Small pistol Magnum Vs stand Chron results

[Draciron]

OK, finally got the chron back out there and in continuation of a thread I started a couple months back and had requests for the results.

The magnum primers seemed to increase FPS by about 20. At least with 125 gn JHPs.

125 gn Jhp using 17 grains Herco 2400 in a .357 mag
magnum primers rounded AVG 1462
Standard primers rounded AVG 1441

Same gun, seated same depth, same OAL fired from the bench.

One unanticipated side effect was that rounds I loaded with Magnum primers were considerably more accurate. I didn't shoot the bars off the chron or anything though I've done that before However I missed 5 out of 5 with standard primers using Speer UDHCP missing twice 158 gn UDHCP with Magnum primers (60+ shots with magnum primers and 1 miss, other than the UDHCPs that one an err reading. 30 shots with standard primers and 9 misses) . A miss being a shot too high to register or that I got an err reading from the chron.

My assumption is that the Magnum primers burned the powder more quickly which meant the bullet was out the barrel before I felt any recoil but with the standard primers the bullet wasn't out the barrel before I felt the recoil causing the barrel to jump. So the bullet was still on paper but too high to register with the Chron. Reasonable assumption or just really weird luck with the standard primers?

This is far from a scientific test and I'm going to explore it further and try it with different powders and bullets. Though once this box of UDHCPs is finished I'll never buy those critters again.

[rc]

Some people say standard primers are more accurate with flake powder so I guess is varies. The only realy need for magnum primers is with ball powder for more consistent light. Otherwise, standard primers work fine. rc

[SL1]

I don't think that your "lack of recoil before bullet leaves barrel" explanation for the accuracy improvement with magnum primers makes sense when the difference in the averge velocities is so small. Neither load gets out of the barrel before recoil affects gun alignment.

Variations around those averages is another story. What variations were you seeing in the velocities for individual shots with the same loads (same charge weights and primers)? Were the velocities more consistent with the magnum primers than the standard primers? If so, then the variation in the AMOUNT of recoil could be causing the difference in accuracy.

Usually, a higher point of impact is telling you that a handgun bullet had a lower muzzle velocity. But, a 21 fps velocity difference should not be enough to make you miss the paper target, or even the chronograph's sensitive area. So, I am guessing that you were getting substantial velocity variations around those averages.

One thought is that a weak grip on the gun can increase the amount of change in the point of impact due to velocity differences.

SL1

[Sport45]

One unanticipated side effect was that rounds I loaded with Magnum primers were considerably more accurate.

Was it a double-blind test? In other words, did you know when you were shooting if the gun was loaded with magnum or regular primers? If not you may have been unconsciously affecting the results.

[Unclenick]

Let us know what the other stats were in velocity? The extreme spread in particular?

The recent Shooting Times article on primers was revealing. A primer has both to provide the ignition spark and to provide initial pressurization of the case to a level high enough for smokeless powder to burn well. Standard primers can produce the lowest extreme spreads when a case is filled with powder and only a small amount of empty space has to be filled with gas to provide that initial starting pressure. But with cases that have empty space in them, there is a lot more volume to pressurize, and the magnum primers do a better job of that, resulting in more consistent burn initialization and more consistent MV.

The article also pointed out that when there was much empty space in the case, not only did magnum primers get better consistency, but the author said that with too little primer for the case volume, he would often experience ignition delays up to 20 milliseconds or so while the powder built enough pressure on top of the inadequate primer pressure to really get burning. That lower initial pressure can start the bullet early and retard total burn speed, resulting in a longer barrel time. That leaves more opportunity for recoil to elevate the muzzle and for disturbance due to hammer fall to occur.

Normally, bullets don't start moving until pressure is well underway toward building up, but if you have a delay like that, it is enough time for dynamic pressure conditions to equilibrate toward steady state conditions, and like firing a round with no powder, the bullet can then start to unseat ahead of schedule, increasing the volume behind it prematurely and compounding the slow start and MV variance and increasing barrel time.

[zxcvbob]

What about using magnum primers with very *light* loads to get more efficient powder burn? (because the initial pressure is higher) I'll be loading some very low pressure rounds soon for some old guns and gonna try using SR primers instead of SP to see if it helps get the most out of the tiny charges of medium burn-rate powder.

BTW, the first message almost looks like you were using 17 grains of Herco I had to read it a couple of times to figure out it was Hercules brand 2400.

[Unclenick]

Let us know how that goes? SP Magnum primers should help with target charge consistency. It does with 231, anyway. I'm not sure I saw a difference in Bullseye that I can recall? The SR's have harder cups than SP, since rifles normally have more firing pin energy, so the potential for ignition issues in a handgun is there. Also, occasionally someone reports too strong a primer unseating the bullet before the powder has a chance to get going (.22 Hornet is known for this), and that drops the pressure and burn rate and messes the consistency and accuracy up. The only way to know if that'll be an issue in your gun is to try it?

[CraigC]

I find it very interesting that your accuracy assessment is based not on groups on paper, from a bench at a standardized range (25yds for pistols) but how they flew over the chronograph??? You'll have to explain that one.

Standard practice and conventional wisdom has held that standard primers are best with 2400. More consistency and lower SD's, extreme spreads. That pressure is often inconsistent with magnum primers. If it's good enough for Elmer Keith, John Taffin and Brian Pearce, it's good enough for me.

[SL1]

Sport45,

I tried a "double-blind" test once, but it was a disaster - - I couldn't hit the target at all with BOTH eyes closed.

Seriously, doing a double-blind test and keeping track of what the loads are doing is a bit tricky without an assistant handing you the ammo and keeping the records for you. SO, it is typically not done by handloaders, and the accuracy results that you see in articles usually aren't attacked on that basis.

I am a little confused about how the OP is judging accuracy, though. If he is using ONLY the number of times his chronograph failed to properly produce a velocity reading, then there are several potential problems that can cause one set of loads to have more errors than another. The first that comes to mind is that the lighting conditions could have changed between the standard and magnum primer strings if he fired them grouped by primer type. And, there are several other possibilities. Even putting 6 rounds in a cylinder with 3 standard and 3 magnums, or even alternating s-m-s-m-s-m could produce systematic errors due to differences in the individual chambers of the cylinder.

When I need to do some careful comparisons between two loads in a revolver, I single-load one round at a time, always using the same chamber, and alternate shoots between the two loads. If I an not using a chronograph, I use two different targets. But, two targets doesn't work well when chronogaphing, because (1) I would be shooting through different areas of the chronograph's sensing area, so results might not be comparable, and (2) it increases the probability of hitting the chronograph if I try to squeeze two shot paths through the sensing area. So, I COULD do a lot of walking to mark shots on the same target, which means that I couldn't do it when others are also using the range. But, ususally, I need to do velocities and accuracy separately, or shoot like loads in their own strings.

SL1

[Sport45]

Seriously, doing a double-blind test and keeping track of what the loads are doing is a bit tricky without an assistant handing you the ammo and keeping the records for you. SO, it is typically not done by handloaders, and the accuracy results that you see in articles usually aren't attacked on that basis.

My apologies to Draciron if he thought I was attacking his methods or results.

Double blind isn't hard at all when testing for accuracy. I used to always find the most accurate during load development was the max load. I'd then be disappointed later on with the accuracy of my rifle. Now, I'll work up to max and then load about a dozen rounds at max, a dozen at min, and a dozen at each of two or three steps in between. I put these in zip lock bags with the load information on a card inside and give them to my wife. She will then take the card out of each bag and write a random number on the back and place a card in the bag with the matching number. That way I don't find out which load shot the best until I get home and she gives me back the original load cards. I suppose this method would be more difficult if you don't live with someone willing to help out.

The dozen round each was for an AR, for bolt guns five would probably do fine. The method works for checking powder charge variance. Of course different bullets and seating depths can be more obvious to the shooter.

[SL1]

Sport45,

What you describe would work fine as a blind test, UNLESS you were chronographing those loads. With a chronograph, I think you would soon figure-out which load was which. The OP was asking about chronographing loads.

SL1

[Sport45]

Yeah, but I was referencing his "considerably more accurate" comment. That's why I quoted it.