Gunsmithing Question: Cone breech rimfire barrel: what angle?

[TresMon]

Hi yall.

So it begins again. I got my CZ 452 .22 for a trainer to supplement practice. But as with seemingly every serious shooter in every shooting discipline- I want more.

The little rifle is a tack driver. It averages about oh- .28" 5 shots at 50 on a calm day.

I'm sure it has a sporter chamber.

I'm guessing if I set it back and chamber it with a tight Lilja match chamber reamer it will shoot at least a little better. A friend has a reamer I can borrow.

My question is I don't want to set up and machine the two extractor grooves unless I just have too. I'm gonna just cone breech the back of the barrel for extractor clearance. What angle do I need to set the lathe compound on?

Anybody been down this road? A 452 will mag feed into a cone breech I hope.....

Thanks for the help guys,
Tres

 

[former naval person]

Re: Question: Cone breech rimfire barrel: what angle?

TresMon...try over at Rimfire Central...those folks know more about the rimfires than us biggy bore folks. JMHO

 

[TresMon]

Re: Question: Cone breech rimfire barrel: what angle?


Thanks FNP...

 

[Alderleet]

Re: Question: Cone breech rimfire barrel: what angle?

Even if you go over to RFC, I'm fairly certain they are going to tell you to find a good local smith/machinist who'd be cool with setting the barrel back and recutting the extractor grooves for a few beers.

I'm entirely doubtful coning the breech will yield nearly the same extraction it has now.

 

[TresMon]

Re: Question: Cone breech rimfire barrel: what angle?

Alder,
Thanks. I'm a school trained machinist with over a decade on the job experience. I can do it, I just don't want to fuss with it. Coning the barrel would be super fast and with
NO fuss comparatively. And these days I like no fuss machining if it is an equivalent option!

(Or maybe I have become lazy?)

Why would you think it would change the extraction???

 

[BBeyer]

Re: Question: Cone breech rimfire barrel: what angle?

I am not sure just what you mean by coning the breech, but if it is whatt I consider a coned barrel, wouldn"t you have to make some adjustment to the forward side of the locking lugs to allow the bolt to fit into the coned area of the barrel, and avoid an unsupported section of the ctg. case.

 

[former naval person]

Re: Question: Cone breech rimfire barrel: what angle?

FWIW,"Coning the breech" in a rimfire rifle, means to angle the chamber edge from outside near the barrel major diameter, up to the major diameter of the rimfire cartridge rim, minus the diameter of the body of the cartridge, so that when the bolt is closed, only the primed part of the cartridge is impacted by the firing pin.This is supposed to decrease the variability between rounds by only crushing the rim that contains the priming compound.You have to be careful so that the firing pin does not contact the chamber edge upon impact upon that case so that the firing shoulder is not dented nor destroyed. Rimfires are a completely different animal. JMHO

 

[BBeyer]

Re: Question: Cone breech rimfire barrel: what angle?

FNP, I think I see what you mean, although I dont see how it would help. Thank you very much.

 

[TresMon]

Re: Question: Cone breech rimfire barrel: what angle?



Thanks FNP.

On a few rimfires, including the CZ 452 the locking lug(s) are on the rear of the bolt instead of right at the bolt face like on a C.fire rifle. On some .22's the bolt handle/knob is the only "lug."

 

[n64atlas]

Re: Question: Cone breech rimfire barrel: what angle?

Considering the firingpin hits the breech, to releave that area would mack for misfires in the long run. the rim of the case needs support all the way around to have consistant ignition. cases can rupture where the extracter isn't healping to support the case. Brass will bulge in thous areas. if you only releave it to the end of the rim, you still will have to cut a groove for the extracter. Don't you think that if this short cut worked, all 22lr's would be made that way?

 

[gszeto99]

Re: Question: Cone breech rimfire barrel: what angle?

There are two reasons that I can see for coning the barrel.

1) Convenience, so you don't have to cut precise extractor grooves.

2) Being able to rotate the clamped-on barrel so you can find out at which point does it shoot the most accurate (Lilja does this with all its anschutz 20xx barrels now because the barrel is clamped on and can be rotated to find which setup yields the best accuracy).

The OP's action and barrel is a CZ452 so it is threaded; so for the OP, number 2 is not a reason for coning the barrel. The only reason for the OP to cone the barrel would be number 1; strictly convenience of not having to measure the extraction groove placement.

Gene

 

[TresMon]

Re: Question: Cone breech rimfire barrel: what angle?

Right Gene except if you think about it it would be like decades faster for me to find the correct indexing of the barrel if I just coned the back with each clocking of the bore instead of setting up and cutting extractor slots EACH TIME I re indexed the bbl.

gszeto99- yeah Many/must top shelf rimfire barrels are coned.

 

[gszeto99]

Re: Question: Cone breech rimfire barrel: what angle?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TresMon</div><div class="ubbcode-body">Right Gene except if you think about it it would be like decades faster for me to find the correct indexing of the barrel if I just coned the back with each clocking of the bore instead of setting up and cutting extractor slots EACH TIME I re indexed the bbl.

gszeto99- yeah Many/must top shelf rimfire barrels are coned. </div></div>

I would definitely cone my barrels too for convenience sake. Now you have two options:

1) call CZ to find out what angle they put in their extrator groove in the barrels--also find out if they put a concave or convex radius on the extraction groove and if so how much of a radius,

2) take a straight edge and measure it yourself with an existing cz factory barrel (straight edge, protractor, and factory barrel).

You can use the measurements of the factory barrel extraction groove to make the cone. That's what I would do.

Gene