Why Not Blue Dot or ?

[EdMc]

Had a chance today to chrono a very small sample of loads with Blue Dot today and compare to some previously loaded Longshot. All were fired from a stock G20SF - Starline brass - 180 gr XTP - WLP primers - COAL 1.260" - Pro Chrony - Temp mid 90s - Humidity 2 feet  - Elevation ~ 500 ft.

            9.6 gr BD                      10.2 gr BD                10.7gr BD                      9.0 gr LS

Avg fsp  1015                              1062                        1092                             1198

The 10.7 gr BD being the max load in Hornady's current reloading manual with the only change being Starline instead of Hornady brass. The LS load being over Hornady's max.

Max case bulge on the BD loads was ~.433 and ~.434 on the LS load.

Trying to duplicate  DM1906's method of measuring I put the flat part of my calipers on a table top with the case sitting upright to measure: the BD loads measured ~.425 and the LS loads ~.430       Quite a difference on what should be the web area of the casing and the small bit that is unsupported by the Glock barrel. I don't have the experience to know if this is of any meaning or not. 

[Taterhead]

Had a chance today to chrono a very small sample of loads with Blue Dot today and compare to some previously loaded Longshot. All were fired from a stock G20SF - Starline brass - 180 gr XTP - WLP primers - COAL 1.260" - Pro Chrony - Temp mid 90s - Humidity 2 feet  - Elevation ~ 500 ft.

            9.6 gr BD                      10.2 gr BD                10.7gr BD                      9.0 gr LS

Avg fsp  1015                              1062                        1092                             1198

The 10.7 gr BD being the max load in Hornady's current reloading manual with the only change being Starline instead of Hornady brass. The LS load being over Hornady's max.

Max case bulge on the BD loads was ~.433 and ~.434 on the LS load.

Trying to duplicate  DM1906's method of measuring I put the flat part of my calipers on a table top with the case sitting upright to measure: the BD loads measured ~.425 and the LS loads ~.430       Quite a difference on what should be the web area of the casing and the small bit that is unsupported by the Glock barrel. I don't have the experience to know if this is of any meaning or not.

Wow. Very interesting chrony readings. 10.7 grains of BD under a 180 XTP gives about 1220 in my G20. So my results are more than 100 fps different. I have chronied that load on a few separate occasions and temperatures with similar results.

9.1 grains of LS averaged 1170 fps. 9.5 grains yielded 1190.  So your data for LS tracks a bit closer to my personal testing.

BD puts out a huge muzzle blast and fireball that is known to mess with chrony readings. I wonder if there might be a bit of error in the BD numbers? It is possible that if you were to back up from the chrony a few feet if your data would come in a bit different. Those charges should have you running past 1200 fps. But then again, things run differently in different pistols. But I would guess there is some chrony error.

[REDLINE]

Wow!   128 fps difference.  Maybe it was the 2' of humidity?

[DM1906]

Had a chance today to chrono a very small sample of loads with Blue Dot today and compare to some previously loaded Longshot. All were fired from a stock G20SF - Starline brass - 180 gr XTP - WLP primers - COAL 1.260" - Pro Chrony - Temp mid 90s - Humidity 2 feet  - Elevation ~ 500 ft.

            9.6 gr BD                      10.2 gr BD                10.7gr BD                      9.0 gr LS

Avg fsp  1015                              1062                        1092                             1198

The 10.7 gr BD being the max load in Hornady's current reloading manual with the only change being Starline instead of Hornady brass. The LS load being over Hornady's max.

Max case bulge on the BD loads was ~.433 and ~.434 on the LS load.

Trying to duplicate  DM1906's method of measuring I put the flat part of my calipers on a table top with the case sitting upright to measure: the BD loads measured ~.425 and the LS loads ~.430       Quite a difference on what should be the web area of the casing and the small bit that is unsupported by the Glock barrel. I don't have the experience to know if this is of any meaning or not.

I'm not exactly sure what you're describing, but it's not exactly what I recommended.  I could be wrong.  I suggest measuring the case web, ABOVE the rim, not to include the rim.  However, your numbers are still very telling.  If you are measuring the rim, and are seeing that difference, then LS is creating a very significant pressure increase over BD.  This would also explain your very anemic velocities with BD, as stated by Tater.  10.7 gr. BD with a 180 gr. jacketed bullet is more near a starting load, not a max.  11 gr. is my target load with jackets or lead.  10.7 gr. BD should get you near/past 1200 FPS, even with standard primers.  If you're in fact at 1092, that's sub-sonic, and can affect chrono readings if you're less than 10-15' away.  Super-sonic won't affect actual chrono readings, but can give secondary errors if too close (the muzzle blast is a second event).  Your chrono should read 2 velocities in this case, one valid, and one error or very slow.  If your chrono is a "Chrony" brand, it should catch more than 7,000 RPM.  The lessers are still good for 4,000 or better.  These cycles are way beyond anything we'll discuss here, or are capable of repeating with a semi-auto.  Anyhoo, there's something not right with your rounds, or chrono data.

[DM1906]

Wow!   128 fps difference.  Maybe it was the 2' of humidity?

Yeah, humidity.  It's been so bad here lately, I can step outside and drink the air.  Still, not 128 FPS worth.

[EdMc]

Hey, I'm always wrong......just ask my wife.  The chrono is a Competition Electronics Pro Chrono. Didn't measure but I was 10 or 12 ft from the chrono. 10.7 of BD is Hornady's 'max' ...1250 fps out of a Delta 5" barrel. Speer shows 11 gr as a max. overall length at 1.25 w/ CCI primer and GD 180gr. ....1295 out of a Smith 1006. Anyway, sound, felt recoil.. it was obvious the LS load was hotter. I consider the web area to be just above the extractor groove, anywhere in this area the LS load measures .003 or more larger. Farther up the case the sizes are around .001 difference, but I'd think this area is more dependent on chamber sizing. Perhaps not....? I've never fired any of the hotter 'boutique' ammo to have a case for reference.

As for the chrono, I don't know?. The LS was consistent with some previously measured LS loads. I also shot a few Win White Box 115gr. 9mm over the chrono the same day. The average was 1164 fps out of a CZ-75B. I have no idea if thats a normal velocity for them or not. It's not often I have access to an area I can shoot over the chrono.....I'll try again when I can.

Humidity.... .I live in the Macon, GA area, the Deep South. The high for today and (I guess yesterday is 100+). Hit 106-108 a few weeks back.....add in the high humidity and....well, you better like to sweat.

[The_Shadow]

I can tell you about humidity in LoUiSiAna...I linked my latest outing numbers with BD.
http://10mm-firearms.com/range-reports/wow-shooting-in-louisiana's-heat-and-humdity/

[EdMc]

Yeah, I ran two mags through the CZ and thought.....this is stupid and went inside where there was A/C.

[Taterhead]

Hey, I'm always wrong......just ask my wife.  The chrono is a Competition Electronics Pro Chrono. Didn't measure but I was 10 or 12 ft from the chrono. 10.7 of BD is Hornady's 'max' ...1250 fps out of a Delta 5" barrel. Speer shows 11 gr as a max. overall length at 1.25 w/ CCI primer and GD 180gr. ....1295 out of a Smith 1006. Anyway, sound, felt recoil.. it was obvious the LS load was hotter. I consider the web area to be just above the extractor groove, anywhere in this area the LS load measures .003 or more larger. Farther up the case the sizes are around .001 difference, but I'd think this area is more dependent on chamber sizing. Perhaps not....? I've never fired any of the hotter 'boutique' ammo to have a case for reference.

As for the chrono, I don't know?. The LS was consistent with some previously measured LS loads. I also shot a few Win White Box 115gr. 9mm over the chrono the same day. The average was 1164 fps out of a CZ-75B. I have no idea if thats a normal velocity for them or not. It's not often I have access to an area I can shoot over the chrono.....I'll try again when I can.

Humidity.... .I live in the Macon, GA area, the Deep South. The high for today and (I guess yesterday is 100+). Hit 106-108 a few weeks back.....add in the high humidity and....well, you better like to sweat.

We have the opposite problem. About 6% humidity and 105+ degrees on some days. I can't keep enough water on my yard. Sinuses and everything dry, dry.

[sqlbullet]

Gotta love the mountain west.

[EdMc]

Well, I tried a few more loads over the chrono. Same new Starline brass, 180 XTP, WLP, 1.260 and 10.7 gr BD individually weighed etc. The only change was a little more crimp...0.419. Avg. velocity was 1128 fps this time, only slightly better than the previous 1092.  Beats me, maybe I'll try some Power Pistol I have and see how close it comes to book values.

[Yondering]

Weird; that sure sounds like you have a "slow" lot of Blue Dot.

BTW, to use the case web measurement method of comparing loads, you need to be using the same brand of brass, with the same number of firings through them. You should also measure them before they are fired, and calculate the difference.

[EdMc]

I bought 2lbs but of course they're the same lot number. Nothing dramatic like a large fireball or very loud report. Average recoil.......

Thanks for the tip on the case measurements. These were about the same as some Atlanta Arms shot at a range.....less than the 9.0 load of LS. I'll continue on.....

Btw, LW shipped the long slide order today, less the BO barrel. Did you find a velocity increase when using the compensator? I read the article on GunBlast.........always thought the opposite, that the comp/brake would decrease velocity.

[Yondering]

I haven't measured to find out if there's a velocity difference with or without the brake. It certainly won't decrease velocity (it doesn't touch the bullet), don't know if it has a significant effect or not. I read that gunblast article too, there were enough errors that I took it with a grain of salt.

[sqlbullet]

If you preserve overall length by removing part of the barrel and replacing it with compensator/brake you may loose a few fps.  But, you have effectively shortened the pressure bearing part of the ride.

If you attach it to the end increasing the overall length of the gun, I doubt it would have any impact at all.  If it did it should be a tiny increase.

It can have a positive impact on accuracy.  It helps normalize the forces that occur as the projectile leaves the barrel, resulting in more stability.  In rifles this can be significant, taking a 1 MOA gun to .75 or better.  In handguns I expect the difference would be hard to quantify.