Twist for 153.5 in 6.5 PRC

[choprzrul]

100' elevation:


6600' elevation:


Difference? Yes.

Significant? Idunno.....

I guess I'd have to calculate out the RPM for each. I believe Berger told him 280,00 RPM max....

 

[dnellans]

100' elevation:
View attachment 1341140

6600' elevation:
View attachment 1341142

Difference? Yes.

Significant? Idunno.....

I guess I'd have to calculate out the RPM for each. I believe Berger told him 280,00 RPM max....

Right, but max velocity (and rpm) is always right out of the muzzle. If it doesn’t blow up immediately, it’s unlikely to blow up as it’s slowing down in either condition. People see the poof down range but the damage is done much earlier as it’s tearing the jacket off.

 

[FrankG]

It's not just rpm that can cause a bullet failure issue.

There are other things that can cause it or it can be a combination of things causing it.

Bullets themselves could have a problem.

How many rounds are on the barrel? The rougher the throat the more the bullet will take a beating when it makes the jump into the rifling.

How is the barrel being cleaned....how many rounds in between cleanings?

Is there damage to the bore of the barrel (from when it was made new or from improper cleaning etc...)and or the crown?

What bore and groove size is the barrel?

Does the barrel have standard/conventional rifling like standard 4 groove or standard 6 groove etc...or does it have 5R rifling?

My 6.75 twist 6.5CM on one of my guns has not had a single bullet failure issue so far (I know I'm on borrowed time). I'm spinning bullets as fast as 298,666 rpm. I've shot 140Amax, 147Eldm's, 150smk, and 135 and 153 Atips.

I will say this the hard line in the sand is 300k rpm. You start approaching that number and for sure when you start going over....expect to see a problem sooner or later.

We all pay a price to push that envelope.

Later, Frank
Bartlein Barrels

 

[wboggs]

I've got three 6.5CM up and running. Two barrels are 7.5 twist and one is 6.75 twist. All have shot great. I've put 140Amax's thru them along with 147's, 150SMK and the 135 and 153 Atips. All 3 of these barrels are 23" finish length.

Really close to getting a 4th 6.5CM up and running. It will also be 23" might be 24" finish. Still have to cut and crown the muzzle and put it on the action. Picked up a nos Savage original left hand silhouette stock and have a late 60's left hand Savage 110 action and basically built the rifle from parts. Savage never listed a silhouette rifle from the factory in left hand. I found the stock on Ebay still brand new and picked it up for a $100. Being a lefty I couldn't pass it up.

I just finally got my 6.5PRC barrel on my F open gun this morning. That's a 7.25 twist. I should be able to get a few rounds on it tomorrow or Saturday. That barrel is 32" finish length. Only bullets I plan on running are the 150smk and the 153Atips.

Later, Frank
Bartlein Barrels

I have found a node at 3120 with the 150 smks in mine

 

[dnellans]

I have found a node at 3120 with the 150 smks in mine

RL-26? I haven't been able to get that fast with any other powder and the 150's

 

[wboggs]

H1000 with 30" Bartlein 7.5tw. RL 26 gives about 50fps more. I did a few tests with RL26 but accuracy was very good with H1000 and I wanted to limit riund count

 

[FrankG]

H1000 with 30" Bartlein 7.5tw. RL 26 gives about 50fps more. I did a few tests with RL26 but accuracy was very good with H1000 and I wanted to limit riund count

H1000 is what I'm going to be loading in mine as well. Hopefully I can send a few rounds down range tomorrow. I've got to load up the ammo tonight after work....but weather might throw a wrench in the works. Suppose to rain most of the day tomorrow. Sunday I have a wedding to go to. So Sunday is out all together.

 

[wboggs]

F215m gives additional 25fps over m210 but increased sd.
It will be interesting to see how the A-tips shoot for you.
The 153s were 90fps slower than my same load using 150smks. They are too expensive for me unless there is a great advantage to using them. But, I have not checked for accuracy since the smks will shoot in the 3s if I am on that day.

 

[wboggs]

F215m gives additional 25fps over m210 but increased sd.
It will be interesting to see how the A-tips shoot for you.
The 153s were 90fps slower than my same load using 150smks. They are too expensive for me unless there is a great advantage to using them. But, I have not checked for accuracy since the smks will shoot in the 3s if I am on that day.

I got a bit off topic and have tested for bullet blow up with my 5R 7.5 tw barrel. Some old sierra 85 grs were run up over 3500fps and were shot 5 rounds rapidly. Hugh jump and no blow up.
Then I started loading some new 107 smks to around 3300 using RL17. Again no blow up and I was able to seat 0.015 off. Grps 0.34moa and I have started using this load for steel to 600 and conserving my low supplies of H1000 and F210m.
I am sure some blow ups would occur with 20 shot strings during competition but the point of this is that you can enjoy the prc by shooting slowly and limiting shot strings even using a 7.5 tw.

 

[Hohn]

Thanks. I couldn’t find it in the menus or by searching. I think when they added the ballistics calculator they accidentally eliminated The tracks to the stability calculator so that you need the URL to find it.

So, you can shoot that bullet in an 8 twist but the calculator says marginal stability at sea level, and that is true whether you are at Creedmoor or PRC velocities. If you only shoot at 3-4000ft plus, 8 twist is golden.

Velocity isn’t nearly the stability lever so many people seem to think it is.

 

[wboggs]

I was hoping to see some results from FrankG but guess he didn't make it to the range.

 

[FrankG]

I was hoping to see some results from FrankG but guess he didn't make it to the range.

I only got three rounds on it Sunday morning before I had to leave for a wedding!

Shot 10 rounds yesterday after work. Medium powered load. Avg. velocity was 2840fps. I cleaned the barrel last night.

I got some other ammo already loaded up ( but it's a max load and I'm stepping on it!) but before I shoot those I'm loading some more ammo tonight. I'm going to load up another 10-20 rounds with a different powder charge and two different primers. I might load two different bullets also.

I only want to put another 10 rounds on it and clean it before I start beating the hell out of it and putting 60 to 80 rounds on it at a time.

Suppose to rain tomorrow and Thursday. So I'll try and get rounds on it Friday before I leave for the weekend with the chronograph set up again. If I do get some more rounds on it I'll post Friday night with a update.

Later, Frank

 

[wboggs]

Thanks Frank. Many of us look forward to your results and comments.