action screw is visible through the hole it screws into when the bolt is removed from the rifle. With the metal piece removed the screw fit about one thread further into the receiver than it did with the piece in place. With the piece removed, the screw fits flush with the inside of the receiver and does not interfere with the bolt whatsoever.
Apparently, the receiver wasn't sitting solidly on the rear pillar with the metal piece in place. When I tightened the rear action screw down enough, the receiver would flex a bit and begin to bind the bolt slightly. Enough so you could feel it when working the bolt.
Not certain what purpose it really serves except to complicate the bedding. With the metal piece removed the receiver fit nicely and solidly onto the pillars with no rocking or sliding around.
I am going to work with the rifle without the metal piece for a bit and see how it shoots. I can always put it back if things refuse to work. I can also remove some metal from the height of the metal piece if I need to put it back.

Did you compete today without that bedding block in the receiver/stock? You shot good today, right?

[OS OK]

Beats me what purpose that part could have. Recoil shoulder? For a .22???

Does CZ build more powerful rifles on that action?

Think of the screw as a micrometer, do a bit of simple trigonometry, and you'll know how much to take off it that block.

I think that receiver will work with a 17 HMR & 22 WMR with a barrel change. https://www.czub.cz/en/firearms-and-products-family/cz-457-miniset

[tazman]

I think that receiver will work with a 17 HMR & 22 WMR with a barrel change. https://www.czub.cz/en/firearms-and-products-family/cz-457-miniset

That is correct.


Did you compete today without that bedding block in the receiver/stock? You shot good today, right?

The block was in there. I had changed the torque on the screws to keep the receiver from flexing. Still not very good. Too many fliers. Just better than I had been doing recently.
I am looking forward to trying it without that block in there. The bedding seems much more solid without it in there.

[OS OK]

How did it group with that bedding block left out?

[tazman]

How did it group with that bedding block left out?

I haven't fired it with the block out yet. I will find out next trip to the range.
I have high hopes for it.
The good score I shot during the competition was with a different rifle. CZ 455 Varmint Evolution.

[Forrest r]

https://youtu.be/iSIUtraui00

Just something to think about

[tazman]

https://youtu.be/iSIUtraui00

Just something to think about

I have never considered torque settings that high. Not to say it won't work, I just hadn't considered it.
The CZ company video suggested around 30 inch pounds so that is where I was working. There and a bit lower. That may well change without the small metal piece in there.
Turns out, they call that small metal piece a recoil lug. Can't imagine the need for it on a 22LR. Seems like another possible failure point to me.
If I get the chance, I will do some testing on torque settings without the lug in there very soon.

[Forrest r]

Typically you wouldn't have that high of a torque setting. Pillar bedding opens up a new world.

That video shows 2 things.

How the actual torque setting can change the group size.
As the torque setting change the poi also changes.

[tazman]

I got to the range and the rain and wind stopped just as I prepared to shoot. Near perfect conditions. Overcast, so no shadows only and the occasional breath of wind. I can't blame anything on wind today.
I had the recoil lug removed from the rifle for all shooting today.
I tried torque settings from 15 inch pounds through 40 inch pounds.
It turned out the rifle liked the same setting(30 inch pounds) that it did with the recoil lug in place. I would get 9 out of 10 shots into a small(about 2 bullet diameters) ragged hole with a flyer that would lose points. This with Eley Tenex ammunition.
I tried some other ammunition from Eley that I had on hand as well. Eley Match and another lot of Tenex. All of it shot pretty much the same.
I was getting the same accuracy with the rifle before removing the lug, so when I got home, I put it back in.

I did notice a small splinter of wood inside the cutout for the lug at the bottom of the hole. I removed that and now with the lug in place, there doesn't seem to be any stress on the receiver when tightened down and the screw fits in the threads to the same depth as without the lug.

Anyway, I don't think I will do any more testing with the lug since it made no difference if it was in or out. The torque setting seems to be right where it is best for this rifle.
I may experiment with other ammo if I can find any and see what happens. This will undoubtedly take some time since none is currently available.

[uscra112]

That nasty splinter!

[OS OK]

check this out tazman...I think he has the same rifle as you?

https://www.thereloadersnetwork.com/2021/05/18/top-3-showdown-standard-plus-vs-flatnose-match-vs-pistol-match-special/

Maybe you can locate some of that SK ammo?

[tazman]

Good video.
I have been following his testing(Buffalo Outdoors) because he does have the same rifle I do.
I would love to get my hands on some SK ammo to try. Can't find any. Can't find much of anything at the moment.
I don't want to burn through the match ammo I have until I can have more on hand.
I do have some second tier target/match ammo to practice with, but it doesn't give the same accuracy as the good stuff.

There is another guy(Pursuit of Accuracy) on the tube that uses the same rifle for testing. He is getting his best groups with Lapua.
I did some testing with Lapua earlier and got groups basically the equal of the Eley Match or Tenex.

I believe SK is made by Lapua.
I believe Wolf is now made by Eley and I am wondering which level of quality the Wolf compares to?

[OS OK]

I don't get it about using 'practice ammo'...'practice with/for what end?'
If the ammo is mediocre then the feedback sucks, means nothing to me. Can't tell if something your doing is going south or the ammo stinks.
I need positive feedback & if the data is bad...what do we learn?

Maybe I have a wrong perspective?

[tazman]

I don't get it about using 'practice ammo'...'practice with/for what end?'
If the ammo is mediocre then the feedback sucks, means nothing to me. Can't tell if something your doing is going south or the ammo stinks.
I need positive feedback & if the data is bad...what do we learn?

Maybe I have a wrong perspective?

I lean that way myself but I can't afford to shoot as much as I want with the good stuff. I just have to accept the fact the groups won't be the same size.

[303Guy]

I don't get it about using 'practice ammo'...'practice with/for what end?'
If the ammo is mediocre then the feedback sucks, means nothing to me. Can't tell if something your doing is going south or the ammo stinks.
I need positive feedback & if the data is bad...what do we learn?

Maybe I have a wrong perspective?
With cheap but lousy ammo, one is practicing sight picture and trigger let-off control. Maybe it would be better shooting at a swinging gong where any hit counts and not make the gong too small.

[uscra112]

With cheap but lousy ammo, one is practicing sight picture and trigger let-off control..

Right. Developing "muscle memory". What little of such practice as I have done, I didn't look at the target, I just tried to remember whether my sight picture at letoff was right. Harry Pope made a point about this.

[OS OK]

I don't shoot like that in this BR dicipline. I mean that I don't think 'shoot' and then purposely let'er loose by pressing the trigger.

Instead, as the sights are slowly weaving around that 1/8" X spot, I am ever so gently adding pressure to the trigger each time I get an alignment.
About the 2'nd or 3'rd time...'BLAM'...she goes off & surprises me. It' doesn't take too much intentional pressure to set off a 10 ounce trigger.
On rifles like the MKII, I think it's trigger pressure is 2 pounds & 8 ounces but it's the same principal, after the first dozen shots your finger re-calibrates it's incremental pressure to work within your breath window and your back in business 'surprising yourself'.
The important part is that your surprise happens with as perfect of a sight alignment as you can manage. The 36 power scope demands that type release as it will show you even the slightest of heartbeats will throw your alignment off by a full 1/8".

If I don't get that positive feedback of seeing that round cut target where my cross-hairs were last pointing when the round released, then I don't know that I've done my part correctly.
Lousy ammo will not show your actual POA on release with the POI.

[tazman]

I am using a 24 power scope on one rifle and a 18 on the other. You would think any movement would show and it seems to.
Once I get settled in on my target, I don't see any more movement. It just sits there.
I do a slow squeeze and the shot always surprises me.
Most of the time, the crosshairs don't move from the aiming point during or after the shot. The bullet hole will appear near the spot the crosshairs were located but not always directly on that spot. My rifles aren't bughole accurate.
I can hold well enough to shoot groups under 1 inch at 200 yards with my centerfire rifles but can't get my rimfire rifles to shoot anywhere close to that accuracy level.

[303Guy]

I'm used to not seeing my impact but now with my 12 power (I think it's a 12 power?) at 25m I can usually see the impact but not as a feedback. For me the 12 power makes me aware of movement (I'm not getting any heartbeat effect) and helps me concentrate on that let-off. And I have to concentrate! I don't have light and crisp triggers. Mine are sporter triggers and it's damn difficult to let off at the right moment. For me, I could practice with cheap ammo but I would like that feed back.

[tazman]

On a side note, CZ sends a graphic printout of a group fired with match grade ammunition with every 22lr rifle it sells.. I have them for a couple of the rifles I have.
I was having accuracy issues with a 455 American. I did fine at 25 yards and barely adequate at 50 for the squirrel hunting I intended to use it for.
Today, I found the printout for the group they sent with the rifle. 27mm at 50 yards. Almost exactly what I was getting with it. No amount of torque changing or ammunition testing would improve on that. Many brands of ammo did much worse.

The MTR printout showed a 14mm group. Slightly over half an inch. I have found ammo that improves on that somewhat.
I have a 455 Varmint that the printout showed 15mm and Eley Match easily beats that group size in that rifle.
I must say CZ has been honest with their group testing as far as the printouts they send with their rifles. I have been able to match or improve on every reported group size they sent with rifles I own.
Kudos to CZ.