I need some advice from the guys that have been doing this much longer than I have. I am loading 90gr Swift Scirocco II bullets, using S365 powder (South African equivalent to IMR4350 I believe) and CCI250 primers in Federal cases. I've seated the bullets .020" from the lands and shooting them out of a brand new Weatherby Vanguard. My problem is that when I run them through a chronograph, the muzzle velocity is roughly 400fps faster than what is stated in the manuals. I started at 40.7gr powder and was working up from there. When I got to 42.5gr, which is roughly in the middle of the spectrum, it blew a primer out of the case. What should I look at to figure out why I am getting these high pressures?

While I've only had one .243 calibre rifle, one thing I was told by another .243 shooter and hand loader was to keep an eye on my case length and outside neck diameter so it doesn't grow too long and cause excessive pressures caused by the necks growing too thick and therefore an issue to release the projectile. This could be one cause for a blown primer. To alleviate this problem I outside neck turned my .243 cases, and always checked overall case length and never had any issues.

In Cartridges of the World, in the chapter on Wildcat Cartridges when talking about the .243 Ackley Improved, (which is the .243 blown out with a 40 degree shoulder and less tapered case), the .243 was described as a bad actor by a number of ballisticians at a number of major ammunition companies because what can be a perfectly normal load can all of a sudden exhibit signs of excessive pressure. According to a number of hand loading experts, it has something to do with the throat design.

That is interesting about the velocity you are getting. I have in my own rifles experienced up to an extra 150 - 200 fps speed over published data, sometimes by 4 to 5 grains over maximum (but only after careful load development) and these loads were perfectly safe, however I have never got that speed you are getting with a conventional lead / copper projectile. I know some rifles have a 'fast' barrel. The powder you are using could be of a slightly different burning rate which may contribute to your faster load. A good example is Hornady Super
Performance which although has a burn rate similar to 4350 type powders actually can give well in excess of 100 fps, according to the manufacturer.

In general, apart from the one load that blew a primer, what have pressure signs been like with some of the other cartridges you have fired through your rifle?

I don't know whether QA on Swartklip powders has improved, but they tended to vary a bit from lot to lot.

If you have a load that is giving your 400fps more than it "should" it means that the pressures in the chamber are higher than the one they developed their loads in, or you have a very fast barrel - from what you say about blowing primers, I'd say it's the first.

Drop back to what the manual tells you to expect and start looking for an accurate load and then stop.

That's what I would do, but I tend to develop a load until I get decent groups - check over the chrony to make sure I'm in the ballpark - 200fps low is neither here nor there, and consider my work done.

quote:

Originally posted by Matlabas Hunter:
I need some advice from the guys that have been doing this much longer than I have. I am loading 90gr Swift Scirocco II bullets, using S365 powder (South African equivalent to IMR4350 I believe) and CCI250 primers in Federal cases. I've seated the bullets .020" from the lands and shooting them out of a brand new Weatherby Vanguard. My problem is that when I run them through a chronograph, the muzzle velocity is roughly 400fps faster than what is stated in the manuals. I started at 40.7gr powder and was working up from there. When I got to 42.5gr, which is roughly in the middle of the spectrum, it blew a primer out of the case. What should I look at to figure out why I am getting these high pressures?

Where are you getting your reloading data? Is the data specifically for S365 and is it coming from the powder manufacturer?

400 fps over book values says the pressure is extremely high.

I reload for three different 243 rifles and reloading for the 243 is not any different than for any other modern cartridge.

Try slipping a bullet into a fired case, if it goes in with little to no effort it shouldn't be a neck thickness issue. If you're getting too much velocity you have too much pressure. Sounds like an overload.

Re check your seating depth/distance from the lands.
I found the shape of the Scirocco's difficult to get accurate distance from the lands measured, I ended up seating them what seemed was overly deep to avoid piercing primers.

The Federal cases have smaller internal volume than Remington and Winchester and that can cause higher pressure. The 243Win that I loaded for with a 100 grain bullet seemed to hit the high end of acceptable pressure at 40 grains of IMR4350, and the bullet seated to touch the rifling. This load in that rifle was more accurate than most experienced shooters, as in groups that were to small to measure. It seems to me that you are just trying to push them too hard.

Matlabas: While this is not a 243 story, it may apply to your particular rifle. Some time ago, I wanted to change my AR 15 barrel to a match barrel with faster twist, so I could shoot the across the course matches. So I bought a brand new DPMS barrel, and installed it, then went to shoot the loads I had worked up previously. I know this is a little long, but bear with me it may help solve your situation. As I shot the 1st few over the chronograph, they were over 300fps faster than the previous barrel, and the book. After a couple, they began to stick in the chamber and tear the rim off the cartridge. I tried for a couple years to figure this out, and I was not successful, Even DPMS could not help. So, I started loading down when I got about 1.5 grains below minimum the velocities fell in line, and the rifle operated perfectly. When I talked with DPMS about this and told them the original barrel performed as the book stated with the same loads. the only thing they could figure, is a small bore or chamber. I really don't care what the problem was, but when I loaded down all things worked out. Maybe you have one of those below minimum chambers/barrels. Just a thought.

Jerry

This makes little sense. If the OP's powder is indeed the same as IMR4350, then 42 grains should give 2958 fps according to Hodgdon. Is the OP actually getting 3358 fps? If so that beats max listed velocity from a .240 Weatherby by over 100 fps. 400 fps more is a LOT!

Questions like an inaccurate powder scale or the wrong or mislabeled powder come to mind. A tight chamber won't give that kind of pressure/velocity increase, I had a .257 Weatherby built with a minimum chamber which won't chamber some brands of brass, yet I could not measure a velocity increase versus a factory chamber with a chrono (was within the ES of the load). A tight bore? High pressure perhaps, but I can't imagine a 400 fps increase. Something just doesn't sound right.

But whatever the reason is - the OP should concentrate on reducing the load to a safe level.


.

I had a similar issue with a friends two 300win mags, one is a Sako and the other is a custom by Hart.

The max load in the Sako shot a 180gr Barnes TSX at about 2,950fps, and we started to get sticky bolt lift and flattened primers.

The exact same load in the Hart and we got 3,175fps without any signs of high pressure.

We assumed the Hart had a tight chamber/barrel causing the increased speed. That high speed was disconcerting to me so we dropped the speeds to 3,050fps and called it good.

On a side note, that was my first experience with a custom. Man, what an accurate rifle they are!

I agree! 400 fps is huge! Something fishy for sure. I'd check everything twice before I shot anymore of those loads.
Good Luck.

I have noticed custom barrels almost always produce published max velocities with a less powder - sometimes a lot less.

One of my reloading manuals mentions case brand as being very important with the .243
I cant remember witch. But I had the same issue with lapua brass and the .308.
I sugjest you scale your brass and do the same with Winchester.
I bet you Federal weighs more. AK thicker walls.
less volume Higher pressure !
...tj3006

Try Federal or Winchester primers. Work better for me. Little softer and seal better JP

Mate, check your load data again, you're two grains over max.
You started 0.4 grains over max...

I don't think this powder is a 4350 equivalant.

http://www.somchemreload.com/search?c=8&f=33

I loaded some cast bullets in my .243 and the Lyman manual said I should get a little over 2400 fps. I was 1/2 grain under max. A guy's chronograph showed 2900 fps. The other guns I checked on the chronie got expected results. The chronograph owner had shot several rounds over it and he said all as expected. I was not getting leading and accuracy was good. No signs of over pressure. Tried it on a deer and the results dismal.