Ruger American longevity/wear update

Hey RCP,

Did your COAL start to change before the barrel was removed for one of your other threads ?

This is a really curious issue you have with your .270 RA.
 
Yes, its been an on going change. I think I only have 100 rounds or so though it since I pulled the barrel off, maybe 150.
 
barrel life of a machine gun can be as little as 150 rounds that is why crew served weapons come with an extra barrel
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A mg barrel will not be shot out in 150 rounds. For one, there are only 100 rounds in a belt so you cant go cyclic for 150 and even in cyclic fire you dont have to change the barrel for 1 minute. You basically have to warp a mg barrel to destroy it. Keep in mind, these barrels arent designed for MOA groups. Crews have multiple barrels to keep from warping a barrel under sustained fire and change it out in different time intervals depending on their rate of fire. For example, 6-9 round bursts the barrel is changed every 10 minutes, 10-13 rounds bursts every 2 minutes, and cyclic every minute. Thats all for a 240B.

The OP seems to be having problems with throat erosion from hot loads not from the barrel getting too hot. I would just back off the loads some to make the barrel last longer or have a gunsmith take a few threads off and rechamber.
 
A 308 is not barrel friendly unless its a low load. Otherwise it wears a barrel out at the same rate.
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I always thought velocity and rate of twist matters . If I understand you correctly , You are saying a standard 308 168gr GMM with a velocity of 2650 will burn out a barrel just as fast as a standard Hornady 270 130gr sst with a velocity of 3050 . Both having a twist of 1-10 . I always thought bullets that travel over 3000fps are the barrel burners .
 
Barrel burners have less to do with the speed of the bullet and more to do with the amount of powder going through a given bore, and barrel heat.
A 223 can quite easily exceed 3000fps with light bullets and it is far from a barrel burner, while a 7mm Rem Mag won't touch 3000fps with 180gr and it is well known for short barrel life. The whole barrel does not wear out at the same rate, the throat wears out much faster as a result of the rolling flowing vortex off the shoulder of the brass, the gases in that vortex are as hot as anywhere in the system and are moving faster then anywhere else, combined with unburnt powder creating an abrasive effect that is where the erosion comes into play.
Measuring the volume of powder being burnt per sq inch/mm of bore is a much better indicator then the speed of the bullet, though in general higher speed cartridges are more overbore.
A 270 Win is a bit overbore but not excessively so, 2000+ rounds would be the norm probably twice that if you did not need match grade accuracy.
The rate of erosion is not a linear equation, a .308 pushing aprox 45gr of powder through a .30 cal bore can have an effective barrel life in excess of 8,000 rounds, while a 300 Win Mag pushing aprox 72gr or powder through the same bore can cut that to 1,500-2,000.
 
I'm in RC's camp...
Calling bs on shooting a "hot" barrel as cause for premature wear.
I've seen, but can't recall, sustained fire rates for the M4/AR platform and I don't think you could duplicate them and get the barrel hot enough with a bolt gun even if you tried.

Throat erosion is a different story but that's a function of the amount and rate of powder burn and the bore diameter as has been correctly mentioned above. Pushing a lot of combustion gas through a small diameter bore-like the .243- is what burns/erodes the throat of the chamber, not repeated firing.

When the op said he thought it would be shot out at 1000, the .243 is what I suspected as 1500 or so is about what's expected with best performance.
 
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Barrel burners have less to do with the speed of the bullet and more to do with the amount of powder going through a given bore, and barrel heat.
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I've heard the 243 is a barrel burner and the 308 not so much in comparison . Why is that if they share the same case and the 308 generally has more powder per round ?
 
Think of the neck of the bullet like a nozzle. The smaller the diameter the more focused the stream coming out. Plus there is less surface area in the bore of the .243 to be eroded than that of a .308 Win.
 
I haven't been firing excessivly hot loads, never at max, but I have come close with 7828 just to see what it would do. Most of my loads are middle of the road.
 
I haven't been firing excessivly hot loads, never at max
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I've shot hand loads from 2600-3200 FPS, 130 and 140gr bullets
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Quickly looking at three of my manuals, not one of them gets to 3,200 fps with either a 130 or a 140 grain bullet 270 Winchester load.

I too would be concerned about the amount of life left, or something, given just how far out those bullets are seated; and how quickly the COL has grown! (Maybe your brass is shrinking!!!)
 
Would 50 or 60 rounds that fast cause it though? That was a NEAR max load with 130gr bullets, and 7828. I haven't used that load since probably March.

They chronoed at 3160-3198, average 3180 over 8 rounds.

The bullet is still pressed into the brass about 3/8". I measure the brass every time. Ones below spec are tossed, and long ones are trimmed.
 
Curious for a clarification...
You say your OAL is .1 longer now to seat the same distance off the lands.

I assume you're using a bullet comparator to get that length- but when using a comparator we normally don't even refer to "OAL" as it's irrelevant because it measures to the tip of the bullet and not the ogive. None of my reloading "recipes" use OAL. It's all comparator lengths.

Is that ".1" the increase in the relative measurement using the comparator?
 
243s and 308 use about the same powder charge they use the same case, so lets compare the powder charge by sq in of bore using a 45gr powder charge for both.
.243 Win .0464 sq inch bore area 969gr per sq inch
308 Win .0745 sq inch bore area 604gr per sq inch

So the 308 is considerably less harsh on barrels then the 243. Anything running over 1,000gr per sq inch tends to be very hard on barrels regardless of the bullets speed.
 
They chronoed at 3160-3198, average 3180 over 8 rounds.
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130 GR. HDY SP IMR 7828 .277" 3.280" 56.0 2862 43,800 CUP 60.2 3085 50,300 CUP
http://www.imrpowder.com/data/rifle/270win-2005apr03.php
I would think that those rounds were "pushing" it a bit; now just how much more that might have accelerated erosion I am nowhere near an expert, but it appears that those 50-60 rounds were a bit on the "hotter" end.
(It is possible that your load data was from an older source; however, at those speeds, current data from the manufacturer would look like those loads were over max. Then again, none of this is taking any other variables into consideration...)
 
Quickly looking at three of my manuals, not one of them gets to 3,200 fps with either a 130 or a 140 grain bullet 270 Winchester load.
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Alliant Powder's Mag Pro is the only powder that I know of that lists 3200 fps for a 130 grain Nosler BT bullets.

Magpro 130 NOS B-TIP (min) 58.5 gr 2,919 fps (max) 65.0 gr 3,234 fps 63,200 psi
 
Did you try this COAL to start with? It could be that you could have used that length to begin with. Different bullets can be loaded longer than other bullets of the same weight.

In my varmint rifle, Cooper MDL 22 VDM, 6.5/284, The longest I can load the 142gr SMK is 3.1". I can load the 140gr Berger VLD match to 3.15".

I was able to call the boys in Stevensville and get the load they used for the test. They recommended I start at 3" and work my way out.

I have had to do everything from scratch, no factory ammo available. I couldn't be happier, 4 shots to zero and the next three were under .3". That's considerably larger than the test, but but I'm satisfied for now. I have yet to shoot the Berger loads.

Point is that I've learned that loading manual COALS are really just suggestions. A safe place to start.
 
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