Question about rifling depth

[tpcollins]

I remember the specs on my Knight .50 cal ml indicated the grooves were .005"/.006" deep and I remember getting a .500" plug barely into the muzzle. On my Tikka .204, I'm not sure of the groove depth is but I can get a .199" plug into the muzzle, and I think a .1995" plug would go as well, not sure if .200" would or not.

I'm wondering how much over, if any, the groove diameter is over .204". And does the depth of rifling get shallower on smaller calibers or is it up to whatever the manufacture feels like making? Thanks.

 

[Rifleman1776]

You got it, manufacturers decision.
Look at the Marlin rifles with their 'micro grooves'. Practically no rifling and they shoot like it.

 

[mete]

Normal grooves are about .004" deep and 'micro groove' is about .002" deep.
The claim that micro groove is not accurate is a myth !! The thing about micro groove is that it's more sensitive to bullet hardness and bullet diameter !For accuracy you can't expect to buy a bullet of variable hardness and diameter and expect much .Cast your own to fit the gun and load and you'll find excellent accuracy.

 

[LukeA]

Look at the Marlin rifles with their 'micro grooves'. Practically no rifling and they shoot like it.

I can demonstrate the falsity of that statement pretty easily, at least in .22LR.

 

[Palmetto-Pride]

Cast your own to fit the gun and load and you'll find excellent accuracy.

But why would you want to? If I have to do that for the gun to be accurate then I will move on to a rifle that doesn't require me to make my own bullets just so I can hit a soda can at 100yds.

 

[Scorch]

I'm wondering how much over, if any, the groove diameter is over .204".

Absolutely, you do not want groove diameter to be over spec, but bore diameter is variable according to the makers, even though they do try to stick within industry specs. For example, a 30 caliber .308" groove diameter barrel will always have a .308" groove diameter (within the capabilities of the maker to produce it), but bore diameter can vary from .300". 22LR barrels can vary from .219" to .224", most tend to run .222". If you look at various barrel makers' sites, you will see tables of bore/groove diameters listed.

 

[HiBC]

A muzzle loader and a .204? Suppose a low velocity sabot or patched ball might require a different rifling than a .204 jacketed high velocity bullet?
Then too,there may be some factor of ratios and porportion to consider.Scale down your .50 with .005 rifling,and a .204 with .002 ish grooves seems to scale.

 

[44 AMP]

Remember that the rifling essentially "digs in" to the bullet, forcing it to spin. Large heavy bullets need, and can take a deeper groove, resulting in the stronger force needed to spin them.

Small bore bullets don't need, and cannot take as much force, jackets are thinner, and speeds are high. So the rifling grooves tend to be shallower. It is a matter of the makers choice, outside of certain calibers where there are military specs to be met.

Also remember that every dimiension has allowable tolerances. GI specs for a .30 cal barrel call for groove diameter of .308" +/- .0005. Therefore a barrel with grooves of .3075" and one with .3085" are both within spec, if at the outside edges of it.

 

[jdoudna]

To add some more confusion to this thread, the British standard back when they developed the 303 Enfield was for a bore diameter of 0.300" with a rifling depth of 0.0055". This resulted in a grove diameter of 0.311". US manufacturers produced a lot of these for the British under contract at the beginning of WW-I since the Brits did not have the manufacturing capability at the beginning of the war. This design got carried over to the US 1917 Enfield when the US got into WW-I since the manufacturers could easily adapt the British design, for which they were already tooled, to shoot the US standard 30-06 cartridge. So, US 1917 Enfields with original barrels have a 0.311" grove diameter. Another oddity is that the British used a 5-groove, left-hand twist, and this also got carried over to the US 1917 Enfield. It seems that things have somewhat come full circle as a lot of US custom barrel makers now offer 5-groove barrels.

 

[RC20]

This design got carried over to the US 1917 Enfield when the US got into WW-I since the manufacturers could easily adapt the British design, for which they were already tooled, to shoot the US standard 30-06 cartridge. So, US 1917 Enfields with original barrels have a 0.311" grove diameter. Another oddity is that the British used a 5-groove, left-hand twist, and this also got carried over to the US 1917 Enfield. It seems that things have somewhat come full circle as a lot of US custom barrel makers now offer 5-groove barrels.

That is absolutely and totally false. It is a common misconception.

US Model of 1917 was bored to US standard. They did use the 5 grove LH twist, but the machinery was adjusted.

You can go one of two ways here.

1. Read Ferris on the Model of 1917 on the barrel.

2. You can accept that I have Model of 1903 Muzzle Wear and Throat Erosion gauges and all my Model of 1917s (those I still own and those that have passed through) had measurements of 1 to 2 on both ends.
To spell that out, a TE/MW gauge is set to a 30 caliber (308 lands) datum, it would be up past 4 -5 in a .311.

Going from memory, the 1917 was .3085 - with the 5 lands/groves its a hard one to measure as there is no direct opposite grove. It was considered a better rifling system as it wore better. It was considered better shooter than the 1903 (average). Almost adopted for the US rifle teams.

 

[ThomasT]

Quote:
Look at the Marlin rifles with their 'micro grooves'. Practically no rifling and they shoot like it.

I can demonstrate the falsity of that statement pretty easily, at least in .22LR.

And so can I with my two 22 mags, two 30-30s and 35 Remington. Marlins are known for their accuracy. My lever actions will shoot right along with most bolt actions. And thats not counting the Ballard rifled Marlins I own.

Most muzzle loaders have deeper rifling than guns designed to shoot jacketed bullets. A BP rifle with .005-.006 rifling is considered on the shallow side but correct for Saboted rounds shot in inlines. Most round ball guns have .008-.010 and sometimes ever deeper grooves.