I think I know the answer to this question already but I figure it cant hurt to ask. If you load several 3 shot groups so that the bullet travels the identical velosity, seat the bullet at the same depth and use the same gun, but use differant powders will the groups be the same? This question stems from an earlier questiom I had asked. Im contemplating buying a chronograph and I am wondering is this tool used to figure out trajectory or to load more consistantly.

strangely enough uniform velocities should yield accuracy.....but they do not necessarily do that at all. Many excellent groups are fired by loads that generate differing velocities and by a surprising variance.

All serious reloaders need a chronograph to tell them if they are getting the velocities they think they are. It's also a very excellent indicator of pressure and us reloaders can't get too much information on that subject.

I strongly recommend a chronograph for reloaders.....they aren't expensive at all.

A chrony is one of the most helpful tools you can get once you progress beyond the basics level of reloading.
I had a 22-250 that I used for Pdog shooting and factory matches. Each spring, I would adjust my bullet jump to cover the throat erosion from the previous year's shooting and then I would use my chrony to adjust my powder charge up to the original velocity.
Additionally, you can use your chrony when you are working upward toward your rifles max. Often your velocity gains will flatten out before you get any sort of pressure signs. This tells you that you're merely burning more powder without any gain and it time to call it quits with that load.

I disagree that bullet speed is an indicator of pressure, a rapid burning powder can give very high pressure with very little speed. It depends on how fast the pressure spike forms. As an example I would think that a healthy load of bullseye could blow up a gun without the bullet ever leaving the barrel.

I think what was said, if you use a crony and your load manual, you can compare what what crony says and what the manual says and arrive at what kind of pressures you are creating.

quote:

Originally posted by b beyer:
I disagree that bullet speed is an indicator of pressure,

b meyer.....suppose you just chronographed your 180 grain bullet from your 30-06 at 3,000'/sec.....do you think this don't suggest that your pressure might be suspect?

You point is correct as you posted. I agree..... low velocity don't necessarily mean low pressure, but to say that velocity is not an indicator of pressure is misleading. It certainly is not linear and certainly is not a pressure gauge but it definitely is an indicator that your pressure is suspect.

1in10 ----- I use a chronograph extensively. This past weekend I shot many groups and chronographed them. One example to illustrate a point, I shot two consecutive shots that were 75 fps difference in speed, yet were touching holes, forming a figure 8. The next time I shot that load two of the shots were in one hole as evidenced by a slightly enlarged single hole. These are sometimes hard to see from the front, but when you turn the target over and look at the back, it is easier to see. When using a chronograph you will find that seldom are two shots or loads the same speed. To get the speed of the load you average the speeds of the shots. The better chronographs do this for you and will print out the results. You also need to average several groups to get a better idea of the speed of that load. Some of my hunting loads I have charted have 100 plus groups that I averaged to ascertain the speed of that load. ----- That group you determine will print slightly different POI some days, most of that comes from the shooter, but some from the rifle and conditions. On a hot day the heat waves affect the shooter aiming the rifle, the crosshairs seem to dance, as compared to a cloudy day. ----- Many things affect where that bullet is going to to, we as shooters simply have to minimize the conditioning factors as much as possible. I hope that is a little clearer than mud. Good shooting.

quote:

Originally posted by Bill Mc:
I think what was said, if you use a crony and your load manual, you can compare what what crony says and what the manual says and arrive at what kind of pressures you are creating.

Hey 1in10, I really dislike picking-on Bill Mc's comment, because he is one of the best guys on the board. And I will agree that most folks who have a chronograph believe what Bill Mc posted.

Only problem is that "logic" can be misleading due to variances in both the actual firearm and the specific Lots of components used to build a cartridge - from what was used to develop the Manuals. Your results might be lower, dead-on, or higher than what the Manual lists.

I'm not condeming chronographs, just letting you know they are not God's Gift to Reloaders.

If you have not read Chronographs and Pressure, I can recommend it highly. It was written by a fellow who frequents this Board and explains how a Chronograph has the potential to be mis-leading.

Best of luck to you.

I think I'm confused. If B Meyer is saying that if you're using one type of powder and getting xxx velocity and then you switch to another powder, when you are getting xxx velocity that the pressure is the same for both loads, I don't think anyone believes that.
But I do believe that if your load book sez that xxx amount of 4350 behind a 165 hornady bullet (with a Rem case ) gives you 2800 fps at 47,000# pressure, when your velocity approximates 2800fps, you're getting close to 47,000# of pressure. Regardless if you haven't yet reached the book max.
A chrony is just like the load books themselves. A tool, a guide, not an absolute.

When building ammo, the win/rem/fed folks load to pressure, not weight, not velocity. When they buy a couple of tons of powder, their lab folks work up the amount that is needed to reach a certain pressure and that's what they load until its gone. And they quote velocity values from that pressure.

As I see this question, the answer is that only one powder will consistantly give the best accuracy at aspecific velocity. It may not be the best powder for that cartridge/bullet combination, but it is at that velocity. Change the velocity and one of the other powders could easily switch places as #1. However, would we all agree that in a single barrel that one powder would rein supreme for a single bullet cartridge combination?

1in10, in a word, no. It could be possible to load a fast, medium & slow powder to the same vel. for a given bullet wt. but pressures will be diff. & that seems to affect bbl. vibrations more. There is a good chance that all of those same vel. loads would not hit the same POA.
I have been using a chrono since they were using paper screens & it has always been helpful & an eye opener as well.

I did not say that equal velocity equals equal pressure. What I did say was that speed is not necessarly a good indicator of pressure. I agree with what Bill and Vapo say in the context that it is in, but to try and determine pressure of an unknown load by its speed is impossible. Sorry for the misunderstanding.

quote:

Originally posted by phurley5:
1in10 ----- I use a chronograph extensively. .

Gidday Phurley5,

I just bought an F1 Chrony but haven'y had the opportunity to use it yet. Is there an easy or best way to set up a chrony? I'm in mortal fear of putting the first shot straight into the chrony.

Thanks,

If you are setting up your Chrony and want to chrony a rifle with a high x scope so that you can't focus the screens, use a rifle with a similar contour and a lower powered scope to make your set-up and then switch rifles.

quote:

I just bought an F1 Chrony but haven'y had the opportunity to use it yet. Is there an easy or best way to set up a chrony? I'm in mortal fear of putting the first shot straight into the chrony.

I set the box up on a tripod about ten feet ahead of the muzzle and the rifle firmly sitting on sandbags on a solid bench and the rifle scope on the target.....with the bolt removed from the rifle.

I walk in front of the muzzle and look over the Chrony into the bore of the rifle and from there I can easily see if the Chrony is about 6" under the path of the bullet.

1in10,

The answer to your question is no for most rifles however, you may find a rifle that will shoot the same or similar groups at the same speeds. A very good quality tube will sometimes net those results.

IMO the reason the answer is no is because of Barrel Harmonics. If you achieve 3000 fps w/ 3 powders but, one is fast, one is medium rate, and one is slow, you will have different harmonic vibrations for each load due to their burning characteristics. The key to an accurate load is finding the best barrel harmonics for the given components.

Browning has alleviated this problem to an extent w/ their BOSS system which allows you to adjust the Harmonics to a certain load for optimum accuracy.

Hope that helped and don't think it was a stupid question, heard the saying "A stupid question is the one not asked."

Good Luck

Reloader

steyrl ----- You will be safe in the set up if you always take out the bolt and bore sight through the barrel to make sure you clear the chrony when firing. Set up the chrony using the scope on low power and aligning directly over the eyes, then with plenty of clearance given to miss the chrony, do the bore sighting as above as a second precaution. If you have an automatic or pump or bolt action that bore sighting is impossible. You can still set up to be firing just under the plastic diffusers at the top. The only problem with the F-1 Chrony is that sometimes you cannot keep the shots over the eyes shot after shot. I used a Beta and Gamma model Chrony for years before going to the Oehler 35-P. ----- Your sand bag or whatever you use for a rest absolutely must be consistent with each shot or you will stand a chance of hitting the diffusers or Chrony itself, check the alignment often to make sure it is safe. Sometimes with testing several loads or more than one shooter using the setup the sand bags or rest will change, if you let that happen you stand the chance of hitting something. Check regularly as in after group. Good shooting.

Thanks phurley5, I do appreciate the reply.

Best Regards,

quote:

Originally posted by phurley5:
steyrl ----- You will be safe in the set up if you always take out the bolt and bore sight through the barrel to make sure you clear the chrony when firing. Set up the chrony using the scope on low power and aligning directly over the eyes, then with plenty of clearance given to miss the chrony, do the bore sighting as above as a second precaution. If you have an automatic or pump or bolt action that bore sighting is impossible. You can still set up to be firing just under the plastic diffusers at the top. The only problem with the F-1 Chrony is that sometimes you cannot keep the shots over the eyes shot after shot. I used a Beta and Gamma model Chrony for years before going to the Oehler 35-P. ----- Your sand bag or whatever you use for a rest absolutely must be consistent with each shot or you will stand a chance of hitting the diffusers or Chrony itself, check the alignment often to make sure it is safe. Sometimes with testing several loads or more than one shooter using the setup the sand bags or rest will change, if you let that happen you stand the chance of hitting something. Check regularly as in after group. Good shooting.

quote:

Originally posted by vapodog:

quote:

I just bought an F1 Chrony but haven'y had the opportunity to use it yet. Is there an easy or best way to set up a chrony? I'm in mortal fear of putting the first shot straight into the chrony.

I set the box up on a tripod about ten feet ahead of the muzzle and the rifle firmly sitting on sandbags on a solid bench and the rifle scope on the target.....with the bolt removed from the rifle.

I walk in front of the muzzle and look over the Chrony into the bore of the rifle and from there I can easily see if the Chrony is about 6" under the path of the bullet.

Thanks for the reply, vapodog.

Best regards,