How does Barrel length affect velocity?

[MattO]

This week I am purchasing a .40 S&W Carbine with a 17.5" barrel. I reload for my .40 S&W handguns using Berry's plated. Typically they run around 900 FPS out of my M&P40C and my Hi Pointe. Berry's says to keep the bullets below 1250FPS but I cannot find data on anything past a 4" barrel for a load with FPS. Is there a way to calculate so I can load some up and Chrono them safely so I can build up to what I want to shoot, but keeping it below the recommended FPS.


Matt

 

[Alk8944]

There is no issue with safety in the velocity recommendation, so let that one go. Simply use the same data as you use for your pistol. If the load gives you ca. 900 FPS then the carbine will give you something around 1050-1100 FPS. There is nothing to calculate, just load them and chronograph to see what you get!

 

[Twoboxer]

[What bullet weight and what powder and charge weight are you using to get 900fps?]

The difference is very much going to depend on your powder choice, but even recommended minimum loads from a 4" barrel look like they will exceed 1250fps from a 17.5" barrel.

Using Quickload, two examples using 155gr bullets:

- 7.5gr Longshot 1075fps** vs 1371fps
- 5.4gr Titegroup 1048fps** vs 1261 fps

Frankly, I would use unrestricted bullets of the same profile and weight and adjust the loads so that the velocity is under 1250fps. Then I'd swap in the Berrys' and try working up to that load over a chrono.

It seems using plated bullets you are likely to be running under the recommended minimums which may or may not cause you other issues.

** Note that these velocities are a bit lower than Hodgdon claims in their load data.

 

[Bkreutz]

I use the thick plated 9mm bullets and push them to 1425fps, haven't had any problems since I've started using them. Don't think I'd use standard plated bullets in a rifle. But that's just me.

 

[rwsmith]

Coated......

The coated bullets are pretty tough at higher velocities and probably cheaper.

Search the site 'ballistics by the inch'

 

[scooter123]

I suspect that velocity limitation is more out of a concern in regards to Pressure rather than the exact Velocity. I would also expect that your 900 fps reloads will feature a powder on the "fast" side and you won't see much more than about 1050-1150 fps from your carbine. I have a 38 special load I worked up using 3N37 that clocks 800 fps from a 6 inch barrel and out of my 20 inch Winchester it only clocks 1150 fps.

If you take a look at the burn rate for this powder it appears to be on the "slow" side but that's an interpretation based on Handgun barrel lengths. Compare it to Rifle powders and it's quite fast. Same thing will probably be true for your 40 caliber loads, the powder you'll be using will "run out of steam" and some point and you won't see that much of a gain in velocity.

So, IMO it will be perfectly safe to put some loads together and run them over a chronograph. Worst case if I'm wrong is you'll have some work to do cleaning up your barrel, so don't shoot more than 3 or 4 if you see velocities over that 1200 fps limit. That way if there is a problem with leading it will be pretty mild and easy to clean up.

 

[MattO]

Thank you everyone for the input.

I guess I should have mentioned I am using the 180 gr Berry's coated bullet and HS-6 powder. I was mostly concerned with doing any damage to the new barrel if I pushed them too hard.


Matt

 

[Rule3]

The concern on plated bullets is if pushed to hard the plating will separate from the lead core. You are not going to damage your barrel. Perhaps just get poor accuracy or leading.

 

[BAM-BAM]

Check out the web site:


Ballistics By the Inch

Don't shoot .40; but, IIRC 9mm and .357magnum can be pushed to 1700+ and 2000 FPS out of a 16 inch barrel

 

[H Richard]

It is dependent on the powder, but there is an old rule of thumb of around 40-50 fps increase with each inch of barrel. I'm sure there is a point of maximum gain somewhere in there but probably up around 26-28 inches. Even at 50 fps p/inch, from a 4" to a 16" barrel starting at 900 fps would yield about 1500 fps from the 16" barrel. I've never been a fan of plated bullets, and personally would not use them in a carbine or rifle barrel. Also, I have heard the copper coating on the plated bullets is not as hard as the alloy used in jacketed bullets, and may therefore deposit more copper fouling in your barrel than regular jacketed barrels. Again, "I heard" this and since I have never used them myself, cannot say that it will happen, but if you value your rifle why tempt fate?

 

[amazingflapjack]

Somewhere around 40% is what I've been told when comparing a 6 inch revolver, and my Winchester 357 Lever gun.

 

[aurora40]

FWIW, factory 9mm ammo gains about 150-200 fps from my 5" pistol to my 16.5" carbine.

In addition to the limited case capacity, I tend to think the blowback action limits extreme velocity. My 9mm carbine is dirty as hell when I shoot it. I'm pretty positive it's because the brass is being extracted enough to break the seal before the bullet has left the barrel. So I tend to think even a slower powder would be limited because the pressure drops off artificially from this event.

 

[Twoboxer]

Thank you everyone for the input.

I guess I should have mentioned I am using the 180 gr Berry's coated bullet and HS-6 powder. I was mostly concerned with doing any damage to the new barrel if I pushed them too hard.


Matt

Quickload shows 6.6gr of HS-6 under a 180gr bullet through a 4" barrel at approx 940fps, which for reference is slightly higher than the 921fps reported by Hodgdon.

Changing to a 17.5" barrel showed a velocity of 1206fps.

Your current loads should work absolutely fine out of the 17.5" barrel. Even if the velocity exceeds 1250fps, the Berrys' can probably handle it and in any case, as others have pointed out, there are no safety factors involved.

GLHF!!

 

[fredj338]

The issue with thin plating & vel is NOT pressure, but the rotation & resulting stripping of the plating. With Berry's & Ranier, I see it about 1250fps. A rough guess on vel gain is 20fps per inch, maybe 25fps, but not more with medium to fast powders. Your barrel will also dictate vel gain; rough, smooth, tight or lose bore. So you may or may not be fine, load them & shoot em. The worst that will happen is accuracy will suck & you may get some leading if the plating strips, but won't hurt anything.

 

[MattO]

Thank you very much. I do make a 6.6 gr load, and I also load a 7.0 gr load using the same bullets. I think I will just load down any that I use for the carbine to be sure and keep the accuracy and leading down. Then I will find a different projectile and build them for the carbine. I'm looking forward to getting it!

Matt

Quickload shows 6.6gr of HS-6 under a 180gr bullet through a 4" barrel at approx 940fps, which for reference is slightly higher than the 921fps reported by Hodgdon.

Changing to a 17.5" barrel showed a velocity of 1206fps.

Your current loads should work absolutely fine out of the 17.5" barrel. Even if the velocity exceeds 1250fps, the Berrys' can probably handle it and in any case, as others have pointed out, there are no safety factors involved.

GLHF!!

 

[Magload]

Watch the bullet holes in the target you can often see if the platting is separating. Also be sure not to dent the platting when crimping. I shoot plated bullets a lot and was using Berry's but switched to X-treme. Last months Blue Press had a article about X-treme bullets and X-treme stated that there plating was thicker on all their bullets. I also shoot a lot of coated bullets. Don

 

[Twoboxer]

Thank you very much. I do make a 6.6 gr load, and I also load a 7.0 gr load using the same bullets. I think I will just load down any that I use for the carbine to be sure and keep the accuracy and leading down. Then I will find a different projectile and build them for the carbine. I'm looking forward to getting it!

Matt

FYI, Quickload shows your 7.0gr load likely has a velocity of 995fps. Changing to a 17.5" barrel, the velocity increases to 1264fps.

Quickload won't exactly match your actual any more than your actual will match manufacturer's published data. And I don't have your COL, nor the actual burn rate of your batch of powder, nor some actual bullet details.

Having said that, QL usually is consistent. So if QL shows your 900fps load to be 940fps, your 7.0gr load is probably well below 1264fps.

Long winded way of saying, shoot both loads from the carbine with fairly high confidence. Chrono them to be sure, of course, but I wouldn't change pistol loads I'm otherwise happy with for this "red line" issue until its proven the carbine shoots them faster than 1250. And once again, the Berrys can probably handle a bit faster too.

They shouldn't separate, and if they don't separate they shouldn't lead either.

 

[Forrest r]

Why not the "holy grail" for velocity. It will at least give you an idea of what your looking at with the different bbl lengths for the different calibers.

BBTI - Ballistics by the Inch :: Results

Let us know what you end up with.

 

[BB57]

Why not the "holy grail" for velocity. It will at least give you an idea of what your looking at with the different bbl lengths for the different calibers.

BBTI - Ballistics by the Inch :: Results

Let us know what you end up with.

OMG.

Methodologically speaking that site is worthless.

They use two chronographs back to back to double their data points, which still does nothing to increase the sample size. Sample size is a problem as they only use three shots.

The end result is that they do not get a large enough sample to get a reliable mean velocity, or a small enough standard deviation to ensure that any differences between barrel lengths are even consistent.

Because of the small sample size and high standard deviations, in many of the tables you'll see bullets getting "faster" in the next one or two shorter barrel lengths. This has contributed to some of the more massively incorrect internet legends such as .22 LR ammo slowing down in barrels over 16" in length. That's only true in some cases with BB caps and CB caps. Even .22 short, let alone standard velocity .22 LR, continues to accelerate even in a 26" target barrel.

In short, given their very small sample sizes and the inability to determine whether a difference between barrel lengths is statistically significant, you have to take their data with an enormous grain of salt.

What ever you do, don't consider it to be the "holy grail" for anything other than junk science.

 

[ruggyh]

In short, given their very small sample sizes and the inability to determine whether a difference between barrel lengths is statistically significant, you have to take their data with an enormous grain of salt.

What ever you do, don't consider it to be the "holy grail" for anything other than junk science

The site draws no conclusions and only presents data. While I agree the sample size is very small it does allow for trends to seen that allow for some generalizations to be made, not absolutes. The sample size for each condition is same but the relevant groups of sample sets are statistically significant.
If you are looking for a trend you can see them. To validate the trend for a sample set you would need to do more testing.

Here it is just some data points, nothing more.