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Chambering issue

TJScharp

Aluminum
Joined
Aug 6, 2011
Location
Alberta, Canada
I am chambering a .300 win mag. It is my second chamber that I have ever cut, and the first with my current set up and lathe.
i am satisfied that my bore is running true, having used both a range rod and Gordy Gritters style of rod.
My set up is follows:
Manson Floating Reamer holder.
Micrometer stop.
Live piloted Manson reamer, with nice fitting bushing.
I know the tailstock is not perfectly aligned, but neither has the floating reamer holder reached it's extreme.
My problem is I have cut the chamber about halfway, I inserted both a dummy round and a fired casing into the chamber (after thorough cleaning) and found that the cases do not sit tight in the chamber, though the case mouth has bottomed out. It seems as though the chamber diameter is too big for the given length.

Any informed advice would be appreciated.
 
get yourself a piece of inch and a half cold rolled and work through your process on a piece.

Why would you "work out your issues" on a real rifle barrel is not something that needs attention.

I suspect that your chamber ream is not "floating" enough. Based on the "too large when too short" description.
 
get yourself a piece of inch and a half cold rolled and work through your process on a piece.

Why would you "work out your issues" on a real rifle barrel is not something that needs attention.

I suspect that your chamber ream is not "floating" enough. Based on the "too large when too short" description.
I am using a take off barrel, if I have to set it back it isn’t a big deal.
Just be happy I didn’t start with the proof research barrel haha.
As for the holder not floating enough it sounds like a logical answer, but as mentioned the holder has not reached the end of its travel. Do you happen to know if the Manson reamer holder compensates for a tailstock that is not aligned 100% parallel to the axis of the bore?
 
Before you get too upset, measure the cases you are using and compare against the SAAMI standards for chambers, not cartridges. The dummy round is most likely minimum size or smaller; remember that ammo is made so that the largest unfired cartridge will fit in the smallest chamber. And even the fired case may have been fired in a minimum chamber.

Although lots of people use cases as gauges, it is not really a good practice as the cases most likely are not the dimensions you think they are.

It would also be a good idea to measure the reamer but that is going to be more difficult without special gauges.
 
How does the reamer fit in the chamber without it being in the holder? If the reamer is loose, then there is a problem with your setup. If it is tight, then it is good.
 
How does the reamer fit in the chamber without it being in the holder? If the reamer is loose, then there is a problem with your setup. If it is tight, then it is good.
Turns out my center height is low on my tailstock, even exceeding the range of the floating reamer holder. Doesn’t make a lot of sense as the tailstock was line bored through the spindle from the manufacturer, albeit 40 years ago. Thanks for all the comments, they were helpful.
 
Turns out my center height is low on my tailstock, even exceeding the range of the floating reamer holder. Doesn’t make a lot of sense as the tailstock was line bored through the spindle from the manufacturer, albeit 40 years ago. Thanks for all the comments, they were helpful.

Well! That is an important discovery!

Don't let indicator droop due to gravity influence your investigations.

Checking tailstock position is not easy!
 
Perhaps you can shim it between the top and bottom.
Exactly. Easy fix, check for tilt. Assuming it's low from wear, the front will typically be more worn as that's where chips and crap tend to work their way under.
 
Exactly. Easy fix, check for tilt. Assuming it's low from wear, the front will typically be more worn as that's where chips and crap tend to work their way under.
Will the Manson reamer holder compensate for a certain amount of tilt or is it more designed for the horizontal and vertical axii only?
 
No, it will only work for horizontal and vertical. There are reamer holder designs out there that will allow for tilt. Some are fairly easy to make.
 
I am chambering a .300 win mag. It is my second chamber that I have ever cut, and the first with my current set up and lathe.
i am satisfied that my bore is running true, having used both a range rod and Gordy Gritters style of rod.
My set up is follows:
Manson Floating Reamer holder.
Micrometer stop.
Live piloted Manson reamer, with nice fitting bushing.
I know the tailstock is not perfectly aligned, but neither has the floating reamer holder reached it's extreme.
My problem is I have cut the chamber about halfway, I inserted both a dummy round and a fired casing into the chamber (after thorough cleaning) and found that the cases do not sit tight in the chamber, though the case mouth has bottomed out. It seems as though the chamber diameter is too big for the given length.

Any informed advice would be appreciated.

Along the lines of post no.4, I would not expect a dummy round nor a fired case to fit tight in a well cut chamber. A round is supposed to chamber easily and a fired case to extract easily. I do not see the point of using them as chamber gauges like you did.
 
Along the lines of post no.4, I would not expect a dummy round nor a fired case to fit tight in a well cut chamber. A round is supposed to chamber easily and a fired case to extract easily. I do not see the point of using them as chamber gauges like you did.
I actually wasn’t using the casings as a gauge, but had cut a short chamber a per Manson’s instructions to verify acceptable throat dimensions (was a new reamer.) While checking that I noticed an unacceptable amount of play , I wish I could figure out how to post pictures.
I later wheeled a center into the case mouth a verified that was hitting on the bottom edge well before the top could make contact. I would approximate.035”-.050” low.
 
Maybe put the mag base on the cross slide and the indicator tip on the exact top of the tail stock ram. Move the cross slide back and forth to find the exact top. Extend the ram almost all the way and clamp it. Then move the carriage back and forth along the ram.
 
+1
If your setup is correct, I never understood the need for one.
Got talked into trying one once, never used it again.
I am with Butch on this one!
Greg
 
Tailstocks on well used lathes are often .010+ low,without the operator realizing why drilled or reamed holes are always oversize....IMHO,the reason is operators never see any reason to clean the tailstock ways to just move it ,and it gets slid back and forth on a sandpaper like surface.
 








 
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