The 6mm Rabbit Hole.

[Coyotecreek]

Hey guys I've got some thoughts on some 6mm stuff I'd like to run by this vast community of knowledge.

I had gotten a barrel from a known manufacturer and there were some issues with the barrel. Made them aware of it and immediately offered to replace the barrel at no charge, awesome.

This is where my little brain goes to work. The new barrel measures 1.238 outside. It'll finish at 28". Straight contour. The barrel is stamped .2365 and .243. 7.5 twist. If my former research is correct I've found that most barrels are .237. I think all of my former barrels were .237. The guru's have stated that the 236 barrels shot the best.

With that being said a smaller bore means more pressure and a faster barrel. Correct?. I haven't chambered the barrel yet.

Heres my plan, the reamer has a .104 free bore. 6mm BRX. I'd like to extend the free bore to around .130. It'll be on a defiance deviant RBLP long action. Berger 105's, 108's and 109's are my options, varget powder.

I'm abandoning the 7mm for a while and in my mind this 6mm will do all I need. Shooting steel plates out to a max of 800 yards.

Let's have some discussion on what the barrel internal diameter, extending the freebore, bullet selection and barrel length. And the do's and don't's.

 

[SKWERLZ]

I did a 6bra with.104 FB barrel a bit back and 107’s have been excellent.
27” at 2880 FPS.

I doubt you’ll find too much issues with the .2365 and cup core bullets, possibly a bit faster.
My first 6mm and I’m loving it.
It’s mostly for 1000 and in on steel but it performed quite well at 1286 and 1525 yards.
Either.104 or .130ish FB should be just fine

 

[DaveTooley]

You will not be able to shoot the difference between any of the options you've listed.
If it ain't broke don't try and fix it.

 

[RGRobinett]

Nothing wrong with a .236/.2365" bore that a .237 won't cure . . . RG

P.S. virtually every [reported] failure of my long/heavy 6mm bullets (J4 jacket) has been via a .236" barrel - tight bores shooting better is a myth. About 55% of the .236 bores have been ok - when I know a customer is using a .236, I try to steer them to another bullet option.

 

[Walt Krafft]

I agree with Dave, use your reamer as is and be happy. You are splitting hairs on those dimensions and will never see a difference on the target changing any of them.

 

[swd]

I’ve had great barrels in both bore sizes. Both shot the same nodes. It’s a non issue.

 

[Coyotecreek]

I agree with Dave, use your reamer as is and be happy. You are splitting hairs on those dimensions and will never see a difference on the target changing any of them.

Is it possible to get more powder in it therefore resulting in more velocity?

 

[Coyotecreek]

The barrel was supposed to be able to finish at 30", so is there any issue with it going to be 2" shorter?

 

[DaveTooley]

In a word no. Every barrel is unique and has it's own limits. And .0005" on the bore is finer than frog hair. I have reamer bushings that cover over .002" in 6MM

 

[Walt Krafft]

Is it possible to get more powder in it therefore resulting in more velocity?

You want more powder and more velocity, go to a bigger cartridge like a 6XC.

 

[Coyotecreek]

You want more powder and more velocity, go to a bigger cartridge like a 6XC.

I don't want that much, LOL. I've been around a few 6XC's and wasn't impressed with accuracy. Maybe it was the guys loading, gun handling, not sure but I didn't get any warm and fuzzies. I've had a Dasher that would shoot low 100's all day but that barrel finally gave it up. I'd do another Dasher but I just wanna try something different.

 

[JEFFPPC]

.236, .237 doesn't mean a hill of beans. As a long time BRX shooter I have learned one thing to consider is freebore because of the short neck. You want to keep the base of the bullet above the neck shoulder junction. I bought a reamer with a short throat and also bought a throater. I seat a bullet with the rear ogive half way up the neck and have my smith throat it so the lands leave a tiny mark on the bullet. This leaves you room to go in or out.I have been through quite a few barrels and it's been a winner for me, many times.

 

[Coyotecreek]

I told a fib. It’s actually.2362.

 

[Capt. Oblivious]

I don't want that much, LOL. I've been around a few 6XC's and wasn't impressed with accuracy. Maybe it was the guys loading, gun handling, not sure but I didn't get any warm and fuzzies. I've had a Dasher that would shoot low 100's all day but that barrel finally gave it up. I'd do another Dasher but I just wanna try something different.

You will have people coming after you with pitchforks. lol

Like the guys have said you won't see any difference, only problem I ever saw with one .236 bore was very light bullets getting ripped to shred at high speed but this was 55s in a 9 twits barrel so the RPM was very high already to start with, as soon as we changed to 70gr BTs the problem was solved

 

[swd]

I have a .140” fb BRX reamer. It’s about perfect for 105-110gr. 2 state championships on that reamer. It’s an incredibly easy cartridge to load for.

 

[Alex Wheeler]

The bore wont matter, but the grooves will.

 

[SKWERLZ]

I don't want that much, LOL. I've been around a few 6XC's and wasn't impressed with accuracy. Maybe it was the guys loading, gun handling, not sure but I didn't get any warm and fuzzies. I've had a Dasher that would shoot low 100's all day but that barrel finally gave it up. I'd do another Dasher but I just wanna try something different.

I have a few friends that are really fans of 6XC.

 

[Coyotecreek]

The bore wont matter, but the grooves will.

What can I check? I chambered it last night and this is what I ended up with!

105 Hybrid

I've had a 284 and a dasher that were seated out like this and they were both nasty consistent and accurate.

 

[Alex Wheeler]

What can I check? I chambered it last night and this is what I ended up with!

105 Hybrid

I've had a 284 and a dasher that were seated out like this and they were both nasty consistent and accurate.

The bore and groove wont have much impact on your oal. The bore wont have much impact on pressure but the groove will. Unless your going to get deep into this stuff and experiment, just go shoot it.

 

[Clancy]

You’re not going to throw Berger jackets unless you try your best to do so.

Just shoot it, keep it clean and if you run out of room switch to the 108.