A Question for the Math Guys

jackie schmidt

jackie schmidt

New member
Today, a good friend had a 22PPC Short at the range, with 2 new 1-14 twist barrel.
To his amazement, very few of the bullets were reaching the target, vaporizing on the trip down.

He spent the better part of the day trying to figure out what was up. He put it through my Chronograph, and he was only shooting a tad over 3400.

He put on the second barrel, and it did not have any problems. I finally looked down the bore of the suspect barrel, and I could tell that it was WAY faster than a 1-14. It turns out, by checking it with a cleaning rod, it is either a 6 or 7 twist.

My question is, what RPM were those bullets spinning. Take 3400 fps at a 1-6.5 twist.

Another question. Since this was supposed to be a 1-14, and either got stamped wrong, or what ever, should the manufacturer be liable for all of the subsequent work ,ie, chambering and fitting it to the Rifle, as well as a new blank.

I have run into this in my business. We have put quite a few dollars in a piece of material that was on later inspection found to be flawed, and all the material supplyer would opt for is a new piece of steel. We had to eat the rest.........jackie
 
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Someone check me. There are 12 inches in a foot, so if we divide 6.5 into 12 we get the number of turns that the bullet will make in a foot, which turns out to be 1.85. Now we need to convert 3,400 feet per second into feet per minute. This we do by multiplying by 60, giving us 204,000 feet per minute. Finally, we multiply the number of feet per minute times the number of turns in a foot (204,000 X 1.85) and get 377,400 RPM.

If your friend paid a gunsmith to install the barrel, and the smith ordered it, to his specifications, then I would say that the smith is on the hook for the correctness of the barrel that he delivered, and that it is up to him to recover any costs from the barrel maker. On the other hand, of your friend dealt directly with the barrel maker, then the maker should furnish a barrel of the correct twist, pay for return shipping of the incorrect barrel, and the cost of chambering. Basically, in a perfect world, in either case, your friend should only be out his time. Now we all know that there is often a difference between what you want and what you get. Good luck to your friend.
 
Here you go

Here you go Jackie. Dimensional analysis 101. Luck, Tim

rpmformula.jpg
 
Ok my carpenter mentality says the bullet rotates 6276.92 times in one second taking for granted that it maintains that velocity thruout. 3400x12=40800/6.5=6276.92x60=376615.38 rpm
12 = inches per ft
6.5''= rev per inches traveled
40800 = inches traveled in one second
6276.92 = revs in one second or 3400 ft. assuming a travel at a constant velocity.
times 60 secs, = 376615.38 RPM

Aloha, Les
 
Jackie

I know wood and metal are 2 different things but it sounds like we have the same issues.
Whether wood or slides(metal) they all want to warranty THEIR product but nothing to the labor spent in fabricating or even replacing their product is ever included.
Sucks to me when a sheet of plywood delaminates or a slide fails they only warrant their part and to heck with all of your labor, initial or otherwise.
 
I ordered the two barrels myself. My gunsmith kept both cut-offs from the barrels. Both were stamped 1X14. I still have my invoice. I would guess that I will not be paid for the chambering, but
should be able to get a replacement barrel. This was the first time this has happened to me and it was quite an experience.

GW
 
Gary, at the very least, it will be interesting to see how they handle this. It is obviously a case of human error, but the human error that caused all of the calamity originated with the initial order, not with the purchaser, and not with the Gunsmith.

Large companies tend to have a policy that treats all the same. They warranty their part of the equation, and nothing more. Even though we purchase thousands of dollars worth of steel a year, we have never been compensated for cost that were incurred due to a problem that rendered the initial material non usuable for that application.

But please do ask. ........jackie
 
I know of at least one

Gary Walters said:
I ordered the two barrels myself. My gunsmith kept both cut-offs from the barrels. Both were stamped 1X14. I still have my invoice. I would guess that I will not be paid for the chambering, but
should be able to get a replacement barrel. This was the first time this has happened to me and it was quite an experience.

GW
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Barrel Maker that sent a friend two barrels for the bad one he got from them. This might be a fair thing to do. Share the pain, eh?
 
Maybe the first step to installing a new barrel should be to verify the twist rate - before the machining begins?
 
For those of us that are less mathmatically inclined, an easy rule of thumb is that a bullet at 3,000 fps in a 1-12 twist barrel will be turning at 180,000rpm. If the twist is 1-6 at 3000fps double the rpm. You can say slight changes in velocity or twist rate will change the rpm by a prorportional amount. 20% slower on the twist rate means reduce rpm by 20%. 10% faster on velocity means 10% faster on the rpm. It's possible to be somewhat close using estimations in your head. Just use the 3,000fps 1-12 rule as the baseline.
 
I talked to the barrel company this morning. They admitted that this happened to several people, so I am not alone. I have to return the barrel to them and then we will
discuss ways to solve the problem. I will ask for two barrels to soften the blow. We will see. I really like their barrels. This is a really great company and somehow one of
the barrels was rifled at the wrong twist rate.

GW
 
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Rpm ?

Does RPM decrease at the same rate as velocity? Just curious.

Les
 
LesWard said:
Does RPM decrease at the same rate as velocity? Just curious.

Les
Click to expand...

Les,

No. This can best be illustrated by an artillery shell fired at a high angle. The projectile will lose all forward velocity and fall to the ground, but still be spinning.

Ray
 
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I built a 22-243 on a 7 twist for the 90 grain bergers. So far every bullet that comes out of the barrel at full load explodes out in front about 25 feet. Even the 80 grainers at 3700 blow up quick. Unfortunately, so do the 90's. It doesnt surprise me that benchrest bullets are blowing up at that speed. We had to slow a 223 down to 3300 to keep 50 grain Hornady SX bullets from exploding in an 8 twist.
 
Pat B. said:
Good luck Gary...

My luck with them hasn't been so stellar as of late ....

In fact, it will be a chilly day before -------
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I guess I can forget name dropping. I had thought about dropping your name on them. I thought you had power and influence with them.

I'm not having much luck with barrels this year. Thanks for the heads-up Pat.

GW
 
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