Gunsmithing Freebore (Throat) question on a new build

[Lynn313]

I’m having a 6.5 PRC built. I sent in dummy rounds from ADG brass & Berger 156 EOLs. The measured throat needed came out to .216 the sales person thinks. The reamer to cut the chamber with has the throat reamer set for .145. How do you cut the extra .071 for my chamber? The throat reamer is part of an overall reamer that cuts the chamber and shoulder also, if I understand correctly. I’m very lacking of knowledge about cutting the chamber and readers in general.

Thanks for the help. The shop is like most gun & ammo businesses in that they are swamped right now. I’m seeking to learn here instead of tying up shop time.

 

[Supersubes]

There’s a tool called a throat reamer. Has the lead angle and freebore only.

 

[Lynn313]

There’s a tool called a throat reamer. Has the lead angle and freebore only.

How is it kept concentric and not cut at a slight angle? Thank you for helping. is there somewhere I can see the process?

 

[Lynn313]

Thanks. I ran a search on rifle throat reamers. Going to watch some video!

 

[Supersubes]

How is it kept concentric and not cut at a slight angle? Thank you for helping. is there somewhere I can see the process?

It’s done immediately after the chamber is reamed, and the tool is held in the same manner as the chamber reamer was. There is such a thing as a uni-throater, which can throat the barrel while it’s installed on an action. A reamer like pictured above used in the lathe during the same setup as the chamber reaming process is ideal though.

 

[Lynn313]

It’s done immediately after the chamber is reamed, and the tool is held in the same manner as the chamber reamer was. There is such a thing as a uni-throater, which can throat the barrel while it’s installed on an action. A reamer like pictured above used in the lathe during the same setup as the chamber reaming process is ideal though.

Thanks very much. You have been a big help. I’ve been reading & watching since you told me throat reamer. It does make sense that the best job with decreased chances of mistakes would be done as you state, right after cutting chamber. I feel that’s how they did it as it also seems like the most time efficient way. They are good folks, cutting a custom throat for me at no extra charge. I dislike tying them up on the phone when times are so busy.
Many Thanks....

 

[FCS]

What magazine system are you planning using or will this be a single shot?

 

[Lynn313]

What magazine system are you planning using or will this be a single shot?

It’s a Defiance GA Hunter XM action. I bought 2 5 round XM mags from APA and 2 10 rd XM mags from Defiance. Also, the XM bottom metal from APA. It will handle the longer lengths. I currently have a 6.5 PRC built on a Stiller XM action with the Stiller XM BDL. Most of what I shoot in my Stiller is around +/- 3.1”. No problems feeding.

 

[bigpeddler]

The measured throat needed came out to .216 the sales person thinks. The reamer to cut the chamber with has the throat reamer set for .145. How do you cut the extra .071 for my chamber?

Maybe a dumb question, but how are those measurements made?

 

[Lynn313]

Maybe a dumb question, but how are those measurements made?

since I enjoying learning I don’t consider any question dumb. Thanks for asking and if I’m wrong maybe someone will giver a more accurate answer.
Where the neck on the chamber reamer ends starts the throat (freebore) - the portion between the neck chamber and where the lands start. The .216 on mine is the distance from the neck to the ogive of the bullet. It is essentially the length of the seated bullet from the case neck to where it touches the lands. I like to seat my bullets with the boattail/bearing junction seated at the neck/shoulder junction of the case.

on Hornady’s commercial 6.5 PRC ammo if you do the math they have significant bullet bearing surface buried below the case neck/shoulder junction in order to work in short actions. That room is normally reserved for powder.

I attached a couple of photos from another site. Please delete my post if not ok. They put this out to teach people so I think it’s ok.
I’m an old man. I’ve been reloading for ~45 years. I smoked bullets to help find my seating depths long before I ever heard of a comparator. Though I only bought and shot factory rifles until about 5 years ago. Have rifles built is creating the pleasant need to learn more. I’m on my 3rd build and only scraping the surface of what I need to know to ensure I get what I actually want.