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Pedersoli and Shiloh Rifling "Choke" Taper
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Here is mention of the slight taper of rifling from breech to muzzle in Pedersoli BPCR:
...
"Depending upon the method of rifling used by some barrel makers, there could be some land tops having sharp thin fuzz or whiskers of steel still attached to the corners of the land tops. These are somewhat irregular and if profuse, have a poor affect on that barrel's accuracy until they are worn off or removed in some manner. If they are removed by the normal shooting of lead bullets and the action of cleaning patches, the lands are left with clean sharp edges and accuracy is at it's Gilt Edge best.

In the case of Pedersoli barrels...we finish all BPCR barrels with a process that imparts the tiny taper to the rifling (from breech to muzzle) and at the same time, removes the little wire fuzz or whisker from each land top.

As a result, we do not require ANY sort of special time taking and expensive "break-in" shooting with jacketed bullets. With a new Pedersoli rifle, just clean the barrel well to removed shipping grease and then commence shooting in a normal manner."
...
For Davide Pedersoli & Co.
Dick Trenk
http://www.bpcr.net/site_docs-...ak_in_procedures.htm

Here is an interesting video on Pedersoli barrel making, narrated by Dr. Pierangelo Pedersoli (son of Davide). Another video on Pedersoli stock making follows that one in the Youtube listings after it.

Pedersoli barrel making: https://www.youtube.com/watch?v=eOo-muzMRp0

What I recall of the process:

1. Drill the hole in the cylindrical blank.
2. Ream the hole to bore diameter.
3. Lap the bore to mirrow smooth.
4. Broach cut the rifling grooves.
5. Smooth the grooves with a button.
6. Exterior barrel shaping, cutting, lapping, polishing, and crowning.
7. Barrel is straightened three times during the process.

My guess: It seems to me the taper or choke must be in the grooves, with a constant bore diameter.
The grooves are cut by a sequence of broaches in line on a rod that could be controlled to leave a taper in the grooves.
The twist angle is set in the broach and in the machining turning the broach.
Depth of cut of groove must be less on the broach near muzzle than at breech.
Likewise the button(s) that follow to polish the grooves?


The nice lady at Dixie Gun Works said "Pierangelo" had just dropped by Union City, Tennessee for a visit 2 days before I ran down there to buy a BPCR.
Pierangelo gets around!

Narrated by Italian babe, more succint,
"DAVIDE PEDERSOLI PREMIUM MATCH GRADE BARRELS"
with better close-up views of broaches and buttons
here:

https://www.youtube.com/watch?...RYRd3YE1WHhgWa5LPE93
 
Posts: 28032 | Location: KY | Registered: 09 December 2001Reply With QuoteReport This Post
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It appears they choke lap the reamed bore.
Then they broach rifle it. Then it is burnished with a button.

In the end the only thing choked is the bore - land diameter.
The groove diameter is not tapered.
 
Posts: 13978 | Location: http://www.tarawaontheweb.org/tarawa2.jpg | Registered: 03 December 2008Reply With QuoteReport This Post
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Choked bore instead of choked grooves?
Whatever process, I missed it in the links I posted above.
Cosmic Squirrel Proprietary Top Secret?

I wonder if the process itself does not just naturally produce a little extra slop in the breech that transitions to lesser plus tolerance near the muzzle?
When the lapping stones start in the breech and finish at the muzzle, broaches and buttons too,
with either pull-through or push-through processes starting at the breech and finishing at the muzzle ... less runout at finish than at start ...
They cut off the last couple of inches of barrel at the muzzle where all the tooling exits ...
 
Posts: 28032 | Location: KY | Registered: 09 December 2001Reply With QuoteReport This Post
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Pedersoli barrels are "cut-rifled" after bore is polished by lapping with stones,
and then both the grooves and lands are further treated with "burnishing" buttons, mainly to flatten any tool marks in the broach-cut grooves.

I SWAG that there is some taper from breech to muzzle in both the bore/land diameter and the groove diameter. Wink
 
Posts: 28032 | Location: KY | Registered: 09 December 2001Reply With QuoteReport This Post
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The bore lapping process they showed uses the same type of honing stone setup as those used on a Sunnen hone. The hone is adjustable in millionths of what ever measurement system is used. The stroke length of the honing machine can be adjusted on the fly so that the muzzle end is not honed as much as the rest of the bore.

Any taper in the groove diameter after it is broached is insignificant. A broach is not adjustable other than by grinding during manufacture and resharpening. The broach is pulled through the reamed bore and what you get is a function of the broach diameter. One upon a time I ran a 20 ton Colonial broach for about 6 months. It was a fast way to make internal splines in helicopter and jet engine parts but the splines were never tapered.


quote:
Originally posted by RIP:
Pedersoli barrels are "cut-rifled" after bore is polished by lapping with stones,
and then both the grooves and lands are further treated with "burnishing" buttons, mainly to flatten any tool marks in the broach-cut grooves.

I SWAG that there is some taper from breech to muzzle in both the bore/land diameter and the groove diameter. Wink
 
Posts: 13978 | Location: http://www.tarawaontheweb.org/tarawa2.jpg | Registered: 03 December 2008Reply With QuoteReport This Post
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Wow, the honing of bore hole can be that precisely controlled?
So all the choke might be in the bore/land diameter, and only in the last four or so inches near the muzzle like sharpsguy says? coffee
 
Posts: 28032 | Location: KY | Registered: 09 December 2001Reply With QuoteReport This Post
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I cannot think of a way to taper the groove diameter using a broach. A solid lap could be used with the number of strokes varied so the muzzle end get less lapping. I have have never heard of Pedersoli doing that.
Anyway Pedersoli barrels seem to perform with the best there is.

The honing process used on Pedersoli barrels is the same process used with smaller machines to hone millions of parts in industry.
Sunnen is one of the well known US names in honing. Honing to a few ten thousandths of an inch is kind of a roughing process in that business.


quote:
Originally posted by RIP:
Wow, the honing of bore hole can be that precisely controlled?
So all the choke might be in the bore/land diameter, and only in the last four or so inches near the muzzle like sharpsguy says? coffee
 
Posts: 13978 | Location: http://www.tarawaontheweb.org/tarawa2.jpg | Registered: 03 December 2008Reply With QuoteReport This Post
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