.40 s&w load question

[showmebob]

I posted this on another forum but didn't get the replies expected maybe because it's not a simple answer?

OK, here's the story. I'm new to loading .40 S&W and almost new to using a chronograph.
I loaded up some test loads according to the Speer manual but using Precission Delta bullets instead of Speer. Same COL, profile, weight, WSP primers instead of CCI 500 which I'm out of at the moment.

Off to the range I go. Set up the chronograph and shoot the TiteGroup test loads. The 4.0 starting loads chrono exactly according to the manual WOW! Maximum charge loads of 4.7grains shoot within 4fps of the manual. DOUBLE WOW!!
I'm excited now thinking this chronograph is really going to be a great useful tool. But I'm even more excited that the loads tract exactly with the book.

Now to test the Unique loads.
Starting load is 6.0 grains and should shoot 849fps according to the Speer manual. My loads shot 992fps WHAT THE HECK?? I try my midrange test loads of 6.4 grains, no fps spec for this load but it shoots 1040 fps. The manual shows a 6.7 grain load should shoot 1000 fps. I didn't even try the maximum load of 6.7 grains as I feel they would be way over pressure.

BTW, the speeds listed are for an average of 5 shots.

Can anyone explain why the Titegroup loads tracted the book exactly and the Unique loads were way off? This has me worried. Can the chronograph be off?

I would appreciate any and all help. Thanks guys and gals!

 

[rcmodel]

Might be a case of your sky-screens too close to the muzzle.

I would imagine the Unique is putting out more muzzle blast then the Titegroup, and you might be measuring muzzle blast.

rc

 

[showmebob]

rc

The crono was about 8 feet from the muzzle. The instructions said 6+ feet so I thought I was fine. Very good idea which I'll try next time I'm at the range. Is there any reason why a chrono couldn't be set out 15 feet or so?

 

[gamestalker]

Although it can be a risky decision, I've actually been setting mine up about 20' away to eliminate muzle blast from giving me false readings and error messages. Since moving back I have had very reliable readings.

 

[Curator]

The farther away you set your Crony, the more accurate the readings are and the more likely you are to shoot through the electronics. Don't ask how I know this!

 

[Stormin.40]

I don't have any experience with Unique but have heard others complain about how it flows for powder measures, I know titegroup meters well. Depending on how you charged your cases could the charge weights be off? Shot in the dark, if your like me your test loads were measured individually to eliminate any variables that can realisticly be control.

 

[rsrocket1]

The Alliant website shows only max loads and min COL. A quick run through with QL shows that 6.7g Unique with a 180g Speer GDHP (same as the Alliant data) at 1.120" COL predicts a nice 1200 fps with a peak pressure of 14.6 kpsi which is 36% above SAAMI rated max.

If you loaded to typical flat nosed lengths of 1.136", you would get 1183 fps with a max P of 43.7 kpsi.

I've been loading 5g Unique under a 180g FP bullet at 1.135" and get mid to high 900 fps readings through my chrony, but most importantly, it is with a 0.290" seating depth. A deeper seating depth will raise the max pressure greatly and give you a slightly higher muzzle velocity. 6.0g would actually start compressing the powder at that seating depth.

Did you check your fired cases for flattened primers or firing pin cratering? 1040fps from a 180g bullet is really not that excessive so long as you were seating to 1.135" and not 1.12"

 

[showmebob]

Stormin.40. A good thought but I'm sure the cases were all loaded the same. I agree Unique doesn't meter all that good.

 

[showmebob]

[Did you check your fired cases for flattened primers or firing pin cratering? 1040fps from a 180g bullet is really not that excessive so long as you were seating to 1.135" and not 1.12"]

Yes I did check and the factory Federal loads showed just a touch of primer flattening but the 6.4 grain loads of Unique didn't. My loads were set at the 1.120 col.
I did NOT shoot the 6.7 grain loads as the 6.4 felt excessive to me and seemed to fast.
As I stated in the OP these loads were from the Speer manual but using PD bullets. While I expected a difference I was surprised at how the titegroup loads tracked fps exactly per the maunual but the unique loads were much faster.

 

[myg30]

Is it possible you might of put a tighter crimp on the pd bullets ? You can check with a caliper.

 

[showmebob]

[Is it possible you might of put a tighter crimp on the pd bullets ?]

Both the titegroup and unique loads used the same cases and bullets so I don't think there would have been any difference.
Good thought though!

 

[gamestalker]

I've had that happen a couple times with my loads too. But usually it's a fluke in which my gun, loads, and atmosphere, just happened to correspond with the data estimates I think?

 

[popper]

You didn't state the bullet weight or type. 6gr. Unique with a 180 or 165 TC is a 'stout' load in my .40 and the brass ends up way behind me. Oops, you did. Most of the plated need to stay under 1100 fps. Drop down to 5-5.5 for a better load.

 

[showmebob]

Popper. You are correct that I didn't mention bullet weight. I didn't feel it made any difference in answering my question as the same bullets and weight were used in both the Titegroup and Unique loads. Just so you know, 180 grain Precission Delta bullets were used and they are jacketed not plated. Regardless of what the chronograph says I will not load more than 6.0 of the Unique behind that bullet and I loaded up some 5.5 grain loads today.

At this point I believe the issue is either muzzle blast as mentioned by several members above or some other kind of chronograph error. I'm new to chronographing and certainly don't know the in's and out's yet.

Be Safe