Chrono early and chrono often

[morcey2]

So I worked up a nice accurate load for my AR (Stag lower, RRA NM varmint trigger, RRA Predator Pursuit 20" upper). Using Hornady 60 gr v-max and sp bullets, 26.5 gr Varget, CCI #41 primers, and LC cases. I'm getting consistent 3/4" 5-shot groups @ 100 yards with the v-max and slightly larger with the SP. So I've got a great shooting load and I load up about 150 of them, 100 Vmax and 50 SP. I plan on taking them out for coyotes and/or jackrabbits in a couple of weeks. (loads were shot off a folding plastic table bench with a couple of home-made sand bags and a rear bag consisting of a rolled-up coat that actually works quite well.)

Mind you, I hadn't chrono'd the loads. I usually do, but I couldn't find my chronograph in the after rearranging my reloading/gun room. I found it last week so I decided to shoot these over the chrono on the range trip last Saturday. The results were surprising to say the least. It's just a bottom-of-the-line Shooting Chrony. Usually I do all load development w/ a chronograph since velocity is a pretty good indicator of pressure and can keep bad things from happening.

I shot 10 shots each of the Vmax and SP. The Vmax had an average velocity of 3144 fps, ES of 54, and SD of 16.4. SP was 3124 FPS, ES of 63, and SD of 21(I think, paper is downstairs and I'm to tired to go get it at the moment.) According to the Hodgdon data, with a 24" barrel, Winchester case, and WSR primer, the max load of 27 gr has a velocity of 3159 fps. Now, I have 20 winchester 223 cases and they have a (very slightly) smaller case capacity than the LC cases that I have. I don't remember the exact numbers off the top of my head, but the LC cases had something like a half-grain more H2O capacity than the LC-14 cases that I was using. Loads weren't crimped.

I was expecting something in the 3000 fps range, about 125 fps slower than I'm seeing. The chamber is a Wylde 223 chamber if anyone wants to know. I know that the #41 primers are effectively magnum primers, but in my larger cases, switching from CCI-200 to #34 primers necessitated only about a quarter-grain of powder load reduction to keep the velocity the same. (30-06 loads w/ H4895 and 150 gr SP bullets from a 1903.)

So, I've got 130 rounds of slightly hot loads that I'm trying to decide if I should pull them down and reload, or just shoot them. Or work up a separate load for my son's Mossberg MVP w/ what is supposed to be a more generous 5.56 chamber and see if they're more within spec for that one.

Matt

 

[TommyD45]

Primers DO make a difference.

I was doing some chronograph work yesterday with my 357 lever gun checking loads with H110 and my cast bullet. 10 shots of each load were fired with the chronograph 10 feet away. All components were identical except for the primers.

WSP (standard) primer: Ave 1635, Std Dev 7.5

CCI 550 (magnum) primer: Ave 1692, Std Dev 8.7

One has to be careful, especially at the higher end loads, to follow the reloading manual recipes with their specified components. Casual substitution of components can be a problem.

 

[Bart B.]

It's common to see a 100 fps or more difference your stuff's velocity compared to load data velocity. Barrels used as well as component lot numbers are different. If you're hand holding the rifle and the load data was developed in a fixed barreled action, your numbers will be lower than theirs with the same barrel and components.

 

[morcey2]

It's common to see a 100 fps or more difference your stuff's velocity compared to load data velocity. Barrels used as well as component lot numbers are different. If you're hand holding the rifle and the load data was developed in a fixed barreled action, your numbers will be lower than theirs with the same barrel and components.

One of my rifles, a Spanish M44 Mauser, is in almost perfect lock-step with the Nosler #7 loads for 200 grain bullets with both IMR4064 and Varget. That's the only one that I've seen that was that close. That was with the same primer, but a different case (Remington instead of Federal... I don't like Federal brass.)

I'm going to borrow a blade mic from one of my co-workers and shoot a few more this week just to see if there is any case-head expansion. If there is, I'll pull them down and re-work-up the load _with_ the chrono. If not, I'll shoot them as-is, but back off some going forward. I've found other people who have the same upper, use the same brass, primers, bullets, and powder load and they get much closer to 3000 fps. Those are over on predatormastersforums.com.

I also picked up some new Winchester brass to use and I may try it with RL-15 or H4895.

Matt

 

[Bart B.]

morcey2,

How much case head expansion will be too much?

I ask because I've never seen any data showing a given amount of safe max pressure (SAAMI spec, piezo transducer or strain gauge measured) causing X amount of expansion (typically at the bottom of the extractor groove) for different cartridge cases.

And all makes of a given cartridge's cases don't have the same metal properties; some are harder than others. A given psi number measured will have different amounts of case head expansion across all makes.

 

[morcey2]

morcey2,

How much case head expansion will be too much?

I'll tell you when I'm done. I've got 3 sets of loads, all using LC brass from the same lot of American Eagle XM193 ammunition. I have twice-fired brass that is loaded with the above referenced load, once fired brass with the same load, and once-fired brass loaded with W748 and 55gr FMJBT. Same primers in all of them. The second firing on the twice-fired brass was from a load with 68gr HPBT and AA-2520 powder. I'll be measuringing parallel and perpendicular to where the nato cross is on the cases. I only plan on shooting about 5 of each to get some numbers.

The I also have some new XM193 from a different lot, but I'll use it as somewhat of a control. If I get more than about two ten-thousandths difference between the varget load and the W748 and control loads, I'll probably pull them down. The reason that I don't just pull them all down now is that it was a bear just to get the first one pulled with the hammer puller.

I'd just go off the fact that the primers weren't flattened, but I'm plumb out of precision flatten-at-the-right-pressure primers.

Matt

 

[Toprudder]

Don't know if this helps, but I recently did a load workup in my 20" Wylde chamber AR, with Hornady 60 Vmax, CCI#41, and Varget, LC brass, and settled on 26.0gn as the best load. My numbers were 2927fps, 8.7sd, 17fps spread. I happened to be shooting at 50 yards that day and had a 3 shot group of 0.21".

I had ladder loads in 0.5gn steps, up to 27.0gn, and at the max load saw 3006 fps, 23.8sd, 43 spread. Now keep in mind these were only 3 shot groups, but I did see a bell-shape progression of both spread and standard deviation, with the accuracy node and SD node at 26.0gn.

I plan to load more and test more rounds at each step, from 25.5 to 26.5gn, and also test accuracy at 100yards next time.

Would I shoot the hot loads? I have a collet puller and they would be very easy to pull, so I would probably just pull them if I was worried about them. But, 26.5 was not a hot charge in my gun. If I did not see primers flattening, or ejector marks on the case, I would be tempted to shoot them up. YMMV

 

[morcey2]

Toprudder: That does help.

By Thursday I knew I wasn't going to have time to shoot them this weekend so I picked up a collet puller and pulled all ~120 down. It's not often that you sit down at the reloading bench and come away with more bullets, powder, and prepped brass than when you started.

I loaded up a new set starting at 25 gr and ending at 26.3. Same primers, brass, and OAL. I also picked up some new Winchester brass and loaded using H-4895, BR-4 primers, and Hornady 60 gr SP. 24-26 gr. I'm taking Thursday off so hopefully the weather will be good enough to have a range-morning. (Afternoon is going to be fishing regardless of the weather.)

Matt