Since I have decided to take my 7x300 Weatherby to Colorado next week to hunt mule deer, AND since I MIGHT need to take some shot at or slightly over 300 yds, I thought I might look into loading some bullets other than my "go to" 115-grain Speer HP, with which I have killed a LOT of critters. Trouble is, while it starts out 'smartly' with a MV of over 3300 f/s, it's BC of .250 causes it to shed that velocity (and more importantly, ENERGY), pretty quick. By the time it's out at 300 yd, the energy is down to ~1200 ft-lb. It drops to 1000 ft-lb at 380. Like I said, I've shot lots of critters with this rifle and bullet combination, and I do not want to shoot at big game beyond much over 325.

I was 'talking' with JaDub, sakorick, and Hunterbug here: http://www.thehunterslife.com/forums/showthread.php?p=151741#post151741, and got to thinking about other bullets. (I LOVE the 115-grain HP. It shoots like a laser and they DIE RIGHT THERE! Inside 300. ) As a result, I went out and bought some 140 Accubonds and some Retumbo powder.

I'm going to relay the gory details of working up a load using some "longer range" bullet for this rifle. One I can confidently shoot out to 350 yd and know it will both have the energy I want AND shoot precisely enough to be confident to put it where I want it to go at that range.

First in what will likely be a bit of a "saga" is a picture of all of the 7mm bullets I have in hand. I will follow this with a data table of some of the important specifications of each bullet. From that will follow some comparisons of external ballisitics, and ultimately a final choice. I will get a load worked up and ammo loaded for Colorado. All in less than 7 days. Let's see if my theory and understanding of QuickLOAD will allow me to achieve this goal.



Paul

PS - There is only one bullet among those you can see in the picture that is ABSOLUTELY "out". It's the Hornady 162-grain BTHP. That is a target bullet with a TINY, CLOSED meplat. It is not suitable for use on big game. I WOULD use it on coyotes and smaller game though. Also, I notice that I have used up all of the Hornady 154-grain bullets that I used to have 'plenty' of.

Paul

I just spent the past hour running all of the above bullets through QuickLOAD, and there were some very interesting results. Many of them have very similar external ballistics. As it turns out, Hodgdon's Retumbo is THE powder for the 7x300 Weatherby (according to QL). It gets higher velocities and lower pressures than my long-time fave - 4831. Retumbo was not available in the 70s, 80s, and I don't think the 90s either. It's odd to me that it "works" for every bullet weight from 100 to 175.

The first priority, (tomorrow), is load up some CHEAP bullets in front of Retumbo, and calibrate it's burning rate. Once I have that accomplished, I can start looking at "real" QL loads. Loads that QL predicts the MV within 25 f/s or so. At that point, I will be able to get the timing right as compared to the 115 HPs. That SHOULD put me very close to "on" precision-wise with whatever bullet I choose. I didn't count how many of the 160 Accubonds I have. If I have enough to work up loads AND load for hunting (20), I'll probably use them. However, Retumbo has revitalized the 115-grainer!

Assuming the real burning rate is not too far off the QL value, Retumbo ups the MV of the 115 HP to 3450 f/s. That means that the 400 yd energy is over 1000 ft-lb. Drop at 400 with a 2" max above line-of-sight is 16". That's "off hair", but I've never shot at a big game animal over 320 yards, and I don't INTEND to start now. At 320, the energy is 1300+ and the drop is 6". Impact velocity is 2270 f/s which I know from personal experience will "hit like a hammer" with that fat meplat on the HP.

There will be more tomorrow.

Paul

PS - I might mention that since this rifle was my first wildcat, I have ALL of it's specifications: Chamber length, barrel length, case capacity, the bearing length of most of the above bullets (and I'll have the rest tomorrow). This is partially why I think I can achieve the goal of getting a precise "heavy" bullet load in the 7 days between now and when I leave for Colorado.

Paul

After a couple of hours of measuring and cypherin', I loaded 3 cartridges with a 139-grain Hornady flat-based bullet seated 0.355" deep (0.050" off the lands), and 85.6 grains of Hodgdon Retumbo. QuickLOAD predicted a MV of 3118 f/s. After pulling the trigger 3 times, I got 3394, 3399, and 3399 f/s. (I LIKE that spread - 5 f/s!) That's almost 300 f/s faster than QL predicted. Now, I adjust the burning rate of the Retumbo powder based on these MVs, load three more with a slightly different charge, (same powder of course), and check to see if QL gets the MV correct after the adjustment.

Making the adjustment to the burning rate of Retumbo, the QL predicted MAX pressure is 73,892 PSI. That's 10,000 PSI over the SAAMI max! I examined the cases closely after firing, and the primers aren't 'flattened'. (There is a bit of extrusion into the firing pin hole though.) No head separation of course. So... I'm not sure this adjustment is correct. I don't like the simplistic way that QL users and the QL author say "Just adjust the burning rate until the QL-predicted velocity matches the actual velocity". There's SO MUCH more to the internal ballistic equation than just the burning rate of the powder.

Moving the charge back to the desired timing node, the charge is reduced by 9.7 grains. That's a lot! I'll try that charge, (75.9 grains), and see if QL predicts the correct MV - about 3070 f/s. That will reveal whether the burning rate adjustment I made is appropriate.

Paul

PS - The change in burning rate was 20%. That's 5% more than author of QL recommends for  the MAX change to the burning rate spec. I'll check the bulk density of the powder too. In the past, actual bulk density was occasionally significantly different than the QL spec'd bulk density.

Paul

The QL spec'd bulk density is 0.925 grams per cubic centimeter. I measured the bulk density of the powder I have in hand at 0.962 g/cc that's a difference of 4% denser. While adjusting the 20% change in burning rate down by 4% gets to almost the max recommended change in burning rate of 15%, the actual effect on the QL prediction cause by changing the bulk density by 4%, was negligible.

Paul

Sumpin' funny goin' on.

Have a look at this article by Layne Simpson. http://www.shootingtimes.com/editorial/ammunition_st_7mmstw20_200812/100178 (Simpson is the creator of the 7mm Shooting Times Western cartridge which is the ballistic twin - almost - of the 7x300 Weatherby. The Weatherby has about 5 grains more case capacity.) The charges he gives with Retumbo are close enough to the 85.6-grain charge I used, to indicate that such a charge should not be producing pressures of 75kPSI.

More investigation needed.

Paul

The 79.5-grain charge produced a MV of 2995 f/s. The predicted MV using the adjusted specs (burning rate and bulk density), was 3068 f/s for a difference of 73 f/s. Too far off for what I want, BUT, better than the 277 f/s difference of the unadjusted powder. I will make another adjustment, and shoot another. I want QL to be less than 50 f/s off of the observed value.

Paul

The last adjustment resulted in a predicted MV of 3092 f/s and the actual was 3082 f/s. A difference of 10 f/s. That's close enough.

Maybe I should reiterate here that I am NOT looking for a MV. I'm looking for a specific TIME. The time I'm looking for AFTER I calibrate the powder, results in a predicted MV. Since I can't measure exit time, but I CAN measure MV, I infer (calclate) the timing using the MV.

So what I now have is the calibrated "new" powder, and the known timing of this rifle. Using the known timing of the laser-straight 115-grain bullet, I can use QL to calculate charges for 140 and 160 grain Accubonds that put me "on" the correct timing node. That SHOULD make the loads "right on" with regard to precision. I might be able to test-fire the new 140 and 160 Accubond loads for precision this evening. If not, I will do it tomorrow. IF, and it's a pretty big if, these loads shoot MoA or better, I'm finished with the workup.

Next post should be dead targets.

Paul

PS - Took me 6 shots to calibrate the powder. The bullets I used are some that I will never otherwise use (139-grain, flat-based, Hornady, spitzers) that cost me 12 cents apiece when I bought them. Each charge cost roughly 40 cents, for a total powder cost of $2.40. Let's call the primers 5 cents a piece for a total of 30 cents. So the total cost so far is $3.42. (And the @#$%^&* powder was the killer!)

Paul

By the way... I made all of these "intermittent" posts because many people don't like to read "the whole story" in one bite. I'll summarize when I get finished.

Paul

Before you "waste" money on Retumbo (ptooey) and if you have some 7828 I'd go that route first.  It's by far the most accurate load in 3 overbore rifles I currently own. The 300RUM, 25-06 and sevumag.

I tried Rutumbo (PTOOOEY) in the 300 and sevumag and groups were ****. If you were closer I'd give you about half a pound of Retumbo (PTOOOEY).

Of the bullet selection I see one that I would load and that's the 140 grain Nosler solid base boat tail. When those are gone the Accubond is hard to beat. If not those then Sierra's 140 grain Gameking.

I'd go for accuracy first.

(whispering) if it was me, I'd go with 150 grain Gamekings, but that's just me

RJ

P.S. I'm getting over 3000 fps with the 150 grain GK and a hatfull of 7828 from the sevumag. Apples n carrots I know, just saying.

RJ

The Retumbo ship has sailed. We'll see how it shoots tomorrow. I have some 7828, but I've never gotten that to work for me for a precision load. But I've never worked very hard at it either.

The 150 is a good-looking bullet, but with the long case and the short (24") barrel, it just doesn't 'pencil out'. Both the 140 and 160 Accubonds will be the 'bullets of choice' as long as they shoot straight. I know this rifle is capable of 0.5 MoA, so any bullet I work on will have to get at least MoA. If Retumbo works, I'll probably give it a whirl with the 115-grain HP. It might push the MV another 150 f/s. I have US869 and H1000. I could try either or both if the Retumbo doesn't work.

Paul

I've taken more elk with the 150 from my 24" sevumag than any other rifle, that's why pencils have erasers



Recovered from under the hide from my last Montana bull. I trust the 150 to do the job out to 350 yards easily. 500 if I were pressed.

I don't trust myself alone when hunting with the sevumag. If I take it hunting I always kill an elk even though I was just thinking about it. Then there's the phone call.

"Hey Gunter, you busy?" :o

RJ

I would have to look through my records to recall what bullet I used most in my 7mm RM. I shot a lot of critters with it before I made the 7x300. I know I wanted to shoot the Barnes 195s, but because of their length, the 9.5 twist rate wouldn't stabilize them. Couldn't hit the broad side of a barn from the inside with those. (That was the beginning of my distaste for Barnes bullets.) It seems like I shot Hornady 154s most.  I know I also like the Hornady 162 BTSP. When I was doing a lot of experimentation, I loaded the 162s backwards. They shot straight, but they didn't perform well terminally. The butt-end of the bullet wasn't designed for "mushrooming". Ultimately, I went to the 115 in the 7mm RM. It was actually an accident. I went on a 10-day fly-in sheep hunt and brought my "regular" bullets (probably the 154s) and thought I would bring the 115s just in case we got sheep early and wanted to hunt some wolves. We flew in, unpacked the plane, put all the base-camp gear up in a tree, and headed off up the glacier. We hadn't gone but about 100 yards when I said, "We should probably load our rifles." I about passed out when I realized I had left my ammo on the front seat of my truck! I knew I had stashed the 115s in the cache in the tree. I was a little nervous about using them on big game, but I didn't have a choice. When I shot a ram right at 220 yds, and the 115 'hammered' him, I was hooked. I've never used another bullet in my 7mm Mags. I load my wife's 7x57 (ptooey) with the 139s. The 7x57 kills caribou, but not as good as a .308 Win does.

As long as it shoots straight, the 140 will be my bullet of choice. When I get some actual target time, I'll post some ballistic numbers.

Had I known what I know now, when I made the 7x300, I would have put a new, 28", barrel on it. That extra 4 inches makes a difference in these big-cased cartridges. Also, while I love the 7x300, for all the extra hoohah I have to go through to make ammo, it's not materially a better cartridge than the good ol' 7mm RM.

Paul

PS - I did use the 175-grain Partition quite a bit in both the 7mm RM and the 7x300 before I discovered the 115.

Paul

7x57 Mauser, 7mm RM, 7x300 Weatherby, 7mm Shooting Times Western. The 7mm STW looks bigger than the 7x300, but in fact, the Weatherby case has about 6 more grains of volume (97 for the STW vs 103 for the Weatherby). The 7x57 has the Hornady 139 Spitzer; the 7mm RM has (I think) the Hornady 162 BTHP, and the 7x300 has the Speer 115 HP.

Paul

By the way, I still have the 7x300 reamer. It has cut exactly one chamber. A gunsmith in Fairbanks did the work, and I must say that I have always been pleased with the result. I often get a hankerin' for that extra four inches, but when analyzed objectively, there's simply no good reason to scrap a rifle that shoots like a laser just to hope to get 150 more MV.

Also, the 7mm RM shoots that 115-grain HP with the same level of precision that the 7x300 does. It's just a good bullet design. Unfortunately, it has a poor BC. The 7mm RM and the 7x300 are Remington model 700 actions. The 7x57 Mauser is a model 77 Ruger. The Ruger has a HORRIBLY out of round chamber, but it shoots sub-MoA. It just occurred to me that I should scrap that 7x57 barrel and put a .308 Win barrel on it. Again, though, if it ain't broke... and this rifle ain't broke.

Paul