General effects of 1-11 barrel twist on pressure and velocity

[EastHumboldt]

I’m relatively new to reloading. It’s my understanding that most 30 cal Tikka barrels have a 1-11 twist and I’m pretty sure that’s true for mine. In contrast to “standard“ for 30-06 at 1-10 twist. I’ve loaded a few different powders and bullets to find what my T3x in 30-06 might like, and I’ve found my measured velocities at max listed loads fall 80-100 FPS below listed velocity. Also no signs of over pressure. So I’m thinking of cautiously pushing past max .2 grains ata time.

All other things being equal..(which I know they never are) Does the 1-11 twist result in slightly lower chamber pressures than 1-10?

 

[Bubblehide]

I believe the Tikka barrels are not as tight as some other companies, and that accounts for being able to push past max ( a bit) without showing pressure signs, i.e., "lower chamber pressure".

 

[smoothie25]

This is an interesting subject and something I've wondered about as well. I have a Tikka 11 twist and am about a grain over max powder charge and under book max velocity.

Does a tighter barrel twist build higher pressure than a slower twist barrel, all else being equal?


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[Trippy]

While I've seen many say Tikkas shoot on the slow side I've also compared some loads in Quickload to the Nosler book. Nosler book speeds were always higher for the same charges, sometimes up to 75 fps more. From an email correspondence with Berger, they stated their data was derived using Quickload although I only have a few cartridge pages from them. Their max charges were usually on the conservative side whereas Nosler is a bit closer to software max from what I recall. It's just a computer program with a lot of variables though, same could be said for any manufacturers using tests for data. My one Tikka still needs a ladder test so I haven't used my chronograph on it.

Edit: I had a 7 RM that shot pretty close to the speeds Quickload spit out which were far below Nosler's book data for 160 grain Partitions. It was a slower twist rifle compared to some others.

 

[EastHumboldt]

Ok when we’re talking about a “slow “ barrel .that means the design of that barrel produces slower than usual velocities?

 

[EastHumboldt]

you would assume a faster twist wuoild make for more friction. Just as a thought experiment if the twist was 1 in 3 the steep angle of the lands would make the barrel feel almost like a corrugated culvert.

 

[Wrench]

Diameter, shape of rifling, twist and freebore all play into velocity....then add in chamber size, brass thickness, bullet diameter, powder / primer lot variations, scale accuracy, chronograph accuracy and bc accuracy of the bullet and jacket material / slug up.

Anything that creates resistance increases pressure which increases velocity for the most part. Twist impacts velocity in a minor way and is more important when looking at the Greenhill charts than the chronograph.

 

[wind gypsy]

I believe litz tested the twist and pressure relationship and didn’t find significant differences.

 

[SamsonMan22]

A lot of it depends on your free bore and possibly your brass from my experience. Every barrel is different I had a Ruger that at book max was around 150fps slow. I was jumping around .230” to the lands at mag length, I went enough past max to make me nervous and still had zero pressure signs. Even with soft federal primers I had no flattening, no cratering and no ejector marks on the brass. I have a nosler 48 right now that shows pressure signs around 3 grains under nosler’s max for the powder/ bullet combo and is making their advertised velocity with the lesser charge. The jump is only around .050” at Sammi max coal.

Some manuals are conservative and others show charges that are too high for particular rifles. Using velocity can be a good indicator of pressure but even that isn’t always true. I had a kimber 30-06 that I had Hart rebarrel, that barrel was extremely fast around 150fps over max book velocity with no pressure signs, same twist same # of lands and grooves, and length as the original kimber barrel but a lot faster even with less free bore.

Using certain brass makes a difference loading with lapua brass in my 308 which has less capacity than some may show slower velocity and pressure at lower charges, in a 300 win I was able to get more powder in Norma brass before seeing pressure signs and that resulted in more velocity and charges that were often higher than book max.