Slow barrels

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tj66

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What makes some barrels run 2-300 fps slower than another? I've got 2 223ai's. One with a 22" Shilen bull 12 twist, and the other is a Savage 20" varmint that was set back and rechambered. Both with the same 0 freebore reamer. The Savage barrel will generally clock 2-300 fps faster than the Shilen using the exact same ammo. Both shoot light out with this load, but the fps is miles apart. Is this just Shilen related? My 22-250ai is Shilen also and it's a little slower than what guy's talk about but I haven't really stepped on it as it shoots well where it's at.
 
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This is a question that has bugged us since day one. I am not sure there is any one answer. In your case with two different manufactures it could be caused by any number of factors, but let me share something from the hay days of IHMSA. There were two brothers who built custom XP100’s for the unlimited class. They chambered them in 250 Savage. Accuracy was fantastic. Before they would ship them they tested them by shooting aspirin at 200 yard. Minimum requirement was three hits out of five. Somewhere along the line they built a matched pair. Cutting the two barrels out of one Douglas blank. All work done on the same equipment, same reamer, lath, mill etc. all reloading done on same equipment, components from same lot etc. both guns were equally accurate but 200 FPS difference. They made every measurement possible, could never find any difference in physical difference. Changed powder, bullets, primers, cases etc. it made no difference, one was consistently 200 FPS faster than the other. I write all this to say, some things are beyound explanation
 
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I usually don't pay much attention to trying to get every last bit of speed out of a barrel. I always run them where the accuracy is. This case just bugs me as the Savage barrel is 2" shorter, a copper mine inside and flat whips the barrel that should be higher quality. I've seen this mentioned on some high end barrels also and wondered what factors into this. The only difference in these rifles is one is a Ruger 77 that weighs around 12 lbs and the other is a Savage that comes in around 10 lbs. I've often wondered if overall weight plays into this as well.
 
On average, Savage just plain breaks the rules. Something like the old 788’s, they perform beyound what they look like they should
 
Originally Posted By: parsonOn average, Savage just plain breaks the rules. Something like the old 788’s, they perform beyound what they look like they should

This is true.
 
Smooth custom bore = more contact and more consistent contact with the bullet's bearing surface = more friction = less velocity? 3% variance?
 
I think that it is the luck of the draw. Bore dia varies, it is all over the map on anything but custom barrels, even then it should be checked for uniformity.

Over size bores are common, so are undersize. If the bore is not sealed, then gas blow by could create all kinds of wierd issues...over size barrels that we call Trombone barrels where the bore could open up from the breach to the muzzle...they are also wierd to tune accurately. One day, they are great, another day, not so great. They also change dramatically as more rounds are shot down the bore, warm barrel opens up the barrel even more.

It should be noted if the slower barrel copper fouls less or more, this is a good indication of bore dia.
 
It doesn't copper too bad. I've noticed the patches are tighter in it though. Most of the problems started when I ran it across the chrony. I need to just forget about it and run it.
 
It might be that the Savage is a 'fast' barrel. How do they compare to book speed?

I believe the internal barrel and chamber dimensions are, at least partly, responsible for 'slow' and 'fast' barrels.

25.0grs. of H335 has a given amount of energy, no more, no less. That finite energy has to swell the brass case to seal the chamber and then propel the bullet down the barrel with the remaining energy.

A loose chamber would use more of that finite energy to swell the brass case, leaving less energy to push the bullet. A bore that is very slightly oversized (or an undersized bullet) might allow some gas to force it's way around the bullet, leaving less energy to push the bullet, resulting in lower speeds.

My 1965 era, Winchester Model 70 in 30-06 requires 2.0grs. more RE19 to get to book speeds.

A buddy has 2 300Win Mags, a Hart custom and a Sako. The exact same load in the Hart is over 200fps faster, with no pressure signs. With a 178gr Barnes LRX, the Sako clocks at 2,950fps and the Hart is 3,175fps.
 
Both barrels are 223ai 12 twist. Chambered with same reamer with 0 freebore. 28.5 gr 335 with 50 NBT is 3360 out of 22" Shilen. Out of 20" Savage it's running 3550. Same brass, powder, bullets. Ammo headspaces the same in both guns and can be swapped. I would think the Shilen should be tighter, but who knows anymore. What is interesting is I have a 20" WOA 223 AR that when loaded with 27 gr 335 and 50 NBT that clocks 3350. Doesn't make any sense for the 223 AR to run right with the bolt action 223 ai. I've gotten the Shilen 223ai up to 3550 with H322 but blanked 7 1/2 primer doing it.
 
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There are so many variables to consider that could be making a difference.

One possibility is the depth of the grooves and lands could allow for more gas venting around the bullet, thus lowering the velocity.

Another possibility is the material that the barrels are manufactured from. Not all metals are equal.

The barrel profile could be accounting for the difference. As the bullet is travelling down the barrel the barrel slightly deforms due to pressure and the bullet driving through it.

As far as an AR staying with a bolt gun in terms of velocity, that is apples to cantaloupes. It has more to do with the caliber, bullet selection, barrel, etc than with the platform as the chronograph showed.

Thanks for sharing the observations.
 
Originally Posted By: tj66One with a 22" Shilen bull 12 twist, and the other is a Savage 20" varmint

Right off the bat, 2" of barrel length will make a considerable difference in velocity.
 
Originally Posted By: reloader326Originally Posted By: tj66One with a 22" Shilen bull 12 twist, and the other is a Savage 20" varmint

Right off the bat, 2" of barrel length will make a considerable difference in velocity.

Right, but he said the shorter barrel is faster. Is that load max in the Shilen? It may take more powder to get there, but I'd think you should be able to get close to the other one. Could try moly or hbn coated bullets as well.
 
Originally Posted By: desertcj Originally Posted By: reloader326Originally Posted By: tj66One with a 22" Shilen bull 12 twist, and the other is a Savage 20" varmint

Right off the bat, 2" of barrel length will make a considerable difference in velocity.

Right, but he said the shorter barrel is faster. Is that load max in the Shilen? It may take more powder to get there, but I'd think you should be able to get close to the other one. Could try moly or hbn coated bullets as well.

I've gotten the speeds up with different powders but was blanking primers before I caught the Savage barrel. Accuracy wasn't good either. It just doesn't like the gas pedal stepped on.
 
My barrels must be fast barrels cause I can't ever see the bullets.
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Originally Posted By: pyscodogMy barrels must be fast barrels cause I can't ever see the bullets.
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It's like I said earlier... didn't have this problem until you guys convinced me that I NEEDED a chrony.
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Originally Posted By: pyscodogThese guys on here have no problem helping you spend your money!!

They are good at that!!
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