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View Full Version : Curious - Gain Twist Barrels



glbreil
04-23-2012, 09:42 AM
How do they lap a gain twist barrel? It seems to me that if they poured a lap to fit in the end of the barrel that it would not go down the barrel because of the twist change with out defroming the lap.

Does anyone know how that works? Seems impossible.

Gary

caroby
04-23-2012, 10:50 AM
Good question Gary,

Wondered this too, the same way it's so "difficult" for the button rifled barrel makers to do Gain Twists....
..?..

cale

Calumet
04-24-2012, 01:36 AM
Well, lapping is one thing. Varying the pitch (think about threads) of the the lands, is another. If the lands tighten with the movement of the bullet down the barrel, I would think the lands would have to become proportionally wider to compensate for the pitch of the the thread change, as the bullet moved down the barrel. If not then all the super hot gasses pushing on the soft copper jacket would be blowing by the bullet. Kinda like a cross threaded or not matching threads!
Not a real accuracy improver

Just my thoughts. Haven't heard much about gain twist barrels lately

Calumet

JD Mock
04-24-2012, 07:56 AM
The gain is so slow that the lap will follow with no problems. I shoot a dasher with a 8.25 to 7.75 gain over 26.5 inches. Tony Boyer has done okay with the gain twist barrels over the last several years. I believe that his are 15 to 14.25. Good shooting...James

jackie schmidt
04-24-2012, 03:47 PM
I would venture a guess that just about everybody shooting a Bartlien Barrel, and winning, is shooting a Gain Twist.
I also know that many top shooters have got the gain down slower than what they started with a few years back. .......jackie

glbreil
04-25-2012, 06:54 AM
I has seen some gain twist barrels that shoot very well, I was just trying to figure out how they lap them. It seems that your lap would be trying to make the twist uniform all the way down and if you did force it though it would only contact one side of the lands in each direction.

I guess they don't remove enough material to matter but it would seem to cause the grooves to grow and the lands to shrink.

Thanks Gary

lefty o
04-25-2012, 07:20 AM
just thinking on what the above poster said, but even when lapping a normally rifled barrel, the grooves will grow, and the lands shrink. its the nature of the beast of lapping a rifled bore.

glbreil
04-25-2012, 07:33 AM
just thinking on what the above poster said, but even when lapping a normally rifled barrel, the grooves will grow, and the lands shrink. its the nature of the beast of lapping a rifled bore.

Agree, but in a constant twist barrel lapping would make the lands and grooves uniform from one end to the other, on a gain twist it seems that it would cause them to widen out at progressively as you go toward the other end becuase the lap fits perfectly in the end where it was poured and does not really fit on the other end where the twist is different.

It would even be worse if there is a point in the barrel where the twist changes rather than changing over then entire length of the barrel. I seem to remember reading that the barrels had a uniform twist for so many inches and then began their change, but I am not sure about that.

I guess it really doen't matter, I was just trying to make sense of how it works and thought someone might have first hand experience.

Gary

MarkR
04-25-2012, 05:36 PM
Maybe equal strokes from front and back...

glbreil
04-25-2012, 05:47 PM
Yeh but progessively greater twist would mean greater pressure to change the lap or barrel the farther you get from the starting point.

I think? I guess that is why we shouldn't worry about such stuff and just shoot.

Gary

Louis.J
04-25-2012, 10:48 PM
Harry Pope probable made the most accurate barrels back in the day of Schuetzen shooting and his barrels were a gain twist and he lapped each and everyone of them. How it works is of little concern as long as it shoots better than the competitions. The idea behind the gain twist with the use of cast bullets is it provided and maintained a perfect gas seal all the way out of the muzzle by the bullet taking on the changes that take place in the bullet by the gain twist. Some say it was to keep the bullet from stripping lead on the start up and the slower initial twist eliminated it but I don't think that was Harry's sole purpose but to eliminate any chances of the gases getting beyond the base of the bullet from what I have read about his work.

MilGunsmith
04-26-2012, 06:50 AM
Harry Pope also lapped a taper or choke into his barrels.

David Sengelaub
04-26-2012, 08:13 PM
I would think if you poured a short (length) lap it would be able to follow the change in the twist rate.

Stonewall
04-26-2012, 09:15 PM
http://www.riflemagazine.com/catalog/detail.cfm?ProductID=68 (http://www.riflemagazine.com/catalog/detail.cfm?ProductID=68)

The Story of Pope's Barrels by Ray M. Smith


http://ecx.images-amazon.com/images/I/614m93HSJQL._SL500_.jpg






Glenn:D

Calumet
04-27-2012, 12:46 AM
Would you think a longer lap would better at making at making contact with the lands/grooves, as it was pushed down the bore? If you think about it, that would give more contact area to the leading and heeling area of the lap.
As the lap was pushed down the barrel with the increase in twist rate seems to me, there would be more contact area with a longer lap, just cuz the the radius of the leading edge, heeling edge would be longer, as the twist rate increased.:confused:

For some "mental block" reasoning, I just can't understand how a gain twist barrel would have an accuracy advantage over a constant twist barrel.

Calumet

alinwa
04-27-2012, 12:59 AM
For some "mental block" reasoning, I just can't understand how a gain twist barrel would have an accuracy advantage over a constant twist barrel.

Calumet

It's because "it's always tightening up, the bullet can't rattle."

:)

al

Calumet
04-27-2012, 02:17 AM
Is that an accuracy advantage Al?
The question was about making a lap that would actually lap all of the surface areas of the bore. My question is how could the width of this impression be maintained, with either a lap, or a bullet, without the widening of the impression area of the lands to keep a constant contact area as the rifling pitch changes. Heck I really dunno, but something in this frail mind of mine tells me that it would leave a wider groove impression on the bullet, allowing room for escape of propellant gasses ahead of the bullet, unless the land width widened, to compensate.
I can relate to an advantage with soft lead bullets, with the pressure behind it keeping the bullet obturated enough to maintain a seal.

Maybe something to do with pressure rings on copper jacketed bullets?

Calumet

roselina366
04-27-2012, 03:58 AM
I agree with your words.Because this the right way to do lap in barrels (http://www.servospares.us).

alinwa
04-27-2012, 10:49 PM
Is that an accuracy advantage Al?
The question was about making a lap that would actually lap all of the surface areas of the bore. My question is how could the width of this impression be maintained, with either a lap, or a bullet, without the widening of the impression area of the lands to keep a constant contact area as the rifling pitch changes. Heck I really dunno, but something in this frail mind of mine tells me that it would leave a wider groove impression on the bullet, allowing room for escape of propellant gasses ahead of the bullet, unless the land width widened, to compensate.
I can relate to an advantage with soft lead bullets, with the pressure behind it keeping the bullet obturated enough to maintain a seal.

Maybe something to do with pressure rings on copper jacketed bullets?

Calumet

Sorry, it was a joke...... but one that I've heard told in all seriousness.

Not as a joke

:)


al