Question for the reloading Guru's?

[GoldTip]

Ok I've been reloading now for around 12-15 years and have always been pretty good at starting with what the book says and maybe going a bit above maximum, or reloading until I see pressure signs, but this is a different kind of question.

I am going to be reloading for my uncles 7mm remington magnum, which is a beautiful Sako with a mannlicher stock, but is a 20" barrelled carbine.  Now my uncle would like to wring a little more speed out of this gun, and usually I would load slower burning powders like RL19 or 22 or maybe some IMR 4350 or something along those lines.  However, with the shorter barrel the powder is mostly going to be burned up past the end of the barrel, and not be very helpful in the velocity department. 

My question is this, would my velocity in this carbine be increased if I used a faster burning powder, designed for shorter barrels and smaller cartridges?  Maybe I'm crazy but just thinking outside the box, the more powder burned inside the barrel, the better for velocity correct?  Just wondering if anyone has tried this.

[Huntbear]

What bullets he wanting to shoot out of that???  Also, why would anyone want a 20 in. barrel on a 7 mag???  That is like putting a 6 cylinder motor in a corvette!!!

[dbllunger]

Your right on in practical sense.  Weird things happen, so don't be afraid to try the old standy by's.  I prefer 4831 in 7mm but there are a lot of options.  Regardless the heavier the bullet the slower you need to go.

[Huntbear]

On the velocity issue.  You lose about 150-200 ft. per second per inch of barrel, according to my experience.  So if the load data says you will get 3000 fps, out of a 24 in. barrel, it is going to be considerably less than that with a 20 in. barrel, no matter what powder you use.

IMR 4831 maybe the powder to try, especially if using lighter bullets like 140s or 150s

[GoldTip]

This gun was inherited by my Uncle from his brother when he passed away, so it's not about WANTING a 20" barrel in a 7mm, it's about HAVING a 20" barrel, and how to get the best of velocity out of this.  I am figuring on trying to start with some 150gr Scirocco's or maybe accubonds and see what I get for velocity from those.  Thanks for the tips.  I've never seen any reports that you lose 150-200fps for each inch shorter of barrel length, I have read 50-75fps.


Oh, and the 1953 Corvette came with a 6 cylinder.

[woodswalker]

Might look at 4350 instead of 4831...its a bit faster and still very flexible.  Nosler.com shows 4350 for the 120 and I'm sure that wider range useage is listed, just dont have books at work.

From IMR:
7 MM REMINGTON MAG.
REM. CASE; REM. 9 1/2 M PR
HORNADY 120 GR. SPIRE PT.
.284" DIA.; 24" BBL.; 3.290" C.O.L.
SR 4759 36.5 2695 51900
IMR 4227 37.0 2705 51300
IMR 4198 44.0 2980 51000
IMR 3031 52.5 3180 51200
IMR 4064 55.5 3245 51200
IMR 4895 54.5 3215 52000
IMR 4320 55.5 3185 51400
IMR 4350 65.0 3300 51400
IMR 4831 68.5 3335 51400

7 MM REMINGTON MAG.
REM. CASE; REM.. M 9 1/2 PR
REM. 175 GR. PTD. SPCL
.284" DIA.; 24" BBL.; 3.290" C.O.L.
SR 4759 34.0 2220 51200
IMR 4227 35.5 2240 51800
IMR 4198 41.5 2440 52000
IMR 3031 47.5 2555 50700
IMR 4064 51.0 2645 51500
IMR 4895 50.0 2645 52000
IMR 4320 50.5 2665 52000
IMR 4350 59.5 2765 51800
IMR 4831 63.0 2790 52000
IMR 7828 66.0 2910 52000

[JoshT]

On the velocity issue.  You lose about 150-200 ft. per second per inch of barrel, according to my experience.  So if the load data says you will get 3000 fps, out of a 24 in. barrel, it is going to be considerably less than that with a 20 in. barrel, no matter what powder you use.

That means he'll be seeing 2200-2400 out of a 7mm Rem Mag?? That'd turn a 7mm Rem Mag into a 7mm TCU.

I personally lost less than 75 fps when I cut a .22/250 from 24" down to 20"... and that was with the same exact load... in the same barrel. All the data I've ever seen (and shot) indicates between 20-40 fps loss per inch of barrel... and the loss decreases as velocity decreases.

[Huntbear]

On shorter cases like 22-250 using a fast burning powder, it will not affect the velocity as much as a much longer magnum case that works best and most effeciently with a longer barrel and slower powders.  I have had the same experience with .308 and .257 roberts... all it seemed to change was the report from the gun going off.  It was louder.

However, if you chrony magnum loads in a 24 in barrel and then in a 20 in. barrel, you will see vastly different velocities.

Guess I should have been more specific.

[JoshT]

Bet it ain't more than 150-200fps... total. But then, the only way to know would be to shoot the same load/same barrel at 24" and 20"... if you're just looking at 20" actuall velocities vs. book 24" velocities... you'd never know what the difference truly was.

For what it's worth... I've seen a 22" barreled 300 Winny shoot the same exact load faster than a 26" barreled 300 Winny Sendero... and those were 165s using RE-22... not exactly a "fast" powder... and a case that's larger than the 7mm Rem. Mag.

[JackOfAllTrades]

However, if you chrony magnum loads in a 24 in barrel and then in a 20 in. barrel, you will see vastly different velocities.

I would lean that direction also.  I am interested in the outcome of the developed loads with that shorter barrel. I also lean that IMR4350 is probably more versital and may provide with best results in this case.

7tcu?  Maybe.. I guess with the shorter barrel for the 7mag, if velocity results were equal to .270win, I'd be happy with that.  Still, the report from that short barrel long mag has got to be horendous! A good recoil pad is in order.

Personally, I'd have a new Schillen barrel installed. (Manlicher or not, there are ways to make it look good and become the shooter it should be)

I'm not a 7mag fan at all, so, I guess I'd also look at a caliber change if a barrel change is an option.

The one thing to point out here though, is that velocity isn't everything. Sure it's a magnum holding a pint of powder, but if you can't work up an accurate load for that thing, it's worthless in my book.

So, work more for the accurate load as you work up with different powders. Pay particular attention to the safety signs of over pressure. Chronograph what you work up. We 'want to know'. You 'need to know'.

-Steve

[NRA4LIFE]

I'd go with the 4350.  I've had great luck with it out of a short barreled .243.

[Huntbear]

Here is a load off of Reloadersnest.com for the 7 mag.

72.1 grs. of Norma MRP-2 with a 150 gr. Scirocco at 3127 fps.  3.27 COL. 

[Buckblaster]

A faster burning powder should give you a velocity boost with that short barrel. Print out a burn rate chart and try a few faster powders and then you will know.

[mazama]

I shoot a 284win. with a 20inch barrel that is free throated with 140nosler and imr4350 i get 3025 also the bullet is seated out.

[haugenna]

There is a sweet spot in barrel length for the magnums.  You are looking at 22-24" barrels for the 300 winny and 7mm.  You step up to the 300 RUM and 30-378 you are gonna want a 26-28" barrel.  Once you go below or above those lengths you are going to loose velocity at a much quicker rate.

22-24" barrel will range 50-75fps per inch
20-22" barrel will range 75-100fps.


The further you go out of the sweet spot the more drastic its going to be.  There is no set formula for any caliber:  1"=100fps is bs.

http://www.loadammo.com/Topics/October05.htm

The table below lists the velocity change for different barrel lengths for several popular calibers.

Cartridge
 Bullet Wt., grs.
 Charge Wt., grs.
 IMR Powder Type
 M.V. in a 24” Barrel
 Difference in velocity for a 2” change in barrel length, f.p.s.
 
20”-22”
 22“-24”
 24”-26”
 26”-28”
 
.223 Rem.
 50
 25.1
 3031
 3,080
 46
 48
 42
 38
 
.243 Win.
 100
 40.6
 4350
 2,920
 56
 50
 45
 32
 
7mm Rem. Mag.
 154
 66.8
 7828
 2,885
 89
 54
 48
 44
 

 
.308 Win.
 150
 40.5
 4895
 2,531
 40
 36
 32
 28
 

.338 Win. Mag.
 200
 66.9
 4831
 2,684
 52
 38
 41
 37
 
 

Note that the greater velocity increase, per inch of barrel length, generally occurs in the shortest barrel length. As the barrel is lengthened the velocity increase, per inch of barrel length, decreases. For instance, the .223 Remington shows a 46 f.p.s. velocity increase by lengthening the barrel from 20" to 22" This drops to 38 f.p.s. when the barrel is increased from 26" to 28". Some of the magnum calibers show more variation in velocity from barrel segment to barrel segment, but the velocity change, per segment, is generally less as the barrel is lengthened.