300 Norma Magnum Throat Erosion

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CMB6o5

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Minuteman
Oct 16, 2022
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Colorado
#1
Looking for some insight on 300 Norma barrel wear. I've got 381 rounds through my barrel (Bartlein 5R 1:9"), and am already seeing close to 0.050" erosion. I've shot mainly N570, some N170, and probably 40 rounds each of H1000 and StaBALL HD. I really havent been pushing it with loads either, as I've been working up to about 3100 now with a 215 Hybrid. 200 of those 381 shots were a 220 LRHT doing about 2950.

I know 300 Norma is brutal on barrels, but I sure wasn't expecting that kind of erosion. Just the way it is, or an odd barrel? No velocity or accuracy issues, so it's really not a big deal now, but I'm trying to get an early feel for how long this particular barrel might last.

Thanks!
 
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#2
I cleaned mine after the first 40 rounds and measured where the rifling was. 191 rounds later at 231 the rifling is about .022" farther away. This barrel has been using H1000 and Berger 230s at 2940fps.

I've heard N570 is extra hard on barrels but it seems lots of guys use it because of the speed it gets and if they are running faster, it makes sense it would wear faster too.
 
#3
Ok, so I’m not too far off that. Yep, I’ve heard that about N570, too. Weirdly enough it’s been a fairly dirty powder for me which I’m not used to from VV, but man is it consistent and gives great velocity
 
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#5
I'm making a point to keep detailed notes on my barrel and measure the erosion whenever I clean it. I'm shooting a pretty standard loading and it's not being rapid fired or babied, so hopefully I'll have some good data to post in the 300 norma reloading section when it burns out.
 
#9
912173 said:
I'm making a point to keep detailed notes on my barrel and measure the erosion whenever I clean it. I'm shooting a pretty standard loading and it's not being rapid fired or babied, so hopefully I'll have some good data to post in the 300 norma reloading section when it burns out.
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Dogtown said:
I’m at 130 rounds through a new Bartlein 400MODBB .300NM barrel, using N170 with 250 A-Tips. I’ll be tracking erosion to see if this barrel material delivers longer barrel life. My first .300NM barrel in 2020 went to 1580 rounds using N570.
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Did you get that straight from bartlein? I’d be super interested in trying that out for something like a 300 Norma.

1580 sounds very, very good for 300 Norma. Why’d you choose to pull it? Accuracy fall off then?
 
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#13
I’ve got H1000 on hand. And StaBALL HD, which is supposed to be very similar to Retumbo. My local store told me that a Hodgdon rep told them that retumbo isn’t really being produced much for the civilian market anymore
 
#14
CMB6o5 said:
I’ve got H1000 on hand. And StaBALL HD, which is supposed to be very similar to Retumbo. My local store told me that a Hodgdon rep told them that retumbo isn’t really being produced much for the civilian market anymore
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It's not! But recently places have been having it for sale. If you catch it when released. Can manage to get a couple pounds. Sometimes some people post it on here on powder instock thread
 
#16
CMB6o5 said:
1580 sounds very, very good for 300 Norma. Why’d you choose to pull it? Accuracy fall off then?
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Honestly, I could have pulled it closer to 1300, but the accuracy degradation wasn’t dramatic enough for what I was doing at the time. The last 600 rounds or so were well inside of a mile, so in the grand scheme of things it may not be a fair comparison. I’ve got 3 new barrels I’m working with now. That 30” Bartlein 400MODBB is insanely accurate with the 250 A-Tips, so I switched to N170 in hopes of extending its life. The other two I’m fine with running hard - both are 1:7 twist for heavy solids.
 
#21
Dogtown said:
Honestly, I could have pulled it closer to 1300, but the accuracy degradation wasn’t dramatic enough for what I was doing at the time. The last 600 rounds or so were well inside of a mile, so in the grand scheme of things it may not be a fair comparison. I’ve got 3 new barrels I’m working with now. That 30” Bartlein 400MODBB is insanely accurate with the 250 A-Tips, so I switched to N170 in hopes of extending its life. The other two I’m fine with running hard - both are 1:7 twist for heavy solids.
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Any experience with N568?
 
#22
Just got some to test out this weekend. Rumor has it that the burn rate is closer to N570 than N565, but with Varget-style temp stability.
 
#24
Probably not easier. The N5xx series are double based, so they generate a lot of heat. Thr N1xx series have similar burn rates but generate 20-30% less heat, which means you lose a bit of velocity. I haven’t shot that series enough to see if it improved barrel life, but I can say in semi-autos a fast string doesn’t build up barrel heat as fast as with N5xx powder.
 
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#25
Dogtown said:
Probably not easier. The N5xx series are double based, so they generate a lot of heat. Thr N1xx series have similar burn rates but generate 20-30% less heat, which means you lose a bit of velocity. I haven’t shot that series enough to see if it improved barrel life, but I can say in semi-autos a fast string doesn’t build up barrel heat as fast as with N5xx powder.
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That’s my experience with N170 vs N570. Barrel heats up crazy quick with N570 compared to N170
 
#26
It was such a noticeable difference that I switched out most of my semi-auto loads to use N1xx, even though you lose a bit of velocity.
 
#28
wvfarrier said:
Barrel.was brand new. I actually sent it back to PVA for evaluation. The cleaned it up some but it never shot as well after.
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I know a guy who's friend had a sps tactical .308 go to shit at 1400 rounds but the one he bought at the same time went over 10k. They both were running varget /175 smk. I'm thinking maybe the bore was out of spec and it just got worse with shooting causing premature accuracy issues.
 
#30
Everyone has different acceptable accuracy requirements. I personally know 2 shooters Running NMs. Neither of them went over 1000. AI on one, 800ish on both barrels. K&P Barrel on a LonePeak on the other, 900 rounds.and no, they weren't doing mag dumps.
 
#31
Are any of you guys doing any special barrel care/cleaning on your 300nm barrels? Right now I'm doing a basic bore cleaning with shooter's choice every 200 rounds. It still shoots good by then, but I'd rather not wait until accuracy falls off.
 
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#35
That's comforting to hear :ROFLMAO:. I had been hoping someone out there had higher round counts on a 300nm that hasn't been pushed hard. I figured a mild 300nm shooting the similar speeds as a hot 300wm handload using the same bullets and powders shouldn't be too much worse on barrel life.

Most of the reason I went 300nm was to get 2900+ with 230s easily with a standard barrel length and have the ability to run it hard with newer bullets at mag length if I want to.
 
#36
CMB6o5 said:
Looking for some insight on 300 Norma barrel wear. I've got 381 rounds through my barrel (Bartlein 5R 1:9"), and am already seeing close to 0.050" erosion. I've shot mainly N570, some N170, and probably 40 rounds each of H1000 and StaBALL HD. I really havent been pushing it with loads either, as I've been working up to about 3100 now with a 215 Hybrid. 200 of those 381 shots were a 220 LRHT doing about 2950.

I know 300 Norma is brutal on barrels, but I sure wasn't expecting that kind of erosion. Just the way it is, or an odd barrel? No velocity or accuracy issues, so it's really not a big deal now, but I'm trying to get an early feel for how long this particular barrel might last.

Thanks!
Click to expand...
Bore and throat erosion is really dependent on powder composition. The important parameter is flame temperature, which is unfortunately immeasurable quantity. Based on thermodynamic calculation, and long experience it is well known fact that higher energy content (i.e. heat of explosion) leads to higher flame temperature and higher throat erosion.

Easiest method to improve ballistic performance is to add nitroglycerol in powder composition. These powders are called double base powders. As you have heard, these powders tend to cause more barrel and throat erosion compared to single base powders. This difference is clear but it is, however impossible to quantify as for example as numbers of rounds to reach same erosion level.

All Vihtavuori N100 (N105...), N300 (N310...) powders, 3N37 and 3N38 are single base powders. These products are made with best available raw materials and manufacturing methods to get maximal performance you can get without using more erosive double base composition. Therefore, these Vihtavuori products cause less erosion than most of other competing powders. Especially high nitroglycerol contents (and thus erosion) are used in spherical powders (ball powders) and some US products.

Among Vihtavuori product line we have only five types we call N500 (N530 ... N570) which are by composition double base powders. N500 rifle powders contain small amount of nitroglycerol to add a bit more performance required mainly for extremely long distances. Even with these products we have added a special additive as well kept nitroglycerol content rather low in order to minimize the barrel erosion effect.

So, my opinion and advice is to keep barrel and throat erosion on minimum by using only single base powders like Vihtavuori N100, N300 and 3N.

Best Regards,

Mikko Vuoristo
EURENCO Vihtavuori Oy
 
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#37
My 6.5 CM barrel had over 1000 rounds on it and I could not measure any throat erosion. I shot Relode16.

I think it’s because I never shot more than 1 round per minute and I cooled the barrel with a mattress pump after 5 shots. Of course I don’t advise anyone to do this. Those 1000 rounds were used for testing and I needed the temperature to be stable.
 
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