Barrel length and velocity increase on 6BR with light bullets

[RAG]

My current 6BR carries a 24" barrel and I have no problem reaching 3800 fps with 55 grain pills. Anyone know what kind of velocity increase I could expect going to a 30" tube?...my hope was that I'd gain an extra 25fps/inch, thus an extra 150fps. But I know there are a lot of variables. Thanks.

 

[RAG]

I'm also toying with the idea of 30" tube with BRX or Dasher. With the 55s, I would hope I could obtain 4100fps, but I don't know. Anywone pushed the 55s out of a long-tubed Dasher or other improved case?

 

[larryk40c]

What are you after, speed or accuracy? What about the wind with a 55 gr?

 

[RAG]

I suppose "both Accuracy and Speed" is the answer I'd like to give

I just want to hit squirrels 300 yards and under. And I want to hit them hard! Splat factor is big for me. The fast/light bullets have served me well there...and I can really see my hits well (especially since it's a 22lb rig).

Certainly, my foremost requirement is accuracy. Current barrel is a standard HV Benchrest Taper finished at 24" with short-range accuracy nearly matching my 6PPCs, but if I can put on a straight 1.25% 30" tube and give up little to nothing in accuracy and gain 150fps, I'm all for it. And in real-world varminting conditions, hopefully a little extra velocity well help in the wind and elevation...but again, I rarely shoot beyone 300 yards (though sometimes I'll hone in on a "squirrel town" at 400 with decent success.

 

[Forum Boss]

This won't give you a direct answer for your situation. However, we did a barrel cut-down test from 33" to 28" in one-inch increments. With a load of H4895 and 105gr bullets we lost a total of 40 fps with the five-inch length reduction from 33" to 28". Based on this test, I would be surprised if you pick up 150 fps going from 24" to 30" ... but then you have a slower twist rate, different powder, and lighter bullets, so our test results won't apply directly. FWIW, the difference in speed was very linear at 8 fps per inch, meaning we only picked up 16 fps from 28" to 30".

 

[RAG]

This won't give you a direct answer for your situation. However, we did a barrel cut-down test from 33" to 28" in one-inch increments. With a load of H4895 and 105gr bullets we lost a total of 40 fps with the five-inch length reduction from 33" to 28". Based on this test, I would be surprised if you pick up 150 fps going from 24" to 30" ... but then you have a slower twist rate, different powder, and lighter bullets, so our test results won't apply directly. FWIW, the difference in speed was very linear at 8 fps per inch, meaning we only picked up 16 fps from 28" to 30".

Wow, interesting results. And kinda depressing...I'd take the stiffer barrel for only 40 fps. I've seen some barrel cut-off tests done with shorter barrels and lighter bullets (on a .223) which yielded 40fps for each inch. Maybe by the time you hit 28" most of the powder has already burned and done it's thing, so diminishing returns has a significant affect, as I'd guess if you went from 28" to 24" you'd see a LOT more than 40fps...but just a guess.

For me, the tradeoff would have to be in the order of 20fps/inch...otherwise I'd just stick with a stiffer/shorter barrel.

 

[Webster]

Why would you need more velocity if your shooting under 300 yds? If you want more splat buy more explosive bullets (V-max Hornady perhaps).

 

[kjcpoint]

3995fps out of a 26 inch brux. 6 dasher. 55gr noslers. fun to shoot at 300.

Kyle

 

[Dave T]

I have a Cooper Phoenix in 6BR with a 26" barrel, can I expect 3800 FPS with 55 grain bullets or even close to that? I haven't gotten around to cronographing this gun, but 3800 FPS?
Dave T

 

[RAG]

3995fps out of a 26 inch brux. 6 dasher. 55gr noslers. fun to shoot at 300.

Kyle

Yeah, that's pretty much what I'm looking for. Except I already have custom dies matched to my own reamer in standard 6BR, so I'm questioning the additional tooling cost to step up to the Dasher...so I'm having second thoughts.

 

[RAG]

I have a Cooper Phoenix in 6BR with a 26" barrel, can I expect 3800 FPS with 55 grain bullets or even close to that? I haven't gotten around to cronographing this gun, but 3800 FPS?
Dave T

Sure. Shouldn't be a problem. My accuracy load chronographs the 55s at exactly 3,800 fps (Benchmark powder) with a 24" Hart. I've fired each piece of brass 8-12 times (barrel has 6500 rounds), and I haven't lost a single piece or brass. In fact, the primer pockets are still very tight. Oh yeah, my last trip to the range produced 4 groups in a row under .23" (with ballistic tip and custom bullets); with that blend of barrel life and accuracy, I am confident saying the 6BR is the King of short-range varminting.