6.5x284 Chamber Length Help

[Joey 3]

As my first foray into rifle building, I recently had a long action re-barreled in 6.5x284 for target and hunting.

I sent the action to the barrel company and told them that I wanted to shoot 140 VLD's & 127 LRX's (for the land of "no lead") and went with their recommendations. I figured that they know their barrels.

When I measured the chamber, the COAL for 140 VLD's touching the lands is only 2.911". I am concerned about how much excess bullet is in the case (0.2"+).

The barrel company freely offered to move the throat and requested that I send them a dummy round to gauge off of.

Here are my questions:
How much difference in performance should I expect to see by moving the throat?
Where is a good starting point to have the throat moved to?

 

[Joey 3]

It has taken me a bit, but from what I've been able to find in the forum, the most common COAL for 140 VLD's at the lands is 3.19".

The common range seems to be about 3.16" to 3.22".

The Berger Reloading Manual lists the COAL @ 3.228". That seems a bit long to start at if you consider throat erosion over time.

Any thoughts?

 

[benchracer]

It sounds as though the barrel company chambered your rifle for 6.5-284 Winchester (the short action version of the chambering) rather than 6.5-284 NORMA (the long action version of the chambering).

Several years ago, I had a rifle barreled for 6.5-284 NORMA, but failed to specify any COAL or throat dimensions. That was a mistake. With a 140g AMAX, base to tip COAL to the rifling is 3.092". That has proven to limit performance to the point that I feel like I wasted my time and money on the build. It barely outperforms my 6.5x55 @ 600 yards and I am pushing it hard to get there.

I would concur that the desirable COAL would be something like 3.15"-3.20" with VLD's or AMAX's.

Rather than have the rifle throated, I am just going to have it re-chambered to .264 Win Mag and be done with it. The extra case capacity will let me use RL-33 (I hope. I expect to know for sure this spring) and the 8 twist will allow me to shoot 160 grain Matrix VLD's at speeds the 6.5-284 can't hope to match.

 

[Greyfox]

My 6.5x284's fall in the range that your research has shown, 3.16-3.19" for a 140 Berger/JLK loaded to the lands. The sweet spot for both my rifles run .075" off the lands. I use Retumbo and H4831sc with Retumbo being my choice for hunting loads using charges that run from 57-59gr. The high end of range does use 100% case capacity with Lapua, Norma, and Nosler brass, and produces the highest velocities up to 3030FPS out of a 24/26" barrel. My best loads using Retumbo are 57.5-58.5gr at 2970FPS. H4931sc at a max of 53gr appears to use about 80% case capacity, is very accurate, but max's out at 2940FPS. I think it's entirely possible that you may be able to produce an acceptable load with your shorter leade, but might trade off some velocity potential. If you decide to try any of the semi-custom loads from companies like HSM, or BOTW, it's you will push the bullet into the lands since there COAL with Berger 140's is 3.1", .050-.1" off the lands. I think you have two options. You could attempt load development and see what kind of results you get. I would back off a couple of grains with my starting loads. The second option, which would be my leaning would be to have your smith set the lead to 3.18-3.19" using a Berger 140 VLD. Given it's a custom rifle, I would want it to be as optimum as possible. I also woulnt want to use up 10-30% of my barrel life, and the time doing load development only to find out I'm not satisfied with the results. I would also confirm that the headspace and chamber neck dimensions are compatible with the dimensions of the loaded 6.5x284 Norma/Lapua case. IMO.

 

[BrentM]

I am not familiar with Winchester SAAMI specs, could look it up on google, but that seems quite short. My rifle is 3.15ish as well. I load .100 off the lands with a 140 at 2.482OAL and touching is 2.582.

On another note, when I do load to the lands I have very little bullet in the case. That drives me nuts and I have bullets get bumped off center. So loading with more bullet in the case is fine with me.

I would make sure they chambered for the Norma not the winchester, as others have mentioned.

 

[Joey 3]

Thanks for the help. That's the info I have been looking for.

I was thinking that they mistakenly gave me the short action cut as well. I was worried about poorer performance and I was planning on sending the rifle back to have the throat re-cut; but I wanted to make sure that it would be worth the effort, and that I wasn't overlooking something.

I'm thinking 3.19" is the way to go. Do you guys think that there would be any gain to going a little longer? I am not 100% sure that they're SAAMI, but I've found a few sets of specs that list COAL @ 3.228".

 

[Greyfox]

Thanks for the help. That's the info I have been looking for.

I was thinking that they mistakenly gave me the short action cut as well. I was worried about poorer performance and I was planning on sending the rifle back to have the throat re-cut; but I wanted to make sure that it would be worth the effort, and that I wasn't overlooking something.

I'm thinking 3.19" is the way to go. Do you guys think that there would be any gain to going a little longer? I am not 100% sure that they're SAAMI, but I've found a few sets of specs that list COAL @ 3.228".

I personally think that anything much over 3.19" has too little bullet contact with the case neck when 140's are loaded to the lands. This can produce runout issues or create a situation where the bullet can be easily knocked out of alignment even carried in your pocket if care wasn't taken. I'd go with 3.19". IMO

 

[BrentM]

I personally think that anything much over 3.19" has too little bullet contact with the case neck when 140's are loaded to the lands. This can produce runout issues or create a situation where the bullet can be easily knocked out of alignment even carried in your pocket if care wasn't taken. I'd go with 3.19". IMO

I totally agree Greyfox

 

[Joey 3]

3.19" it is. Thanks for the help.