Freebore is 100,000ths instead of intended 40,000th. Reamer screw-up, or the smith?

[VaniB]

Al,
Thank you so much for trying to help. You've taken a lot of time to detail the procedure that you think would help me make a determination....but, it's kind of a trial and error relay, and I just don't feel up to that much fussing and testing right now.


PEI Rob,

Well, I'll be a son-of-a-witch (with a B) if I didn't try the simple procedure you suggested, and came up with some enlightening results!

I reloaded a dummy round to the length that the bullet has good neck grip. (which I have been stating "is not long enough to contact the lands", and is .1" short of the lands) I then stuck a thin wooden dowel into the primer pocket to serve as a handle and a guide rod. I used a candle to blacken the bullet with soot, and then proceeded to very gently guide the dummy cartridge into the rifle chamber. I tried this twice, and each time I pulled the case back out carefully and examined it, I found a round circumference of soot that had been rubbed off of the bullet a good bit above the case neck.

Well, now I can see that the bullet certainly seems to be contacting something in the chamber. I know if I push that bullet the additional .1" it will definately stop dead cold on something that I had previously been calling the lands. I don't know what that "something" is further up that I had previously been shoving the bullet up into when using the bolt. But right now, I have just discovered that without using the bolt to shove the bulet way up into the chamber, it is definately contacting chamber metal! Perhaps this is really where the "lands" start? I don't know what to call the surface it is contacting now, but hopefully this is the surface that Dave intended the bullet to be .04" off of, and will provide the accuracy I seek. Hopefully this surface in the bore I've discovered is just what you guys talk about when you say how you get your bullets to touch, or how how little jump you seat your bullets for.

 

[PEI Rob]

Your very welcome.

Just ahead of where the neck of the brass stops in the chamber, the reamer continues to cut that same neck diameter a ways deeper, for safety reasons.
Further in than that is what is called the freebore, which is cut to barely larger diameter than the bullet diameter.
The throat is ahead of that and is the angle cut from the freebore that tapers into the lands. This means the throat is the very beginning of the lands. However, the throat angle also tapers the freebore cut into the bore diameter so there is no edge. Since your bullet is larger than your barrel, you will often see a ring mark instead of the land marks. If you force the bullet you may notice the ring is brighter towards the nose because you are forcing it into an angle. If you force it even more, you will likely notice a numer of land marks.
Some chambers show land marks before the ring shows up and others vise versa, depends on the reamer.

This is how I understand it but I stand to be corrected, into the lands means no jump so if you see a ring, your in.

Cheers,
Rob

 

[Al Nyhus]

It takes about the same amount of time to do it as it did me to type it. I'll not comment on the 'ring'....

 

[VaniB]

Your very welcome.......

.....Cheers,
Rob

Errrr....thank you.

As I explained to you earlier, the contact area on the blackened test bullet is more like a ring around the entire circumference of the bullet. Reexamining that blackened dummy test bullet again, the ring starts up the base of the bullet to about a good 1/8" above the case neck. The bullet is seated out as far as I can get it while retaining good bullet grip. (OAL @ 2.295") I did not observe any other marks further up the bullet near the ogive. I'm guessing that this described ring is probably produced by the 45 degree angle in the reamer in front of the case neck.

Justin, Charles E, Kenny, yourself, and others have tried to convey some technical detail about chambers and the reamers that cut them. The chamber is obviously more sophisticated and difficult for me to understand then simply a .204 straight and smooth bore that has lands suddenly start out front somewhere. There are angles and tapered walls that I don't profess to understand how to measure.

So, now I'm really not sure how to measure the bullet "jump" in my chamber, and how long I should leave the OAL of the cartridge. Would you agree that I should probably just continue to leave the bullet out as far as it can go at 2.295" OAL?


Justin, if you're still out there. The measurement of the case rim to the ogive is 1.930"

 

[BR guy]

So, now I'm really not sure how to measure the bullet "jump" in my chamber, and how long I should leave the OAL of the cartridge. Would you agree that I should probably just continue to leave the bullet out as far as it can go at 2.295" OAL?

Post number 19 explains how to do it.

 

[PEI Rob]

... I'll not comment on the 'ring'....

Please do, in no way do I want to argue, I want to learn.

I tried the 0000 steel wool and like it much better, thank you, I've never heard of that one.

I grabbed a rifle and the steel wool worked easier than smoking the case but both showed the same result. Steel wool being easier and cleaner was the better method.

I reached for a few factory barrels and using the same projectile, noted "the ring" caused the bullet to seat deeper into the case. It took quite a bit of effort to get the lands to show up, the ring mark was about .060" thick before the lands made any marks using the same case and bullet as on the rifle I used. The only difference was the factory reamer VS cutom reamer. I have noted this many times in the past and didn't think it was a problem, just the reamer and bullet shape relationship.

If anyone, inc Al Nyhus, has more about this "ring" please let me know. No arguements, just education.

Cheers,
Rob