H4831sc and 6.5 Creedmoor

[Ian]

The nose is the last part to upset at launch. The force on the base is transferred through the bullet but the compressive force that the inside of the bullet "sees" is less and less going forward toward the nose. Some of the hardest-hitting powder charges I use and softest bullets barely swell the middle of the nose into the grooves. I used to have a different opinion, but since have concluded that nose "slump" from static inertia is a non-factor for cast, if the nose "sets back" during launch it's because of pressure from behind swelling the bullet.

Bumping the nose isn't really gaining you a lot due to the wasp-waist effect, that middle needs to fit too and if it doesn't it will buckle like an arrow does when the clutch is dumped except the arrow will flex itself straight again and the bullet will remain a banana shape. Ever throw a banana? A lot of the inertial deformation can be overcome with slow powder and gentle push (press vs. smack, remember that acceleration is the second derivative of velocity), but as you increase velocity the lack of fit in the middle will show up at a certain point.

 

[Intheshop]

More like an aluminum arrow being spat out of the extruder..... than coming off a bow. While it's in the die(barrel),there's a set limit on bending moment. But you do have compression in an accordion fashion. For now,that's the direction I'm betting on.

Got me some brandy new cases today from a real gunshop. The older salesman was pleasantly speaking of having a 7-08 prior to it being a commercial offering and was interested in my CB's. Got the original Remington corelok 140's @2850.... getting "pulled".

Co went with me and had fun,so behaved...knock on wood. We did a perimeter check on the gunstore,off leash..... trying to get her a job as a greeter there?

 

[fiver]

BW.
I'm gonna say this straight up.
I've shot over a 5gallon bucket and at least 16lbs. of powder down the pipe messing with them.

the RCBS silhouette bullet will flat fall on it's face once you start going up in velocity.

1900 is really it's total limit in a 30 cal. rifle and even less in the 7mm.
alloy, powder, nuthin is gonna help it.
I actually thought about having the base of the 7mm. mold milled off and just using the nose portion as a paper core.
the bullet relies on the nose waaay too much, alignment, engraving, initial rotation it does all that and a bit more.
the base is basically a gas block.
a slower powder will help because of the design, but it is just not suited nor capable of higher speeds.

 

[Ian]

The Barlow "silhouette" bullets all suffer from velocity limitations for the same reasons.

 

[waco]

Somebody should design a 7mm XCB style mold?.....

 

[Brad]

Somebody should design a 7mm XCB style mold?.....

There is a 35 cal version that I hear is the most advanced and scientifically designed bullet ever. Seems it didn’t shoot well for most.....

 

[waco]

Most probably run it too fast in a 1:10 twist.

 

[Ian]

The NOE "xcb" concept has a few good points ans some bad points. The good is little unsupported nose and at least a straight taper vs. parallel nose portion. The bad is it has little provision for efficient metal displacement, too short of a fas check shank, and little to no self-alignment properties. Funny how it shoots best in a .308 having a total mis-match of tapers as compared to the 1.5⁰ per side taper of the throat it was designed to fit.

I thought NOE had a 7mm mould that was somewhat decent but I must have misremembered and instead is this .277 design. Something like this will do much better than a Barlow bullet at HV:

http://noebulletmolds.com/NV/images/N.O.E._Bullet_Moulds_279-126-FN_GC_E2_Sketch.Jpg

 

[Intheshop]

The 7-08 starting JB loads with Varget,4350's,and 4831 using 150's (this mould drops @153)..... aren't what I consider HV for cast. They're all running around 2300,to around upper 2400's. That to me is slow?

The first load out of the gate is bugholes going 1800fps @100 yd with the 145SIL fueled with H4198.I could,and if reading comprehension is considered (poster's observations above)..... quit with this load. But,will proceed.

Got a cpl loads to try..... looking at 2200 with Varget. Then see what IMR4350 can do. I might learn something...... or not?

 

[fiver]

keep going I might learn something new.
plus if I listened to everyone that said I couldn't do it I never would have.


there is a higher velocity 7mm design out there.
Lyman made it [287 sumthin] then discontinued it's production years back.
that design was slightly modified by Von Gruff and carried up into the mid 2-K speed zones and used for goat hunting.
had that outfit in Australia cut it [LBT?]
I been half watching for one of those molds to pop up for a number of years now.

 

[Ian]

Them 7mms are unique ducks. I ran WQWW alloy up to just over 2600 fps in my 7mm-08 (trying for 200K rpm with MOA accuracy, following someone else who took up Dan's challenge for a free mould years ago). Using a worn-de-flock-out Savage barrel with .002" land height (you read that right) and military blank brass necked down in a modified die to give me .022"-thick necks (IIRC) and of all things the little LEE 130-grain bullet with no lube capacity, parallel nose, and everything else that's wrong with it, I managed 8-9 of ten into an inch but there were always flyers, very random ones too. In hindsight it was probably the lube. Pretty sure I was using H414 and buffer. Buffer makes a huge world of difference in what you can get away with. Anyway, I never caught a bullet but am convinced to this day that I was hitting those little things so hard with pressure that they simply slugged up to fit the throat and squirted on through. The solid necks and near interference fit of neck to chamber (I even trimmed and beveled them to match the length of the chamber, so no space for lead to extrude) kind of made it impossible for the back of the bullet to get a crooked start, so I guess the nose either flowed into the grooves or by luck most of the time stayed in the center of the bore.

 

[Intheshop]

Interesting twist on burn rate chart from the folks at Norma.

 

[fiver]

see where I mentioned the H-4895 and 3031 relationship above?
you can also see where AA's 2230 is in the position you'd expect 3031 to occupy, but in other places it WILL act more like H-335.
I have seen it mentioned in both positions on the interwebs, and I have used it like a real slow AA-1680 using it's end data as start data.

I preach treating every gun as a law unto itself, treating each powder like it is in a family group and not an individual.
aaand that one should load as if they were loading a wildcat even if it is a long established cartridge.
that's probably one of the best actual truthful statements written in a reloading book ever.

as an aside I broke down today and actually paid money for a gun magazine.[like 9$ jezuz Christ I have paid less for full length novels before]
it's the current Rifle magazine addendum full of nothing but 6.5 cartridges and reloading data for them.
I'm sure they are all reprints from earlier.
but,,, it will be neat to browse through and make direct comparisons between data and look at side by side real world numbers if they are provided.

 

[Spindrift]

That chart is very interesting. The powders are listed in order of «relative pressure», and in most cases the «relative velocity» follow suit. But some powders are different, in that the «velocity» and «pressure»- curve is slightly different.

Firing a .308- case with 43,2grs of N350 was probably also quite interesting.

 

[Intheshop]

I'm staring at 4831 compared to 4350.....hmmm?

The 308 case vs 7-08,in how the smaller exit hole amongst other ballistic differences,"changes things"..... powderly speaking would make for some interesting reading. Not to mention, 243 and 260.

Fiver, I hear ya on the gun rag price. And understand buying it. But,I have really been getting some tips and tricks from the new to me(bought used but,it was essentially new) David Tubbs book. His work in pro level,high power rifle and silhouette competition translates exactly to hunting/field rifle craft. At first blush(if you were skimming or reading reviews),it don't make a lot of sense but...... like I posted somewhere else,this is so well written,chocked slam full of.....dang,why didn't I think of that...... you keep it in the truck or deer blind and read it over N over.

 

[fiver]

I have one of the tips and tricks books by glen zeideker in it he recommends the David Tubb book high power rifle.[and another one of Tubbs books]

they both of course are dealing with reloading for high power NRA type shooting, but the basic techniques are discussed in simple enough terms that he doesn't get over bearing or come close to saying this is the only way to do it.
but he goes deep enough into each subject to give a good understanding on what you should be doing allowing you to figure out for yourself how to get it done.

 

[fiver]

BW put the powder rate together with expansion ratio and pressure time.
or like I like to say it 'when the bullet is'.
you'll see why the little bores like slow powders, and why the big stuff like 45-70 thinks H-322 is a magnum speed powder.
the 7mm is where the world starts to change in that regard.

what happens on the slow powder side of the spectrum is you just went from the 335/748 group of powders with the 308,,, all the way back to the 4831 group of powders as a jumping off point for the 7mm.
you lose about 20-25% of the bore volume, bullet weight, and gain pretty much that amount back in pressure [if you don't use the slow powders there] all in that one diameter step down.

the 4350 powders are in their own little world, they don't visit the 64 side and they don't go to the 831 district too often.
but where they work, they seem to work quite well almost like the volume-pressure gods were beaten down into saying okay you can have this one.
just fill the case up and go shoot, now leave me alone.

 

[Intheshop]

Pulled factory Remington 140g coreloks. Powder shape was a smooshed ball,like a miniature biscuit. Charges(which are volume dropped) ran from just below 44g to,just above 45. With a very well represented "range"..... all through that min/max.

This pic is a #12 Lyman Accumeasure rotor that drops my go-to .223 Lee 225-55/H4198,look no further accuracy/varmint load. It also is that powder's starting,RCBS 145SIL load that is another,look elsewhere for excuses cause,it ain't the loads fault you missed.

Gotta make a nose die for the 145SIL.... the bore ride section is a few "tenths" (.0001) big. It "works" but..... if you don't hold your mouth just right,you can't eject a loaded round. Don't cut the muster,in the field.

 

[fiver]

little smear of lanolin or vasoline on that nose will help.

 

[Ian]

BLL helps too. Many many moons ago re 6.5x55 with a tight nose fit I used to dip just the exposed part of the bullet in 45/45/10 after loading and hang the cartridges up on a clothesline by the rims to drip dry.