Short Barreled 7 Rem Mag

rgv said:
curious,

do you own a chronograph?

what is your idea of "Practically the same ballistics"?
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No, I don't own a chronograph. I couple guys I shoot with do and they are interesting to play with but my lack of one doesn't exclude me from the discussion. By practical ballistics I mean the difference you are talking about between the .280 and the 7 mag. in 22 inch barrels would never cause anyone to loose a game animal or even discern a difference in knockdown power.
 
Mike Webb said:
By practical ballistics I mean the difference you are talking about between the .280 and the 7 mag. in 22 inch barrels would never cause anyone to loose a game animal or even discern a difference in knockdown power.
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You're right, but this can be said about any multitude of different cartridges. .270 vs. .280, .308Win vs. .30-06, 7RM vs. .300WM, .243 vs. .257 Roberts, etc, etc.

The one practical advantage is seen at long range. Bullets with 150-200fps more velocity will drift less in the wind and expand at greater distances.
 
Mike Webb said:
I think the traditional definition of over bore is a cartridge which can be loaded with more powder than can be efficiently burned in a standard length barrel, e.g., 22 inches is considered standard today. Everything I have seen suggests that over bore cartridges are affected more(velocity and noise) by shortening the barrel.
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With modern powders, traditional "over-bore" cartridges, such as the 7RM, are becoming less and less qualified to be given that label. With advancing technology in powders, these cartridges are also affected less and less by shortening the barrel, which starts to level out the playing field between these magnum cartridges and standard ones. See my results between my 7RM (21.5" barrel) and my .280 (22" barrel) above.
 
Mike Webb said:
No, I don't own a chronograph. I couple guys I shoot with do and they are interesting to play with but my lack of one doesn't exclude me from the discussion. By practical ballistics I mean the difference you are talking about between the .280 and the 7 mag. in 22 inch barrels would never cause anyone to loose a game animal or even discern a difference in knockdown power.
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No, not owning a chronograph certainly does not exclude you fromthe discussion.

Federal Ammo shows a 280 pushing a 150 at 2890 and the 7RM pushing a 150 at 3110, both out of 24" barrels.

That is a 220 fps difference, or, the equivalent of 100 yards of range.

Even if you assume that the 7RM will lose more by cutting to 22", it will still have a 150+ fps advantage

If, in your own hunting and game experiences, 150 fps does not constitute a "practical difference", that's fine. To declare it as being universally the case, is not really true.
 
Chronographs always humble people.:D

Years ago I had bought some factory 338 Win Mag with the 225 TBBC's.

Reading the box it claimed the velocity was 2800 fps. Out of a 24" barrell I believe the velocity averaged right around 2650 fps. Big difference.

I cross reference all my loading manuals and look on the web for load data when starting load development. I shoot all loads over the chrony to get a baseline for the velocity I expect.

As for these new "wonder powders" giving extra velocity, I'm not entirely sold yet.

I shot some 100 grain Nosler BT's out of a 257 Roberts last year using H100V.
Hard to believe but I was getting 3350 fps without pressure signs. Too bad it shot 4" groups. That's warmish 25/06 territory.

As for the barrel length issue I think some cartridges benefit from the length. I have a 257 Wby, a 264 WM, and a 7 RM all with 26" barrels. Would be kind of silly to have a 26" barrelled 30/30.:D

I also know a guy with a 7.5 lb 20" barrelled 300 Weatherby.:eek:
 
rgv said:
Boomer, aren't you the guy with a shorty 375 RUM that outperforms a 375 H&H? IIRC, the idea was to get a big combustion chamber behind a short barrel, in order to drive bullets fast.

How does that renconcile wth your above claim that 7 mag and a 280 will have essentially identical ballistics?

They will not. Optimal barrel lengths or not, the bigger case will always outperform the smaller one.
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No I'm the guy with the 20" .375 Ultra who wanted to get long barrel .375 H&H velocities from a short compact gun and did. The omnly bullet weights where I out perform the H&H is with the 350s and 380s.

Perhaps you should compare 150 gr data for the .308 vs the .30/06 and then reconsider that statement. Now with very heavy for caliber bullets things change a bit. If someone made a 212 gr 7mm bullet, the 7mag would drive that bullet faster in a short barrel that the .280, just like a .308 loaded with a 240 gr Woodleigh can't compete with the '06 loaded with the same bullet.
 
here you say (regarding the 280 and 7RM), the big case and the small case get the same velocity

Boomer said:
I expect both cartridges would produce 3000 fps + or - 50 fps from that 22" barrel.
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and here you say (regarding the 375 RUM and 375 H&H), the big case in a short barrel gets the same velocity as the small case in a long barrel, i.e. big case outperforms the smaller case.

Boomer said:
No I'm the guy with the 20" .375 Ultra who wanted to get long barrel .375 H&H velocities from a short compact gun and did. The omnly bullet weights where I out perform the H&H is with the 350s and 380s.
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it can't be both.
 
rgv said:
No, not owning a chronograph certainly does not exclude you fromthe discussion.

Federal Ammo shows a 280 pushing a 150 at 2890 and the 7RM pushing a 150 at 3110, both out of 24" barrels.

That is a 220 fps difference, or, the equivalent of 100 yards of range.
Even if you assume that the 7RM will lose more by cutting to 22", it will still have a 150+ fps advantage

If, in your own hunting and game experiences, 150 fps does not constitute a "practical difference", that's fine. To declare it as being universally the case, is not really true.
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do expand...

the 7RM has about 15 yrds greater point blank range,a little more at best..

at what distance is the 7RM giving you an extra 100 yrds of range with 220 fps more speed...I am very eager to know, sounds like you're getting over 50 yrds more point blank range with the 7RM over the .280....???

For me, I shoot a 7mm-08 at about 300-340 fps slower than the 7 RM
some loads a bit closer, some further apart, but I'd say 300-340 fps on average slower with the same bullet..

The kicker for me, is that the 7RM is gaining 300 fps by using 23-27 grains more powder...

So in other words, it uses roughly 50% more powder to get another 25-30 yrds PBR... with another 300-350 fps.

I find it fitting that the guys who think an inch in length makes a gigantic difference, are also the ones who own magnums...;)
 
sealhunter said:
do expand...

the 7RM has about 15 yrds greater point blank range,a little more at best..

at what distance is the 7RM giving you an extra 100 yrds of range with 220 fps more speed...I am very eager to know, sounds like you're getting over 50 yrds more point blank range with the 7RM over the .280....???
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spitzer hunting bullets will lose 200-250 fps per 100 yards, so a bullet from a 280 will be travelling as fast at 300 yards as the same bullet will be travelling from a 7RM at 400 yards.

With the advent of LRFs, if you intend to shoot beyond 300 yards, you can't depend on PBR anyways
 
^ I agree, but it all depends on the bullet, the criteria, and the atmospheric conditions. If I launch a 162 A-Max at 2950fps, I have 2357fps remaining at 400 yards. If I launch the same bullet at 3100fps, I hit that same velocity at 565 yards. That is 165 yards difference.

When launched at 2950fps, the bullet drops down to 1800fps by 825 yards. When launched at 3100fps, it gets all the way to 1055 yards before dropping below 1800fps. That is 230 yards difference.

It all depends on your criteria. If we assume that the effective range of a bullet is the range at which said bullet drops below 1800fps and will no longer expand reliably, then the 150fps advantage provides 230 yards of additional range, with this particular bullet, in the atmospheric conditions I typically shoot in.
 
and with Barnes TSX loaded by Federal... using factory specs.

the .280 is putting the 140 gr bullet at 1880 fps at 500 yrds with 42.8 inches drop

the 7RM is putting the 140 gr bullet at 2007 fps at 500 yrds with 38.1 inches drop.
 
Jordan Smith said:
^ I agree, but it all depends on the bullet, the criteria, and the atmospheric conditions. If I launch a 162 A-Max at 2950fps, I have 2357fps remaining at 400 yards. If I launch the same bullet at 3100fps, I hit that same velocity at 565 yards. That is 165 yards difference.

When launched at 2950fps, the bullet drops down to 1800fps by 825 yards. When launched at 3100fps, it gets all the way to 1055 yards before dropping below 1800fps. That is 230 yards difference.

It all depends on your criteria. If we assume that the effective range of a bullet is the range at which said bullet drops below 1800fps and will no longer expand reliably, then the 150fps advantage provides 230 yards of additional range, with this particular bullet, in the atmospheric conditions I typically shoot in.
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Do you shoot to 800 yrds? and if so, what load is it you are using?
Thanks
 
Jordan Smith said:
It totally depends on the powder, bullet, and on the individual barrel in question. Some barrels will lose 20fps/in, while others with the same specs and components will lose 60fps/in. Obviously the inside diameter of the groves/lands makes a difference. Every barrel is an individual. There's only one way to know what kind of loss you're getting on any given rifle- shoot over a chrony, chop the tube, and re-chrony.
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Barrels are made within tolerances with most being within well within +/- of average I.D. to not make a significant difference. And yes to state the obvious powder, barrel, and bullet will cause changes but for all intensive purposes the guys asking for a ballpark not a course in it. My range was 100-160 fps depending on ambient temp, bullet wt, powder, throat length, etc, etc, etc.

Losing from 20 fps/in to 60 fps/in......hmmm.....interesting conjecture, now that rivals x^-1 (in math this is called an imaginary number)

To come up with a practical loss per inch instead of chopping your tube down (LOL) just rely on guys who run their guns over a chrono and compare their data to book data (w.r.t barrel length of course). And take that as a reference instead of going overboard.
 
Traps said:
To come up with a practical loss per inch instead of chopping your tube down (LOL) just rely on guys who run their guns over a chrono and compare their data to book data (w.r.t barrel length of course). And take that as a reference instead of going overboard.
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Where do people come up with this stuff?

Have I said that somewhere here before?
 
sealhunter said:
What are you shooting the 162 grain with and what recipe at what distance?
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I shoot it out of the 7RM and the .280. The 7RM is currently down for maintenance, but I'm using the 162 AM out of the .280 at 2947fps ave. I'm using 60gr of IMR7828SSC, Fed210, and RP brass.

I'm not sure what you mean by "at what distance", but I can only assume that you're talking about elevation correction? At 950 yards I'm dialing in ~22MOA, depending on the day.
 
Traps said:
Barrels are made within tolerances with most being within well within +/- of average I.D. to not make a significant difference. And yes to state the obvious powder, barrel, and bullet will cause changes but for all intensive purposes the guys asking for a ballpark not a course in it. My range was 100-160 fps depending on ambient temp, bullet wt, powder, throat length, etc, etc, etc.

Losing from 20 fps/in to 60 fps/in......hmmm.....interesting conjecture, now that rivals x^-1 (in math this is called an imaginary number)

To come up with a practical loss per inch instead of chopping your tube down (LOL) just rely on guys who run their guns over a chrono and compare their data to book data (w.r.t barrel length of course). And take that as a reference instead of going overboard.
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The problem with oversimplifying is that you run the risk of giving the guy false information. To say 40fps/in is what I call oversimplifying. His particular barrel/load combination could lose 25fps/in or it could lose 60fps/in. There's only one way to find out for sure.

Actually x^-1 is simply 1/x, not an imaginary number.

To suggest that you can simply derive your velocity loss per inch of barrel from book data says to me that you haven't much experience with this tube chopping business. The suggestion to assume 40fps/in is a good one, since the guy isn't going to chop his barrel to find out the true loss per inch, but he should be aware that it can vary tremendously from rifle to rifle.

Have you ever mic'd a handful of factory tubes for inner diameter? They DO vary substantially. Premium barrels, less so.
 
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