There has been great discussion on other shooting boards about 7mm Lap IMP cartridges shooting lead bullets with BC's over .750 at 3500 fps.

HORSE HOCKEY.

I will say this right now.

1) The BC of the Cauterruchio bullet is exagerated.

2) You can not shoot a bullet with a higher BC faster if the caliber is smaller, all things being equal. The smaller bullet requires more twist rate and has less cross sectional area to push against and cause acceleration.

3) Nothing in lead smaller than .300" shoots an honest 15 MOA up from 100 yards to 1,000 yards, at sea level at normal scope heights, out of a barrel shorter than 32 inches.


How to cheat, and convince yourself you have done the impossible:


1) Use ball powders on cold days

2) Design your reamer so you have lots of freebore and can not load close to the lands

3) Tell yourself great case life is 3 Firings!

4) Ignore any semblance of common sense pertaining to what is "Reasonable and Safe Pressure" in a modern firearm. Pretend you know more than the professionals who set safe guidlines.



Just because you can .......does not mean that you should. Some things are just imprudent and unsafe.

Every one wants the hottest, flattest shooting rifle, what are you willing to pay?????? Your eyesight, your Health???

One reason I backed down from the 3250-3300 fps in my 30-338 Lapua Imp in my 30" tube, that and pressures were a bit more over time at the same MV's too. 70,000 psi with this brass is what I feel the top end is, 65,000 psi if you want to stay well away from the top. The 338 Lapua brass survives very well into the 75,000 psi range and can be very misleading if normal pressure signs are your indicators. Severely tall primer craters are very good indicator in my particular action that I'm into the mid 70k psi range, but I've corralated it with pressure testing equipment to really find this out. I also know what my MV will be at certain pressures with a couple powders and where to stop, so two things point to my actual chamber pressure.

It will be interesting to see what Len gets with the 7/338 LI. I know the .264 won't do what the .284 will do with the same bullet weights, same case capacity, same charge... much higher pressure and MV is way down, that smaller bore thing you talk about right there.

If Bob's BC for the 176 is inflated, this will suck!

[i]2) You can not shoot a bullet with a higher BC faster if the caliber is smaller, all things being equal. The smaller bullet requires more twist rate and has less cross sectional area to push against and cause acceleration.[i/]

All things being equal. The main advantage is the Lapua case has more capacity than the 7 Ultra, much more than the 7 Dakota. Hard to put numbers on things when they get overbore like that though, efficiency falling might just keep it from doing much more than the 7 Ultra. That said, you still have the best 7 of the bunch, one that has large case capacity and uses the Lapua brass. I still prefer the 30 for it's larger diameter, never know when you cross a Grizz up here.

Sam, what is the expected barrel life for the 30 Wolf, and what would be for this (very overbore?) 7/338 imp?

Tiro....I have over 4,800 rounds on my 30 Wolf. It still shoots close to 1/3 Moa for 3 shots at 600 yards, and is the barrel I won with at Viper's sniper match two weekends ago. If sub half minute performance is the criteria, I believe 5000 rounds is very achievable. Keep in mind that I am not rapid firing this rifle, it is a 3 groove, and I typically shoot Danzac coated bullets loaded into the lands.

I do not believe that there will be a significant difference between the .284 and the .308 as far as barrel and throat wear. These calibers will be shooting the same powders with similar flame temps at similar pressures. How the rifle is shot and cared for is the big slice of the pie here. Big cartridges do not burn barrels, Shooters burn barrels.

Je wis Sam ya mean 3450 with 140g out of the 6.5 WSM aint safe Just because I gota tap the brass out with a cleaning rod dont mean its too hot does it
Seriosly is it cheating if you use ball powder(872)on a cool day if your shooting is done at tempts below 60deg.Sure preasures will go through the roof above 70 deg but if its a huntin gun and will only be used in the fall when its cooler whats the foul?

Whats the foul? Good Question.

The foul only occurs when you get older and put the ammo on an inside pocket rather than an outside pocket. Or perhaps it is a 48 degree day and sunny, and you leave the rifle and ammo in your truck while you eat lunch, or any number of other scenarios that all stack up against you and allow for a passive condition to make the weapon unsafe with that particular ammo. Just one man's opinion.

You make a great point that I often think about, and everyone hunting LR should, at least everyone interested in first shot kills, and that's the temp your ammo is. Most can easily monitor the ambient air temp, but where are we storing our ammo when hunting and are we even considering the effects of this "loose" variable often not well controled.

I mean, I've kept ammo in every concievable location and temperature there has varied as compared to ambient air temp so much it isn't funny. I've kept it in the magazine, the pack, in the loops on my sling, inside and outside coat/pants pockets, ammo pouch laying in the sun, possibly on a superheated rock from sunlight and on and on...

NOW what I do is TOTALLY different. Every time I'm either at the range or on the hunt I can only keep track of the air temp (also for air density purposes), and that's even got the hitch of making sure the Kestrel 4000 is a stable ambient temp as well but, also my ammo. I think it's impossible to really tell what the ammo in the mag "really" is, so what to do about that? Well, for a good LR shot you probably have time to grab some ammo that's stored in a temp stabilized location and single feed them in the event that your rifle is over 100 friggin degrees in the sun, and probably the ammo in it, IMO.

Knowledge of the MV your ammo produces at various temps is still an all important variable to test/log and employ, too many assumptions cause misses. Using inaccurate, non-up to date MET data is another primary mistake many people make, and feel not much need to understand its effects on drops, nor do they test/log them regularly.

How much of a temp swing will this load tolerate before POI rises or falls .25 MOA from the average? What is the average? Were all my actual fired drops tested in a real high, or real low air density environment? Is it every 5, 9, 13 degree temp change that requires me to add/subtract .25 MOA from my average due to just a temp induced air density change? Was it every BP change of 1.0, .8, or.?.?.?.. from the average that results in a .25 MOA POI shift?

More food for thought.

Brent ive been reading your post for several years, and the only thing you have ever written i wondered about was your last post. Are you sure you have ever seen a super heated rock? Beacause i belive we have the market cornered on them, the chamber of commerce here will not ever print the real temp. for fear of scareing off the tourist. I bought 40 lbs of wc872 amd have almost quit using it, you could get a nice group going and then fliers come out of the wood work. Ive been using retumbo but my friend with the 300-338 lap mag gets some of his best groups with reloader 25. I thought that my 30 jarret was toast when shooting 872 but seems to shoot good with h1000. Seems that there would be a way to determine what powder would be best from th burn rate and a formula. I am so jealous when i read your stats and you were shooting and it was 32 degrees, it would be nice to have a feww cold days, I guess you can tell ive been welding inside in a warehouse with no windows and only 1 door for the past few weeks. Bitch over!!!! Ebb

Just in case someone is really hungry, here is some more food for thought.....


People naturally assume that as the temp drops, so will the impact of the bullet because in external ballistics we all know that relative air density increases, and in internal ballistics, cooler temps mean the primer lights off a little slower, the powder oxidizes a little slower, and the colder barrel acts as a more influential heat sink, countering the pressure slightly that the oxidizing powder can build in a fixed barrel length.

Here is the RUB:


Where is your ammo tuned on the 3rd mode vibration cycle????


At what range are you shooting???

If you are tuned before the very top of your vibration cycle in warm temps, at shorter range it is possible to create a scenario where your bullet hits higher on the target, or in the same place as it will at the higher temps.

The possibilities become even more complicated when the gun is hot and the ammo is cold, or the gun is cold and the ammo is warm, and how all this interacts with barrel vibrations.

Most guys have a Fluke 77 multi-meter or something similar. Snap-On sells a probe that you can touch to the brass that will plug into your multi meter and give you an instant temp reading of the ammo. This is very handy for testing, and I used to use it all the time. One of my employees trashed the probe trying to check the temp of a cast iron differential casing while preheating it before welding. They are very handy, just do not touch them to anything hotter than 800 degrees fht.

What I have learned over the years to get the best results in an unpredictable world.

1) Design a system with a barrel length that tunes just past the top of the vibration cycle when near max pressure. Back off slightly on your load so the ammo is tuned just before the peak of the cycle. Pick your bullets and powder accordingly.

2) Only use temp insensitive powders for hunting/unknown range work. The interaction of larger velocity variances with barrel harmonics becomes too complex and too time consuming, not too mention what it does to barrel life and lead time getting a system ready to kill.

3) Keep your ammo warmed to body temp at all times until just before shooting. Do this while tuning, hunting, practicing....MAKE IT A HABIT. This constant will pay dividends as other variables change on you. Powder and primer temp inside the case is the biggest variable to initial velocity. Make it as consistent as possible. When bear hunting I keep a couple of rounds in the gun for any short range stuff that may pop up, or when walking around. But when I acquire a long range target those rounds get exchanged for two warm ones out of the ammo wallet up against my body just before the shot.

4) Vertical variance caused by relative air density changes is not linear, and the interaction of this with internal factors like muzzle velocity variance and barrel harmonics is too complex to keep in your head...so KEEP A DETAILED SHOOTER'S LOG BOOK and write down what happens under various conditions RELIGOUSLY!

5) For Big Game sized targets, focus your data collection effort past 500 yards. A properly tuned rifle will show insignificant changes for large targets inside 500 yards, Especially if your ammo is a constant temp.

6) Take advantage of any opportunity to tune a load near the place, altitude and time and temp that you will be hunting.


How to really screw things up:

Buy a rifle that tunes up on the low pass in the vibration cycle at max pressure, tune your ammo short of the bottom (safety margin from max pressure), use a ball powder like 872 or 870 or 8700, keep your ammo in the gun all night instead of your sleeping bag, leave your gun outside the tent but uncovered so as much moisture can creep in as possible, and believe things like my rifle always hits a quarter minute low when it is cold. Leave your log book on the fireplace mantle at home when you travel so your wife can use it as starter fuel for next fire she builds once you are out of sight and out of mind.

Ebb,

I had replied but accidentally deleated that part too when I saw that the discussion had moved.

The superheated rock probably wasn't the best way to word that. I just meant if one set their ammo down on a rock that had been baking in the sun, but was now in the shade, it could still be heating the ammo far above ambient temps as it holds the heat...

I have heard the term superheated rocks before, I don't recall exactly why they refered to them as such?

No , i was just raggin you because i am envious of some of your cool weather. Dont get me wrong i dont like it 30 below, but a couple of days a week where you need a long sleeve shirt would realy be a neet thing. I am also envious of the ability to load something hot for hunting and have a reasonable expectation that it wouldnt be in the 90s when you actually get to go. I was actually drug here by my parents from Tenn. they have moved back but left me here to sweat to death. ebb

My friend (the guy who got me addicted to long range shooting) took me shooting this mourning. We talked about how a summer load would be mandatory (97 degrees several times this week). Well i went to the Hodgdon site and found that the starting load for 300RUM is 84 grns, the last bunch i made was 86.5 grns and they showed pressure early in the spring. I decided to load 84.5 grns and be safe, well guess what. They have mildly flattened primers. I would love to be able to load something close to max, just once!!!!! I decided to put a 200yd zero on all my guns and start countin clicks like the rest of you guys and stop shooting the mildots for hold overs. Only problem was the ultra has no clerance between the scope and barrel and when i put it together i used burris signature rings and couldnt get 20 mins of angle, and with 15 moa it hasnt got enough clicks to get there. Burris needs to make super highs in the sinature line. I think some shims are in order. the 6.5 has loppy lr base and super high loopy rings and it worked perfect. I you left a gun in an open case in the sun it was too hot to shoot just layin there. ebb

ebb, I think "max" is a relative term regarding loads and temp. I like to think that our northern friends are being required to spend extra pennies for their loads because we get there with less powder. Just my simple minded rationalization.

BTW, I don't recall seeing too many rocks around Loxahatchee, but then I didn't dig too much either.

Was wondering if you know any of the family too. Off of the main hiway, turn right on B Rd. 2nd on the left. An A-frame on 5 acres. You know those folks?

Max Rode the 4 wheeler by the other day. i think i found the A frame you were talking about, looks to be about 800 plus yards due west of me, maybe a click to the north of due west. Dark brown shingles back in the pines from B roadfaces east and west , white horse trailer in the yard? E mail me and ill tell you the adress i was lookin at, dont want to put it here . ebb

Well it now seems that the reality of physics has set in with You know Who's 7mm 338 Lapua project. Rumors of case head separation and several attempts to chamber have yielded a Nesika action up for sale and a project that failed.

At the Risk of sounding like Rush Limbaugh......See, I told you so. The real problem lies in discernment. Some think that they can hire a gunsmith to do engineering. The guys that have sponsored both Snipers Hide and have cut deals with guys like Len Backus and his moderators have got the bullshit meter pegged. The Len Backus types of the world will never tell you about the failures, not good for business. Len does not need the money, just to save face. The truth is, they are all in over their heads, Len and his KC boys are in over their proverbial heads on a regular basis and just too proud to admit it. People are going to get hurt. Thank goodness it did not happen to Len..... this time.

Once again the "I will get a .257 bullet with a B.C. of .738 to run 3500 fps. out of a 30 inch barrel" morons have come out of the woodwork. Here is a post from a guy who lives on fantasy Island.

"What will set them apart will be the velocity produced with these rounds in my rifles. They will be designed around 30" barrels in sporter style rifles that will weight in at 9 to 9 3/4 pounds. Pretty light for a 30" barreled rifle.

They will run very well out of anything 26" and over but they will be originally designed around this rifle platform.

Velocity expectations are as follows with these bullet weights:

115 gr---------3850 to 3900 fps
120 gr---------3800 to 3850 fps
130 gr BC------3600 to 3650 fps
145 gr FBSP----3450 to 3500 fps
150 gr BC------3400 to 3450 fps
145 gr ULD-----3400 to 3450 fps"


Obviously this guy must not have learned a single thing from Len's project. Well, I guess you can't blame him, Len got awful quiet about the 7mm Super Duper 15moa from 100 to 1,000 yards Fantasy Island rifle. The sad part is people actually believe his bullshit projections. Every thing I said about Len's 7mm applies to this character, thats right, the same guy that torques his barrels to 50 ft. lbs.

Expect the velocity projections to start inching down, when the laws of physics and reality set in........Or.......We may have the next Lazzerfoni on our hands. All cartridges are fun to shoot, some more than others, why can't these guys stop pretending that their 'special' cartridges defy the laws of physics???