Balistics by the inch

[Larry Poho]

There are sometimes Questions about barrel length and the effects of it on velosity. Here is s0me info to give you an Idea on some calibers in some cases.
https://matchgrademachine.com/velocity-testing-thompson-center-barrels/. Also http://www.ballisticsbytheinch.com. Keep in mind that in some circumstances these figures change. A pistol caliber in a revolver verses a closed rifle chamber also is usually a bit faster in a closed chamber vs oped revolver due to pressure escaping by the revolver design. Also slower burning powders in a pistol caliber tend to make bigger differences in longer rifle barrels than with faster burnibg powders.

 

[Ks5shooter]

Cool thanks

 

[chicharrones]

There are sometimes Questions about barrel length and the effects of it on velosity. Here is s0me info to give you an Idea on some calibers in some cases.
https://matchgrademachine.com/velocity-testing-thompson-center-barrels/. Also http://www.ballisticsbytheinch.com. Keep in mind that in some circumstances these figures change. A pistol caliber in a revolver verses a closed rifle chamber also is usually a bit faster in a closed chamber vs oped revolver due to pressure escaping by the revolver design. Also slower burning powders in a pistol caliber tend to make bigger differences in longer rifle barrels than with faster burnibg powders.

I've never seen the matchgrademachine link before. Thanks and welcome to the forum.

 

[MCMXI]

@Larry Poho , that's a good first post. I have a 24" 6.5CM Bartlein barrel on my AI AW that's super accurate but the 6.5CM chart sure makes a good case for lopping 2" off the end. I run a suppressor on that rifle so shortening the overall package by 2" is appealing. I'm not going to shoot anything lighter than 140gr so I see no downside.

 

[jmr40]

There is a lot of data out there if you look for it. The TC website was one I'd not seen before, but their data is pretty much in line with others I've seen. The BBI website is a great place to find a lot of handgun data all in one spot.

But with all of these it is important to look at the data from the right perspective. The only data that is relevant is that done with the same barrel cut shorter as you go. That doesn't mean that YOUR 22" barrel will be the same as the 22" barrel used in the test. But when you start looking at data from different barrels the data is useless because there can very well be a HUGE difference in velocity with 2 different barrels of the same length. Enough so that it isn't uncommon for rifle A with a 20" barrel to shoot faster than rifle B with a 22" or even a 24" barrel. And rifle C with a 20" barrel could easily be more than 150 fps slower than rifle B with a 22" barrel.

One glaring example on the BBI website shows a 6" 357 mag Colt Python shooting consistently slower than several other guns with 5" and even 4" barrels. This is more common than a lot of people realize. They show all of the loads from a single barrel and again from "real" guns. The data from "real" guns is often all over the place and unpredictable. Just like in the real world.

 

[Wreck-n-Crew]

For what it's worth (as the op eluded to) the ballistics by the inch for pistol have no real world value other than the rounds tested. I did some testing in 9mm ballistics using my own loads to see just how much a slower powder affects velocity in a longer barrel vs a faster powder. Test platform was a 4.5" 9mm pistol and a 16" carbine. 4 test loads varying from fast (Red Dot) to slow (slowest was Power Pistol). Results in my post here... https://www.thehighroad.org/index.p...-vs-factory-chrono-test.799017/#post-10190193

 

[Larry Poho]

Thanks for the welcome guys. Great forum here. I have a few crono’s and love to play with load data. I don’t just assume a "longer is better, or faster after doing some testing. I have two 444 marlin Marlins. one an 18 inch 444P Outfitter, and one 444s with a 22 inch. One has Ballard 1:20 twist and the other has 1:38 microgroove barrel. The micro groove barrels tend to be faster than most other barrels with fast twist rate, deeper grooves. but they dont shoot or stabilize 340 grain boolts very well. Kinda what jmr40 was saying. There is a point where propelant/powder burn, stops and the slowing effect of barrel friction actually lowers the velocity read out on the crono. AND WOW Wreck-n-Crew. Very cool test. Thanks for that link. very in depth. Very educational and great info. I’ll save that link for future reference. That could be a showcase article in any gun publication.

 

[Pat Riot]

Welcome Larry Poho

I knew about BBTI but not the Thompson site. Thank you for that.

 

[old heeler]

Welcome, Interesting and one of my hunting rifles is 280AI with 27" lilja barrel and it's long throated.

 

[MachIVshooter]

I have a 24" 6.5CM Bartlein barrel on my AI AW that's super accurate but the 6.5CM chart sure makes a good case for lopping 2" off the end. I run a suppressor on that rifle so shortening the overall package by 2" is appealing.

Or even 4". 20" is a good balance for .308 based cartridges with suppressed rifles. Of course, if you're not traipsing through the woods with it, not much reason to.

 

[stillquietvoice]

Welcome to the forum interesting info. I've seen test like this before. I never gets old.

 

[MCMXI]

But with all of these it is important to look at the data from the right perspective. The only data that is relevant is that done with the same barrel cut shorter as you go. That doesn't mean that YOUR 22" barrel will be the same as the 22" barrel used in the test. But when you start looking at data from different barrels the data is useless because there can very well be a HUGE difference in velocity with 2 different barrels of the same length. Enough so that it isn't uncommon for rifle A with a 20" barrel to shoot faster than rifle B with a 22" or even a 24" barrel. And rifle C with a 20" barrel could easily be more than 150 fps slower than rifle B with a 22" barrel.

What is significant is the trend for the barrel tested as the length is changed. Obviously if I cut my 24" barrel down to 22" I wouldn't expect to see the exact same velocity as shown in the data set for a given load, but I would expect to see a similar change in velocity. The data implies that a 2" reduction from 24" doesn't make much difference for a 140gr bullet and so I would expect a similar result for any 24" barrel.


MGM is sufficiently confident in the results to recommend a barrel length for any 6.5 CM barrel based on those results.

Velocity Testing Length Recommendation (6.5 CM):

• 140+ grain bullets: 22″
• 129 grain or lighter: 24″ with very little loss if 22″ is needed

 

[MCMXI]

Here's another test in which a 6.5 CM barrel was cut down inch by inch. Going from 24" to 22" resulted in a loss of only 34 fps for a 142gr SMK load and just 46fps for a 120gr A-MAX load. The trend for this test is very similar to the other test results that were posted. The author includes drop and drift data too for various barrel lengths.

https://rifleshooter.com/2016/02/6-...el-length-on-velocity-cutting-up-a-creedmoor/

 

[taliv]

But with all of these it is important to look at the data from the right perspective. The only data that is relevant is that done with the same barrel cut shorter as you go. That doesn't mean that YOUR 22" barrel will be the same as the 22" barrel used in the test. But when you start looking at data from different barrels the data is useless because there can very well be a HUGE difference in velocity with 2 different barrels of the same length. Enough so that it isn't uncommon for rifle A with a 20" barrel to shoot faster than rifle B with a 22" or even a 24" barrel. And rifle C with a 20" barrel could easily be more than 150 fps slower than rifle B with a 22" barrel.

i'm not going to say i completely disagree with this statement. but my experience is very different. sure, there are some barrels that shoot fast or slow, but by and large, the same type of barrel will shoot about the same. awful lot of PRS competitors out there shooting the same cartridge with the same load and getting the same velocity. all the barrels i've had of the same length shot the same speed; i can't recall having one that shot super fast or super slow.

not just that, but i don't necessarily buy that the data from a single barrel cut down is valid because the bore diameter changes in most barrels, hopefully being tapered toward the finish length, which if nothing else, means more friction. would the cut down test be more or less meaningful if you custom ordered a blank with no taper?

 

[Larry Poho]

But you are talking a few feet per second. These tests are for an overall idea what you can expect. When compared to other experiments, these two are very close. You can guarantee for instance that after 14 inches of barrel length in a good 44 magnum barrel, that there is little to be gained in an 18 inch barrel, and that after 19 inches, most of the time the velocity seems to decrease. Just a general idea of how it will act. I have a Ruger Sup Blabkhawk in 10 1/2 inch barrel. Also had a Tompson contender with a 10 inch barrel. Both in 44 mag.The closed chamber TC gun was almost 80 fps faster with same ammo. Both were 1 in 20 twist. The closed chamber was as close to 100% efficient as you can get. so I would assume that the closed chamber has a more efficient result than a revolver using same ammo. Would it be minute of deer superior? I doubt it. Again, these actual tests done by people who understand ballistics, are pretty accurate, and they both give details about how they were done. Wreck-in-Crew went to great length to actually say for sure how his tests were done, and the recorded outcome. Very well done and IMHO as good and professional as it gets. I would definitely use his data to aid me in determining barrel length and velosity expected. For some reason, a 357 magnum in a rifle seems to really increase velosity significantly.