My guess is you'll loose 50-80fps over a 28".
Anyone own a 7mm 300 Win Mag?
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My guess is you'll loose 50-80fps over a 28".
Trooper21986
Well-Known Member
I can live with that ! I'm building this for a hunting rig , not competition , so even getting a 180 to 3150 would be acceptable.
Trooper21986
Well-Known Member
Could have swore Bros had posted 3250 ? Even 3100 would be acceptable! Don't plan on shooting over 1000 for big game . Should still be ok !
I have had two 28" barrels the 180 hybrids which have a very short bearing surface pressured out around 3200 with H1000 but my accuracy load was 3165 with both. I would say those numbers will be repeatable. In any case I would not build a rifle expecting a certain velocity. It may leave you disappointed.
yobuck
Well-Known Member
I don't own a 7x300 Win, but I own two 7x300 Wbys.
One has a 30" barrel, the other a 27" barrel, and using 7828 powder with 162 gr Hornady bullets, there is no velocity loss with the shorter barrel.
One has a 30" barrel, the other a 27" barrel, and using 7828 powder with 162 gr Hornady bullets, there is no velocity loss with the shorter barrel.
That is simply a difference in your two barrels and/or your load. It is a proven fact the barrel length effects velocity. The point remains if you are dead set on getting a certain velocity you may end up being disappointed when you can't reach it or there is no accuracy at top speed.
yobuck
Well-Known Member
Well I wouldn't argue that 2 different barrels might produce different results, but im referring to the same powder charge in my two guns not showing any appreciable difference. Barrel length dosent cause the velocity. There just needs to be enough of it to burn the powder that does cause it before the bullet exits the barrel. And in my case 27" is enough to produce the same results as 30" does using the same load. Using heavier bullets, and less powder, the shorter barrel would be even less criticle.
You are over simplifying it. If your thought process were true then the friction from extra barrel length would actually slow the bullet down. Your statement is to some extent true but just not that simple. Obviously there is a point at which the barrel length is causing more harm than good. The only way to truly know is actually chop your barrel and measure as you go. I have seen countless times where the same charge in one barrel is faster in another of the same length. Over hundreds of thousands of rounds from different people and different rifles the rule of thumb is about 25-50 fps per inch. Obviously different cartridges respond differently and different powder burn rates have an effect. Bearing surface of the bullet has en effect. One of the many examples I personally can give is my 28" 300WM was about 50fps faster than my 27" with the same load.
Trooper21986
Well-Known Member
It's all good , I know 3100 is achievable , pretty sure 3150 is as well . Just not sure where my accuracy node will be . If it's less , it is what it is.
elkaholic
Well-Known Member
It's pretty well been proven that most magnum rifles will continue to gain velocity up to 36" or more!
yobuck
Well-Known Member
Your accusing me of over simplification. But could it also be your complicating what isn't complicated? lol Dan Lilja of Lilja Barrels did do a barrel shortening test probably 25 years ago.
Since then new powders have come along which allow for using shorter barrels. There can also be differences in velocity of loaded ammo from day to day due to temp differences. But thats why we have dials on scopes.
smack
Well-Known Member
That same fire forming load 3 days later with only the powder Lott changed. I'm shooting 3306. This is with a 28" R5, 8 twist, Schneider barrel.
yobuck
Well-Known Member
True 30 years ago, especially with the larger cases like the 30x378 Wby which was then a wildcat. Very few powder selections were available, with some like H870 being too slow, and others being too fast. So the long barrels were necessary for using the slow ones. Surplus H570 worked well, but very few people had any of that, and even that was better with a long barrel. Also until about the late 70s very few barrel makers made barrels longer than 30".
Newer powders have changed much of that, and are the reason the 7x300 Win Mag is gaining in popularity.
I have seen an increase of about 200 fps since changing from H870 to 7828 in my 7x300 WBY using the same 162 gr bullets in the same barrel.
