barrel shortening

[Dekers]

I thought the same thing about the p/x sentence, but then again, it does put a used rifle on the market which would affect new sales anyway. Who knows.

 

Personally I believe them about the choke, because my .22LR and HMR have tighter bores towards the muzzle, as felt by my cleaning rods getting tighter at the end. How much difference does it make in the field ? I don't know, perhaps only a benchrest shooter could tell the difference.

 

 

 

Well, probably because less solvents have got that far and you are at the end of the rod push, so it seems harder work.

 

The way brushes wear (never the same size twice) and your ability to tell the difference in bore sizes this way is impressive.

 

Nevertheless, if the difference is that great you can tell, I can but think the bullet is rattling around all the way up the barrel to the muzzle!

 

In truth, I suspect the only way to establish this for sure is to get some untouched NEW CZ and get them measured...anyone got the appropriate equipment to do this?

 

ATB!

Edited March 17, 2011 by Dekers

[Dunkield]

How much difference does it make in the field ? I don't know, perhaps only a benchrest shooter could tell the difference.

I think that is the point.

I use less accurate (apparently) Winchesters, and yet mine will shoot a ragged hole at 50 yards, maybe drifting out to 5p sized from time to time, and I don't claim to be some amazing marksman that is just the gun/ammo combination.

[Catweazle]

The way brushes wear (never the same size twice) and your ability to tell the difference in bore sizes this way is impressive.

 

Nevertheless, if the difference is that great you can tell, I can but think the bullet is rattling around all the way up the barrel to the muzzle!

 

Don't take my word for it, try it yourself. You misunderstand the idea, the bullet doesn't rattle up an oversized bore until it reaches the end, it sizes itself to the bore as it leaves the case and as long as the barrel doesn't get larger it remains fairly snug in it until it reaches the muzzle end where a slight choke compensates for any looseness that has occurred and holds it tightly for a consistent launch.

 

Custom gunmakers understand this well and decide where to cut a barrel based on bore dimensions.

 

Luckily for us I have just learned that hammer forged barrels actually constrict the bore if the barrel outside diameter is turned down, so by chopping the barrel and then turning it down for a moderator we are adding a small choke, which might account for the good accuracy some people have experienced.

 

 

Read this for more details http://technology.calumet.purdue.edu/met/higley/rmfireHammerForgedBarrels.pdf

 

The choke they measured was only 0.0002", but they say it is readily felt when slugging a barrel.

[Vermincinerator]

I dont believe they can feel the resistance created by .0002" of choking of the barrel.

I had been in engineering for nearly 25yrs mostly as a precision machinist but before my early retirement, as a qualified QC engineer.

For tolerences of .0005" or less finished conponents were measured in an temperature controlled environment and gauged optically because we do not have the finesse to measure extreme tolerenced components by mechanical means.

 

TB.

[Catweazle]

I dont believe they can feel the resistance created by .0002" of choking of the barrel.

I had been in engineering for nearly 25yrs mostly as a precision machinist but before my early retirement, as a qualified QC engineer.

For tolerences of .0005" or less finished conponents were measured in an temperature controlled environment and gauged optically because we do not have the finesse to measure extreme tolerenced components by mechanical means.

 

TB.

 

Remember that they're not actually measuring the size of the bore, just doing a comparison, so temperature isn't an issue. To slug a bore they would expand a lead slug into the bore and push it up to find loose or tight spots, in this context I think they would be able to find the choke.

 

I don't know if they measured the slug, but a good micrometer can measure 0.0001" http://www.mytoolstore.com/starrett/micro009.html

[Dunkield]

A soft material like lead would deform that much surely?

 

When I used go/no go gauges they were tool steel or similar.

[al4x]

thanks all for your reply's everyone got a few good options, Donaldson's quoted me £70 will give r&k stockcraft a ring as i found them very helpfull the other week when i was in there,will also give a ring to the man semiautolee gave me, the reason was when i got my hmr i got a bargin £300 new but it was 20inch barrel and thought that would be fine but after using it in the car Monday i realized the difference with it and my 16inch .22lr,

so thinking is if its not too dear to get chop then i still got a good price gun,

as for the proofing of it after a long chat with chap at Donaldson's i was told of a land mark court case that he said meant that it was not a legal requirement to have it proofed but don't jump on me about that as its just what i have been told and i guess they should know

thanks again all will let you know how i get on

colin

 

I believe Donaldsons use someone nearly to cut down and re thread, the plus point is turn around time which is fast. I had to have my .243 threaded as its the only sako where it doesn't come as an option from the factory and sadly my local mob sent it to riflecraft and then for proofing so the whole process took a month. As for choking I'd not be too worried about cutting it to 16" if you want to see how velocity changes etc with length Chuck hawks I think has some info on his website

[Vermincinerator]

I don't know if they measured the slug, but a good micrometer can measure 0.0001" http://www.mytoolstore.com/starrett/micro009.html

Catweazel, i am well aware of what a micrometre can do, after all i have been using them for 30yrs, maybe you did not see the parts of my post, "precision machinist" or "QC engineer"

Micrometrs may resolve .0001" but its with a barrel vernier scale, its the finesse or "Feel" of the operator that is the weak point in reliable measureing of extreme tolerences, hence the need for more consistant means of measurement.

 

Ian.

[Catweazle]

Catweazel, i am well aware of what a micrometre can do, after all i have been using them for 30yrs, maybe you did not see the parts of my post, "precision machinist" or "QC engineer"

Micrometrs may resolve .0001" but its with a barrel vernier scale, its the finesse or "Feel" of the operator that is the weak point in reliable measureing of extreme tolerences, hence the need for more consistant means of measurement.

 

Ian.

 

Relax Ian, I wouldn't dream of questioning your expertise but I wasn't sure if you'd read the article correctly.

 

The authors wrote that when pushing a slug through the bore they could detect a choke. Presumably they could tell the difference between the feel of the barrel before and after they had machined the end and caused the choke.

 

You can see this has nothing to do with actually measuring the bore. Incidentally, the micrometer I linked to doesn't need a vernier scale, it has a coarse and fine barrel by the looks of it.

[Catweazle]

A soft material like lead would deform that much surely?

 

When I used go/no go gauges they were tool steel or similar.

 

I'm sure it would deform, but to do so requires energy which can only come from the rod pushing it, which I assume the authors felt as increased resistance.

[Dekers]

Don't take my word for it, try it yourself. You misunderstand the idea, the bullet doesn't rattle up an oversized bore until it reaches the end, it sizes itself to the bore as it leaves the case and as long as the barrel doesn't get larger it remains fairly snug in it until it reaches the muzzle end where a slight choke compensates for any looseness that has occurred and holds it tightly for a consistent launch.

 

Custom gunmakers understand this well and decide where to cut a barrel based on bore dimensions.

 

Luckily for us I have just learned that hammer forged barrels actually constrict the bore if the barrel outside diameter is turned down, so by chopping the barrel and then turning it down for a moderator we are adding a small choke, which might account for the good accuracy some people have experienced.

 

 

Read this for more details http://technology.calumet.purdue.edu/met/higley/rmfireHammerForgedBarrels.pdf

 

The choke they measured was only 0.0002", but they say it is readily felt when slugging a barrel.

 

You are taking my comments too literally, and I do try it every time I clean my barrels, and 2 of my current 3 CZ rimfires have factory length barrels!

 

Feelings that I believe have been expressed earlier about sales pitch would appear to be ringing true, especially IF threading may produce a choke of sorts?

 

We are at best/worst, apparently now talking of fractions so small, it is of infinitesimal potential difference in the field!

 

[Catweazle]

You are taking my comments too literally, and I do try it every time I clean my barrels, and 2 of my current 3 CZ rimfires have factory length barrels!

 

That's the trouble with forums, sometimes the mischevious smirk doesn't come across very well

 

Feelings that I believe have been expressed earlier about sales pitch would appear to be ringing true, especially IF threading may produce a choke of sorts?

 

It could be a sales pitch, who knows for sure, but if EB say there is a choke who am I to say there isn't ? When I get a bit of time I might slug a barrel and find out.

 

We are at best/worst, apparently now talking of fractions so small, it is of infinitesimal potential difference in the field!

 

True, but it's interesting. ( Well to an anorak like me it is ).

[colin lad]

any phone call back yet colin??

thanks lee spoke to him today and sorted it very nice chap i am going to take it down to him in the autumn

 

colin

[Vermincinerator]

No probs Catweazel, what i originally meant was that i dont believe that the authors could feel a change in effort needed created by a .0002" choke whilst pushing the slug up the bore.

I would only be convinced if i could feel it myself.

 

Ian.

Edited March 17, 2011 by Vermincinerator

[Dunkield]

So we seem to have come round to most people's original thinking, that for most of us this 'choke' talk is irrelevant.

I would argue that a cheap mass produced rifle isn't even made to the tolerances being talked about here?

[Catweazle]

So we seem to have come round to most people's original thinking, that for most of us this 'choke' talk is irrelevant.

I would argue that a cheap mass produced rifle isn't even made to the tolerances being talked about here?

 

The tolerances quoted in this thread are irrelevant, they are just an estimate of the amount of choke produced by turning down an unchoked Ruger barrel. The article explains it quite clearly. Interestingly, it also states that button rifled barrels open up when the O/D of the barrel is turned down.

 

We don't know how much choke is on a factory CZ barrel, or even if there is a choke as we only have the importers word on it and my somewhat subjective experience of tight spots in my barrels when polishing them.

 

For Ian, and anyone else who thinks you can't detect a tiny choke, I'll leave this quote from Bill Calfee, builder of many world record holding rifles, on his experience of turning down a hammer forged barrel;

 

I cleaned the bore carefully, started a slug in the turned end of the blank, pushed it up the barrel about 10 inches, inserted two bumping rods and bumped the slug up.....( I want to add something here; when I pushed the slug through the turned down section, even without bumping it up, I already had my answer as to whether the bore closes up or opens up when the outside of a rotary forged barrel is turned down on the exterior....)

 

Anyway, I bumped the slug up, then took my slugging rod and pushed back toward the turned section of the barrel.....

 

When the slug got to the reduced section of the barrel, it was like it hit a brick wall....I had to bump the rod the rest of the way, with the heel of my hand, to move the slug out.......

 

The section I turned down now measures exactly .0002" "smaller" in diameter than the balance of the bore....

 

 

The full post is here; http://www.rimfireaccuracy.com/Forums/showthread.php/181-Rotary-forged-barrels/page2?highlight=choke

 

I'll leave this subject now, it seems as if there is some resistance to learning about the effects of chopping lumps off rifle barrels.

Edited March 18, 2011 by Catweazle