Velocity loss in a semi vs manual action

[colroggal]

So I had a friendly debate today with a coworker. Being that I am not a SA fan and have never really worked with one, my opinion and knowledge is nigh on worthless but... I can't see loosing 'up to 20%' in a semi. 5% maybe and it would depend on the system. Thoughts?

Colin

[elkhunter11]

20% is not even remotely realistic, in fact 5% is likely too high.

[Rio56]

put it over a chrony and see ....

[colroggal]

Originally Posted by Rio56

put it over a chrony and see ....

I'd like to see that. A box of match grade say .308 . Ten out of a bar and 10 out of an Xbolt - same twist and barrel length. The results would be interesting.

Anyone got about $2500 to offer up in the name of science?

Colin

[elkhunter11]

Originally Posted by colroggal

I'd like to see that. A box of match grade say .308 . Ten out of a bar and 10 out of an Xbolt - same twist and barrel length. The results would be interesting.

Anyone got about $2500 to offer up in the name of science?

Colin

And that experiment wouldn't mean a lot , because the barrel and chamber would be different. If the BAR had a smaller chamber, it could produce more pressure, and more velocity.

[colroggal]

Originally Posted by elkhunter11

And that experiment wouldn't mean a lot , because the barrel and chamber would be different. If the BAR had a smaller chamber, it could produce more pressure, and more velocity.

(Not knowing much about brownings) what if you could use the same tooling and reamers on both barrels? Or better yet, the same barrel on both - cutting gas ports after the bolt has been shot.

I don't want to hamstring my own thread, but there has to be some proofed method of testing this.

Colin

[Dick284]

The variance in velocity would be about the same as comparing it between any two separate rifles. Action style is pretty much irrelevant.

Can't we just debate cartridges instead.........

[Nyksta]

This m1a discussion says theres no notable difference.

http://m14forum.com/m14/65980-veloci...s/65980?page=1

However this one says in FN FAL discussion says about 30 fps... so 1% loss

https://www.thehighroad.org/index.ph...lt-gun.379393/

[colroggal]

Originally Posted by Dick284

The variance in velocity would be about the same as comparing it between any two separate rifles. Action style is pretty much irrelevant.

Can't we just debate cartridges instead.........

are there any left to debate?

Colin

[elkhunter11]

Originally Posted by colroggal

are there any left to debate?

Colin

We could debate shotgun gauges for a change.

[Dick284]

Originally Posted by colroggal

are there any left to debate?

Colin

244 Rem vs. 6mm Rem perhaps..

[colroggal]

Originally Posted by Dick284

244 Rem vs. 6mm Rem perhaps..

30-30 vs 30wcf?

Colin

[catnthehat]

I had s guy last year tell me that he uses #71/2 shot in his 20 gauge because it was faster than in a 28!
Cat

[elkhunter11]

Originally Posted by catnthehat

I had s guy last year tell me that he uses #71/2 shot in his 20 gauge because it was faster than in a 28!
Cat

And some people still believe that a person needs 3" 12 gauge loads for pheasant.

[gtr]

Originally Posted by elkhunter11

And some people still believe that a person needs 3" 12 gauge loads for pheasant.

Some people still believe that a person needs a 7mm stw for deer.

[bubba300]

I had a browning bar 270 with 22 inch barrel and a weatherby vanguard 270 with a 24 inch barrel.
I cronied some 130 fusions in both because I wanted to see if the semi would rob some speed.
The bar was around 40 fps slower,might have bin the barrel length thow but I don't think a deer would beable to tell the difference.

[catnthehat]

Originally Posted by gtr

Some people still believe that a person needs a 7mm stw for deer.

Some people use only one rifle for hunting everything because they like it , not because they think it is better be it a 7 mag, 300 mag or even a 338 for antelope
Cat

[Grizzly Adams]

My dad always claimed semi autos had a lot less velocity than bolt actions. Think that's cause he had to use a Mauser 98 in WWll and was envious. Nothing there to lose any sleep over.

Grizz

[Salavee]

Originally Posted by elkhunter11

And that experiment wouldn't mean a lot , because the barrel and chamber would be different. If the BAR had a smaller chamber, it could produce more pressure, and more velocity.

..and if a Frog had wings, he wouldn't bump his azz on the ground.

The difference in true velocity would be less than the velocity spreads of your ammo. Almost impossible to detect.

[58thecat]

Some people....

[Coiloil37]

It would be pretty simple to test in my XCR by closing the gas block off for a few over the chrony. If the thread doesn't completely self destruct I could post some results in two weeks when I get home.

[fps plus]

Originally Posted by Salavee

..and if a Frog had wings, he wouldn't bump his azz on the ground.

The difference in true velocity would be less than the velocity spreads of your ammo. Almost impossible to detect.

Not necessarily depends on the ratio of wing size to azz size !

[700-223]

Originally Posted by Coiloil37

It would be pretty simple to test in my XCR by closing the gas block off for a few over the chrony. If the thread doesn't completely self destruct I could post some results in two weeks when I get home.

Just for giggles, you should shoot a few shots over a chrono on each setting from closed to four. Wouldn't be super generalizable as there is different types of gas systems and semi auto actions out there and confounders like typically shorter barrels on semi-autos.

I can't think of a simpler, purer way to test the theory than what you're proposing though. I suspect the magnitude of velocity change is less than that caused by lopping off a couple of inches of barrel. I'd be interested to see what you find.

[Smokinyotes]

Originally Posted by Coiloil37

It would be pretty simple to test in my XCR by closing the gas block off for a few over the chrony. If the thread doesn't completely self destruct I could post some results in two weeks when I get home.

When i owned this xcr l i tried 10 shots of nosler custom 60gr ballistic tip over the chrony. They averaged 2695. I cant remember what the gas setting was at. The advertised muzzle velocity on the box is 3050fps.

[Nyksta]

Originally Posted by Smokinyotes

When i owned this xcr l i tried 10 shots of nosler custom 60gr ballistic tip over the chrony. They averaged 2695. I cant remember what the gas setting was at. The advertised muzzle velocity on the box is 3050fps.

The numbers on the box are not going to match your gun. Your rifle's barrel length and throat lead will very much change the velocity when compared to the numbers on the box. Depending on cartridge, you lose about 20-40 fps per inch of barrel and you lose about 1 fps per 0.002" of throat jump distance. I think barrel twist has its factor too but i dont know the numbers. If the powder is temp sensative that could slow it down too.

[elkhunter11]

Originally Posted by Nyksta

The numbers on the box are not going to match your gun. Your rifle's barrel length and throat lead will very much change the velocity when compared to the numbers on the box. Depending on cartridge, you lose about 20-40 fps per inch of barrel and you lose about 1 fps per 0.002" of throat jump distance. I think barrel twist has its factor too but i dont know the numbers. If the powder is temp sensative that could slow it down too.

While the jump to the lands can effect the velocity, you can't be sure what the jump to the lands was that the ammunition manufacture used in their test rifle, so you can't calculate any losses or gains compared to the ammunition manufacturer 's listed velocity. And the chamber may be larger or smaller than the chamber that the ammunition manufacturer used, which could effect the velocity more than the jump to the lands. I have seen variations of well over 100fps from the manufacturer 's rating to the velocity measured in a specific rifle. Then again, since the only variable in this case will be the gas valve being opened or closed, the barrel length, chamber volume, the jump to the lands and the temperature sensitivity of the load , are all irrelevant, as far as the difference in velocity is concerned.

[Coiloil37]

I'll try it when I get back in Canada next week.

I'll do a group on each setting, show the groups and velocity and just for giggles I'll run a five shot group with the gas block on a different setting for each shot to see if there's any poi change.

[trooper]

It seems to me that with a gas operated firearm, the gas port is further down the barrel. wouldn't the projectile have reached max velocity by the time the projectile passes the gas port where some of the energy is bled off to recock the action? Maybe a blowback action would be different?
I'm thinking that if the breech is locked when the round is fired and doesn't unlock and start it's rearward motion until the bullet passes the gasport, the bullet should have reached the same MV that a bolt gun of the same caliber would.

[colroggal]

Originally Posted by Coiloil37

I'll try it when I get back in Canada next week.

I'll do a group on each setting, show the groups and velocity and just for giggles I'll run a five shot group with the gas block on a different setting for each shot to see if there's any poi change.

I'm looking forward to seeing your results.

Colin

[West O'5]

Interesting experiment.
I also have an XCR and chrony....and I'm also away on hitch for another couple weeks.
In response to smokinyote's 300fps+ loss of published MV,I'll assume you have the standard 18.6" barrel on XCR,yes?
-Advertised MV is likely from 24" test barrel....probly 200fps+/- difference from barrel length alone.
-XCR has a 5.56 chamber,your ammo was tested in .223
I'd say it's reasonable to guess that those two factors alone would have a significant impact on actual vs advertised MV even if the XCR gas was blocked in single shot mode.