why my 1-10" Brux .308 won't shoot 195gr and up?

[DukeDuke]

I am in the process of finding out.

 

[D-4297]

For the most part I always said... the style and number of grooves doesn't make a difference when it comes to barrel life and or accuracy.... until Aug. 2022.

A very good test was done with like 12 barrels. 7 of them had spec 6 groove and 5 of them had 5R rifling. I didn't know at the time we made all the barrels for the test that was going to be run.

What they found was interesting. All accuracy was done at 200 yards and the 5R barrels barrel out shot the 6 groove barrels (by a slim margin) but what they found was the bullets out of the 6 groove barrels all had burrs on the sides of the jackets which compromised the bc by 5%. None of the bullets out of the 5R barrels had this happen. So if you take those targets further down range the bc error is going to show up more in terms of the accuracy being off/unpredictable. A total of 320 rounds where fired and every bullet got photographed right after it left the barrel. The burr was as big as a 1/32" of an inch.

This backs up what Hornady and the Army did testing by accident with 6.5mm about 5 years earlier. All accuracy testing was done at 1k and 1200 yards. They shot 4 groove and 5R barrels. They didn't know why all the bullets that where fired out of the 5R barrels flew more consistently and again the testing was done by accident. The test in Aug. 2022 and now with data confirm what Hornady and the Army seen and now we know why.

Obermeyer always claimed the 5R barrels where more accurate as well but never had data as to why or anything to back it up. It wasn't necessarily more accurate but the 5R rifling helped the flight of the bullet.

What are your thoughts on "Polishing" the Bores of the Six flute barrels , before shooting them ? A fine grade "lapping" process to assist in potentially reducing , or eliminating the Burring issue . Since I have two ; I am considering doing this to one of them before putting it in play .

 

[FrankG]

What are your thoughts on "Polishing" the Bores of the Six flute barrels , before shooting them ? A fine grade "lapping" process to assist in potentially reducing , or eliminating the Burring issue . Since I have two ; I am considering doing this to one of them before putting it in play .

You mean 6 groove barrels/bores. Not 6 flutes on the outside of the barrel correct?

I'm going to assume there is no burr in the bore at all to begin with.....

So in saying that and either way you can't get around the conventional rifling. In conventional rifling the lands meet at the top edges and basically down at the grooves with pretty much a 90 degree corner/edge. It's this hard edge of the lands that's putting the burr on the bullets jacket. Most likely the driving side of the land. The bullet is being forced/jammed against the driving side of the land and the hard edge is what's causing it.

Also being an even groove barrel you have one land directly opposing another land. So the bullets jacket is getting deformed more. That's probably not helping anything and both things are working on each other.

Later, Frank

 

[DukeDuke]

I wonder why some barrel makers continue with the 6 grooves bores.

 

[Acyr]

I wonder why some barrel makers continue with the 6 grooves bores.

In the last 5 years, 6 groove barrels have won multiple State, 2 National and 1 world championship in F Class competition.

 

[DukeDuke]

I see.
good to know!

 

[BradY]

Try a regular 200H. They were easier to get to shoot when I got FTR. 2670fps they hammered. 2710 was great too but case life was definitely less. That was a 1:10 bartlein 5r. If I was shooting ftr again I would be using the same. 30 inches HV profile was all that was needed. But 28” really hammered too.

 

[FrankG]

I wonder why some barrel makers continue with the 6 grooves bores.

It's what some places are tooled for or only what they're machines are capable of doing. That's the biggest determining factor usually.

It's also what a given caliber can be possibly spec'd as being Saami standard. So they tool up for that spec and nothing else. 243win for example the Saami spec. is 6 groove. This is another variable.

Depending on caliber we've done 2 groove (don't ask for one...your not getting it), 3 groove (again don't ask for one...your not getting it), 4 groove, 5 groove, 5R, 6 groove, 7 groove and 8 groove.

Again some calibers need or have to have a specific number of grooves. Take for example 408ct barrels. Original spec is 6 groove but our two biggest customers want these to be made in 8 groove configuration. 50BMG barrels standard spec is 8 groove but we've done them in 7 groove also.

Some calibers like in 416 we can do 5R and the standard 6 groove but after 416cal the groove dimensions wont' be proper to do a 5R or 5 groove barrel. So you have to go to a more numbered groove barrel.

 

[D-4297]

Thanks for the response , Frank . As a retired Tool-maker , I read a little into it , and having two barrels , I will do the polish of the Bore on one . At worst ; it can only "Break" the sharp corner at the top of the Lands , and create a slight improvement . Can't improve things if we don't do a little experimenting .

 

[XTR]

My suggestion is to slow it down and try again. There are an absolute s#!+ ton of long range FTR shooters hammering lights out with 200s at 2650 give or take 30 FPS. (Assuming the chamber is cut for it.) … We’re talking about cleaning F class targets for 20 shots at 1000 yards.

YMMV

 

[mgunderson]

Enjoyable thread, discussion, and group of participants. Combustion is an interesting beast. Orig author has proven the barrel shoots. That's a big hurdle. Big bullets in a 308 are challenging and it seems we are chasing velocity too. Slow it down or speed it up.... the bullet is not happy there! Logic says slow it down or the pressure will bite you. Try a different powder. The system is not happy. You need to keep an open mind. Some combos do not work in some barrels. You can fight it and struggle or change something....

The combo is telling you it's not happy.

 

[William Vogel]

I really think it’s a load problem. Using a load from a different barrel is probably going to be off. I have a 6Dasher that is the sister rifle to that of the Smith that built both guns and my load is different from his. As far as grooves, I have an old Remington 700 factory barrel Police model 308 that shoots 168’s 2820 and it shoots 2 1/2 inch groups @ 700 yards and through the same hole @ 100 yards. It’s a 6 groove 12 twist factory barrel. Your barrel might be the problem but because it shoots the 185 so well, you should adjust your other loads and test. I never expect two guns to shoot the same load and because you changed the gun, it’s like a second gun.

 

[cmysix]

33 a bit long, ain't it? cut it down to 28