Barrel length vs velocity

kbis · Posted: Mon Nov 14, 2005 10:39 am Post subject: Barrel length vs velocity

My son is looking to buy one of the Rem 700 model rifles in 308, but is not sure which one to get. He will be using it on deer in Az. and will require long shots ( his uncle just shot a deer at 300 yards). I suggested getting one with a long barrrel ( they range from 22 inches to 26 inches). Is there a general rule for how much velocity you gain with each inch of barrel? I thought I had read it some where, but am having senior moments Very Happy

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Thanks

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

Depends on the caliber of course, but 25fps to 50fps is the norm. For non-mag calibers I usually guess 30fps per inch of barrel.

shrpshtrjoe · Posted: Mon Nov 14, 2005 3:45 pm Post subject: Re: Barrel length vs velocity

Howdy kbis. I would agree with dallans numbers but once and awhile you get an exception. I have a rem mod 788 in 308 with a 18 1/2" barrel a load i use to shoot was 47 grains of IMR 4320 with a 150gr bullet the book said 2840fps out of a 24" test barrel my average was 2812 with my 788 shorty. I have always liked shorter barrels they are easier to swing in the woods, less weight to carry but i'm not shooting 300 yds with it either. Witch ever one your son gets just chonograph the loads and there won't be any guess work with it. Let me no what ya get ( I love my 308)
Joe

calsibley · Super Member Joined: Jan 28, 2005 Posts: 317

I figure 50ft. per inch of barrel. That's a generally accepted figure although it does vary a bit from one gun to another. The powder you use will also have a slight effect on your velocity. Best wishes.

Cal - Montreal

kbis · Posted: Mon Nov 14, 2005 8:10 pm Post subject: Re: Barrel length vs velocity

Thanks folks.
It will be hard for me to put a on chronograph on his gun since 1. I don't have one yet ( birthday is this weekend, we can only hope Smile

) and 2. my son lives in Tucson Az. and I live in East Texas.
You are right about the 308, I bought a 308 bull barrel for my Handi and I love it, made short work of a deer this past weekend.
Ken

mikekuzara · Posted: Tue Nov 15, 2005 12:58 am Post subject: Re: Barrel length vs velocity

The item your son might wish for as a birthday or christmas present is a good range finder. Unless he has a lot of experience judging distance in open spaces, he will likely be putting shots over and under deer.

I have seen many a person come to Wyoming and put shot after shot over the top of an animal that was only 150 yards away.

Something that might help as well is a good pair of binoculars. Under no circumstances should your son use a variable power scope as a spotting scope. One of the best ways to learn how to judge distance is to use a fixed power scope or keeping a variable power scope on one power. Once you get used to how big a deer looks at different ranges, you can start messing with the power setting.

The only way to become proficient at long shots is to practise at long distances. A bipod or shooting sticks also are handy.

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

mikekuzara wrote:

The item your son might wish for as a birthday or christmas present is a good range finder. Unless he has a lot of experience judging distance in open spaces, he will likely be putting shots over and under deer.

I have seen many a person come to Wyoming and put shot after shot over the top of an animal that was only 150 yards away.

Man I really need to write a guide on how to use a Scope's subtend to rangefind... its truely amazing to me 95% of the shooters out there dont have a damn clue their duplex crosshairs can be used to calculate distance, holdover and even lead.

Quote::

Something that might help as well is a good pair of binoculars. Under no circumstances should your son use a variable power scope as a spotting scope. One of the best ways to learn how to judge distance is to use a fixed power scope or keeping a variable power scope on one power. Once you get used to how big a deer looks at different ranges, you can start messing with the power setting.

For me and in my hunting, a Spotting Scope > Bino's. I couldnt function without carrying my 15x45x spotter... course thats why at the end of the day I can say I've seen hundreds of critters while other hunters keep asking "Where at???" Smile

Quote::

The only way to become proficient at long shots is to practise at long distances. A bipod or shooting sticks also are handy.

Absolutely. I have both bipod and shooting sticks. For something like prarie dogs or where I have a fixed flat area I stick with bipod... but when out hunting where terrain changes from hills to low and high brush I like my Steady Stix.

Good advice

-DallanC

Handloader · Posted: Tue Nov 15, 2005 3:45 pm Post subject: Re: Barrel length vs velocity

Expansion ratio has a notable effect on velocity per inch of barrel length. The higher the expansion ratio, the less the effect. If we take two cartridges for examples, the 257 Weatherby and the 250 Savage, the expansion ratio is significantly higher with the Savage and the loss of an inch in length would be marginal. Not so with the Weatherby.

We had a 257 Weatherby with a 28" barrel and cut it to 24" and with the same loads we loss 62fps per inch.

OTOH, I cut the barrel on my Ruger No1S in 338 WinMag from 26" to 23" and loss a total of only 96fps. As you might surmise the 338 has a higher expansion ratio than the Weatherby.

With 22lr, velocity will often drop after 18" to 20" of barrel length. Muzzle velocity would be lower with a 24" barrel, again due to very high expansion ratios.

and, FWIW, length of barrel has very little to do with choosing the burn rate of powder specific to velocity. By example, if a rifle with a 26" barrel gets its best velocity with Powder X, it should also get is best velocity even if the barrel is cut back to 16" with the same powder.

kbis · Posted: Tue Nov 15, 2005 6:22 pm Post subject: Re: Barrel length vs velocity

I am the one with the birtday wish list, I just hope my wife found all the adds laying around for chronoghaphs and the Midway adds with their phone number high lighted.
My son is just interested in buying a gun so he can go deer hunting and was asking my opinion. He actually very good at judging distances and hitting at what ever the distance is. Just getting out of the USMC after 5 years might have something to do with it.

squirrelbait · Posted: Fri Nov 18, 2005 7:40 am Post subject: Re: Barrel length vs velocity

Handloader, where does "expansion ratio" come from? What determines this? I'm a little confused. Based on the info I have read, I tend to agree with DallanC on 25 to 50 fps/inch......but really like to know more about the expansion ratio.

Spacedone · Member Joined: Nov 04, 2005 Posts: 266 Location: missouri

Dallan please explain the crosshairs thing. i just asked my gunshop that question yesturday and they couldnt answer it.

i think that would help people even more than the ballistic calc.

PLEASEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

Handloader · Posted: Fri Nov 18, 2005 10:44 pm Post subject: Re: Barrel length vs velocity

While we are awaiting DallanC's response, a visit to the Leupold website or a review of the instructions on all VariXIII and VXIII scopes will give some detailed information. These scopes have the distance to target on the backside of the power ring, so where you see the power numbers, just look back behind them (shooter's side) and the distance is noted.

From the top of the point of the duplex to the center of the crosshairs is a theoretical 18". Increasing or decreasing scope power until the backbone of a deer is on the crosshair and the brisket on the top of the duplex will give a reasonable range to target. Knowing your trajectory will enable the proper holdover for the distance ranged. It works.

squirrelbait · Posted: Sun Nov 20, 2005 9:27 pm Post subject: Re: Barrel length vs velocity

Kbis, looks like we lost sight of your origonal question.
I was following it because I interest in the same info. I was hoping to get some understanding of "expansion ratio" as an interier balistic parameter.

1895ss · Posted: Sun Nov 20, 2005 10:29 pm Post subject: Re: Barrel length vs velocity

Handloader wrote:

Expansion ratio has a notable effect on velocity per inch of barrel length. The higher the expansion ratio, the less the effect. If we take two cartridges for examples, the 257 Weatherby and the 250 Savage, the expansion ratio is significantly higher with the Savage and the loss of an inch in length would be marginal. Not so with the Weatherby.

squirrelbait
PostPosted: Fri Nov 18, 2005 7:40 am Post subject: Re: Barrel length vs velocity
Handloader, where does "expansion ratio" come from? What determines this? I'm a little confused. Based on the info I have read, I tend to agree with DallanC on 25 to 50 fps/inch......but really like to know more about the expansion ratio.

I would also like to know what this expansion ratio is all about ????????
I have never heard of it, please explain.

Handloader · Posted: Sun Nov 20, 2005 11:30 pm Post subject: Re: Barrel length vs velocity

Basically ER is the total volume of the barrel relative to the total volume of the cartridge. From that point it digresses into factors of pressure, load densities and proper burning rates. The importance of ER doesn't stand alone from its inter relationship with these other factors, but, they are predictable and to a major extent form part of Homer Powley's ballistic work.

I'll post further on the matter, but, right now its out the door for tomorrow's varmint calling. We have to drive a few hours to get there, grab a room and be ready before Dawn awakens.

later