5R cut rifled barrels not recommended by Krieger in 6mm - slower twist then 1-9t

[mwezell]

I wouldn't think LT30 would increase the starting pressure but change the slope of the pressure curve. Thicker brass, stronger brass, steeper lead angle, harder bullet material I can see increasing the starting pressure.

Thanks Joe. I think you are spot on.
I probably should have asked if faster powders might overcome the lower starting pressure of the R type rifling, in turn, addressing the potential loss of accuracy discussed here. Reason being, the pressure would come earlier as compared with 133, for example.

 

[Frank Green]

Less jacket deformation likely translates to lower starting pressures. If that's relative to the issue of poor accuracy from the 5R style rifling in slow twist, light bullet combinations discussed here, could we not go about reaching more optimal pressures by other means, such as powders? The new LT30 comes to mind.
Thanks!--Mike

I cannot comment one way or another with the shorter jackets/bearing surface and starting pressures if that is the case or not.

For the most part total surface area of the bore/grooves effects pressures. Not the style of rifling with everything else being equal.

When we make ammunition test barrels for ammo makers, bullet makers, gun manufacturers etc....there is in most cases on standard calibers (not wildcats) bore and groove specs. as well as twist and groove width etc...also listed is the total min. surface area that the barrel is suppose to be.

We've made ammunition pressure test barrels with 5R rifling for .300wm, .338 Lapua and .308win.....and the lightest bullet being tested was a 175gr match bullet in the .30cal. but there was no difference in pressures and velocities between a conventional 4 groove and the 5R style rifling. This is the feed back I've gotten from the ammunition makers. Like 5 different ones. The test barrels had the same chamber reamer used in them and the bores and grooves were made to the same specifications as far as size goes. The only difference was the number/style of grooves.

So if the above is any type of an indicator I would lean towards the answer being no. As well as Randy R. comments about our 5R barrels shooting the .30cal. Ten ogive bullets just fine but other brands he wasn't getting the same results. Reread Randy's post.

We've done a couple in 6.5mm calibers and one in a fast twist 6mm as well in ammunition test barrel with 5R rifling also.

Later, Frank

 

[Joe Woosman]

Thanks Joe. I think you are spot on.
I probably should have asked if faster powders might overcome the lower starting pressure of the R type rifling, in turn, addressing the potential loss of accuracy discussed here. Reason being, the pressure would come earlier as compared with 133, for example.

The large bore Hart barrel I was working with was a mediocre shooter. I did try H322, N130 and H4198 and it didn't get better than N133. It did respond to more neck tension though. Not sure that explains anything.

 

[Wilbur]

Frank wrote - "I feel the bullets quality and size has a lot to do with it as much as the barrel does. "

Seems this is important to the discussion. I've mentioned that I once made some really fat 6mm bullets that would go one of two ways - really good or really bad. The rifles that shot them "really good" wouldn't shoot as well with smaller diameter bullets. So, I'm just saying that the difference between a mediocre barrel and a great barrel could be the bullet diameter...or the barrel diameter...either one. This question and I'll shut up - why do barrels shoot better with a particular bullet given that all bullets tried are proven good by other means?

 

[Jefferson]

if you take about 2 tenths difference in the bullets you are using


and take 2 or 3 tenths difference in the barrel you are using (more or less if it is a tight bore)

then your results MAY be significantly different than you were expecting


Jefferson

 

[Frank Green]

Frank wrote - "I feel the bullets quality and size has a lot to do with it as much as the barrel does. "

Seems this is important to the discussion. I've mentioned that I once made some really fat 6mm bullets that would go one of two ways - really good or really bad. The rifles that shot them "really good" wouldn't shoot as well with smaller diameter bullets. So, I'm just saying that the difference between a mediocre barrel and a great barrel could be the bullet diameter...or the barrel diameter...either one. This question and I'll shut up - why do barrels shoot better with a particular bullet given that all bullets tried are proven good by other means?

Wilbur, As you've noticed there are a ton of variables. I feel a lot of times the barrel are blamed for not shooting good when at times it's the bullets or other things. I'm not a bullet maker but I do know the bullet dies will wear as they are used over X amount of bullets being made.

I won't say who the maker or what bullet it is as that would give it away but they are heavy 6mm bullets (over 100gr.) I've had some lots that would hold 1/3moa at a 1k yards and some lots that wouldn't do any better than 3/4moa no matter what I did at any distance. I gave up on shooting those bullets. Still a great bullet maker and I still buy they're bullets just not those one particular bullets.

Later, Frank

 

[Frank Green]

if you take about 2 tenths difference in the bullets you are using


and take 2 or 3 tenths difference in the barrel you are using (more or less if it is a tight bore)

then your results MAY be significantly different than you were expecting


Jefferson

Jefferson, On bore size do you mean the physical bore size (tops of the lands) or the groove size? I don't feel the bore size is that critical. I think the groove size makes more of a difference. A .0001" or .0002" on the bullets or the groove I don't think that has a huge impact on accuracy.

but

I did a few years ago shoot a button rifled barrel (match barrel supposedly) by a brand name maker for testing (I won't say who made the barrel as that is not the point here). That barrel was a .308win. caliber barrel. The bore size was .301" and the groove size was .309". That is a full +.0005" over the max. Saami spec. That barrel shot good but nothing better than 3/4moa. Most of the time it was around 1moa.

Again it goes back to what I always say.....what is your accuracy requirement and what are you using the gun for.

Later, Frank