I say no - or practically nill but I have a very stubborn technically minded friend who wants a good explanation for if\why a bullet shot out of a semi auto wouldn't be going slower than one out of a bolt? His belief, that I have failed to counter to satisfaction, is that the energy used to cycle the action must be reducing the "accelleration energy" available to the bullet itself? Someone help me with this one please. Feel free to be as mathematical as you like. I was finally able to convince him that muzzle breaks work but that took some doing. Just this weekend I gave him examples on recoil that he was OK with but never got this particular item put to rest.
IMHO the gas used to cycle the action will decrease the speed as compared to a bolt gun. I may be wrong, but I have never chrono'ed a semo auto that was as fast as the same ammo was in a bolt gun with the same barrel lenght..The difference IME was between 100 and 200 fps difference...
In theory, yes. In practice, no.
First the gas "lost" isn't really lost completely. So even though there's a small pressure drop, it is very VERY small, percentage-wise.
Second, most gas actions tap the gas fairly near the muzzle, so there's little time left before the bullet clears the muzzle - and nearly all the bullet speed already attained.
Third, you'd have a hard time deciding, because the individual variation from shot to shot is almost always larger than the loss of speed due to gas bleedoff.
All these can be clearly demonstrated by simply blocking or turning off the gas system (in guns like the Garand where you can do so.) Measure bullet speed with the gas system on and off and compare.
I sure have to agree with Rocky on this account. In fact, I had a Remington 742 in 243 Win and a Win Model 70 in 243. With identical loads the 742 shot faster over my chrono. Maybe the Remington just had a "faster" barrel than the Win.
So will a gas auto shoot slower? ,, maybe.. but sure not enough to make a bit of difference downrange. Mine actually shot faster,, go figure??
All these can be clearly demonstrated by simply blocking or turning off the gas system (in guns like the Garand where you can do so.) Measure bullet speed with the gas system on and off and compare.
BINGO--Apples to apples is the only way to measure for sure.
BMT
Years ago in Precision Shooting magazine there was an article concerning how many FPS were lost from gas bleed off.
The Author I believe was Derrick Martin, and he took a barrel off an AR15 and mounted it on another action.
He left the gas hole open and did tests over a cronograph.If I remember correctly it was about 7 fps.
Ask your friend this rhetorical question as a way of explaining what happens.
"Does the water level in the ocean rise if you pee in it?"
"Does the water level in the ocean rise if you pee in it?" [/quote]
Yes it does, just about the same as the difference between a semi auto and a bolt action,,, not enough to get excited about or notice.
Rocky (and others), after receiving the the first two responses I cut and posted them in a note and added comments that turned out to be nearly identical to yours. Being unfamiliar with firearms workings I think his mental assumption about recoil (identified by my last comments to him)is likened to a recoil operated rather than gas cycling action. My take is that if talking about a recoil operated action then the best answer might be that it takes very little energy for the bullet to break the bond of a crimped case that holds it - though I might never believed that after hammering away on one of those blasted enertia bullet pullers. Here are my responses if interested. Let me know how to improve on them - or if I am in error. Thanks folks.
Pete,
thought I would ask your question about speed loss due to cycling a semi automatic action to see if anyone came up with something different. Here are the first two responses:
IMHO the gas used to cycle the action will decrease the speed as compared to a bolt gun. I may be wrong, but I have never chrono'ed a semo auto that was as fast as the same ammo was in a bolt gun with the same barrel lenght..The difference IME was between 100 and 200 fps difference..
I call this a "possible indication" more than scientifically measured. The reason might be that this particular barrel is slower than others. Two identical loads fired from two different barrels, even if the barrels are on identical rifle models, will yield at least slightly different speeds. Other factors in barrel speed include manufacturing techniques- ie button rifled or hammer forged as well as how fresh the cutting tools were when they made a particular barrel. If I bought a box of 270 ammo and put one round in my CZ and one in a Savage there would be a difference in speed. Just the nature of absolutes. Certain makes do 'tend' to be faster than others and twist rate of the rifling is assumed to be the same here- BUT in certain calibers you can find different twist rates because some are geared towards shooting lighter or heavier bullets in that caliber. 223 is a good example of this. So, overall is there a difference? A small one possibly is the answer- just as suspected.
Here is the second response:
In theory, yes. In practice, no.
First the gas "lost" isn't really lost completely. So even though there's a small pressure drop, it is very VERY small, percentage-wise.
Second, most gas actions tap the gas fairly near the muzzle, so there's little time left before the bullet clears the muzzle - and nearly all the bullet speed already attained.
Third, you'd have a hard time deciding, because the individual variation from shot to shot is almost always larger than the loss of speed due to gas bleedoff.
All these can be clearly demonstrated by simply blocking or turning off the gas system (in guns like the Garand where you can do so.) Measure bullet speed with the gas system on and off and compare
Note here Pete is that I believe you were looking at recoil in the way it is used in an inertia system firearm. Like a Benelli rifle or shotgun or a lot of semi pistols. The recoil on these are noticeably sharper in my experience- but the cycle times are faster. You can shoot a Benelli recoil\enertia operated semiauto shotgun - maybe some Beretta's too - Martin's new one might be recoil operated, -anyway you can pop three rounds off with amazing speed. Very fun but you don't want to keep doing it. For a practical application of your question as it pertains to rifles we should consider it as it pertains to gas operated devices and that is what the post above is speaking to.
Your friend may have in mind a simi-auto "blow-back" system, which most if not all simi-auto .22`s use. In my experience, and non-scientific testing, he`s right.
Still no loss. In recoil-operated and "blowback" systems, the action does not begin to open until the pressure in the barrel drops almost to zero - meaning the bullet has left the muzzle. That being the case, there can be no possible effect on velocity.
Rocky's right-
Nothing happens, action-wise, until Elvis has left the building.
I have all the respect in the world for Rocky's expertise. That being said, I have compared Browning BAR's in 25-06 and 280 to bolt guns by shooting the same the loads side by side over a chrony.
Chrony said the BAR was shooting the same loads ~ 200 fps slower.
I believe Browning has publicly admitted the same.
Of course the 200 fps only matters to the chrony. Neither the operator nor the intended critter will notice a practical difference without reading the chrony.
GE
differant barrels could account for that much ..
That's true. Two bolt guns an be that far apart. The real test would be if you could block the gas port in the BAR and shoot it that way. I bet there'd be absolutely no notable difference in the muzzle zoom.
I have a Ruger Mini-30 with an adjustable gas block. This allows me to adjust the size of the gas port. I will load 20 identical rounds. Fire 10 with the gas port open and 10 with the gas port completely shut off and record the velocities. I will try and get this done on Sat. Maybe this will help settle this.
hey thanks Steve- it is kind of interesting and something a lot of us have probably wondered. Looking forward to the results. anyone taking bets???
I will bet one BoreSnake (new) in 12-gauge size that there is no appreciable difference.
.
This sounds very interesting. I am suffering velocity loss because of the energy required to cycle the action? Then how much energy/velocity loss is caused by recoil itself, even in a bolt gun? A heavy recoiling rifle or shotgun, bolt or semi-auto, expends a lot of energy in coming back to thump the shooter. How much velocity does that cost?
So, if I place the butt of my 30-06 against a tree to prevent recoil motion I should see a velocity gain when fired, as compared to firing from my sholder? Hmmm...
How much velocity do I gain when shooting road signs and mailboxes from my truck traveling 60 mph?
This is giving me a headache.
.
.
How much velocity do I gain when shooting road signs and mailboxes from my truck traveling 60 mph?
This is giving me a headache.
.
About 88 fps subject for adjustment between angle of travel and sign. Which is also subject to whether the gunner is A) Driving B) Drinking C) Passenger D)A&B or E) B&C.
Questions like this on the SAT would fill Harvard with kids from North Dakota.
GE
JBLEDSO, the recoil idea is something I haven't considered but the logic works. Interesting.
I will bet one BoreSnake (new) in 12-gauge size that there is no appreciable difference.
HA HA- - that word "appreciable" is so ripe for lawyer interpretation Rocky. Heck, have you seen the hairs we split around here at times? I can just hear it, if the difference is 100fps someone would say, "well if I threw a 165 grain bullet at you at 100 fps I bet you would call it mighty appreciable upon impact?" and maybe follow that with the old "nuff said" to punctuate. Unlike my friend, who asks an intelligent if unenlightened question, I don't see anyone here saying the difference will be noticeable, just wondering if it exists and if so- how measurable.
I have all the respect in the world for Rocky's expertise. That being said, I have compared Browning BAR's in 25-06 and 280 to bolt guns by shooting the same the loads side by side over a chrony.
Chrony said the BAR was shooting the same loads ~ 200 fps slower.
I believe Browning has publicly admitted the same.
Of course the 200 fps only matters to the chrony. Neither the operator nor the intended critter will notice a practical difference without reading the chrony.
GE
My results are the same as yours, every time that I have chronographed a semi auto of the same caliber and barrel lenght as one of my bolt actioned rifles the velocity has always benn lower in the semi auto... by as much as 200 FPS..
All due respect...but run both typs of guns over a crony...bolt .22 and semi .22. I did this a few years back just for fun. The semi was slower by about 65 fps. Just my guns?? Maybe we need someone to test accuratly and report back??
I have all the respect in the world for Rocky's expertise. That being said, I have compared Browning BAR's in 25-06 and 280 to bolt guns by shooting the same the loads side by side over a chrony.
Chrony said the BAR was shooting the same loads ~ 200 fps slower.
I believe Browning has publicly admitted the same.
Of course the 200 fps only matters to the chrony. Neither the operator nor the intended critter will notice a practical difference without reading the chrony.
GE
My results are the same as yours, every time that I have chronographed a semi auto of the same caliber and barrel lenght as one of my bolt actioned rifles the velocity has always benn lower in the semi auto... by as much as 200 FPS..
A lot a semi's have chambers that are even sloppier than factory bolt guns, and therein lays your difference.
I've seen 270+fps difference between chambers, and they were both cut in the same barrel, mounted on the same receiver, and using the same lot of handloads. At 26" with a oversize throat the ammo was chron'ed at 2725, at 25" with a tight throat the same ammo chron'ed at 2995
My Ruger Mini-30 has a custom ASI barrel chambered in 7.62x39 with a .308 dia bore. I fired identical rounds with the gas port wide open and then completely closed. Same action,same barrel, same chamber and same rounds.
This is what I came up with. Temp 22*, wind 18 MPH and damn cold.
AA 2230 125gr Sierra PH.
Open GP 2107
2081
2102
2095
2098
2102
2098
2093
2096
2079
Avg 2095fps
GB Closed 2118
2107
2095
2095
2119
2120
2121
2106
2090
2086
Avg 2106fps
R-7 125gr Sierra PH.
Open GB
2434
2392
2396
2389
2388
2418
2413
2383
2412
2415
Avg fps 2404
GB Closed
2400
2405
2434
2430
2418
2397
2438
2440
2430
2423
AVG 2421fps
H322 110gr VMax
Open GP 2318
2340
2324
2321
2308
AVG 2322fps
Closed GP
2337
2345
2329
2348
2321
AVG 2336fps
H322 125gr Sierra PH
Open GB
2297
2300
2303
2306
2256
AVG 2294fps
GB Closed
2292
2300
2291
2322
2326
AVG 2306fps.
By my rough calculations the closed gas port has an increased velocity of about 15fps in this little round. Kinda like pissing in the Ocean as far as the 7.62x39 is concerned.
That's about .65% increase in velocity. With a 3000fps round that would be about 20fps.
And it's also less than some of the round-to-round variation in a given string. Verdict: no change.
Does that mean I don't get the Bore-Snake?? Ah, Crud.
I didn't hear a counter-bet, Steve. But if you want the durn thing, I'll send it to ya.
Steve, I forgot to thank you for providing the excellent scientific info. Commendably done. I forwarded your findings along with my note that the differences seemed to be more or less within standard deviation of a single load. My friend is funny about it. We weren't arguing over this, merely conjecturing, but he is tenacious and his response was to note that the difference definitely was measurable, (which seemed a far cry from his original supposition) - so he kind of felt he was "right" so to speak. I sent him a note back chiding him that if his wife had argued his position on this subject he would scoff and say something like, "Yeah, its measurable. About as measurable as a fart in a hot air balloon". CC'd a mutual friend who got a good chuckle over that. Thanks again. Great stats, made the conversation very satisfying.
As I posted earlier I have never chronographed a Semi Auto that wasas fast as a bolt even when useing the same ammo on the same day.I assumed from this that the semiautos action was the culprit, but after reading Steve's results this was a faulty assumption...