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 also discusses a high 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.

 

[JAS-SH]

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 don't agree. It's just a reflection of a part of the barrel that might be wearing out a little slower right at the front end of the erosion area. All rifles do that especially high power rifles. And it's probably more reflection than wear. These type of images don't tell you much about how a rifle shoots.

Rifles that shoot well start doing so from the get go, no need for borescopes. Then, get tighter and tighter groups until they settle. I just broke in a 6mm GT rifle. It took 202 shots to break it in. Shots 200 to 202 went into a .14 inch group (pic below). That rifle never shot any group over .48 MOA.

If your rifle was shooting bad, or not as good as expected from the get go what you show in that pic is not the cause. It's something else.

Pic:

 

[GBMaryland]

I don't agree. It's just a reflection of a part of the barrel that might be wearing out a little slower right at the front end of the erosion area. All rifles do that especially high power rifles. And it's probably more reflection than wear. These type of images don't tell you much about how a rifle shoots.

Rifles that shoot well start doing so from the get go, no need for borescopes. Then, get tighter and tighter groups until they settle. I just broke in a 6mm GT rifle. It took 202 shots to break it in. Shots 200 to 202 went into a .14 inch group (pic below). That rifle never shot any group over .48 MOA.

If your rifle was shooting bad, or not as good as expected from the get go what you show in that pic is not the cause. It's something else.

Pic:
View attachment 8688014

Yeah, I had that happen with a 65 CM PVA CF barrel that I was shooting at Frank Galli’s course and during the first 70 rounds of the course something changed with respect to the barrel and that was that it sped up nearly 100 ft./s

Got a little more accurate, but generally, it sped up.

 

[JAS-SH]

I think at this point I would try another scope. Check everything and monitor / check the action screw torque between strings. I had issues with a magnum once and the cute was to bed the action and use a small amount of lock tight on action screws. I would not rule anything out and get a bit more methodical about eliminating one thing at a time.

Leave the scope replacement for the last diagnostic step. Easy steps first. Have someone else that is competent with high power shoot the rifle. If that's not possible then take the rifle apart to make sure everything is lined up with the chassis and carefully re-torque everything. Do all of that first first.

Then and only then you look at replacing the barrel. AND, use factory ammo! You can use reloads later. If a rifle really shoots it will shoot really well with Hornady factory ammo.

 

[JAS-SH]

Yeah, I had that happen with a 65 CM PVA CF barrel that I was shooting at Frank Galli’s course and during the first 70 rounds of the course something changed with respect to the barrel and that was that it sped up nearly 100 ft./s

Got a little more accurate, but generally, it sped up.

Not unusual at all. My new 6 GT went from the mid 2700s to 2900 and change in the first 150 rounds. That's from the original barrel erosion. All with factory ammo (same lot#). When I get a new rifle I shoot factory ammo exclusively for testing. I buy a 200 round case so I can use the same Lot#. These days factory ammo (same lot#) is quite accurate.

 

[Jrb572]

You lucky bastards. I never get any gain in my velocity after a few rounds down the barrel. Maybe 10-20fps. But nothing more than that. Now going from virgin brass to once fired I have seen some gain occasionally.

 

[EXSOCAL]

The chambering looks fine. Nothing I would worry about. Not saying you (OP), but people love to get their bore scopes out and nit pick every microscopic imperfection in the bore and chamber and blame shitty shooting on these things. 9 times out of 10 it's the shooter or ammo. I build rifles for a living and had the fortune of seeing some pretty grotesque chambers and rifling on rifles that come into my shop that still stacked bullets.

I just helped another SH member with a 7 PRC that wasn't getting the accuracy he expected. I went through the whole rifle, which was also built by another reputable smith in southern Idaho. What I found blew my mind and these are things you may be inclined to check if you have the time and tools. First, the crown was extremely rough. There was no sharp edge to it. Whether it came to him like this or something happened during cleaning, I have no idea but that is a red flag for accuracy. Second, I made the call to take the barrel off and re-crown it. When I did so, I was able to remove the barrel from the receiver with a little more than hand pressure... I probably could have loosened the barrel by hand had I tried that first. Literally zero torque. Now, in a lot of cases having a hand tight barrel works, in fact benchrest shooters do this and we only hand tight the barrels on the Terminus Zeus QC actions (albeit they are retained by set screws), but the standard in non-quick change repeater rifles is a barrel torqued on with anywhere from 70-110 or so ft lbs of torque. Between re cutting the crown and torquing the barrel to spec, this rifle went from 1.5-2" to .5" with the same ammo.

In a nutshell... systematically go through everything. After you shoot, a nice little test is to stand the rifle on the butt and loosen the rear action bolt. Index your off hand so it is touching the stock and action so you can feel any movement and loosen the front action bolt and see if the barreled action drops back in the stock to the rear. If that happens, bedding is in your future. Check all action bolts, I use 60 in lbs or torque on those and blue loc tite in some cases. Check scope rings to ensure they are tight up against the front of the picatinny slot and torqued properly. Check scope cap rings and torque to scope manufacturer's spec. Get a magnifying glass or jeweler's loupe and inspect the crown. Make sure you are judging accuracy with a fouled barrel. Barrels have different "personalities" and some like to be a bit dirty.

Ammo... ammo is huge. I've never had the best results with any Hornady bullet. To me they are just decent.... I'd try some Bergers, specifically the 245 EOL. You opted for a twist rate that suites the heaviest 30 caliber bullets so put it to use. Spinning the living daylights out of a lighter so so bullet won't do you any favors in the accuracy department. Run a bullet better suited to your fast twist and I'll bet you have better results. The 245 EOL is incredibly easy to load and tune, more so than the 245 LRHT in my experience, at the cost of only a slightly lower BC.

Shooting... I don't pretend to know your shooting experience, specifically with heavier recoiling rifles but In my 20+ years of doing this and training people, heavier recoiling rifles are harder to shoot small with unless you've done it a lot. Even experienced shooters get a little jumpy on the trigger after a few rounds in anticipation of the recoil. I have a good buddy who shoots a 6 BRA like a house on fire, you put my .25 MOA 300 NMI in his hand and he's a 1.5" shooter at best. Not saying that is you, but something to be aware of in the journey to sort this out.

Barrel.... I have a couple X Caliber barrels on personal rifles... nothing precision based (300 BLK / 375 Raptor). My experience with them is limited but they do appear to be good. Would that be my first choice for an all out, high-end precision build, as others have said, nope. Bartlein, Brux, Proof are where its at with a few other really good manufacturers out there like Ace, Benchmark, Mullerworks, and others. Now, if your barrel the culprit? Probably not. Your chambering appears concentric from the limited pics, and based on what I've seen the X-Caliber blanks are just fine... but then again, any manufacturer can put out a bad barrel from time to time. That would be the final thing I looked at.

Be systematic in your approach to tracking this down. If the rifle checks out, turn to ammo. Some rifles just don't like certain bullets and even powders. Like my good buddy says, don't try and fit a square peg in a round hole. Just move on and try something else.

I hope that helps, please feel to reach out if you need any help.