groups dropping advice

[tunered]

I wouldnt keep cranking on the scope every time. You will allways chase it. Leave it where you last shot and see if it repeats with a cold barrel. Im thinking scope not gun.

 

[LitLBoy]

Make sure your barrel is tight in the action, just had this same problem, loose barrel by about 2%.
LitLBoy

 

[rockwind1]

hi, thanks turnered.

i am not sure what kyou mean by "keep crankin on the scope" it's on a good rail that seems tight, in a spuhr mount torqued to specs, and once i set the zero, i don't even touch the turrets.

 

[smoooth]

What did you discover today? Any changes or did it still drop groups off incrementally?

 

[ronemus]

Increasing the powder charge can make the groups drop - I have seen it occasionally with my rifles. As you change the charge, the bullet exits the muzzle at a different point in its vibration(s). Try shooting the groups in reverse order; I predict they will rise 1" for each. Especially with the can on the muzzle of a long barrel, the barrel vibrations will be lower frequency so it may take a while to see the usual sinusoid; it seems that you're shooting small increments in charge weight which helps obscure the cycle.

A friends rifle would put some groups to either side of the nominal zero, depending on the load. He kept trying to make it go away, but it is what it is. As long as the result is reproducible, you can choose a specific load as your zero; change anything and you can no longer expect it to print a group in the same spot.​

 

[gambleone]

sent you a pm.

 

[tunered]

hi, thanks turnered.

i am not sure what kyou mean by "keep crankin on the scope" it's on a good rail that seems tight, in a spuhr mount torqued to specs, and once i set the zero, i don't even touch the turrets.

I thought you were rezeroing the scope. Sorry.

 

[rockwind1]

Well, i was sort of rezeroing, i mean, usually i go out, i generally check my zero with a shot or two, for some reason every know and then i have to change it. when i say i don't touch the turrets, it is because i am shooting the load developlemnt at the same yardage the whole time so don't need to change the dope.

but thanks though! everyone here is very helpful, ironically, i was helping a new guy out at the gun range the other day, and i don't know nothing.

but i think i have figured this problem out and this gun/load developement is on the back burner while i move onto my 6.5 saum, which is acting like a real gun should!

 

[smoooth]

Enquiring minds want to know!

What did you figure out?

 

[rockwind1]

hi, apologies to all, i didn't figure this was a bit of a cliffhanger. readers digest version. i started reloading for my 6.5 saum hunting rifle but i decided to practice on my 308 first. so as i learned to prep, weigh, and assemble the ammo, i learned a lot and enough to start on my 6.5 with out making any stupid mistakes ( WRONG!!!! i did) I figure why spin my wheels when the gun is not cooperating but i am having much better success on my 6.5 saum so i kind of put the 308 on the back burner and long story short, i haven't figured out what is making the groups drop down in a perfect verticle line for 6" at 200 yds! but,,,, i think it is heat related as i was probably shooting too fast and i think it is either the base is loose and changing with the heat(per gunsmith aquaintence), or the action/barrel are up against something in the stock and as they heat up, it torques something. but that is obviously not scientifically proven yet so,,,i promise the second i can i will post results and I definitely appreciate all the advice.

my stupid mistakes you ask? well, here are my tips for anyone starting to reload.

1. make sure if you have a carbon ring in your barrel, get it out. wow. h1000 is dirty and the 6.5's are famous for a carbon ring apparently unbeknownst to me. thanks to a genius named logan in tennessee who diagnosed my problem over the phone from 2000 miles away in about 30 seconds! this guy is the 6.5 saum guru!

2. keep your cases upside down until you put the primer in because for some weird reason the primer helps keep the powder in.

 

[rockwind1]

WELL, it sure wasn't the base nor the floated part of the barrel, that just leaves scope (nightforce atacr i've used before) or action. weird

 

[josh shrum]

If you were shooting free recoil then your situation would make some sense. In general, when shooting free recoil, I notice that as I increase powder charge my poi will shift down.

As MV increases the bullet is exiting the barrel "sooner" than previous slower loads. As such, the rifle has not moved as far under recoil and as such the angle of the buttstock has not changed the angle of the barrel in regards to the target as much as a slower load where the rifle has moved further back.

You said you are loading the bipod forward, so I don't know if this pertains to you, though instinct makes me think this is indeed the case.

Would be easy to check though, just shoot your test loads in reverse, from highest to lowest charge weights. If the groups rise instead of dropping then you will know it is not heat at the very least.

 

[rammac]

As MV increases the bullet is exiting the barrel "sooner" than previous slower loads. As such, the rifle has not moved as far under recoil and as such the angle of the buttstock has not changed the angle of the barrel in regards to the target as much as a slower load where the rifle has moved further back.

First, when the bullet moves faster then there is greater recoil energy and rifle recoil velocity increases which would cause the barrel to move at your hypothetical angle faster. In other words, the ratio of barrel angle to bullet velocity would stay pretty much the same but it would simply happen faster. This means that the effect on the point of impact wouldn't change with changes in powder charge weights.

Second, if this theory were true then accuracy shooting would be impossible because we'd have to know the exact muzzle velocity before we shot in order to know how to adjust our sights in order to impact the same spot all the time.

Finally, no firearm recoils to any substantial amount until the bullet leaves the muzzle so any firearm movement isn't caused by the bullet until the bullet exits the bore. Most rifle bullets leave the muzzle somewhere around 1 ms after the powder charge ignites and studies show that recoil movement doesn't usually happen until around 10 ms which means that the rifle starts to move when the bullet is about 2.8 feet beyond the muzzle (assuming a muzzle velocity of 2,800 fps).

 

[Dusty Stevens]

Finally, no firearm recoils to any substantial amount until the bullet leaves the muzzle so any firearm movement isn't caused by the bullet until the bullet exits the bore. Most rifle bullets leave the muzzle somewhere around 1 ms after the powder charge ignites and studies show that recoil movement doesn't usually happen until around 10 ms which means that the rifle starts to move when the bullet is about 2.8 feet beyond the muzzle (assuming a muzzle velocity of 2,800 fps).

If that were true a lead sled would produce the same groups as a $2000 mechanical rest and nobody would be able to see the difference in even the sand in the bags when in fact we can see that. Maybe this is another case of math muddying the waters. Dont get me wrong im actually an engineer by trade but instead of believing a theory on paper its easy enough to check it in real life.

 

[josh shrum]

First, when the bullet moves faster then there is greater recoil energy and rifle recoil velocity increases which would cause the barrel to move at your hypothetical angle faster. In other words, the ratio of barrel angle to bullet velocity would stay pretty much the same but it would simply happen faster. This means that the effect on the point of impact wouldn't change with changes in powder charge weights.

Second, if this theory were true then accuracy shooting would be impossible because we'd have to know the exact muzzle velocity before we shot in order to know how to adjust our sights in order to impact the same spot all the time.

Finally, no firearm recoils to any substantial amount until the bullet leaves the muzzle so any firearm movement isn't caused by the bullet until the bullet exits the bore. Most rifle bullets leave the muzzle somewhere around 1 ms after the powder charge ignites and studies show that recoil movement doesn't usually happen until around 10 ms which means that the rifle starts to move when the bullet is about 2.8 feet beyond the muzzle (assuming a muzzle velocity of 2,800 fps).

It is indeed a theory based upon my own experience and the experience of other short range benchrest shooters whom I compete with.

I think that the OP could try my suggested test to see if he can isolate/eliminate heat as a culprit. Likely, if the reversed test produces the results that I indicated it would likely rule out scope issues as well.

 

[rockwind1]

so, per ronemus, josh and someone else on here, who are apparently s super smart guys, i did some experimenting
i changed the experiment a little bit as i didn't want to load up a bunch of ammo if it didn't pan out so i shot my old lake city m118lr that i had been shooting for a while and i shot like 8 groups of 3 and i shot them even faster than the load developement rounds and they stayed pretty much straight. my barrel got pretty hot WTF!!!!!

so apparently, and i still don't understand it, but as i increase my imr 4064 in .3 grain increments, my groups actually drop about 3/4" at 225 yds for every RELATIVE increase in velocity.

FYI i did check some stuff out on my rifle, ran a dollar bill under barrel, checked action screws, checked base screws, checked spuhr mount screws,

THAT IS CRAZY!!!!!!!

i am even going to start a new thread

 

[Webster]

as i have been testing out some loads, once again today, 6 loads, 6 different targets at 225 yds. as i went left to right with the different loads, my groups kept dropping about an 1" for each new group of 5. by the time i did the 6th load, the group was 6" low.

i have a suppressor on the end of my remington pss 308 24" stock barrel. it it a pretty thick barrel, the only thing i can think is the barrel is drooping as the it gets hotter. the groups were pretty good and the barrel did not get super hot. i think it took me about 45 minutes to an hour to shoot the 30 rounds (5 per load) plus about 5 for some warm up zero shots.

i just find it hard to believe that after 30 shots, my barrel will shoot 6 inches low at 225 yds. does that seem normal?

in case i didn't describe it properly, imagine shooting groups but for each group you adjust your scope down 1/2 moa, only i am not adjusting anything.

Is the barrel free floating? No contact with the stock?

 

[BoydAllen]

[QUOTE="Finally, no firearm recoils to any substantial amount until the bullet leaves the muzzle so any firearm movement isn't caused by the bullet until the bullet exits the bore. Most rifle bullets leave the muzzle somewhere around 1 ms after the powder charge ignites and studies show that recoil movement doesn't usually happen until around 10 ms which means that the rifle starts to move when the bullet is about 2.8 feet beyond the muzzle (assuming a muzzle velocity of 2,800 fps).[/QUOTE]
If this was true then bag slickness would have no effect on accuracy. It would not matter that a rifle stuck a bit and then slid, and it does. Also, stock angles would not matter and they do. For example, taking this out of benchrest a bit, a friend has a custom Martini Cadet that has a 3" wide forend and has been converted to .22ppc. The toe angle of the stock is extreme by target rifle standards and he was having some consistent vertical issues. I noticed that he was not shouldering the rifle and advised him that because of the toe angle and probably inconsistencies in how the rifle recoiled from shot to shot that he probably would get better results if he held and shouldered the rifle. It worked. I learned this from a friend who shoots a schutzen rifle with a similar toe angle. Shooters who shoot free recoil tend to pay a lot of attention to things that affect how a rifle slides on the bags. If the rifle didn't move until the bullet was clear of the muzzle, then that should not matter. When shooters are not constrained by the rules they generally choose to have a flat butt angle for rifles that will be shot free recoil. I think that this is based on experience. In my experience, studies may or may not be conducted in a manner that yields results that are consistent with real world data. When there is a conflict, I do not automatically assume that the study is right and experience is incorrect.

 

[Bart B.]

Finally, no firearm recoils to any substantial amount until the bullet leaves the muzzle so any firearm movement isn't caused by the bullet until the bullet exits the bore.

Then please explain why:

* tuning weights moving back and forth on barrels change the frequency muzzle axes vibrate vertically to compensate for bullet drop changes at target range caused by muzzle velocity spread.

* double rifles bore axis cross 10 to 30 yards down range.

* several people shooting the same rifle and ammo have different zeros on the sights for a given range.

* when rounds fire and bullet starts out of the case, bore axis is not aligned to a place on target above point of aim equal to bullet drop plus sight height. It is when the bullet finally exits the barrel.

A dollar bill thickness clearance from barrel to fore end is not enough. Measure how much the fore end bends across different ways the rifle is held, rested and external forces applied.

http://www.varmintal.com/aeste.htm

 

[Bart B.]

studies show that recoil movement doesn't usually happen until around 10 ms which means that the rifle starts to move when the bullet is about 2.8 feet beyond the muzzle (assuming a muzzle velocity of 2,800 fps).

Show me the studies. Even though I'm not from Missouri.

10 ms after a bullet leaves at 2800 fps, it's 28 feet beyond the muzzle. 2800 fps x .010 second.