Very weird POA results with reloads for Mosin

[fireflyfather]

So, I'm at the range today dialing in new sights for my mosin (mojo microclick snapsights....beautiful sights). I get it all dialed in at 100 yards with 1960's vintage Czech light ball (147 grain). Then as I started generating bullet drop with various reloads using jacketed and cast bullets, I found one load that was a complete anomaly.

All my other loads shot lower than my zero with the Czech ball ammo, as I expected. However, I had one batch of brass set up with Ed Harris' "The Load" of 13 grains of red dot under a 160gr Gas-Checked Lee bullet meant for the SKS (312-160-TL-2R). That load, with it's wimpy recoil, was shooting FIVE TO SIX INCHES HIGH with the sights set to zero. That is, a 1600fps load was shooting six inches higher than a 2850fps load with only a modest change in bullet weight (5-10 grains, depending on gas check weight). I'm pretty sure I wasn't flinching or anticipating recoil, and I went back and forth between the two loads since I had some extra of both lying around, and I was able to repeat the results several times, and it obviously wasn't the sight moving around or being loose, since the zero with the Czech ball was still dead on, and the recoil was what I would expect with full-power military ammo and deliberately wimpy cast bullet reloads.

The BC of the two bullets was .401 for the Czech stuff (http://7.62x54r.net/MosinID/MosinAmmo011.htm), and .276 for the Lee. I'm just scratching my head to try and figure this out. I had assumed that the ball ammo would be the flattest shooting, and I could generate bullet drop data with that as my baseline, and then adjust for each of the different load recipies I have by using the range adjustment dial on my sights. Now I have to hold under six inches or back off on that recipe quite a bit.

I think I've weeded out the other variables like wind, etc, so I have no idea what's going on here. I figured bullet drop at 2.5 inches for the ball, and just under 8 inches for my reloads. The targets however, were showing that instead of being 5.5 inches lower, it was a similar amount higher.

Can anyone give me some insight here?

 

[KansasPaul]

This is in theory only as I have no confirmation of this hypothesis. When the lighter loads are fired the bullet takes longer to exit the barrel. As the barrel rises as result of recoil the slower bullet exits the barrel when the barrel is located at a higher position resulting in strikes on target at a higher point of aim.

 

[fireflyfather]

I had thought of that. I am shooting a 91/30, so the 29 inch barrel is long enough that that could theoretically be a factor I guess. The recoil was so piddly, however, that it's hard to swallow that one. I had another load that fired a jacketed 150 grain soft-point bullet with a BC in between the other two. Same powder & charge, 10 grain lighter bullet, a little slower (1450 fps or thereabouts due to increased friction from the jacket), and it was shooting about 3 inches LOW, with perceived recoil about the same as the lead bullet load.

I didn't see any leading, either at the range, or during cleaning.

At these ranges, the BC of the bullet probably doesn't matter, and it certainly couldn't be enough to change POI by five inches! Just trying to figure this out.

 

[kingmt]

The only thing that could cause recoil before the bullet leaves the barrel is the little bit of air in front of the bullet. I just have a hard time accepting that significant. I do believe the chocolate ice cream theory or a reverberating barrel.

http://optimalchargeweight.embarqspace.com/

By the way 13gr of Red Dot may have a wimpy recoil but that is a high pressure load that I would watch. My norm is a 8gr load which flattens primers & your close to doubling that.

 

[Gadzooks Mike]

The only thing that could cause recoil before the bullet leaves the barrel is the little bit of air in front of the bullet.

I'm pretty sure that recoil begins as soon as the bullet begins to move, not when the bullet leaves the barrel. "For every action, there is an equal and oposite reaction" doesn't have anything to do with the "location" of the objects. Once the bullet begins to move, so does the firearm.

 

[kingmt]

But the action & reaction is against the back of the bullet & the sides of the chamber. I'm not saying there is no recoil because I don't know for sure how much that little bit of air in front of the bullet can cause. I've heard people explain why there is. I have no way of testing the theory myself. Maybe one day I will get a camera that can check it. Maybe someone should pass it on to Mythbusters.

 

[Gadzooks Mike]

Poppycock. When the bullet starts forward, the gun starts backward. There is no special rule of force that says the gun doesn't start backwards until the bullet leaves the barrel.

 

[scythefwd]

gadzooks, how bout the friction on the bore pulling the rifle foreward?
http://www.youtube.com/watch?v=cVHMu7YyTGk
in this slow motion video, it appears that the round has exited before the recoil starts on a .50 bmg

 

[kingmt]

Thanks for adding that link scythefwd. I've looked before but never found one that you could tell much about. I'll be sure to bookmark it. As for the friction on the barrel the action & reaction could only be between the two until it left the barrel. That one is a little harder to explain though unless you think about jumping off the loaded hay wagon then doing it if a hard wind was pushing you back at the same time. I don't know if that helps or not.

As for the reaction in the chamber think of the chamber as a balloon that your blowing air into it can't blow away(recoil) until your finger is away from the end. One with a marble in it might have been a better way of explaining it.

 

[R.W.Dale]

Recoil and in barrel dwell time are the factors at work here. IMO this phenomena is most pronounced in handguns and long barreled rifles.

I had a devil of a time getting my swedes to not shoot high until I brought the velocity up with slightly over book loads.

A bullet has mass, that mass is being accelerated in one direction. Therefore THERE WILL BE an opposite force pushing the gun backwards. This is FUNDAMENTAL physics

A good example of this is a waterhose that's stretched out straight. With one person holding the end and and another turning on the flow. The guy at the end will notice the hose recoil back a few moments before it actually clears the end of the hose.


What you've learned is bullet drop tables are only a loose guide to calculate from a known zero with that load and that load only and are no replacement for sending bullets downrange.

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[R.W.Dale]

Oh and on "the load" for the love of all things ballistic this is the 21'st century. Use an appropriate gallery load powder that will give safe load density.

ALMOST WITHOUT EXCEPTION when someone blows a bolt action rifle to pieces "the load" or a variation thereof and an invisible double charge is to blame.


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[scythefwd]

rw - not disagreeing but i have yet to see a slow motion video of a rifle showing the effects of recoil until after the round has left the barrel. I agree that the recoil pulse starts at primer ignition... but I believe that the physical effects of the recoil doesn't come into play until after the round has left the barrel.

Now that said, there are oscillations in the barrel and this round could just be exiting at the wrong time. That wouldn't surprise me at all. +1 to the load and appropriate powder for the gun.

Now here is an old post from 1911Tuner
Here's an old fluroscope photo of a M1911 pistol caught about a half-inch before the bullet reaches the muzzle. Look closely at the position of the link, and at the relationship between the rear of the slide and frame. Here, the slide has moved approximately .075 inch or maybe a bit less.

http://i40.photobucket.com/albums/e243/1911Tuner/Gun20Fired.jpg

 

[R.W.Dale]

rw - not disagreeing but i have yet to see a slow motion video of a rifle showing the effects of recoil until after the round has left the barrel. I agree that the recoil pulse starts at primer ignition... but I believe that the physical effects of the recoil doesn't come into play until after the round has left the barrel.

Now that said, there are oscillations in the barrel and this round could just be exiting at the wrong time. That wouldn't surprise me at all. +1 to the load and appropriate powder for the gun.

Now here is an old post from 1911Tuner
Here's an old fluroscope photo of a M1911 pistol caught about a half-inch before the bullet reaches the muzzle. Look closely at the position of the link, and at the relationship between the rear of the slide and frame. Here, the slide has moved approximately .075 inch or maybe a bit less.

http://i40.photobucket.com/albums/e243/1911Tuner/Gun20Fired.jpg

Well the kicker would be to find a did that showed a long barreled rifle firing both STD velocity and very low vel loads to make a valid comparison.

MOST of what we perceive as recoil is the high pressure gas stream exiting the muzzle and pushing the gun into your shoulder like a rocket. However the bullets mass being accelerated does have an effect.


The tricky part about laying this at the feet of bbl harmonics is that there's no garentee that they're only acting in the vertical plane


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[scythefwd]

agreed - there are other factors to take into account.

Yes, for every action there is an equal and opposite reaction. But there is also and object at rest tends to stay at rest.

The bullet, being extremely light, has inertia. So does the gun. The bullet will start moving before the rifle due to this. There is force acting on both, but until the amount of force acting on the 2 objects (the bullet and the rifle) is high enough to overcome inertia, then movement doesn't happen. The recoil force does act on the bolt face the instant it starts acting on the bullet, but the bolt face doesn't start moving at the same time due to the much greater inertia that force has to overcome. That bullet weighs what... >1% of what that rifle weighs?

I'm still agreeing about it being barrel harmonics though.

 

[kingmt]

I had a devil of a time getting my swedes to not shoot high until I brought the velocity up with slightly over book loads.

Probably from flinching down to hold the recoil back.

Therefore THERE WILL BE an opposite force pushing the gun backwards. This is FUNDAMENTAL physics

A good example of this is a waterhose that's stretched out straight. With one person holding the end and and another turning on the flow. The guy at the end will notice the hose recoil back a few moments before it actually clears the end of the hose.

The part about the balloon wasn't understandable was it? The reaction is in the chamber. The water hose can't even come close to comparing because it isn't traveling in a straight line. The movement in the hose is it expanding. If you don't believe me put your sprayer(closed) on the end & see if you don't fell it even more.

I did want to add 2 more youtubes that were really good & they show both happening.

This one shows the recoil in a hand gun after the shot http://www.youtube.com/watch?v=sM_dDH9I1x8&NR=1

This one shows just a very small amount before the bullet leaves & also shows the air in front of the bullet that is causing the recoil.

http://www.youtube.com/watch?v=otpFNL3yem4&feature=related

 

[R.W.Dale]

Flinching huh!?

That's why I could hold a nice 3" group at 100yds centered nicely appx 9" above the bull. A problem that MAGICLLY disappeared when I added another grn of imr4320

I guess this is also why I had to install a Shorter front sight to keep my 357 mag rolling block from shooting the dirt below the target board when I swapped from 38spcl zero to a magnum zero @ the same bullet weight. Now it throws specials over the target.

It's obvious who has the most experience here shooting and reloading. Otherwise Kingmt you would be agreeing with me instead of linking to YouTube gems and making goofy ballon analogies.


But flinching? REALLY? Even if you throw a flinch in the mix it remains a constant across all loads meaning the low vel loads are still printing higher

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[kingmt]

Easy. I was trying to joke a little. I posted the youtube videos because they had great info showing what I was saying. Even if you believe the balloon thing is silly it is still the truth. If you watch the last video(assuming the camera doesn't move) It shows the air coming out ahead of the bullet causing it to recoil ever so slightly before the bullet left. The others show most of the recoil is after the bullet.

 

[R.W.Dale]

And what makes you assume the displaced air is causing the recoil and not the bullets mass being accelerated

The ballon theory is silly because it ONLY accounts for the recoil action of the high pressure gas stream and explains nothing about the bullets mass being accelerated.

Awhile back I had a thread where a low pressure 38 load was sticking bullets about 14" down the bbl of my 22" 357 rolling block. Both times while it was obvious the bullet had stuck there was a slight recoil impulse and in this case the bullets never left the gun.

Guns do recoil even before the bullet clears. How much depends on many variables and you can count on a 1000 FPS + mv disparity as being a pretty large one.

You cite YouTube vids as proof this is not the case but remember to cause a 6" POI shift at 100yds your effective muzzle movement needs only be the slightest fraction of an inch.


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[kingmt]

I don't know how adding more powder lowers POI. I'm not that good with a hand gun to start with so testing it would be pointless for me. Don't rule out you doing something subconsciously.

I by no means know it all but what I know we can build on.

I just wanted to pat myself on the back a little by saying I am pretty good with a rifle yet but was even better when my eyes were good. With the M16A2 I always qualified expert. I use a scope anymore tho.

 

[kingmt]

Both times while it was obvious the bullet had stuck there was a slight recoil impuls

What you probably felt is the hammer fall. I stick bullets all the time. I have never felt recoil. I use a bolt rifle & there is nothing. No sound no recoil nothing but a click.

Again tho I said I believe there is some recoil from the air in front of the bullet.