Cutting barrel /velocity testing? Update Feb.3

Fir the love of god, man, check the internet before chopping away on your property.

Within two seconds of Google searching barrel length and muzzle velocity of 308/7.62 I found this:

https://rifleshooter.com/2014/12/30...ato-barrel-length-versus-velocity-28-to-16-5/


308 Winchester Barrel length in inches versus Muzzle velocity in feet-per-second (ft/sec)
Rifleshooter.com

Barrel length Winchester 147 FMJ IMI Samson 7.62 150 FMJ Federal 168 Gold Medal Winchester 180 PP
28 2965 2823 2706 2632
27 2962 2800 2697 2607
26 2955 2801 2673 2597
25 2917 2769 2659 2585
24 2909 2766 2635 2553
23 2877 2744 2618 2553
22 2837 2718 2597 2527
21 2807 2683 2580 2507
20 2804 2679 2565 2478
19 2757 2634 2532 2441
18 2739 2595 2523 2411
17 2707 2577 2481 2401
16.5 2682 2561 2466 2373
AVG velocity loss fps/inch 24.6 22.8 20.9 22.5

Summary: You're losing about 300 fps to go from a 28" barrel to a 16.5" barrel.

While this may not seem like much, it may actually mean the difference between hitting what you're aiming for from 200-300m.
 
IvoB said:
if your going to test for accuracy the gun must be fired using a vise to eliminate human error - all factors being equal (clean barrel / cooled barrel) with each 5 shot strings. Only then, can you conjecture that a shorter barrel may or may not be more accurate.
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Best I can do is a sled.
I’m thinking it’s going to be close ,or the groups from the cut barrel are gonna be all over the place.
 
I’m not trying to do a write up for the internet. I just want to see how much speed I’m going to lose.
And which length barrel is more accurate,if at all.

And I was looking for advice on the best method of cutting the barrel.
Keeping in mind,it’s gotta be battery operated.

If anybody is interested in what I come up with , or have anything they would like me to try, let me know.
I’ll post a follow up thread, when I get all the gear together.
 
Brianma65 said:
I was also thinking that the more uniform the cut,the better it should be.

Gander,should I do five shots, over the chrony,and take the average of those?
Click to expand...

5 shots over chrony may give you a curve where each shorter barrel session shots lower velocity. less shots won't.

If the barrel is to be scrapped, why stop at 19". Take it down to 2", as has been done before.
 
Petamocto said:
Fir the love of god, man, check the internet before chopping away on your property.

Within two seconds of Google searching barrel length and muzzle velocity of 308/7.62 I found this:

https://rifleshooter.com/2014/12/30...ato-barrel-length-versus-velocity-28-to-16-5/


308 Winchester Barrel length in inches versus Muzzle velocity in feet-per-second (ft/sec)
Rifleshooter.com

Barrel length Winchester 147 FMJ IMI Samson 7.62 150 FMJ Federal 168 Gold Medal Winchester 180 PP
28 2965 2823 2706 2632
27 2962 2800 2697 2607
26 2955 2801 2673 2597
25 2917 2769 2659 2585
24 2909 2766 2635 2553
23 2877 2744 2618 2553
22 2837 2718 2597 2527
21 2807 2683 2580 2507
20 2804 2679 2565 2478
19 2757 2634 2532 2441
18 2739 2595 2523 2411
17 2707 2577 2481 2401
16.5 2682 2561 2466 2373
AVG velocity loss fps/inch 24.6 22.8 20.9 22.5

Summary: You're losing about 300 fps to go from a 28" barrel to a 16.5" barrel.

While this may not seem like much, it may actually mean the difference between hitting what you're aiming for from 200-300m.
Click to expand...

There seems to be quite a lot of published internet data, on this subject.
Now, why so many? Why didn’t everybody just take the first guys word for it?

:) :)
 
Ganderite said:
5 shots over chrony may give you a curve where each shorter barrel session shots lower velocity. less shots won't.

If the barrel is to be scrapped, why stop at 19". Take it down to 2", as has been done before.
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Ha, I was thinking of going shorter, but not sure of the legality of that.

I’ll be at the range,with a friend ,who also happens to be a verifier.

If need be ,he can keep calling it in,verifying after each chop.. :)
 
Oh gawd Bubba. Just go tell your father you discovered girls.

It's all been done. 22 to 23" should be a sweet spot for an 11 degree 1/4" recessed crown. Scrap or not, at least ask for a favor of your local smith.

Do you have a lathe? Otherwise you are simply screwing in and up time.
 
I am building a sporter on a Lee Enfield No.1 action, using a medium weight 308 target barrel. It will get a 303 Brit chamber.

I have been wondering about barrel length - something between 20 and 18" comes to mind. The barrel is now 28", so we will cut in steps and I will see how it "feels".

I was thinking of maybe going to 18" and installing a brake, since it would have to be shot with muffs, anyway. It would be nice to dump some of the recoil.
 
Last edited:
A barrel cut to <18.5'' is prohibited. Most probably no one would know, but you'd still have a prohibited weapon in your hands for a small amount of time.
 
Ganderite said:
I am building a sporter on a Lee Enfield No.1 action, using a medium weight 308 target barrel. It will get a 303 Brit chamber.

I have been wondering about barrel length - something between 20 and 18" comes to mind. The barrel is now 28", so we will cut in steps and I will see how it "feels".

I was thinking of maybe going to 18" and installing a brake, since it would have to be shot with muffs, anyway. It would be nice to dump some of the recoil.
Click to expand...

From my online research, I think 19 inches is the sweet spot.
That’s why I ordered my new barrel at that length.

As for the one I’m cutting, I’m going to stop at 18.5 and recrown it.
We are going to put a Target crown on it. And yes,it’s going on a lathe.

Then ,I’ll have a spare .308 barrel, if I ever decide I want to use it.
 
Cool ! I like a guy that experiments rather than just google and know it all . You may find surprising results , just as good an excuse to play as punching paper ( same old same old )
Please follow up with any interesting observations
 
Brianma65 said:
From my online research, I think 19 inches is the sweet spot.
That’s why I ordered my new barrel at that length.

As for the one I’m cutting, I’m going to stop at 18.5 and recrown it.
We are going to put a Target crown on it. And yes,it’s going on a lathe.

Then ,I’ll have a spare .308 barrel, if I ever decide I want to use it.
Click to expand...

Good plan.

I did something like that once. The "spare" barrel shot so well I never used the "good" one.
 
Keithjohn said:
Cool ! I like a guy that experiments rather than just google and know it all . You may find surprising results , just as good an excuse to play as punching paper ( same old same old )
Please follow up with any interesting observations
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The internet is full of "surprising results" that someone who knows nothing about scientific experimentation found by doing invalid tests and made inappropriate observations leading to bad conclusions. The first principle of ballistic testing is that WAY more than one or two rounds are needed to get reliable results from any chronograph. The original plan to shoot one round for a velocity reading is proof of a failure to understand anything about testing for velocity. There is also lots of proof here that the OP has done very little testing over a chronograph, or he would understand that fact and the concept of extreme spread, and know that one shot will not cut it.

I will repeat that testing can be fun. But designing and executing a test that will give you results that mean something is a lot harder than some here seem to think. It is always unfortunate when someone on a forum posts results and conclusions about ballistics that have no validity due to bad measurement and testing. Doing a bad test is a waste of time and money, and proves nothing worth knowing. If you don't do it right, Google may be a much more economical and informative process.

I can do five over the chrony and five for the group.

It’s only for kicks, but I want it to be done right.
Click to expand...

If that's true, you need to re-think a lot of this plan.
 
rral22 said:
The internet is full of "surprising results" that someone who knows nothing about scientific experimentation found by doing invalid tests and made inappropriate observations leading to bad conclusions. The first principle of ballistic testing is that WAY more than one or two rounds are needed to get reliable results from any chronograph. The original plan to shoot one round for a velocity reading is proof of a failure to understand anything about testing for velocity. There is also lots of proof here that the OP has done very little testing over a chronograph, or he would understand that fact and the concept of extreme spread, and know that one shot will not cut it.

I will repeat that testing can be fun. But designing and executing a test that will give you results that mean something is a lot harder than some here seem to think. It is always unfortunate when someone on a forum posts results and conclusions about ballistics that have no validity due to bad measurement and testing. Doing a bad test is a waste of time and money, and proves nothing worth knowing. If you don't do it right, Google may be a much more economical and informative process.



If that's true, you need to re-think a lot of this plan.
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Your right, I don’t have a lot of experience with a chrono graph.
Or cutting barrels.

That’s why I asked here,for advice on the best cutting tool,battery operated of course.

My testing is not to be taken as a professional test, but just something to pass away some time,and for my ownself.

So I thought I could get away with one rnd but now understand why I can’t.

So tell me, what’s wrong with shooting 5 over the chrony and taking the average?

And what about the five rnd groups? When I find an accurate load for the original barrel and then use that for all my tests, would that not give me an idea of its accuracy?

Shoot five over the chrony, take the average, shoot five more , measure for the group.
Repeat this process for every barrel cut.

Please give some advice on the process.

Hey ,I’m only shagging around, not meant for anybody to use it as any kind of formal info.
 
5 shots will give you a useful average velocity good for this purpose.

5 shots, just once, is not much of an accuracy test.

And besides. if you start with a load you developed for that barrel, bigger groups at shorter lengths might only mean you need to develop anew load for each shorter barrel length.

But cut and shoot and let us know how it goes.
 
Ganderite said:
5 shots will give you a useful average velocity good for this purpose.

5 shots, just once, is not much of an accuracy test.

And besides. if you start with a load you developed for that barrel, bigger groups at shorter lengths might only mean you need to develop anew load for each shorter barrel length.

But cut and shoot and let us know how it goes.
Click to expand...

Ya,I kinda figured that each time I cut the barrel ,it’s like using a whole new barrel.

I guess if I were to recrown with every cut, that would be a better test. Shoot five with the raw cut,recrown,shoot 5 more.
But that’s not gonna happen,as it’s a 1 1/2 hr trip, back to the lathe.

I could get two accurate tests though, maybe.

I could shoot 5 through the 24 inch finished barrel,cut the crown off,shoot 5 more.
And then the last two groups at 18.5 ,one with the cut barrel ,then one group with the finished barrel.
 
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