Progressive twist rifling

[feelinducky]

I have currently been shooting my 270WSM 24" Brux, I'm hoping you guys can help me some questions.

I have been using the 129g Barnes LRX trying to get a good load worked out. I have only been able to get a max velocity of about 3100fps and that is with a firm bolt lift. I have not been able to get this bullet to work in my current rifle. I have used many different powders and primer combinations along with seating depth. Never being able to get any decent grouping. The last load I tried was with RL 26 and the groups were average but nothing stellar running about 3050fps. I finally decided to change bullets thinking that maybe my rifle doesn't like this bullet.

I tried some 130g Barnes TTSX that I had and began load work up with RL26. Using the book charges were between 66.0g and 69.0g. Book max is 70.3g. With 69g I'm now getting a little over 3400 fps and the groups are looking good, it is my current hunting load.

What stumps me is why is there such a velocity spread between these 2 bullets? So I'm wondering is it bearing surface between the 2. I have attached a picture the 129g LRX is on the Left and 130gTTSX is on the left. The LRX has 3 grooves and the TTSX has 4 groves.

Funny thing looking at the ballistics with the Berger calculator:
129g LRX:
3050fps: 700yds=velocity 1758 drop 101.49 wind (5mph) 19.66
130g TTSX:
3400fps: 700yds=velocity1801 drop 87.73 wind (5mph) 20.92

With theses numbers if the LRX shot well in my rifle, why should I bother with the extra cost of the LRX? It's not much of an LRX as they advertise.
Would a progressive twist barrel change some of the pressure problems associated with the LRX bullet?

I would like to build a 300WSM for backpack hunting, however, living in California I have to shoot copper bullets only. I'm looking at the Hammer and Cutting Edge bullets to fill my need here. I'm also going to be purchasing a new barrel and was wondering if a progressive twist barrel would help with some of the pressure spikes in the copper bullets.

I know that this is just one rifle with 2 different bullets, I'm not stating that this is true for everyone. Does this happen in other rifles? Has anyone else seen this?

Thanks for your time.

 

[RockyMtnMT]

I have currently been shooting my 270WSM 24" Brux, I'm hoping you guys can help me some questions.

I have been using the 129g Barnes LRX trying to get a good load worked out. I have only been able to get a max velocity of about 3100fps and that is with a firm bolt lift. I have not been able to get this bullet to work in my current rifle. I have used many different powders and primer combinations along with seating depth. Never being able to get any decent grouping. The last load I tried was with RL 26 and the groups were average but nothing stellar running about 3050fps. I finally decided to change bullets thinking that maybe my rifle doesn't like this bullet.

I tried some 130g Barnes TTSX that I had and began load work up with RL26. Using the book charges were between 66.0g and 69.0g. Book max is 70.3g. With 69g I'm now getting a little over 3400 fps and the groups are looking good, it is my current hunting load.

What stumps me is why is there such a velocity spread between these 2 bullets? So I'm wondering is it bearing surface between the 2. I have attached a picture the 129g LRX is on the Left and 130gTTSX is on the left. The LRX has 3 grooves and the TTSX has 4 groves.

Funny thing looking at the ballistics with the Berger calculator:
129g LRX:
3050fps: 700yds=velocity 1758 drop 101.49 wind (5mph) 19.66
130g TTSX:
3400fps: 700yds=velocity1801 drop 87.73 wind (5mph) 20.92

With theses numbers if the LRX shot well in my rifle, why should I bother with the extra cost of the LRX? It's not much of an LRX as they advertise.
Would a progressive twist barrel change some of the pressure problems associated with the LRX bullet?

I would like to build a 300WSM for backpack hunting, however, living in California I have to shoot copper bullets only. I'm looking at the Hammer and Cutting Edge bullets to fill my need here. I'm also going to be purchasing a new barrel and was wondering if a progressive twist barrel would help with some of the pressure spikes in the copper bullets.

I know that this is just one rifle with 2 different bullets, I'm not stating that this is true for everyone. Does this happen in other rifles? Has anyone else seen this?

Thanks for your time.

I think I spoke with you on the phone the other day. If it was not you it was someone else with the same basic question.

From my end I will answer the pressure question. With our PDR (parabolic drag reduction) technology, the engraving forces are greatly reduced. The PDR because of the multiple radius on the baring surface there is just enough bullet surface in contact with the grooves to seal the bore. The actual contact is taken to a very small amount. The down side of the PDR, or the valleys, are deeper than the bore dia allowing the displaced copper from the rifling a place to deposit. Because of the shape of the PDR the rifling as it engraves the bullet is increases the amount of bullet it engages as it engraves deeper in to the PDR thus giving plenty of 'meat' for the bullet to fully engage the rifling and not have any trouble with spinning out. Spinning out meaning slipping in the rifling and not fully stabilizing. The bullets are plenty tough to handle launch in big horse power heavy bullet combos with the same exact design as in our smaller bullets. The need for a progressive twist rifling is not needed with our bullets. Because of the PDR on the Hammer Bullets they do not have the high pressure typically developed by non lead bullets. Usually they will run a little lower pressure than like weight cup and core lead bullets. In most rifles producing a little more vel than is typical for the bullet weight. So as the bullets ease into full engagement with the bore and grooves because of the PDR, it eliminates the problems typically seen with other all copper bullets.

I hope this helps.

Steve