AIAE .308 Velocity Loss Going From 24" to 20" Barrel

[limamike56]

I am sure someone here must have chronographed the velocity of a 20" AI barrel vs a 24" AI barrel using 168 and 175 gr bullets. Damned if I can find it here with the search engine. I am leaning toward the 20" barrel and know AI barrels are fast but would like to know the difference before I purchase. Thanks.

 

[Dacam]

Someone once told me that you will lose or gain 20fps per inch of barrel length or increase of barrel length.

 

[midmoguy]

I've heard more like 50 fps per inch but that's just hear say

 

[ChemE1975]

The article at the following web address talks about barrel length and velocity specifically for a 308 and 300wm. It does not address the AI AE specifically, but the findings in the article should be applicable to the AI. It is a good read...I'd guess you will end up with the 20" if you read this article.

SWAT Article BARREL LENGTH

 

[limamike56]

Thanks for the replies and the link to SWAT article.

We can all guess about the difference in velocity between a 20" and 24" barreled AI in .308 with 168 and 175 gr ammo, but that is not really what I am looking for here. If anyone has chronographed these rounds in an AI the data would be greatly appreciated.

 

[EricCartmann]

150 fps DIFFERENCE is the more accurate number. Which is about smack in the middle of 25 and 50 fps per inch (37.5 fps).

For the barrels I have chron'd (about 12 total), I would say on average 20" barrels get about 2550fps for FGMM 168 gr ammo, and 24" barrels get about 2700 FPS with the same ammo.

 

[ChemE1975]

you might look in the reloading section...it would require digging but there are stickies for people to post load data. those load data threads usually include MV and rifle used.

 

[Defusion]

Perhaps not so much a comparison, but I'm pretty sure someone must have chrono'ed a 20" and someone else must have chrono'ed a 24" with approximately the same loads.
I'd be interested in some data from a 20" as well.

I have a 20" on the way, and have some 168gr SMK's to try when it gets here ... but don't have a chrono just yet. If I can borrow one, I'll be sure to post the results.

 

[gstaylorg]

My .308s all fall very close to 20-25 fps per inch of barrel length in the barrel length you're talking about. They are all Bartlein .299/.308 5R barrels; so YMMV. Having said that, I strongly doubt you are going to see a 50 fps loss in velocity per inch of barrel, anywhere from 15-25 fps seems to be the norm.

 

[Graham]

The article at the following web address talks about barrel length and velocity specifically for a 308 and 300wm. It does not address the AI AE specifically, but the findings in the article should be applicable to the AI. It is a good read...I'd guess you will end up with the 20" if you read this article.

SWAT Article BARREL LENGTH

There's that article again: Critical reading skills required.

The only truthful answer is: It depends.

Will there be a velocity loss in the same barrel if it is shorter? Yes. In a different barrel? Probably. How much? You will have to measure it yourself. Does it matter? It depends. What should you count on as a rough guide without having done it to your rifle? Between 20fps and 40fps per inch from 24" to 20" with factory ammo.

 

[limamike56]

Again thanks for the posts, but to keep this on track has anyone actually chronographed .308 168 gr and 175 gr ammo out of an Accuracy International rifle with a 20" and 24" barrels?

 

[tylerw02]

Fact is you need to narrow down which loads specifically, not a bullet weight. Beyond that no two barrels are the same. One barrel can easily shoot 50fps faster than an identical barrel with the same load. The information you're requesting does not exist. Nobody can tell you exactly how much the sample you get will lose, if any.

I actually chopped a barrel from 27" to 22" and picked up 20 fps with the same load. Part of which, I think was because the barrel had broken in a bit.

 

[limamike56]

I am not asking for exact. Just the difference in velocity between a 20" and 24" AI Barrels with 168gr or 175gr bullets with the same loads. There is likely some difference and I wondered what it was before making a buying decision.

 

[tylerw02]

For one, nothing is unique about AI barrels that are going to be so much different than other makers.

The same generalizations apply to your question. Nobody can tell you exact.

If I try really hard, I could really load 175s hot and get more velocity in a 20" than the next guy does in a 168 in a 24". Your best bet is to accept the generalizations. Decide what is most important for you, speed or portability. Then pick your poison.

 

[6brshooter]

No two barrels are the same, plus too many variables. I am too cheap to own one ai, much less two. If u handload the loss of velocity can be stifled somewhat by running a faster powder like h4895. Since i live in a nonsupressor friendly state i have no use for less then 24" barreled rifles, except m4 and 16" varmint ar for calling yotes.

 

[bmt]

My 308, PacNOr Stainless Match 1 in 10 twist barrel lost 64 FPS when I cut the barrel from 24 inches to 20. That is with black Hills match 175 grain BTHP.
BMT

 

[limamike56]

Thanks for the information bmt.

 

[Graham]

Again thanks for the posts, but to keep this on track has anyone actually chronographed .308 168 gr and 175 gr ammo out of an Accuracy International rifle with a 20" and 24" barrels?

Yes.

I am not asking for exact. Just the difference in velocity between a 20" and 24" AI Barrels with 168gr or 175gr bullets with the same loads. There is likely some difference and I wondered what it was before making a buying decision.

You have the answer already. If you don't like it, it won't change.

Thanks for the information bmt.

He answered a different question than the one you asked.

 

[limamike56]

Graham,

For example, I have two STG 58 rifles built by DSA. As close to identical as two rifles can be with the exception of barrel length. One barrel is 21 inches and the other barrel is 16.5 inches. Using the same ammo in each rifle, there is a consistent difference in muzzle velocity between the two barrels of about 92 to 106 fps. The 16.5" barrel on average, produces about a hundred fps slower muzzle velocities than the 21 inch barrel. That is the kind of information I was looking on AI rifles with 20" and 24 inch barrels.

As far as thanking bmt for the information, I appreciate everyone taking the time to respond and his information was helpful. I am not sure what you are trying to say here.

 

[Graham]

Using the same ammo in each rifle, there is a consistent difference in muzzle velocity between the two barrel lengths of about 93 to 106 fps. That is the kind of information I was looking for here on AI rifles with 20" and 24 inch barrels.

That's not a consistent difference.

You are looking for something that isn't there. A 10fps spread between two shots is not unusual, even with good ammo.