Strange results with 7mmSTW

[stagpanther]

I just put together a frankenrifle based on a 7mm STW action that I had put together a while ago but never really developed any kind of load that seemed to deliver consistent results--in other words it might shoot an acceptably tight and accurate group one day--but then the next using the same loads they might open up a lot. After putting the rifle together I shot a few test groups to see if I was headed in the right direction. These are 5 shots of 180 target hybrids driven by 84.4 grs of RL 33 with a COL 3.725"

The labradar figures were, in a word, terrible. The ave velocity was just under 3,150 fps (this is out of a Shilen 28" tube) but the Es was 79 fps and the SD was 36 fps. I've read on-line that people have gotten groups well under .5 MOA--but I've never done that with any loads I've developed. Interestingly--the highest impact in the group was from the first cold bore shot which also had the lowest velocity.

 

[Brian Pfleuger]

Accuracy might be explained by undue pressure points on the barrel from the stock? Maybe torque on the action bolts?

ED and SD not so much though... your chosen powders behave in other rounds? The bullets consistent and consistently seated? Brass annealed?

Honestly... what you have there seems like a "real-world" group but you're comparing it to "internet" groups.... don't forget to add a 200%... uh... "error" factor to those internet group sizes.

 

[stagpanther]

Accuracy might be explained by undue pressure points on the barrel from the stock? Maybe torque on the action bolts?

ED and SD not so much though... your chosen powders behave in other rounds? The bullets consistent and consistently seated? Brass annealed?

Honestly... what you have there seems like a "real-world" group but you're comparing it to "internet" groups.... don't forget to add a 200%... uh... "error" factor to those internet group sizes.

Except for the first cold bore shot--all 4 of the rest were within .5 MOA of the POA; so I thought that wasn't bad for the most part. I don't use RL 33 in any other loads--usually I opt for H1000 if there is any overlap. Since the brass is reformed from 375 H&H I guess it's possible they are not uniform. I generally just load and fire, and as long as there is no resistance in the bolt and the brass isn't showing signs of over-pressure for my 7mm STW loads I figure I'm good. I think the torque in the action bolts is a possibility.

 

[Unclenick]

Would never have occurred to me that a 7mm STW could have erectile disfunction.

To get your ES and SD down, start by reading the first post in this thread and doing the matching prep. I like to get one package of Lapua or Norma brass, as they generally need no additional case prep. Be careful to handle your cartridges and chamber them so the powder always falls back over the flash hole (unless the load is compressed; one of the secrets of Federal Gold Medal Match 308 loads with the 168-grain SMK).

For variability, in any hard-recoiling rifle, you need to watch out for the gun settling in the bedding in more than one distinct location and that the action screws maintain tightness for every shot. Also, depending on how your forestock is set up, you should try resting the magazine floor plate on your sandbag or rest rather than further forward.

Let's see what happens.

 

[stagpanther]

Would never have occurred to me that a 7mm STW could have erectile disfunction.

I thought all barrels have whip issues when fired? I'll have to try the blue Lucas bore cleaner next time.

Admittedly--I don't think the stock I installed it in was meant for anything like the 7mm STW and I did modify it quite a bit in the process of getting the large magnum bottom metal to fit properly. Thanks for the info--I'll read it carefully.

Read the first post--and the ones that came after it. I guess it's fair to say that at closer ranges those factors may not manifest themselves as dramatically as they would at longer distances?

 

[44 AMP]

You're getting sub MOA groups from a high velocity 7mm magnum sporting rifle cartridge and you're whining about it??

I'd be bragging!

 

[stagpanther]

You're getting sub MOA groups from a high velocity 7mm magnum sporting rifle cartridge and you're whining about it??

Sounds a lot like something I said before. Seriously, I know something's not right here.

 

[georgehwbush]

within 1/2 moa of poa == 1moa if i read it correctly.


edit; ah point 8 3 9 0.839 it's on the picture. sub moa.

 

[georgehwbush]

stagpanther; did you hand weigh those charges ?

i only ask; because the only two reasons i normally get large es/sd numbers is if i don't weigh just dump and go, or if the powder is too slow for the project. (i normally push the envelope on slow burning powder looking for lower pressure and lower heat at the same velocity) so i do find that if the powder is not all burning inside the tube i get eratic sd's .

but your 28 inch tube should be burning all of that... that's why i asked.

 

[stagpanther]

stagpanther; did you hand weigh those charges ?

i only ask; because the only two reasons i normally get large es/sd numbers is if i don't weigh just dump and go, or if the powder is too slow for the project. (i normally push the envelope on slow burning powder looking for lower pressure and lower heat at the same velocity) so i do find that if the powder is not all burning inside the tube i get eratic sd's .

but your 28 inch tube should be burning all of that... that's why i asked.

Used my RCBS dispenser--though it can vary despite what it indicates. RL 33 actually is a tough one to meter correctly. Bore doesn't seem to be unusually fouled after using it, though like I said RL 33 generally isn't my first choice when it comes to a slow-burning magnum powder--though the energy is very good--that average velocity of around 3,150 fps was quite a bit more than what QL said it would be--by about 100 fps.

Unclenick was correct in his assumption of the action "settling in" to the stock--when I first installed the action I torqued the screws fairly tight--but after just 5 shots I found the rear screw was somewhat loose.

 

[Unclenick]

You could take a torque wrench with you and reapply it to the screws after every shot. With the rear screw loosening, check bedding or inletting along the sides of the rear of the action to reduce whipping there. If the screws still loosen, try Loctite 242, which is removable.

 

[stagpanther]

Thanks Unclenick--I've followed much of the advice here and put more effort into equalizing the components upon reloading. I used my labratory grade scale which has 1/100 gr accuracy--interesting to note that some of the individual sticks of RL 33 exceed .02 gr in weight. I did, however, switch from the 180 gr target hybrids to Sierra's 183 gr MKs which I've had great results with in high-power .284s for my next test.

 

[Mike38]

I found the best accuracy (0.5moa) with my 7mmSTW down around 2900 fps with 160 grain bullets. Kind of kills the idea of a belted magnum, I know. If you want high velocity, you sacrifice a bit of accuracy. My findings, yours may vary.

 

[Jim Watson]

Early days of the 7 STW, an enthusiast here was annoyed that his fireform load was more accurate than a load in fireformed cases.

 

[stagpanther]

Early days of the 7 STW, an enthusiast here was annoyed that his fireform load was more accurate than a load in fireformed cases.

I've seen this happen on occasion now that you mention it. Conceptually, it's taking a design for big bullets and turning it into a small diameter blow torch. The chamber in my barrel looks a bit different post-firing from what you might expect, the throat step-up to the leade shows the kind of cutting you would expect--but what is unusual is that when cleaning the bore the hardest deposits to get rid of are in the initial free bore and especially in the step down from the case mouth--it looks like there is a turbulation of superheated gas and residue that rapidly builds in that area and looks like it even might back pressure into the chamber as the case contracts. It is very hard to get rid of when cleaning. I bought some nickle-plated 7mm STW brass from a custom brass manufacturer and was amazed when the necks split wide open after just a few firings. The splits did not happen when firing--but when running them through the sizing die. It's never happened with any of my all-brass cases, even after many firings.

 

[stagpanther]

I found the best accuracy (0.5moa) with my 7mmSTW down around 2900 fps with 160 grain bullets. Kind of kills the idea of a belted magnum, I know. If you want high velocity, you sacrifice a bit of accuracy. My findings, yours may vary.

You might be on to something-- I did some "poking around" in QL with numbers for the 162 ELDx--what jumps out is that simply stepping down a bit in bullet weight significantly reduces pressure numbers--and presumably overbore wear and tear. I may try a load or two to see how it works.

 

[Unclenick]

when cleaning the bore the hardest deposits to get rid of are in the initial free bore and especially in the step down from the case mouth

Might be two overlapping phenomenon. It's common to get a hard carbon ring at the step, and brushes and patches can't conform into the sharp corner. I had one of those in my AR match barrel that I first saw when I got a borescope, and it annoyed me that it wouldn't come out (borescopes often introduce new worries). But when Gunzilla was first introduced, I got a free sample of it at Camp Perry and decided to try cleaning that barrel with it. Nothing unexpected happened right away. Patches were coming out clean, but the ring was still there. But after I put one last wet patch in, just in case, I got called away by something and didn't get back to finish cleaning for almost 24 hours. When I did, I started with a dry patch, and it came out with a black ring around it. I got the borescope out, an lo and behold, the carbon ring was gone. Gunzilla is slow to soften carbon, but it does do it. Same with rust. It will loosen it until it falls off, but you need to give it a week sometimes to act. Once I left on business and it had six weeks to act on an old Springfield '03 bore and when I got back all the rust and carbon in several bore pits had oozed down to the bottom of the bore, so it is something for you to try. Saves a lot of frustrated elbow grease.

I think the carbon ring problem is generally worse in belted cases because they specify them so the shoulder is back enough to be sure the full range of head-to-shoulder specs won't allow shoulder contact with the chamber shoulder over the full range of the belt headspace tolerances. You may change that to headspacing on the shoulder instead of the belt if you choose, but the new ammo and fully resized ammo will leave a bit of extra room for carbon and gas blowby around the bullet when the neck expands to release the bullet. That and the sheer volume of powder burned are probably all you need to account for extra carbon build-up where you have it.

Incidentally, Slip2000 Carbon Killer is another product that will likely let you get the ring out and will do it faster (15 minutes of sitting), but it is harsher and you still need a bit of mechanical effort, so I tend to prefer letting Gunzilla and time do the work. In a pinch, though, when you haven't got the time to wait (big match in the morning), having the Carbon Killer option available may strike you as useful.

The second phenomenon will just be the buildup of copper in the first two or three inches of the bore. This is where the bullet is located when the peak of the pressure curve is reached. At that location, the bullet is experiencing the biggest pressure differential between its base and nose, which tries to squash the bullet. It isn't able to squash the bullet, but it is enough to apply some upsetting force outward against the bore, so bullet-to-bore friction peaks together with the pressure, and that rubs copper off faster than anywhere else in the bore, except in some special cases where the bore tapers down in diameter toward the muzzle or where extra rough tooling marks exist further down. I was thinking maybe if your carbon buildup extended to the start of the copper buildup portion of the bore, it might look like one big problem when it is actually two.

Incidentally, in the 1995 Precision Shooting Reloading Guide, one of the authors had a 300 WM that wouldn't shoot below 2 moa regardless of what loads or components he tried. Then, one day, he got an outside neck-turning tool and tried it on his 300 WM cases. Bingo. Its groups immediately shrank to 1 moa. The way the statistics of group error work, that would make the effects of other things he tried (powder, primers, bullets) start to be visible when the 2 moa group was covering them up.

I'm not saying that particular treatment would necessarily help your particular gun, but it is another example of the extra shoulder wiggle room of the fully resized case making consistent bullet alignment more fussy.

 

[stagpanther]

Might be two overlapping phenomenon. It's common to get a hard carbon ring at the step, and brushes and patches can't conform into the sharp corner. I had one of those in my AR match barrel that I first saw when I got a borescope, and it annoyed me that it wouldn't come out (borescopes often introduce new worries). But when Gunzilla was first introduced, I got a free sample of it at Camp Perry and decided to try cleaning that barrel with it. Nothing unexpected happened right away. Patches were coming out clean, but the ring was still there. But after I put one last wet patch in, just in case, I got called away by something and didn't get back to finish cleaning for almost 24 hours. When I did, I started with a dry patch, and it came out with a black ring around it. I got the borescope out, an lo and behold, the carbon ring was gone. Gunzilla is slow to soften carbon, but it does do it. Same with rust. It will loosen it until it falls off, but you need to give it a week sometimes to act. Once I left on business and it had six weeks to act on an old Springfield '03 bore and when I got back all the rust and carbon in several bore pits had oozed down to the bottom of the bore, so it is something for you to try. Saves a lot of frustrated elbow grease.

I think the carbon ring problem is generally worse in belted cases because they specify them so the shoulder is back enough to be sure the full range of head-to-shoulder specs won't allow shoulder contact with the chamber shoulder over the full range of the belt headspace tolerances. You may change that to headspacing on the shoulder instead of the belt if you choose, but the new ammo and fully resized ammo will leave a bit of extra room for carbon and gas blowby around the bullet when the neck expands to release the bullet. That and the sheer volume of powder burned are probably all you need to account for extra carbon build-up where you have it.

Incidentally, Slip2000 Carbon Killer is another product that will likely let you get the ring out and will do it faster (15 minutes of sitting), but it is harsher and you still need a bit of mechanical effort, so I tend to prefer letting Gunzilla and time do the work. In a pinch, though, when you haven't got the time to wait (big match in the morning), having the Carbon Killer option available may strike you as useful.

The second phenomenon will just be the buildup of copper in the first two or three inches of the bore. This is where the bullet is located when the peak of the pressure curve is reached. At that location, the bullet is experiencing the biggest pressure differential between its base and nose, which tries to squash the bullet. It isn't able to squash the bullet, but it is enough to apply some upsetting force outward against the bore, so bullet-to-bore friction peaks together with the pressure, and that rubs copper off faster than anywhere else in the bore, except in some special cases where the bore tapers down in diameter toward the muzzle or where extra rough tooling marks exist further down. I was thinking maybe if your carbon buildup extended to the start of the copper buildup portion of the bore, it might look like one big problem when it is actually two.

Incidentally, in the 1995 Precision Shooting Reloading Guide, one of the authors had a 300 WM that wouldn't shoot below 2 moa regardless of what loads or components he tried. Then, one day, he got an outside neck-turning tool and tried it on his 300 WM cases. Bingo. Its groups immediately shrank to 1 moa. The way the statistics of group error work, that would make the effects of other things he tried (powder, primers, bullets) start to be visible when the 2 moa group was covering them up.

I'm not saying that particular treatment would necessarily help your particular gun, but it is another example of the extra shoulder wiggle room of the fully resized case making consistent bullet alignment more fussy.

Great stuff--thanks! I'll definitely be look into those bore solvents, though I often shoot every single day so might try the accelerated stuff. I'm really not getting any significant copper build-up with the exception of the last few inches prior to the muzzle where I do get some stubborn streaks in the grooves; but the throat and bore after the throat generally stay remarkably clean--not sure why that is.

Since most of my brass is necked down from 375 H&H the neck turning thing might be a good thing to try; I'll have to see if my set-up can handle the case.

In some respects, the 7mm STW seems to be a lot like a big weatherby cartridge, the actual engagement of lands happens way beyond the max COAL typically. I've loaded some that were hand-load only propositions--getting out to 3.8" and still off the lands--but it was pretty obvious pressures were ramping up fast as a result.

 

[Unclenick]

Check your barrel with a borescope to see if you pick up any difference in the surface where the streaks appear. I would run a pure lead slug in from the muzzle and see if you feel it getting any tighter as you approach the area where the copper fouling is or if it feels any looser when you push it beyond that area. If there is a constriction in that area, it can be lapped out pretty easily.

Another possibility is you have an anti-coppering agent in your powder that doesn't last quite all the way down the tube. I just bought 8 lbs of N140 for Garand loads and was surprised to see it labeled as temperature stable and having a de-coppering agent. These are changes from the last time I got any, and I'll have to see how it affects performance. The Vihtavuori powders are known for being clean burning, but the copper fouling reduction agents in the Hodgdon CFE powders are generally considered to contribute to powder fouling. I find out if Vihtavuori has figured out how to stop copper and stay clean at the same time.

One other thing you can try regarding fouling is using Tubb Dust. It's a grade of hBN dust that you add to powder directly (13 grains per pound of powder) rather than coating bullets with it. It deposits the stuff in the bore and mitigates copper adhesion. However, note that it will reduce bore friction, too, which means you may have to increase your powder charge slightly to stay at your current velocity. Reduced bullet/bore friction gives the powder less resistance to build pressure against, so it burns a little more slowly. Also, once that stuff is in your bore, it may take a while to clean and shoot out completely, so I look at it as a thing to try after other things have failed to perform the way I want. I use it in an old Savage 308 barrel I have that wants to copper foul particularly badly, and it helps quite a bit, and accuracy has been good. But that's just one data point.

It is also the case that the chelating copper removers are great. Bore Tech Eliminator is a good general cleaner, and their Cu++ is faster on copper once the other fouling is out of the way. KG-12 is a really good one, too, though it doesn't turn blue like the Bore Tech ones do, so you have to use a borescope with it to be sure you have the copper out.

There was an article in Precision Shooting about this sometime in 2006. And while a lot of folks don't want to wait around for a cleaner to work, the article said they can often keep working for 20 minutes or so if you don't wipe them away with the next patch. So, I have abandoned my old routine of running patch after patch without a break until everything is clean. I now usually wait at least five minutes after a wet patch before the next one goes through. Saves a lot of patches.

Did you know that you can boil water, grind coffee beans, and get the water dripping through a filter in five minutes? Run your next patch, then get your finished coffee.

 

[stagpanther]

KG 12 is what I use--my whole house reeks of it! Gotta watch out about totally removing it after use cause if it seeps down into other parts it can pool up and cause damage over time, I've found. So I like to follow up with tactical advantage since it foams up and gets into the nooks and crannies.

In the 30 or so cartridges I've fired in the past few days--generally spacing the shots out to keep the barrel luke warm to the touch--I can now see a notable change in the fire-cracking at the throat region. I'm wondering if I should call it a day and have the barrel--a 28" shilen 6 groove--rechambered to something not quite as super-heated.