.25 Vulcan Gen2 barrel lands/grooves sizes

[fe7565]

I am planning to buy a Lee die press. But need to know what size die to get for it. While I had the gun partially apart I decided to measure the barrel grooves and lands diameter. I hammered a JSB pellet to almost 1.5 times of its normal size and pushed it inside the barrel from the breech end about 5-6 inches deep. Then pushed it back out the same way. It looked almost like a pile driver pellet and had some decent grooves on it all the way around. 

Using a caliper and a 20x jeweler's magnifying glass I tried my best to make sure the caliper is on the top of the grooves 180 degrees apart, and next that its also within the grooves the same way. The measurements: 0.246 (6.25mm) lands and 0.252 (6.4mm) grooves. 

I know measuring like this with a caliper can be unreliable, any suggestions on how to be more sure?

If my barrel has 6.44mm grooves, what size pellet-die should I get?

 

[ajshoots]

I always order dies to the exact groove size. If you have a barrel with a groove slightly over say .252, I would get .252 and .253 and see if one is better than the other.

 

[Richard300]

fe7565... I'm in the same boat as you. I am getting ready to order the dies also. I was getting ready to ask the same thing...You beat me to it.. : )
Its funny my groves on my .25 are exactly the same as yours.... . : ) .246 
looks like I'm ordering .246 and .247
Richard

 

[fe7565]

Thank you ajshoots Does 0.252 sound right?

@kris: I did yank out my entire barrel during cleaning because I already had the airtube out and the holding clamps were loose. Lesson learned

@richard300: I am pretty sure that that die should be sized to the groove and not the land. If you measured 0.246, are you sure that's the groove and not the land?

 

[ajshoots]

Standard .25 caliber bore dimensions are .243 land .250 groove. I know LW barrels are much large as are the korean barrels. .252 is surely in the .25 cal realm. If you are unsure, just push a bunch of pellets in and back out to measure and assure you that you have the true bore size.

 

[fe7565]

Thanks AJ. I will measure again in a couple of other ways just to make sure. I know ballpark is not good enough in case of die sizes, but I am glad it fits the bill for a .25 caliber.

One thing I am wondering about: for a 6.44mm barrel groove size I want a 6.44mm die to size the pellet. But I measured the size of the JSB 6.35mm pellets and the head was 6.34mm and the skirt around 6.50mm. If my groove diameter measured at 6.44mm, I do not think the 6.34mm pellet head can be sized to the groove diameter just by the pellet probe pushing it in deeper? Does the skirt need sizing too? And the Lee die would reduce the diameter of the pellet, correct? What diameter gives the most consistency as far as friction/resistance as it travels down the LW barrel in relation to barrel-groove diameter? What about the choke area of the barrel which is even smaller?

 

[ajshoots]

I always size to actual groove diameter. Yes, sometimes that means heads don't get sized, but in most cases, head and skirt are sized.

 

[kk4iz]

What are some of the places to order dies?

 

[ajshoots]

http://leeprecision.com/custom-lube-and-size-kit/