Reamer specs on new builds

[sbruni]

I've had more than a handful of custom rifles built and have always left it up to the smith. I do generally provide a dummy round and have them throated for that bullet and OAL. Interested in learning what other reamer specs I should be investigating to ensure accuracy potential or performance out of future projects. What should I be asking or telling my smiths about the reamers they'll use? Thanks

 

[L.Sherm]

I would let them know what kind of bullet you want to use so you get the correct amount of freebore. Next I would ask what the neck chamber dia. is so you know how much clearance you will have with a fired case depends on different brass and if you wanna turn necks or a no turn. I like enough freebore that the boatail bearing surface junction is at or just above the brass neck shoulder junction.

 

[Jud96]

I would let them know what kind of bullet you want to use so you get the correct amount of freebore. Next I would ask what the neck chamber dia. is so you know how much clearance you will have with a fired case depends on different brass and if you wanna turn necks or a no turn. I like enough freebore that the boatail bearing surface junction is at or just above the brass neck shoulder junction.

I agree with everything he said. That's what I look for and go off of.

 

[L.Sherm]

.004 -.005 neck clearance is what I like also.

 

[AZShooter]

I believe you should own the reamer with the specifications that meet your needs. No reason to compromise with a SAMMI spec or a reamer that the gunsmith happens to own. In addition it will be sharp reducing the chance of reamer chatter producing a good finish in the chamber.

I believe all the dimensions have been discussed except throat angle.

My friend and I have 20 reamers between us. Most of the reamers use a 1 1/2 degree throat angle. There are a few exceptions the 284 win uses a 2 degree and the 300 RUM uses a 1 degree. The 1 1/2 degree works well with VLD style bullets including all versions of Berger bullets as well as Nosler, Hornady and Sierra bullets.

My friend and I do our own machining. Some of the reamers have been used for multiple chambers amortizing the cost. You can always sell your reamer if you move on to other chamberings.

 

[L.Sherm]

In addition it will be sharp reducing the chance of reamer chatter producing a good finish in the chamber.

I own most of my own reamers to and it's a good idea especially if the Smith doesn't have what you need. That being said if he's got dull reamers it's time to go somewhere else.

 

[sbruni]

Thanks... good stuff... some follow ups... how does one determine the best leade or throat angle for the bullet/chambering? Is that being set with a throating reamer or spec'ed into the reamer? Floating vs fixed Pilot? If fixed what would appropriate spec be? On Sami spec reamers what throat angle and neck clearance do you generally get? Appreciate that neck clearance depends on the brass but order of magnitude how sloppy are sammi spec throats?

 

[sbruni]

Also if specifying freebore rather than setting with a throating reamer is there a best practice for determining the right freebore for the selected bullet?

 

[AZShooter]

I like to send in a dummy round with bullet seated close to the length limits of the magazine with instructions for the bullet to be able to contact the lands or a specified jump to lands.

Talk to the reamer maker and ask questions as to what throat angle and freebore might work best with a particular bullet or bullets.

 

[Edd]

Thanks... good stuff... some follow ups... how does one determine the best leade or throat angle for the bullet/chambering?

The current fad seems to be 1.5°. I don't think it makes much difference.

Is that being set with a throating reamer or spec'ed into the reamer?

It can be done either way. It is easier and cheaper and arguably more accurate to have the throat angle an integral part of the chamber reamer.

Floating vs fixed Pilot?

Floating gives you the ability to choose a bushing that is a good fit with the barrel bore. Even though a fixed pilot that was the exact size to fit would have less slop than a floating, floating is the best choice.

If fixed what would appropriate spec be?

I think .0004" smaller than the assumed bore diameter would be appropriate.

On Sami spec reamers what throat angle and neck clearance do you generally get? Appreciate that neck clearance depends on the brass but order of magnitude how sloppy are sammi spec throats?

There is no standard. It will vary based on the opinion of the designer. You have to check the SAAMI specs of the individual cartridge you are thinking of.
https://saami.org

 

[sbruni]

Thanks

 

[L.Sherm]

If I remember right reamers usually come .0004 smaller pilot than the bore unless you spec something different. Some Smith's that pre-bore dont use a specific pilot bushings and the ones that dont have bushing kits that they can use to match bore size.