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9/22/2017 12:11:25 AM
Posted: 11/9/2003 3:01:44 PM EDT
Had a friend telling me that 1/9 barrel lasts 50% longer than 1/7 barrel due to slower twist. Is this true??
Link Posted: 11/9/2003 3:38:27 PM EDT
A slower barrel twist will last longer then a higher one (less throat erosion over time). The same holds true as far as heating goes (Faster rate= more friction= more heat). 50% sounds WAY over blown too me! Folks around here worry WAY too much about these issues.
Link Posted: 11/9/2003 5:47:29 PM EDT
Tell him to put down the gun mag, and pick up his rifle and use it more...
Link Posted: 11/9/2003 6:09:43 PM EDT
Faster twist does have greater wear result, but 7 up to 9 in dif., is more than the % that I'm familiar with. However, The ammo type is also a factor, so is the cleaning between rates of fire and length of bursts. The percentage can vary from a lot of other factors, to include chrome or not, stainless vs, moly, etc, etc. Worst case scenerio could make it very high in percent of wear. Jack
Link Posted: 11/9/2003 11:54:36 PM EDT
Link Posted: 11/10/2003 9:50:41 PM EDT
I see, if that's the case, does lighter bullets wear out the barrel faster or slower? I'm wondering why people are getting the Colt 1/7 barrels instead of BM 1/9 ones, is stabilizing heavier grain rounds that important?
Link Posted: 11/10/2003 10:42:32 PM EDT
"I see, if that's the case, does lighter bullets wear out the barrel faster or slower? I'm wondering why people are getting the Colt 1/7 barrels instead of BM 1/9 ones, is stabilizing heavier grain rounds that important?" If you want accuracy it is. otherwise yeah everything will leave the barrel and fly in a pretty much linear path. : ) If you have a sound suppressor an un-stabilized round could take out your suppressor. (Low velocity heavy rounds are a big risk.) [b]Just an observation, but whenever I fire a 1/7 I notice they get hot in 40 rds (toasty near the chamber), while my 1/9's don't get hot nearly as quick, honestly I think that the friction is causing that heat. The 1/9 makes a much better bullet hose, as long as bullets are 62grains or lighter.[/b] granted these barrels are generally not gov't profile and most 1/7's are gov't profile so some of it could be the added weight.
Link Posted: 11/11/2003 6:35:34 AM EDT
[Last Edit: 11/11/2003 6:36:57 AM EDT by ks_shooter]
I don't think that the majority of barrel heating is caused by friction. It is mostly the result of contact with the super-hot gases from the burning powder. Heavier bullets and faster twist rates both cause the bullet to "dwell" longer near the chamber during its initial acceleration. This increased dwell time results in higher gas pressures (and thus higher temperatures) and provides a longer time for the hot gases to heat the barrel before they are expelled out the muzzle. If friction was the major cause of barrel heating shotgun barrels wouldn't get very hot, but of course they do.
Link Posted: 11/11/2003 6:57:39 AM EDT
GreenO, i have a question for you, i saw a pic posted by you on another thread that should a M4 barrel that had a unfortunate mishap(a gapping hole in the side of the barrel). so this was most likely a 1in7 twist, was it a FA that destroyed this barrel? also, what was the bullet weight going through this at the time of detonation? has anyone destoyed a M4 profile that has a 1x9 twist? and for that matter what about the old skinny barrel carbines that are 1x12? have those ever been blown out?
Link Posted: 11/13/2003 9:08:25 PM EDT
[Last Edit: 11/13/2003 9:10:25 PM EDT by Beyond_Visual_Range]
So now I wonder this, why doesnt' Colt do 1/9 twist barrel? Is it because they make 1/7 bbl for the military so they just don't change the tooling? Also is it true that lighter the bullet wt the faster it wears the barrel? you'd think opposite is true since heavier stuff would cause more friction on the rifling. Yet I've heard 40gr stuff can really wear out 1/7 bbl.
Link Posted: 11/13/2003 9:13:58 PM EDT
BVR, I don't often see 1/7 colts. Come to think of it, all the 1/7s I have seen or owned were pre ban.
Link Posted: 11/13/2003 10:58:50 PM EDT
I'm not too familiar with postban Colts, are there any? What do they have now? 1/9?
Link Posted: 11/14/2003 4:16:32 AM EDT
When we (USMC) finished testing the six each prototype M16A2's with Colt 1:7 chrome barrels side by side with M16A1 Colt 1:12 for barrel life at Aberdeen Proving Ground in 1982-1983, the 1:7 were still meeting the accuracy specification at 12,000 rounds. We stoped shooting the 1:12's at 6,000 rounds because that was the spec. We doubled-up on the 1:7's to increase "our confidence level" that a small sample of six rifles would be a valid predicter of subsequent M16A2 barrel life. As I recall, the firing schedule was pretty aggressive. Ten, 1,200 round stings were fired between cleanings. The 1,200 round stings combined slow and rapid semi-auto, along with lots of 30-round magazines firing 3-round bursts. I also think the barrels were forced-air cooled at 300-round intervals. I also remember all the bitching at the test site because we were using Canadian Army "donated" SS109 linked ammo. And the technicians had to obviously de-link a ton of this stuff and re-load into 10-round stripper clips before stuffing magazines.
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