Barrel rifling question

[scott2345]

I have a question about barrel rifling. I have been thinking about a new rifle and was reading about barrel rifling and I have a question I'd like to ask.

I assume that a bullet is not yet spinning when it exits the cartridge because it has not yet encountered rifling. The spinning of the bullet must begin when it interacts with the rifling. But I would guess that it is not spinning at the same rate early in the barrel as it is when it exits the barrel.

I have watched gunsmiths putting rifling in barrels rifles on YouTube and they seem to use a consistent rifling pattern through the length of the barrel. A .308 normally gets a 1:10 rifling and it is the same throughout the barrel.

My question is based on my assumption that the bullet does not reach its full spin rate until later in the barrel. I imagine that it is blowing past rifling early in the barrel where it is not yet spinning at the same rate as the rifling. I suspect that during that period where the bullet is not spinning at the same rate as the twist in the rifling that the rifling causes a certain amount friction to the bullets journey down the barrel; possibly impacting velocity. I wonder if it would be more efficient to use a gradual increase of the twist of the rifling, that doesn't reach full twist until later in the barrel. I am wondering if that gradual approach to rifling would be more realistic given what I suspect is a gradual increase in spin of the bullet along its path through the barrel. Has anyone ever experimented with that?

 

[rcoody]

I have a question about barrel rifling. I have been thinking about a new rifle and was reading about barrel rifling and I have a question I'd like to ask.

I assume that a bullet is not yet spinning when it exits the cartridge because it has not yet encountered rifling. The spinning of the bullet must begin when it interacts with the rifling. But I would guess that it is not spinning at the same rate early in the barrel as it is when it exits the barrel.

I have watched gunsmiths putting rifling in barrels rifles on YouTube and they seem to use a consistent rifling pattern through the length of the barrel. A .308 normally gets a 1:10 rifling and it is the same throughout the barrel.

My question is based on my assumption that the bullet does not reach its full spin rate until later in the barrel. I imagine that it is blowing past rifling early in the barrel where it is not yet spinning at the same rate as the rifling. I suspect that during that period where the bullet is not spinning at the same rate as the twist in the rifling that the rifling causes a certain amount friction to the bullets journey down the barrel; possibly impacting velocity. I wonder if it would be more efficient to use a gradual increase of the twist of the rifling, that doesn't reach full twist until later in the barrel. I am wondering if that gradual approach to rifling would be more realistic given what I suspect is a gradual increase in spin of the bullet along its path through the barrel. Has anyone ever experimented with that?

http://bulletin.accurateshooter.com/2008/08/boyer-succeeds-with-bartlein-gain-twist-barrel/

 

[scott2345]

Thanks for the link @rcoody. So that is called a "Gain Twist".

 

[Mikecr]

The bullet is spinning at the same rate, while that rate is displacement. That is, an 8:1 twist will cause the bullet to turn once in 8" no matter what point in the rifling the bullet is in.
Your perspective seems tied to time, or RPM, which is not the same.
A gain twist may slow recoil torquing, and reduce harsh forces on bullet jackets. The final twist rate is still just that.

 

[FEENIX]

Thanks for the link @rcoody. So that is called a "Gain Twist".

... sometimes called progressive, incremental, or transitional (T-style by Bartlein) twist.

 

[J E Custom]

I have a question about barrel rifling. I have been thinking about a new rifle and was reading about barrel rifling and I have a question I'd like to ask.

I assume that a bullet is not yet spinning when it exits the cartridge because it has not yet encountered rifling. The spinning of the bullet must begin when it interacts with the rifling. But I would guess that it is not spinning at the same rate early in the barrel as it is when it exits the barrel.

I have watched gunsmiths putting rifling in barrels rifles on YouTube and they seem to use a consistent rifling pattern through the length of the barrel. A .308 normally gets a 1:10 rifling and it is the same throughout the barrel.

My question is based on my assumption that the bullet does not reach its full spin rate until later in the barrel. I imagine that it is blowing past rifling early in the barrel where it is not yet spinning at the same rate as the rifling. I suspect that during that period where the bullet is not spinning at the same rate as the twist in the rifling that the rifling causes a certain amount friction to the bullets journey down the barrel; possibly impacting velocity. I wonder if it would be more efficient to use a gradual increase of the twist of the rifling, that doesn't reach full twist until later in the barrel. I am wondering if that gradual approach to rifling would be more realistic given what I suspect is a gradual increase in spin of the bullet along its path through the barrel. Has anyone ever experimented with that?

Even though the bullet is not spinning as it leaves the cartridge, it does start at the moment of contact with the rifling. If it did not start right away, it would show on spent bullets and the accuracy would be bad.

It is a sudden event, but the bullet is not traveling very fast at the moment of contact with the rifling
so it starts engraving and rotating at this moment.

There have been lots of debates on this and gain twist rifling. In theory, the gain twist should be better but it has not been proven or all barrels would be rifled that way. The down side of gain twist rifling is the engraving on the bullet will end up being wider than the rifling and may be another problem all together.

Once the bullet engages the rifling rotation is controlled by the rate of twist and as the bullet increases in velocity, it also increases in RPMs so it does not start at 3000 ft/sec at the throat or it probably wouldn't engrave properly.

There are people that will swear that one Type of rifling is better than the other but again, it has not been proven and the largest percent of barrels are constant twist configuration.

So essentially, the bullet starts rotating at the twist rate immediately after engaging the rifling and should not slip, but if it does, accuracy will be lost.

You can verify this by finding a spent bullet and studding the engraving.

J E CUSTOM

 

[scott2345]

Thanks for your replies; very informative!

 

[Frank in the Laurels]

Not sure if they make them anymore but some company offered a gain twist barrel rifling, watched a few shoot at the super shoot many moons ago, didn't seems to do much either way in the winning departm..

 

[MagnumManiac]

I have a question about barrel rifling. I have been thinking about a new rifle and was reading about barrel rifling and I have a question I'd like to ask.

I assume that a bullet is not yet spinning when it exits the cartridge because it has not yet encountered rifling. The spinning of the bullet must begin when it interacts with the rifling. But I would guess that it is not spinning at the same rate early in the barrel as it is when it exits the barrel.

I have watched gunsmiths putting rifling in barrels rifles on YouTube and they seem to use a consistent rifling pattern through the length of the barrel. A .308 normally gets a 1:10 rifling and it is the same throughout the barrel.

My question is based on my assumption that the bullet does not reach its full spin rate until later in the barrel. I imagine that it is blowing past rifling early in the barrel where it is not yet spinning at the same rate as the rifling. I suspect that during that period where the bullet is not spinning at the same rate as the twist in the rifling that the rifling causes a certain amount friction to the bullets journey down the barrel; possibly impacting velocity. I wonder if it would be more efficient to use a gradual increase of the twist of the rifling, that doesn't reach full twist until later in the barrel. I am wondering if that gradual approach to rifling would be more realistic given what I suspect is a gradual increase in spin of the bullet along its path through the barrel. Has anyone ever experimented with that?

This is an interesting theory, but, unfortunately it is wrong.
Most bullets engrave the rifling while still in the case neck, easy to figure out, seat a bullet long and see how much is in the neck after jamming it in the rifling.
The bullet engages the rifling instantly, it doesn't strip or slip for an amount of barrel.
(Although lead bullets pushed too fast can strip the rifling.)

Gain twist has proven to be a non performer, as in, the theory doesn't match the results.
There is also the common belief that the amount of bullet shank, or bearing surface, influences accuracy. This is also a myth, as bore riding, barrel banded projectiles all work extremely well in their said application.

Cheers.
gun)