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Barrel Life

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britrifles View Drop Down
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    Posted: July 19 2021 at 2:42pm
My Long Branch No. 4 Mk 1/3 is a great performer in the vintage military Rifle matches, and I’m not looking forward to the day that accuracy drops off.  It may suddenly occur, as the bullet looses stability from the advancing throat.  It’s a BSA 5 groove that was new when I got the rifle. 

I came across an interesting article written by Col. B.R. Lewis and a staff member at Frankford Arsenal, in the late 1950’s, on .30 Cal (.30-06) barrel life.  Test barrels at FA showed a gradual accuracy improvement when shooting the M72 Match cartridge (172 gr Boattail hard point and IMR 4895 Powder), quickly for the first 500 to 1000 rounds, then slowly out to about 7,000 rounds, then leveling off from 7,000 to 10,000 rounds.  No data beyond that.  

What is really interesting is a statement made that M2 Ball (152 gr flat base bullet) did not show this trend.  Accuracy leveled off after only 2,000 rounds and then started “to deteriorate a few thousand rounds after that”. 

I wondered why this would be.  I suspect it may have something to do with the bullet velocity and amount of powder in the case causing the M2 cartridge to wear the bore faster. If that is true, then shooting the 174 gr SMK with a relatively mild charge of powder in the .303 might explain the long barrel life I’m getting with my No. 4.  I don’t know how many rounds I’ve put through it, but I suspect it’s in the 8,000 to 10,000 range.   

New barrels are hard to find, I just hope it keeps performing for a few more years of shooting…




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2021 at 3:40pm
I think you have a valid point.
Backing off "hot" loads prolongs barrel life, so maybe firing a fairly mild load (like .303) & backing THAT off should give much more barrel life.
After all, historically speaking, loads about 100 FPS under MAX usually give better accuracy too.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2021 at 4:15pm
Thats what I’m hoping for Shamu.

The M72 .30 Cal match loading was relatively mild (compared to the M2 Ball ammo), loaded to 2640 fps, measured 78 feet from the muzzle.  The M72 bullet is quite similar to the 174 gr .311 SMK, which I am loading to around 2380 fps, measured 20 feet from the muzzle, in the .303.   

I’m now tracking round count in all new barrels I install.  I put a new barrel on my M1 in March of this year, and I’m already at 870 rounds fired over the last 4 months.  It’s shocking how quickly it adds up, I’ve probably shot a similar number of rounds thru my No. 4 over this same period.  Extrapolate that back 5 years when I started serious match shooting practice mode and I’m now over 10,000 rounds thru each rifle.   



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2021 at 9:07am
I think that the modern powders are easier on the barrel throat than the older cordite stuff. So combine that with dropping the velocity a wee bit and I think you have a substantial difference in bore life expectancy. 
Obviously cleaning routine may play a role as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2021 at 10:43am
Yes ^^^^this.
I use the "M-pro-7 Bore Cleaner & Copper Remover" (2 separate chemicals you alternate them when cleaning) I no longer brush except for the first 3 dry passes to remove loose stuff.
I find patches on a jag & letting solvents do the work chemically cleans well enough, & the M-Pro was the first "modern" ammonia (& smell) free chemicals that actually dissolve copper as well as fouling.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2021 at 11:55am
 I’ve probably been overzealous with my cleaning of rifle bores in the past.  Barrel makers caution you from pulling a brush or jag back into the bore when exiting the muzzle.  I used to use a nylon brush every time, pulling it back into the bore.  But, even after 10,000 or so rounds, it still shoots very good.

Cordite is well known to burn hotter than NC powder, and accelerate throat erosion.  The FA tests done in the 1950’s with M72 Match ammo was with IMR 4895.   

James Sweet in his book Competitive Rifle Shooting stated that 7000 to 8000 rounds can be expected from a .303 barrel before it is worn out at the rifling lead.  He does not say if this is firing Mk 7 or 7z ammunition.  The first edition was written in 1948, so it may have referred to Cordite.  Does anyone know what propellant the Australian ordinance factories used during WWII?  If it was mostly Cordite, he may have been referring to that.  Since Sweet was a Australian shooter, I suspect he mostly used AU made Service Ammunition. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote BJ72 Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2021 at 2:59pm
All military Mk7 ammo loaded in Australia was with cordite and corrosive primers. Certainly into the late 50's anyway. There was some commercially loaded ammo with NC powder but surplus ammo was so readily available back than it would have seen very little use. I haven't read Mr Sweet's book but if it was written back in the 40's, I'd be willing to bet he was referring to cordite loaded ammo with corrosive priming to boot. Providing the rifle was cleaned straight away, the corrosive priming shouldn't have had much affect on barrel life, if any at all. The cordite was the culprit for throat erosion. So many 303 barrels were ruined in this country though by shooters who knew no better and didn't clean them properly after using corrosive ammo. You still come across rifles that seem to have done limited work with barrels you can hardly see through for rust. I think most people would struggle to wear a 303 barrel out. It's only high volume shooters like you britrifles who can hope to achieve that milestone. You're making me jealous LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2021 at 4:07pm
Thanks BJ72, I suspected that the AU .303 production was mostly Mk 7 Cordite.  Sweet does cover cleaning methods to neutralize the primer salts and in several places refers to the propellant as Cordite. 

So, if barrel accuracy life with Cordite was 7 to 8,000 rounds, I can hope for double that with shooting exclusively NC powder loads. Smile That’s very encouraging….

I try not to think about how much money I’ve put into the berms at the range.  Confused



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: July 21 2021 at 10:40am
Rule of thumb, if its Brit, or commonwealth  & doesn't end with a "Z" suffix its Cordite. Same with South African.
.303 is cordite, R1M3Z is nitro.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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