Barrel wear: 7mm Rem Mag vs. 300 Win Mag


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ForeverArmed
January 6, 2007, 06:05 AM
Hi folks,

I'm in the market for a new bolt rifle and and am mainly considering the above two calibers. One thing I'm wondering about is barrel wear: I seem to remember reading somewhere that the .300 has only about half the barrel life of the 7mm. Is that true? And can anyone provide an estimate of the barrel life of either of these for long-range target shooting (which is something I'd like to get into but have little experience with)?

Thanks.

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ojibweindian
January 6, 2007, 12:12 PM
Barrel life estimates:

http://fieldandstream.blogs.com/gunnut/2006/04/barrel_life_par.html
http://www.socnetcentral.com/vb/showthread.php?p=826683
http://www.riflebarrels.com/faq_lilja_rifle_barrels.htm#Life

Looks like, for the 7mm Remington Magnum and 300 Winchester Magnum, barrel life ranges from, on average, 1500-3000 rounds, based upon what these articles present.

My bet is that, unless you're really good, or a bench rest competitor, you won't ever notice slight barrel wear that would reduce your groups a few tenths, or one-hunredths, of an inch.

Plus, if you reload, you don't have to accept screeching velocities. Load to the slower velocities you want, and you'll most likely (depending on the powder chosen) extend the life of your barrel.

Grumulkin
January 6, 2007, 12:55 PM
You said "caliber" so I assume you're talking about barrel diameter and not about a particular cartridge in that caliber. If this is true, there should be no significant difference in wear between a .308 caliber weapon and a .284 (7mm) caliber weapon providing powder capacity and bullet velocities were about the same. I also believe that you would have to shoot close to 5,000 rounds out of say a 300 Win. Mag. before you would have barrel wear that would affect accuracy enough to notice. A 300 RUM would probably be harder on the barrel and a 300 Whisper a lot less hard on the barrel.

aspade
January 6, 2007, 12:57 PM
All else being equal, the chambering with the greater powder to bore area ratio will erode away the throat faster.

The 7mm RM is more overbore than the .300WM, but the difference is only about 3%. In practical terms, there will be no difference in barrel life.

CB900F
January 6, 2007, 01:15 PM
Forever;

It would be interesting to know if you're a reloader or not. That's one area that allows you to control many of the variables that contribute to 'barrel wear'.

The other, and vastly more important, variable is the time the barrel is allowed to cool between shots. Consider this, either is propelled by incandescent gasses at something around 55,000 psi. That gas column is as hard as steel I'd think. An acetylene torch doesn't pack the pressure of the gas column behind either one of those rifle calibers.

The saving grace of the conditions in the rifle barrel is that the duration is measured in micro-seconds. However, if you shoot at a rapid pace for an extended length of time, you are going to significantly accelerate the throat erosion of the barrel. And that's going to occur regardless of which caliber you choose.

IMHO, the erosion factor isn't one of caliber in this case, it's one that you yourself control.

900F

900F

dakotasin
January 6, 2007, 01:39 PM
agree w/ cb.

barrel/throat wear is vastly overrated for non-br shooters. i have 7 rem mags, 7 rums, 300 win mags, and a 300 wsm and barrel wear still has not become a concern to me - and i shoot a lot.

ForeverArmed
January 6, 2007, 04:28 PM
Thanks for the replies, guys. It sounds like I heard wrong about the 7mm Rem Mag having twice the barrel life (all other factors being equal).

I'm not a benchrester and am not even really interested in competing at this point (or good enough yet), so a little opening of the groups will not be something I'm likely to notice. Basically, to me a "shot-out" barrel is one that can't shoot as well as I can -- and I'm certainly not going to be dominating the competitive world any time soon. :)

It would be interesting to know if you're a reloader or not. That's one area that allows you to control many of the variables that contribute to 'barrel wear'.Nope, I'm not a reloader (yet). That is something I'd like to get started with at some point. For now, though, I'm pretty much stuck with commercial stuff.

hagar
January 6, 2007, 07:27 PM
You should still consider the 7mm, as it has superior ballistics and sectional density compared to the 300 Win mag.

CB900F
January 6, 2007, 09:48 PM
Fella's;

Well, I don't believe that previous statement holds true across the board. The 7mm simply does not have the heavier bullets available to make a one-for-one comparison. When one consults Speer #13 though, the 7mm 175 grain data does not in fact show a superiority to the 180 grain .30 caliber bullets in the .300 Winmag data.

The best B/C of Speer's 175 7mm's is .465 with a sectional density of .310, and a max velocity of 2940 fps. The .300/180 data shows a best B/C of .540 boat tail, or .483 spitzer, sectional density of .271, but over 100 fps faster in three loads.

It's obvious that when heavy bullets are used, the .300 delivers more energy on target.

The above comparisons also only show the closest bullet weights at the top of the 7mm scale. Keep in mind that in the .30 caliber lineup, there are many bullets available from several different manufacturers that go up to 220 grains in weight. Which, of course, improves the sectional density and B/C to the detriment of velocity.

Another useful bit of information to know is that B/C is a moveable feast. The single number shown in load manuals is not a constant. B/C will change with velocity and air density.

900F

Shrinkmd
January 6, 2007, 10:29 PM
I see the question get tossed around from time to time.

Given using open sights and surplus ammo at 100 yd or so, can you ever shoot out your mosins and mausers? I know that you're supposed to stop shooting for a bit if you can't touch the end of the barrel for more than an instant.

I can't imagine only putting 200 rounds through a bolt action. I like putting about a hundred or so through my mosin every trip to the range!

Then again, we have no idea how many miles are already on these "pre-owned" rifles:)

hagar
January 6, 2007, 10:57 PM
According to my ballistic calculator, if you start a 180 grain Sierra Spitser BT out of a 300 Win mag at 3100 feet/sec, at 500 yards it will have a remaining velocity of 2266, energy of 2051 ft/lb and drop 60 inches. A 175 Sierra from a 7mm mag with the same velocity will have a remaining velocity of 2304 feet/sec and 2063 ft/lb and drop 55 inches. At 1000 yards the 7mm will still be going at 1644 feet/sec with 1051 ft/lb and drop 282 inches. The 300 on the other hand will do 1583 feet/sec, have 1002 ft/lb remaining and drop 290 inches. The 7mm will have better penetration because of better sectional density. Maybe the 300 Win can use heavier bullets, up to 220 grains while the heaviest bullet I see listed for the 7mm is 195 grains. Let's take the heaviest low drag bullet, the 220 grain Sierra HPBT Matchking at 2800 feet/sec. At 1000 yards it will go 1607 feet/sec with 1262 ft/lbs of energy and drop 327 inches. You can push a 7mm 162 grain AMax bullet at 3200 feet/sec easy, and it will still do 1895 feet/sec at 1000 yards and have 1292 ft/lbs of energy left, and drop only 243 inches. The 7mm wins hands down in my book.

slzy
January 6, 2007, 11:31 PM
nothing is gonna last for ever. do what ya want when you can. i mean if you have a vette or a cobra,yer going to do the rings eventually.

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