Deliberately throating a match barrel long

[Tumbleweed]

This thread is also posted in "Gunsmithing" in the hopes of more exposure and better feed back.


Hi guys. I will be re-barreling my 300Rum with a 31+" Broughten 5C 12.4 heavy palma 9 twist in a couple of months as well as blueprinting the receiver and bolt. Found my smith for the job, he seems more than qualified. I will be setting this up to run the 230 Hybrid Targets. Here is my question:

I want some feedback on the 'idea' of deliberately throating the chamber .25-.5" longer than a standard chamber with a match reamer that would allow say .0005-.001" bullet side clearance in the throat portion. I'm sure it would lend itself to very nice velocity above a standard chambering but my question and concern is would I be giving up any accuracy even with the very tight throat? With .0005-.001" throat clearance the bullet should still start out lined up with the rifling straight right? Would the heavy hybrid put up with this kind of jump without giving up any accuracy? I do have a Wyatt's box it my 700 now and it measures right around 3.860". I will probably keep it magazine feedable, so yes that's a lot of jump. I am going all out on this build looking for max accuracy, if I would need to sacrifice accuracy in any way I will not do it. Does anyone have experience with setting up a chamber this way and what kind results did you get? (Accuracy, velocity, ES, pressure, ect)

P.S. I know a guy that built a 7STW with 1" of freebore along with a special i.d. bore and claims to have been able to run 3600fps with a 175 grain gameking with .5MOA accuracy.

 

[Sako7STW]

Would that be basically the same thing as Weatherby's freebore? Or am I thinking wrong?

 

[Tumbleweed]

Would that be basically the same thing as Weatherby's freebore? Or am I thinking wrong?

I don't know that I would call what I am talking about freebore as compared to a Wby. I believe their "freebore" is a much, much looser fit between the throat and bullet than what I am inquiring about. Again, I'm talking minimal clearance here, .0005"-.001".

 

[AZShooter]

Have you talked to the reamer maker? My friend who shoots 1000 BR and I use Pacific Tool and Gauge. We talk with Dave Kiff and discuss things like this with him. He usually has an answer for what has worked.

When I wanted a no turn neck 300 RUM reamer he and I talked. I was surprised to hear that the 300 RUM performed better with a lead angle that wasn't the usual 1 degree 30 min he recommends, it is 1 degree. The diameter just before this is .3091"

If you are jumping the bullet I don't see how that would cause accuracy issues. Expecially with the 230 hybrid, the same bullet my 300 RUM is shooting which makes a jump to the rifling. As for performance, the load was easy to find trying two different powders with excellent accuracy.

 

[Edd]

I don't know that I would call what I am talking about freebore as compared to a Wby. I believe their "freebore" is a much, much looser fit between the throat and bullet than what I am inquiring about. Again, I'm talking minimal clearance here, .0005"-.001".

Weatherby's freebore fit is tighter than most. The specs are .0004" over groove diameter.

 

[Tumbleweed]

Weatherby's freebore fit is tighter than most. The specs are .0004" over groove diameter.

Wow, I guess I've been misinformed. I thought their freebore tolerances were a lot looser than that.