Barrel wear or a manufacturing problem?

[JAS-SH]

When you build a rifle and you know all the components that go into the build diagnosing problems becomes really easy.

Diagnosing problems is based on assumptions based on facts and experience. The big elephant in the room - the shooter, is looked at first. Powerful cartridges require more from the shooter. So, can the shooter handle the recoil? If the shooter is experienced with large cartridges then there might be a problem with the rifle. Simple process of elimination. And so on...

Then to the rifle. Assuming (but tested assumptions) that the rifle is put together correctly the next question is - was there a gunsmith involved, and if so, did that person have a good track record, and most importantly, experience with chambering the particular cartridge?

Diagnose from most likely to less likely. In my personal experience it tends to go that way. The latest problem I personally encountered was the result of a problem with the contact between the stock and the rear bag. Way down the list but it did not take very long to find.

All that said and done, the barrel is usually the culprit. And that includes the gunsmith if there was one involved.

 

[Aftermath]

That specific Berger calculator is flawed, it's only good to tell you if you don't have enough twist, it DOES NOT tell you that you have too much twist. Put in their 300 230gr, fps 5000, twist of 1, it says you are good to go.... blahhahahaha, BS.

Also not clear to me where the accuracy is failing, is it 100yds, or 1mi? I assumed this 300PRC build was for long distance.

More digging for punching one hole at long distance, is showing up that you choose a twist on the low end of rpm's that stabilize the bullet+muzzle fps, and when you get near max rpm's for bullet the accuracy starts to suffer. I myself cannot validate that, others can though.

Not flawed at all, maybe misunderstood.
Sure.
5000 fps is stable. Of course it is. That fucker is spinning.
Sure...round construction would dictate whether it would stay together but the SHAPE is good to go.
Notice that it IS stable as OP advertised velocity, etc. Try using other, slower twist rates, as you have stated.
Now...try decreasing velocity and see just how slow you can go with good stability.

 

[Genin]

Thermal shift from the carbon barrel? I know for my carbon barrels I will absolutely have a shift after 10 rounds if I do not allow them to cool (less in my PRC). Even though they look like those big fat truck axel steel barrels, they don’t necessarily behave like them in my experience. Once again, just something I’ve observed personally. Might consider that if you get another barrel. Get a good old steel pretty fluted one or something.

 

[Baron23]

You need glasses then. This is a machining anomaly. Nothing to do with normal fire cracking.

View attachment 8686432

Are you familiar with with machining?

I have zero idea why you are upset. I said nothing offensive to you at all.

As for that little spot in the groove, dunno what it is. Looks a lot like the reflection seen elsewhere it the pic. Ot it could be a very small flaw. I can’t really tell

Cheers and I hope your day gets better. Positive energy, yeah

 

[lash]

I have zero idea why you are upset. I said nothing offensive to you at all.

As for that little spot in the groove, dunno what it is. Looks a lot like the reflection seen elsewhere it the pic. Ot it could be a very small flaw. I can’t really tell

Cheers and I hope your day gets better. Positive energy, yeah

I’m not upset. No real insult intended.

 

[Evintos]

Would a chassis problem settle down after 10 rounds and then start to hammer? Or would it be random shit constantly.

Random shit constantly.

OP needs to start over. Orient barreled action and Chassis vertically (muzzle up), ensure recoil lug is making contact with the chassis' recoil lug abutment, torque properly (double check action screw torque after the first few rounds), double check scope base torque, scope ring torque, remove suppressor (eliminate suppressor as factor), etc.

If it was me, I'd check the recoil lug to chassis fitment first. If it isn't making contact or making partial contact, (uneven anodizing wear), bed the rear of the recoil lug so there is full contact. Having the action screws take the brunt of the shear force will eventually cause the action screws to fail in addition to the random POI after recoiling.

 

[GBMaryland]

What the OP needs is a TRG-42A1 with a 300WM BBL and a 300PRC CF Bartlein by Mission Specific!

It calls to you.... just say'n!

 

[610yd]

Not flawed at all, maybe misunderstood.
Sure.
5000 fps is stable. Of course it is. That fucker is spinning.
Sure...round construction would dictate whether it would stay together but the SHAPE is good to go.
Notice that it IS stable as OP advertised velocity, etc. Try using other, slower twist rates, as you have stated.
Now...try decreasing velocity and see just how slow you can go with good stability.

SG 1 to 1.5 is considered "stable". Less than 1 is no-go, more than 1.5 falls into the unpredictable area.

It's not just about destruction from spinning forces, too much spin impacts flight (pitch/yaw/Ip/Sd/Sg/ etc) as it travels. Just like too little is no good, same applies to too much spin, the RPM's is a window. Most data however only defines that window in terms of bullet self destruction, very little data that shows flight characteristics as a function of spin RPM. Flight characteristics are more significant in obtaining accuracy and precision.

2830fps in 1:8 is getting close to max RPM's. Hornady told me cup & core max 295k, Berger tells me 300k.
We must also consider the "massive" non-uniform drag forces that arise from bullet deformation from rifling and the RPM's as the bullet travels. Literally no data that defines this rotational friction and how it impacts flight.

I guess what I am saying, from all the info I can gather, the sniper folks appear to choose lowest RPM's that put the bullet SG in the 1-1.5 area, which means loading the round to achieve an FPS that matches desired SG("rpm") for whatever twist rate the barrel is. More spin for any twist rate means kicking the bullet harder in it's rear. And if you look at the setup in say a 1:10 or 1:12 (vs the 1:8), you can maintain same spin but achieve higher FPS, as long as chamber PSI is safe. More FPS usually equates to more reach.

Lots of good readings out there:

Barrel Twist and Bullet Stability

Barrel twist rate has a real impact on your rifle's accuracy - here's why

bisonballistics.com

Bullet Stability

The details of gyroscopic and dynamic bullet stability

bisonballistics.com

 

[GBMaryland]

Yeah, I had MS make that 300PRC BBL a 1:9.

The 300WM is 1:10 and is stabilizing 180WTC solid copper bullets (which is 225gr lead core class/size) to the point that are same hole at 100 yards and about 1/2in at 300 yards.

Rifle also stabilizes 225 ELDM without any issues... also same hole... not the same velocity...

The SD on the WTC 180 could’ve been better, but I used a whole bunch of Peterson brass I had lying around that had never been shot before… History tells me that the first reload on that brass will cut it down in half.

I can only imagine what velocities I get out of a 300 PRC…

 

[Evintos]

 

[610yd]

Notice #2 in that rate page, it might be misleading to most. If SG=9 that does not mean it's good, but if I take what it says literally then SG=9 is ok. Not so. There is a crossing point where maxRPM crosses over some SG #, and IIRC you get to maxRPM before getting to a horribly high SG # (for many bullets). Also recall that the "maxRPM" number is a self-destruct number, we could reach an RPM that is lower than maxRPM but yield a horribly high SG.

To be honest, not sure why FA writes a math statement like that, I suspect they mean design range, more like 1.2 <= Sg <= 1.5
FA discusses too much Sg that yields bad flight.
From Fulton Armory:

Bullet and gun designers usually prefer sg > 1.2...1.5, but it is also possible to introduce too much stabilization.

Reference: https://www.fulton-armory.com/faqs/Genl-FAQs/Fly/stab.htm

Gyro stability seems to be acceptable in the 1-1.5 window, the actual desired # depends on some other factors.
When is SG=1.6 or 1.7 or 1.75 a good number? I guess that requires range testing with loads that are producing SG > 1.5 and you shoot targets within well documented environmentals (temp, RH, elevation, distance, etc etc).

#5 is most concerning. I suspect to achieve #5 the bullet becomes expensive. It's also a bit misleading. Twist rate # by itself does not mean a whole lot, we need to know FPS to obtain RPM's. Might I suspect #5 is in the context of fixed round, so as the twist rate increases so does the RPM's. Once we have a barrel we then have fixed twist and length, so the variable then becomes the round itself. I still argue that the 225gr @2830fps in 1:8 falls into the warning of #5.

One last note: there is no good set of data that defines when SG is too high for any given bullet. Like mentioned, SG could be 1.9 (off the chart for Berger calculator) with RPM's still being below maxRPM, yet 1.9 could be (could be) too high and perhaps places that specific bullet into over-stabilized mode, which will yield bad results.