Pre-range load testing, .408

[Benchrest Braxton]

the 475 grain cutting edge lazer looks like a nice option?

 

[davidjoe]

the 475 grain cutting edge lazer looks like a nice option?

Yes, the “single shot” designation on these bullets really indicates that they have pursued maximum BC above other considerations, which suits this gun well. I thought it was odd that they say G1 is “TBD” but the G7 of .463 and minimum twist rate of 1:11 do look very good to me. The A-Tips indicated a bit more but needed more weight to arrive there, which works against that advantage.

Even the US 869 powder should work well. Your suggestion is a good one and I ordered 100 of them. The rifle should be extremely accurate at distance; its harmonics are as dead as I could make them, short of a true barrel block installed in the forend.

 

[ImBIllT]

IM, ^

Looking at bullet selections that are the proper diameter for this barrel, it’s a little unfortunate that either, one of the separate calibers didn’t die off back in time, or that CheyTac selected this particular one. I’ll stick with this project by the book, though, as I also bought the reamer for any future barrels. For me, needing to tap the bolt closed is a no-go under any scenario, and I won’t neck turn brass. I did tap the bolt handle base for these two test rounds, thinking it was just an alignment issue.

On my fired brass neck sizes, which do rechamber under a closed bolt with zero resistance, each piece measured as indicated below.

I measured five pieces of virgin brass as well.

How are these diameters, relative to expectations?

What does it measure with a bullet seated in a sized or virgin case? Does a bullet drop loosely through the fired cases neck or is there friction?

I’ve shot a rifle as a “fitted-neck” which is where you turn necks to a hair under .001” total clearance in a tight-neck chamber and you can reseat without sizing, so technically it’s not necessarily unsafe if the bullet has a little friction in a fired case neck BUT, fitted necks can by pretty finicky and you can’t make any mistakes. Plus that’s with hand turned necks. If you’re not turning necks, and a bullet had a little friction sliding into a fired case neck, then a different case out of the box might not have any clearance at all, possibly even interference. That can make things blow up. If a bullet takes substantial force to seat into a fired neck, then there absolutely isn’t enough clearance.

 

[davidjoe]

What does it measure with a bullet seated in a sized or virgin case? Does a bullet drop loosely through the fired cases neck or is there friction?

I’ve shot a rifle as a “fitted-neck” which is where you turn necks to a hair under .001” total clearance in a tight-neck chamber and you can reseat without sizing, so technically it’s not necessarily unsafe if the bullet has a little friction in a fired case neck BUT, fitted necks can by pretty finicky and you can’t make any mistakes. Plus that’s with hand turned necks. If you’re not turning necks, and a bullet had a little friction sliding into a fired case neck, then a different case out of the box might not have any clearance at all, possibly even interference. That can make things blow up. If a bullet takes substantial force to seat into a fired neck, then there absolutely isn’t enough clearance.

Here’s a picture of the bullet in the fired shell. Inverted, and the same bullet is used in both pictures for a more reliable comparison between fired and virgin necks. No, it’s not going to fall through that neck at all. It was definitely neck resistance that kept the bolt from going forward without being tapped forward.



By comparison, the virgin brass displaces the bullet even further, below.




Theoretically, looking at the difference between the two, and knowing that both pieces of empty brass chamber equally easily, I would predict that if reloaded, that piece of fired brass would need much less assistance if any, in both seating and in bolt closing, relative to what it did the first time. This is an inescapable conclusion because the bullet sits so much deeper in the fired brass. The neck wall thickness thinned itself out a bit when fired. That would still leave the issue of the jackets being engraved more deeply and I think, blowing up downrange.

But that first time of seating and chambering, that was too much. I don’t really want to seat and measure another one in virgin brass because it won’t come out any other way than by firing.

I follow what you’re saying and a great many shooters do like to neck turn, and looking at the pictures, doing so would definitely overcome that particular issue, but then there is the jacket. If there was any data that says a big jacketed bullet over lead core can endure .008” under spec, and then if charge weights started low down in the true bottom basement range, it would be an interesting tunnel test to see done. I’d read a write up on it. I have found the subject intriguing of how close we just might be to the edge of losing a good portion of our bullets in matches.

I have the personal belief that prior to an outright miss from disintegration, you will likely get a 1, 2 or even 3 minute flyer, where something is happening to the bullet mid flight but it hasn’t come completely apart yet.

 

[ImBIllT]

Here’s a picture of the bullet in the fired shell. Inverted, and the same bullet is used in both pictures for a more reliable comparison between fired and virgin necks. No, it’s not going to fall through that neck at all. It was definitely neck resistance that kept the bolt from going forward without being tapped forward.

View attachment 1406964

By comparison, the virgin brass displaces the bullet even further, below.

View attachment 1406965


Theoretically, looking at the difference between the two, and knowing that both pieces of empty brass chamber equally easily, I would predict that if reloaded, that piece of fired brass would need much less assistance if any, in both seating and in bolt closing, relative to what it did the first time. This is an inescapable conclusion because the bullet sits so much deeper in the fired brass. The neck wall thickness thinned itself out a bit when fired. That would still leave the issue of the jackets being engraved more deeply and I think, blowing up downrange.

But that first time of seating and chambering, that was too much. I don’t really want to seat and measure another one in virgin brass because it won’t come out any other way than by firing.

I follow what you’re saying and a great many shooters do like to neck turn, and looking at the pictures, doing so would definitely overcome that particular issue, but then there is the jacket. If there was any data that says a big jacketed bullet over lead core can endure .008” under spec, and then if charge weights started low down in the true bottom basement range, it would be an interesting tunnel test to see done. I’d read a write up on it. I have found the subject intriguing of how close we just might be to the edge of losing a good portion of our bullets in matches.

I have the personal belief that prior to an outright miss from disintegration, you will likely get a 1, 2 or even 3 minute flyer, where something is happening to the bullet mid flight but it hasn’t come completely apart yet.

I wasn’t suggesting that you neck turn. I was just suggesting that if the bullet doesn’t drop straight through, then you don’t have enough clearance. I only brought up the fitted neck to address the fact that it CAN be done, but a fitted neck is a special circumstance. It looks like your chamber was indeed designed for using .408” bullets. At the very least you would need to have your chamber neck reamed larger to go forward with .416” bullets if you did not plan to turn brass.

I don’t buy the big fliers before midair blowups theory. A number of competitors shooting Berger’s in 243Win and 6.5-284 Norma had midair blowups with no apparent warning. Berger had the thinnest jackets on the market and had to thicken them to cure the problem.

Even so, that doesn’t mean you’ll experience any negative issues shooting a tight bore(assuming your barrel is .401”x.408”). That would likely depend a lot on jacket thickness compared to the bullet diameter. Of course it’s possible that the two bullets you already fired would not have remained intact to 1000yds.

 

[davidjoe]

I wasn’t suggesting that you neck turn. I was just suggesting that if the bullet doesn’t drop straight through, then you don’t have enough clearance. I only brought up the fitted neck to address the fact that it CAN be done, but a fitted neck is a special circumstance. It looks like your chamber was indeed designed for using .408” bullets. At the very least you would need to have your chamber neck reamed larger to go forward with .416” bullets if you did not plan to turn brass.

I don’t buy the big fliers before midair blowups theory. A number of competitors shooting Berger’s in 243Win and 6.5-284 Norma had midair blowups with no apparent warning. Berger had the thinnest jackets on the market and had to thicken them to cure the problem.

Even so, that doesn’t mean you’ll experience any negative issues shooting a tight bore(assuming your barrel is .401”x.408”). That would likely depend a lot on jacket thickness compared to the bullet diameter. Of course it’s possible that the two bullets you already fired would not have remained intact to 1000yds.

Wouldn’t it be ironic if after so much circumspection, the .408 solids that are on the way actually produce more signs of pressure on the primer and case, with the same powder charges than the heavier, lead cored .416’s did?

I’ll definitely be showing a picture of the case heads with the CE .408’s after they arrive. This is just a theoretical materials application type question, but - at their own safe pressure with 7-9 reloads - which would likely be harder on a barrel or cause more fouling, a 408 heavyweight solid with a longish “bearing” surface, gas bands considered, because copper alloy is not very dense, or a cup and drawn, lead core match bullet that is .008” bigger in diameter and heavier, being swaged down?

 

[ImBIllT]

If you have any neck clearance, I would be surprised if either bullet made a huge difference in pressure if they’re the same weight. If you have some interference in the neck, then I’d expect a huge pressure drop, but if you had interference on the two that you fired I’d have expected pressure signs. The fact that your bullet is tight in a fired neck means that you have very little clearance if any, and since your brass isn’t turned, I wouldn’t fire any more of them with .416” bullets for fear that a case might have a thicker neck than the two you already fired.

Jump might play a role in pressure, and you’re essentially jammed very hard with the .416”s due to the undersized freebore.

Fouling with solids depends a lot of the driving bands and the alloy.

I guess you’ll know for sure soon enough!