Hunting Washington Forum

Equipment & Gear => Guns and Ammo => Topic started by: wraithen on June 30, 2012, 08:13:02 PM

Title: Shorter barrel = higher fps?!
Post by: wraithen on June 30, 2012, 08:13:02 PM: So the wife and I were watching american guns last night and the smiths had an arguement about whether shortening the barrel 2" (as requested by the customer) would increase or decrease the fps. They chrono'd it and it was 50 fps faster with 2" less barrel. How is this possible? This goes against everything i've read!
Title: Re: Shorter barrel = higher fps?!
Post by: buckfvr on June 30, 2012, 08:15:57 PM: maybe it was too long for the caliber......leaving the barrel after it had started down on the pressure curve....rather than exiting at the peak.
Title: Re: Shorter barrel = higher fps?!
Post by: jamesjett on June 30, 2012, 08:17:38 PM: What caliber and how long was the barrel before it was shortened?
Title: Re: Shorter barrel = higher fps?!
Post by: Huntbear on June 30, 2012, 08:18:23 PM: You almost need to be a physics/calculus specialist to do the math. It would depend on the caliber, and what the original length of barrel it was to begin with.

At some point you get quickly diminishing rewards as barrel length increases depending on caliber. So yes, this can happen. some rounds were actually designed with 20-22 in. barrels in mind. :dunno: :dunno:
Title: Re: Shorter barrel = higher fps?!
Post by: wraithen on June 30, 2012, 08:19:20 PM: I'm assuming .45 but they never clarified. I believe the barrel started at 20 and was chopped to 18 or 18 to 16
Title: Re: Shorter barrel = higher fps?!
Post by: buckfvr on June 30, 2012, 08:21:16 PM: Yep....all the above
Title: Re: Shorter barrel = higher fps?!
Post by: Huntbear on June 30, 2012, 08:22:38 PM: Quote from: wraithen on June 30, 2012, 08:19:20 PM
I'm assuming .45 but they never clarified. I believe the barrel started at 20 and was chopped to 18 or 18 to 16

.45 LC? .45ACP? 45-70???? The first two are pistol rounds and would perform much better in a shorter barrel. 45-70 ? Not really.
Title: Re: Shorter barrel = higher fps?!
Post by: wraithen on June 30, 2012, 08:26:51 PM: .45 acp, thanks, makes sense now. didn't realize the pressure spike could be that quick.
Title: Re: Shorter barrel = higher fps?!
Post by: TheSkyBuster on June 30, 2012, 08:41:23 PM: I havent watched that show lately, but the last one I saw they modified a mossberg ATR for a guy to hunt Alligators. He paid them big bucks to "build" him the Rifle. I only saw one problem with it. He's a Lefty. :chuckle:

http://dsc.discovery.com/tv-shows/american-guns/videos/gator-gun.htm (http://dsc.discovery.com/tv-shows/american-guns/videos/gator-gun.htm)
Title: Re: Shorter barrel = higher fps?!
Post by: Bob33 on June 30, 2012, 08:55:04 PM: Once all the powder has burned, acceleration stops.
Title: Re: Shorter barrel = higher fps?!
Post by: wraithen on June 30, 2012, 09:54:48 PM: Quote from: Bob33 on June 30, 2012, 08:55:04 PM
Once all the powder has burned, acceleration stops.

I got that, but I didn't know that deceleration would begin in the barrel more so than in the air.
Title: Re: Shorter barrel = higher fps?!
Post by: YellowDog on June 30, 2012, 09:59:39 PM: Quote from: TheSkyBuster on June 30, 2012, 08:41:23 PM
I havent watched that show lately, but the last one I saw they modified a mossberg ATR for a guy to hunt Alligators. He paid them big bucks to "build" him the Rifle. I only saw one problem with it. He's a Lefty. :chuckle:

http://dsc.discovery.com/tv-shows/american-guns/videos/gator-gun.htm (http://dsc.discovery.com/tv-shows/american-guns/videos/gator-gun.htm)

LOL I saw that episode and that guy got screwed. He paid like $8,000 + for a slightly modified shotgun and a fairly basic handgun and the frickin shotgun was for a righty and he was left handed. :yike:
Title: Re: Shorter barrel = higher fps?!
Post by: elkinrutdrivemenuts on June 30, 2012, 10:21:00 PM: What are you talking about? I thought that show was about his smokin hot daughter?
Title: Re: Shorter barrel = higher fps?!
Post by: wraithen on June 30, 2012, 10:24:18 PM: The one with the giraffe neck that wears a pushup bra that puts em around her neck? :drool:
Title: Re: Shorter barrel = higher fps?!
Post by: Bob33 on June 30, 2012, 10:34:40 PM: Quote from: wraithen on June 30, 2012, 09:54:48 PM
Quote from: Bob33 on June 30, 2012, 08:55:04 PM
Once all the powder has burned, acceleration stops.

I got that, but I didn't know that deceleration would begin in the barrel more so than in the air.
There is more friction in a barrel than air.
Title: Re: Shorter barrel = higher fps?!
Post by: david0 on July 01, 2012, 07:16:09 AM: http://www.bellmtcs.com/store/index.php?cid=580 (http://www.bellmtcs.com/store/index.php?cid=580)

Here is an article about shorter barrels for the TC Encore. He cuts them down and gets better accuracy.
Title: Re: Shorter barrel = higher fps?!
Post by: Biggerhammer on July 01, 2012, 08:43:20 PM: Quote from: wraithen on June 30, 2012, 10:24:18 PM
The one with the giraffe neck that wears a pushup bra that puts em around her neck? :drool:

Hahaha! Exactly, I've shot things cuter. :tup:
Title: Re: Shorter barrel = higher fps?!
Post by: elkinrutdrivemenuts on July 01, 2012, 09:51:20 PM: Quote from: Biggerhammer on July 01, 2012, 08:43:20 PM
Quote from: wraithen on June 30, 2012, 10:24:18 PM
The one with the giraffe neck that wears a pushup bra that puts em around her neck? :drool:

Hahaha! Exactly, I've shot things cuter. :tup:

Maybe I need to quit drinking so much, seems like I have permanent beer goggles :dunno:
Title: Re: Shorter barrel = higher fps?!
Post by: Helix on July 01, 2012, 10:41:03 PM: Three things can cause this. The first and most obvious is error in setting up the chrony. Such as setting it too close to the muzzle blast. More docketing gas out the muzzle crossing the curing will register faster.

The second is when you have more barrel time than it takes to burn all the powder. Most common in .22 and smaller calibers. It is actually observable with a 9mm carbine. Barrel friction in this case can slow the round in the last part of the barrel. But this is rare in major caliber rifles.

Last and if I were going to win this argument (by cheating) would be a hotter loaded cartridge used with the shorter barrel. If this is for tv expect the producers to create drama by cheating.