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Gunsmithing 243 Chambers

Re: 243 Chambers

i wish i had a link for you, i just read on the same subject, with test results. the results they came up with was, like you said, just case capacity, coupled with longer barrels, is how they get those higher velocities. thier research shows that there is no majic shoulder angle.

i wish i could remember where i read that, it might've been on the hide, but it was withing the last few days...
 
Re: 243 Chambers

What are you seeking to accomplish? What kind of shooting? You may find that there is no reason to deviate from a plain ol' .243.
 
Re: 243 Chambers

larger capacity=more velocity= shortening an already limited barrel life= less $$$ in your pocket

A standard 243 would be as large as I would go. We went through the 243 Imp phase about 15 years ago in 1K comp and found out barrels don't last long enough. There are some bullets that you would use that can't stand the velocity and spin rates of several of those cartridges. I know of no one who shoots one in 1K BR competition now.
 
Re: 243 Chambers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Tooley</div><div class="ubbcode-body">larger capacity=more velocity= shortening an already limited barrel life= less $$$ in your pocket

A standard 243 would be as large as I would go. We went through the 243 Imp phase about 15 years ago in 1K comp and found out barrels don't last long enough. There are some bullets that you would use that can't stand the velocity and spin rates of several of those cartridges. I know of no one who shoots one in 1K BR competition now. </div></div>

That about covers it.

Most shooters I know, myself included, are looking into reduced capacity cases (6XC, 6Creedmoor, 6-6.5x47L, Super6LR, etc)that can still shoot 107-115's@3000-3100fps and extend barrel life.
 
Re: 243 Chambers

When people discuss shorten barrel life, that definately means different things.

I've asked many of people who state that but never give an accrurate answer.

If the rifle is a BENCHREST only rifle i can see that being extremely important if your not gettting tiney groups. What do you consider is shorten barrel life?? 1000rds, 1500, 2000, 5000????

IF its not a benchrest rifle.
When the barrel was new and the rifle shot .25moa and after 1500rounds it shot 1/2 moa and then after 2500 its still under 1moa groups. Whats the problem???


Also so whats the difference between the diffeences of those 243 cases above??
 
Re: 243 Chambers

What are the pros and cons:

243 Super Rockchucker
243 Winchester Ackley IMP 28º
243 Winchester Imp 30º
243 Winchester Imp 40º

We all know more capacity resulting in great velocity, but you say barrel life. (see comment above)

A Standard 243 going to the 28degree vs the 30degree vs the 40degree. whats the difference?
 
Re: 243 Chambers

What we saw for barrel life in 1K comp was accuracy would start to fall off after about 900 rounds. We could stretch the life out to maybe 1200 but at that point the throat erosion and heat checking were getting bad. The heat checking had an affect on bullet life. The effect was you didn't know whether the bullet was going to reach the target. In the winter you get by but in the summer heat which was when we shot most of our matches it was very easy to turn bullets in grey clouds. Once the heat checking got unmanageable you screwed a new barrel on.

Comparing all the cases you listed the one thing that seperates them from a std 243 is work, velocity and money. All have to be fire formed which means even shorter barrel life. I haven't shot all those rounds so I can't give velocity differences. I shoot a 243 Ack but I use 80 gr bullets not heavy bullets at about 3500 FPS. I do not like 40 degree shoulders. I've made FL sizing dies for a lot of the calibers I chamber for and 40 degree shoulders are a pain. You don't really massage the shoulder back, you collapse the sidewalls. Brass work hardens and then you get inconsistent bump back. I like no steeper than 30. Body taper is something else. I don't like them too straight either.
 
Re: 243 Chambers

Thanks Dave. would you say you started off a .25moa or better setup and your accruracy would fall off at 900rounds? What would it be at 1200rds? 1/2moa?? Did you cut barrel shorter and set back or did you install new barrel.
 
Re: 243 Chambers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: matthewusmc8791</div><div class="ubbcode-body">
Also so whats the difference between the diffeences of those 243 cases above??
</div></div>
The oddball in that list is the 243 Super Rock Chucker. It is based on a 30-06 case. It will require a long action.
 
Re: 243 Chambers

Matthew

I can't give you a number that would mean anything to you. The decision to replace a barrel can only be made by you for reasons that only matter to you. Here's what I/we do with our 1K rifles. Most of us tune rifles at 100-200 yds. Some use chronographs some don't. Then we sit shoulder to shoulder 10-12 shooters at a time and have a tough man contest. One winner for group and one winner for score move on. The target tells you how your rifle is shooting and then we adjust accordingly. Maybe a little more powder, maybe a change in the seating depth to change the pressure. To be competitive rifles have to be capable of shooting groups that <span style="font-weight: bold">measure</span> .4MOA or less at 1K. Less is always better. I've seen days when a 5 shot 3" group got you nothing except a little sympathy and you got very little of that. I've seen days when a 5" 10 shot group got you nothing. It's the shooting shoulder to shoulder thing that tells us when it's time to move on to a new barrel. When you get tired of getting beaten by your loud mouth buddies there will come a day when the decision is easily made for a new barrel. The smaller rounds are affected more by age and heat checking than say a 30 cal. When they die it's usually in a pile. 30's seem to fade off into the sunset. I still have some old 30 cal barrels around that I could screw on and be competitive. When I shot a great deal I timed my barrel replacements to be ready for the National Championships. I always wanted at least one category of rifle with pretty fresh barrel on that had already proven itself and the other one still shooting well maybe half way through it's life.
As far as setting a barrel back. I don't do it. There are a number of reasons. From a smiths standpoint all that heat checking is full of carbon and extends a long way down the barrel. Reamers aren't cheap and neither is my labor. You're better off to run that barrel until you lose confidence in it then screw a new one on. Labor costs the same either way and you may only extend the life of the barrel 30% and that's only if you do it early before it's toast, burnt toast.

I have a stereo microscope for close up inspection here in the shop. Here is a pic of the interior of a well used barrel between the lands. 338 Lap Imp 1173 rounds 15" down the barrel. That's heat checking with the cracks full of copper. That barrel's toast. No reason to rechamber it.

If you look closely at the picture you'll see there is no copper on either side ( top or bottom). The copper shows the contact area of the bullet in the groove. The bullet touches maybe 40% of groove with the base upsetting to form a gas seal.


33815groove1173rnds.jpg
 
Re: 243 Chambers

Dave,

You should do a barrel pic thread. Your posts are more informative than entire books I have read on the subject, complete with excellent pics.
 
Re: 243 Chambers

If I had time to do it properly I'd get with Frank and discuss the best way to put it out and keep it available to everyone. Right now I'm just too busy. It takes time to inspect and dissect barrels, photograph and catalog everything. I would want to shoot out a couple of barrels, different calibers, while documenting with photos the deterioration of the bore then section and take detailed photos in one inch increments down the barrel. Maybe some day when I'm rich and have nothing else to do.
 
Re: 243 Chambers

I know you have probably answered this before, do you have any advice about extending barrel life in calibers like 300 win mag? Nitride, cleaning processes, different types of rifling, buton barrels vs cut rifling?
 
Re: 243 Chambers

Nitriding works. I haven't shot out a nitrided barrel yet so I have no first hand knowledge of how much longer they last. I hear numbers like 2x or 3x longer but I find that hard to believe. cut vs. button no difference it's the same steel. The most important thing is managing carbon build up and heat checking. Carbon will raise pressures considerably. You can't abuse a Win Mag like you can a 308W. Heat checking has a carbon element to it but when the cracks get large enough to strip off jacket material as in the photo the accuracy of the barrel is pretty much gone and can never be brought back. On a Win Mag I would start using abrasives around 300-500 rounds depending on how it was treated. Heat is a barrels enemy. One string when the barrel is smoking hot and you've done some damage. The larger the cartridge the more damage is done.
 
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