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A couple questions about accuracy
bassassassin007
Member Posts: 87 ✭✭
Hello all
I have been handloading for two rifles for about a year. Both are Rem 700s (a VLS in .308 and PSS in 7mm Rem.Mag) and have heavy barrels. My first question is what is reasonable accuracy for theses rifles at 100 yards. (Please do not respond and tell me how great your specific load works in your gun as what you shoot may be better that reasonable.)
My second question revolves around isolating some of the variables to determine accuracy. What methods do you use when trying to determine if a particular rifle shoots better cold, warm or hot, in conjunction with barrel cleanliness?
Thanks, Dave
I have been handloading for two rifles for about a year. Both are Rem 700s (a VLS in .308 and PSS in 7mm Rem.Mag) and have heavy barrels. My first question is what is reasonable accuracy for theses rifles at 100 yards. (Please do not respond and tell me how great your specific load works in your gun as what you shoot may be better that reasonable.)
My second question revolves around isolating some of the variables to determine accuracy. What methods do you use when trying to determine if a particular rifle shoots better cold, warm or hot, in conjunction with barrel cleanliness?
Thanks, Dave
Comments
You are on the right track with "isolating variables" to promote accuracy.
Case length ultimately affects case volume. The same powder charge igniting in a slightly larger or smaller case volume will affect the ammount of pressure generated and therefore velocity and trajectory and therefore accuracy. Trim your cases to uniform length.
Seating depth must be consistent since a slight variable will affect case volume so watch your OAL.
Weigh your charges. Even the very best volumetric measurements will vary from one round to the next.
Use the same primers.
Uniform primer pockets and flash holes. This promotes consistent ignition.
Weigh your bullets and sort them. Even high quality commercial swaged bullets will vary slightly. Slight changes in bullet weight will affect pressure/velocity/trajectory (Accuracy.)
Chronograph each load and watch the spread closely. For some unknown reason, slightly different charge weights will produce more consistent velocities. Lets say a 37 grain charge gives you a 2500 fps velocity but has an 80fps spread and a 36 grain charge only averages 2450 but has a variance of only 10fps. You are better off with the slightly slower but more consistent velocity.
As for your gun being cold or hot--in my book the only shots that will count are the first one or two out of a cold barrel--presumably you will "Use" your gun cold and a hot barrel is pretty much what you shoot at the range. Otherwise, You can "tweek" your loads to suit a hot gun if you are competing in 10+ round situations.
Just my .02[:D]
Hot doesn't count, so don't fool with it. A cold bore will be your testing platform. Run 1 string and set the rifle down to cool before the next string.
length of case won't affect pressures, but inconsistent external dimensions will (ie FL sizing one and NK sizing the other). This is rare but can happen if you aren't paying attention or switch dies in the middle.
seating depth if varied by only .010" or so won't make an appreciable pressure difference, but if you are seating the pills in close proximity to the lands, then the seating depth variances will show up as a degredation in accuracy as one will contact the lands sooner on the pressure curve and one will contact later on the curve causing a change in the burn time and bullet travel time in the bore.
it's simple,..load good quality ammo with quality components, keep everything uniform, and run a load ladder with your choice of powder and bullet. Those 2 rifles are capable of superb accuracy for factory rigs.
Come to think of it, case trimming should not have an appreciable affect on case volume and ultimately pressure. I agree that variances in seating depth would more importantly change the pressure curve phase during lands engagement rather than the ammount of pressure generated. You stated that in a way that makes more sense to me.
Do you agree that there is a "sweet spot" within the acceptable load range that produces more consistent velocities and if so, Why is this so? I believe this to be true in practice yet I have never found any lit explaining it. Thanks
Both your rifles can shoot sub .5 MOA With quality glass on top. With the right combination they can shoot same hole. But like you said it will take isolating the variable that needs to be tweaked to get you there. There are a lot of variables to isolate though.
Just some things to consider;
What are the twists of the barrels. What is the optimum bullets for those twists. Would a slightly different bullet work better at slower or faster speeds? Powder type and charge may be changed with each until you discover just how close you can get barrel harmonics to work with each.
Have you checked the concentricity of your bullets as you load them? Seating depths that work best with each rifle need to be worked out.
I'm assuming your bore cleaning program included breaking in(polishing) the barrels and proper cleaning technique so as not to ding the rifling at the crown. Using a bore guide? You should if you dont. It will save the rifling at the throat.
Like JustC said only cold counts. Although a heavy barrel is supposed to absorb more heat enough to keep it that way through a string. A freshly fouled bore is crucial I think to determining your accuracy. Clean the bores completely. Take one or two fouler shots then shoot a string. Then set it down and repeat when barrel has cooled a bit. You might just run a dry patch down the bore to remove carbon between strings.
I know that is kind of scattered but those are some places to start.
-good luck
I do know that the accuracy is a function of harmonic nodes produced during ignition and bullet travel. The muzzle rotates in the shape of the infinity symbol (sideways figure 8). The point at which your pressures and bullet travle time are all very consistent, is when the bullet will leave the muzzle as it is at the intersection of the two "loops". If you picture the sideways "8",..you can now imagine that during this fracion of a second,..your muzzle is actually moving around in this motion. Now,..the larger groups occur from loads that are inconsistent, and therefore the bullets exit the muzzle at any given point along the vibrational path of the infinity symbol. That will VISUALLY explain the reason for some flyers and poor groups. The best groups will come from the load that allows the bullet to exit at that intersection, every time. This is where the pressure curve creates a certain "travel time" where the bullet reaches the muzzle and exits right at that intersection point during the node.
low ES and SD numbers usually mean you have a load that is coming into just the right density to be very consistent,.and very often will produce the best groups,..but sometimes not. HTH
Weigh the cases to get uniform brass. If you eliminate variables like primers of the same box, bullet weights split into 1/10 grain. Cases weighed to keep them all the same. Even neck annealing, clean uniform primer pockets and turned (trued) case necks all add up to smaller groups.
You fine rifles should able to group about half inch but you are going to have to work for it.
Clean cool barrels are the way to go. Monitor the chronograph ES and SD to see if you are getting peak performance from your hand loads. A super clean barrel down to bare metal is the place to start. It may not shoot the best there but it is a variable to be eliminated. Butches Bore Shine and JB bore paste is the way to go IMO. If you go to benchrest.com there are some great archived articles on the .308 that may help you in load development.
Good luck.
Please do not take the following as bragging.
I already have worked up some loads in both rifles that consistently group in the .2 to .3 range (though sometimes better and sometimes worse). My brass is the same length within a few thousanths, my powder charges are done by hand to the same amount, and my over-all-lengths are the same within a few thousanths. All my primers are federal match. I don't weigh the brass or bullets and separate them, and I have so much new brass that everything I am shooting is still full sized.
The problem is that the groups I am getting are when the barrel is warm or hot, almost never cold. I was under the impression that a hot barrel made the groups worse not better, but I am finding the opposite to be true.
So should I now focus on a recipe that I will use when the gun is cold and then switch to the other recipe when it is hot?
Can I reasonably expect my groups to get better if I pay attention to the brass and bullet weights and start neck sizing?
Thanks, Dave
BUT,..if you are hunting with this rig, as well as some informal target work,.you are far better off finding a good cool barrel load with proper fouling of course.
Thanks to all that have responded thusfar.
....The problem is that the groups I am getting are when the barrel is warm or hot, almost never cold. I was under the impression that a hot barrel made the groups worse not better, but I am finding the opposite to be true....
As the Barrel heats up it expands at a constant rate, per degree per inch. Since the Barrel is longer than it is thicker, the expansion is most notable in its length. The Barrel gets longer as it gets hotter.
Now look at the Barrel Vibration over time as a sine wave. As the barrel warms up, it gets longer, and the barrel muzzle is in fact moving further down the sine wave. In effect pointing in a different direction, however minute. This is the reason Point of impact changes as the barrel heats up. Heavy Barrels heat up slower, so this effect takes longer to be noticeable. The fact that your rifle shoots better warmer can mean a number of things. First many people take a fouling shot or two, to remove excess lubricant out of the barrel. This may be the cause some of your results. Also, since your barrel is expanding as it is heating up. Its dimensions are changing in relation to the cartridge (and to its Bedding). So taking this in mind, it should be possible to adjust your reloading to increase the accuracy of the rifle when it is cool. In most cases, the shots you will take are from a cold gun, so I would make adjustments to my reloads so that these were the most accurate.